Switches

 

Switches

SWITCHES :- Solid State Relay (SSR), Relay, Printed Circuit Board (PCB) relays, all types of control switches.

Solid State Relays
Soft Starters
Frequency Drives
Push Buttons & Pilot Lights
Limit Switches
Motor Protection Unit
Solid State Relays Accessories
Variable Speed Drives
Electromechanical Relays
Sockets And Modules

SWITCHES :-

Solid State Relay (SSR) :-

A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. SSRs consist of a sensor which responds to an appropriate input (control signal), a solid-state electronic switching device which switches power to the load circuitry, and a coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

Packaged solid-state relays use power semiconductor devices such as thyristors and transistors, to switch currents up to around a hundred amperes. Solid-state relays have fast switching speeds compared with electromechanical relays, and have no physical contacts to wear out. Application of solid-state relays must consider their lower ability to withstand momentary overload, compared with electromechanical contacts, and their higher “on” state resistance. Unlike an electromechanical relay, a solid-state relay provides only limited switching arrangements (SPST switching).

Coupling
The control signal must be coupled to the controlled circuit in a way which provides galvanic isolation between the two circuits.

Many SSRs use optical coupling. The control voltage energizes an internal LED which illuminates and switches on a photo-sensitive diode (photo-voltaic); the diode current turns on a back-to-back thyristor, SCR, or MOSFET to switch the load. The optical coupling allows the control circuit to be electrically isolated from the load.

Most of the relative advantages of solid state and electromechanical relays are common to all solid-state as against electromechanical devices.

Slimmer profile, allowing tighter packing.
Totally silent operation.
SSRs switch faster than electromechanical relays; the switching time of a typical optically coupled SSR is dependent on the time needed to power the LED on and off – of the order of microseconds to milliseconds.
Increased lifetime, even if it is activated many times, as there are no moving parts to wear and no contacts to pit or build up carbon.
Output resistance remains constant regardless of amount of use.
Clean, bounceless operation.
No sparking, allows it to be used in explosive environments, where it is critical that no spark is generated during switching.
Inherently smaller than a mechanical relay of similar specification (if desired may have the same “casing” form factor for interchangeability).
Much less sensitive to storage and operating environment factors such as mechanical shock, vibration, humidity, and external magnetic fields.

Relay :-

Relays are used wherever it is necessary to control a high power or high voltage circuit with a low power circuit, especially when galvanic isolation is desirable. The first application of relays was in long telegraph lines, where the weak signal received at an intermediate station could control a contact, regenerating the signal for further transmission. High-voltage or high-current devices can be controlled with small, low voltage wiring and pilots switches. Operators can be isolated from the high voltage circuit. Low power devices such as microprocessors can drive relays to control electrical loads beyond their direct drive capability. In an automobile, a starter relay allows the high current of the cranking motor to be controlled with small wiring and contacts in the ignition key.

Electromechanical switching systems including Strowger and Crossbar telephone exchanges made extensive use of relays in ancillary control circuits. The Relay Automatic Telephone Company also manufactured telephone exchanges based solely on relay switching techniques designed by Gotthilf Ansgarius Betulander. The first public relay based telephone exchange in the UK was installed in Fleetwood on 15 July 1922 and remained in service until 1959.

The use of relays for the logical control of complex switching systems like telephone exchanges was studied by Claude Shannon, who formalized the application of Boolean algebra to relay circuit design in A Symbolic Analysis of Relay and Switching Circuits. Relays can perform the basic operations of Boolean combinatorial logic. For example, the boolean AND function is realised by connecting normally open relay contacts in series, the OR function by connecting normally open contacts in parallel. Inversion of a logical input can be done with a normally closed contact. Relays were used for control of automated systems for machine tools and production lines. The Ladder programming language is often used for designing relay logic networks.

Early electro-mechanical computers such as the ARRA, Harvard Mark II, Zuse Z2, and Zuse Z3 used relays for logic and working registers. However, electronic devices proved faster and easier to use.

Because relays are much more resistant than semiconductors to nuclear radiation, they are widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery. Electromechanical protective relays are used to detect overload and other faults on electrical lines by opening and closing circuit breakers.

 

Number and type of contacts – normally open, normally closed, (double-throw)
Contact sequence – “Make before Break” or “Break before Make”. For example, the old style telephone exchanges required Make-before-break so that the connection didn’t get dropped while dialing the number.
Contact current rating – small relays switch a few amperes, large contactors are rated for up to 3000 amperes, alternating or direct current
Contact voltage rating – typical control relays rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15,000 V
Operating lifetime, useful life – the number of times the relay can be expected to operate reliably. There is both a mechanical life and a contact life. The contact life is affected by the type of load switched. Breaking load current causes undesired arcing between the contacts, eventually leading to contacts that weld shut or contacts that fail due erosion by the arc.
Coil voltage – machine-tool relays usually 24 VDC, 120 or 250 VAC, relays for switchgear may have 125 V or 250 VDC coils,
Coil current – Minimum current required for reliable operation and minimum holding current, as well as, effects of power dissipation on coil temperature, at various duty cycles. “Sensitive” relays operate on a few milliamperes
Package/enclosure – open, touch-safe, double-voltage for isolation between circuits, explosion proof, outdoor, oil and splash resistant, washable for printed circuit board assembly
Operating environment – minimum and maximum operating temperature and other environmental considerations such as effects of humidity and salt
Assembly – Some relays feature a sticker that keeps the enclosure sealed to allow PCB post soldering cleaning, which is removed once assembly is complete.
Mounting – sockets, plug board, rail mount, panel mount, through-panel mount, enclosure for mounting on walls or equipment
Switching time – where high speed is required
“Dry” contacts – when switching very low level signals, special contact materials may be needed such as gold-plated contacts
Contact protection – suppress arcing in very inductive circuits
Coil protection – suppress the surge voltage produced when switching the coil current
Isolation between coil contacts
Aerospace or radiation-resistant testing, special quality assurance
Expected mechanical loads due to acceleration – some relays used in aerospace applications are designed to function in shock loads of 50 g or more
Size – smaller relays often resist mechanical vibration and shock better than larger relays, because of the lower inertia of the moving parts and the higher natural frequencies of smaller parts. Larger relays often handle higher voltage and current than smaller relays.
Accessories such as timers, auxiliary contacts, pilot lamps, and test buttons
Regulatory approvals
Stray magnetic linkage between coils of adjacent relays on a printed circuit board.

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called “protective relays”.

Magnetic latching relays require one pulse of coil power to move their contacts in one direction, and another, redirected pulse to move them back. Repeated pulses from the same input have no effect. Magnetic latching relays are useful in applications where interrupted power should not be able to transition the contacts.

Magnetic latching relays can have either single or dual coils. On a single coil device, the relay will operate in one direction when power is applied with one polarity, and will reset when the polarity is reversed. On a dual coil device, when polarized voltage is applied to the reset coil the contacts will transition. AC controlled magnetic latch relays have single coils that employ steering diodes to differentiate between operate and reset commands.

Relay types

Latching relay

A latching relay (also called “impulse”, “keep”, or “stay” relays) maintains either contact position indefinitely without power applied to the coil. The advantage is that one coil consumes power only for an instant while the relay is being switched, and the relay contacts retain this setting across a power outage. A latching relay allows remote control of building lighting without the hum that may be produced from a continuously (AC) energized coil.

A stepping relay is a specialized kind of multi-way latching relay designed for early automatic telephone exchanges.

An earth leakage circuit breaker includes a specialized latching relay.

Reed relay
A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas-filled glass tube which protects the contacts against atmospheric corrosion; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid or an external magnet.

Reed relays can switch faster than larger relays and require very little power from the control circuit. However, they have relatively low switching current and voltage ratings. Though rare, the reeds can become magnetized over time, which makes them stick ‘on’ even when no current is present; changing the orientation of the reeds with respect to the solenoid’s magnetic field can resolve this problem.

Sealed contacts with mercury-wetted contacts have longer operating lives and less contact chatter than any other kind of relay

Mercury-wetted relay
Mercury relay
Polarized relay
Machine tool relay
Coaxial relay
Time delay relay
Contactor

Solid-state relay

Solid state relay with no moving parts

25 A or 40 A solid state contactors
A solid state relay or SSR is a solid state electronic component that provides a function similar to an electromechanical relay but does not have any moving components, increasing long-term reliability. A solid-state relay uses a thyristor, TRIAC or other solid-state switching device, activated by the control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-emitting diode (LED) coupled with a photo transistor) can be used to isolate control and controlled circuits.

As every solid-state device has a small voltage drop across it, this voltage drop limits the amount of current a given SSR can handle. The minimum voltage drop for such a relay is a function of the material used to make the device. Solid-state relays rated to handle as much as 1,200 amperes have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients and in general may be susceptible to damage by extreme cosmic ray and EMP episodes.

AC Geared Motors

all types of motors

Static relay

A static relay consists of electronic circuitry to emulate all those characteristics which are achieved by moving parts in an electro-magnetic relay.

Solid state contactor relay

A solid state contactor is a heavy-duty solid state relay, including the necessary heat sink, used where frequent on/off cycles are required, such as with electric heaters, small electric motors, and lighting loads. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls.

Buchholz relay
Force-guided contacts relay

Overload protection relay

Electric motors need overcurrent protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings. The overload sensing devices are a form of heat operated relay where a coil heats a bimetallic strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized.

This thermal protection operates relatively slowly allowing the motor to draw higher starting currents before the protection relay will trip. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided.

The other common overload protection system uses an electromagnet coil in series with the motor circuit that directly operates contacts. This is similar to a control relay but requires a rather high fault current to operate the contacts. To prevent short over current spikes from causing nuisance triggering the armature movement is damped with a dashpot. The thermal and magnetic overload detections are typically used together in a motor protection relay.

Electronic overload protection relays measure motor current and can estimate motor winding temperature using a “thermal model” of the motor armature system that can be set to provide more accurate motor protection. Some motor protection relays include temperature detector inputs for direct measurement from a thermocouple or resistance thermometer sensor embedded in the winding.

Vacuum relays
A sensitive relay having its contacts mounted in a highly evacuated glass housing, to permit handling radio-frequency voltages as high as 20,000 volts without flashover between contacts even though contact spacing is but a few hundredths of an inch when open.

Safety relays
Safety relays are devices which generally implement safety functions. In the event of a hazard, the task of such a safety function is to use appropriate measures to reduce the existing risk to an acceptable level

Multi-voltage relays
Multi-voltage relays are devices designed to work for wide voltage ranges such as 24 to 240 VAC/VDC and wide frequency ranges such as 0 to 300 Hz. They are indicated for use in installations that do not have stable supply voltages.

Protective relay
For protection of electrical apparatus and transmission lines, electromechanical relays with accurate operating characteristics were used to detect overload, short-circuits, and other faults. While many such relays remain in use, digital devices now provide equivalent protective functions.

 

Railway signalling

Part of a relay interlocking using UK Q-style miniature plug-in relays.

Signalling relay and base.

Railway signalling relays are large considering the mostly small voltages (less than 120 V) and currents (perhaps 100 mA) that they switch. Contacts are widely spaced to prevent flashovers and short circuits over a lifetime that may exceed fifty years. BR930 series plug-in relaysSince rail signal circuits must be highly reliable, special techniques are used to detect and prevent failures in the relay system. To protect against false feeds, double switching relay contacts are often used on both the positive and negative side of a circuit, so that two false feeds are needed to cause a false signal. Not all relay circuits can be proved so there is reliance on construction features such as carbon to silver contacts to resist lightning induced contact welding and to provide AC immunity.

Opto-isolators are also used in some instances with railway signalling, especially where only a single contact is to be switched.

Widely used on railways following British practice. These are 120 mm high, 180 mm deep and 56 mm wide and weigh about 1400 g, and can have up to 16 separate contacts, for example, 12 make and 4 break contacts. Many of these relays come in 12V, 24V and 50V versions.

A relay is an electrically operated switch. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal.

Printed Circuit Board (PCB) relays, all types of control switches etc.,

 

Limit Switches , Limit Switch Accessories

 

How do proximity switches work?
A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor’s target. Different proximity sensor targets demand different sensors.

What is the use of proximity switch?
A proximity switch is a device which causes a switching action without physical contact. SCHMERSAL proximity switches respond to targets that come within the active range of their generated sensing fields.

 

What is NPN sensor?
The outputs of some sensors will behave like transistors, when a sensor senses an object it will trigger the transistor controlling the output (which essentially acts like a switch) and depending on its design it’ll act as an NPN or PNP type transistor. An NPN output is commonly called a “sinking” output

 

Optical Switches are usually used in optical fibers, where the electro-optic effect is used to switch one circuit to another. These switches can be implemented with, for example, microelectromechanical systems or piezoelectric systems.

 

Applications
Electro-optical sensors are used whenever light needs to be converted to energy. Because of this, electro-optical sensors can be seen almost anywhere. Common applications are smartphones where sensors are used to adjust screen brightness, and smartwatches in which sensors are used to measure the wearer’s heartbeat.

 

What is an optical switch?
In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another.

 

Float Sensor :-
A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices.

How does a float sensor work?
The purpose of a float switch is to open or close a circuit as the level of a liquid rises or falls. Most float switches are “normally closed,” meaning the two wires coming from the top of the switch complete a circuit when the float is at its low point, resting on its bottom clip (for example, when a tank is dry).

What is a liquid level sensor?
Level sensors detect the level of liquids and other fluids and fluidized solids, including slurries, granular materials, and powders that exhibit an upper free surface.

What is a float switch in an air conditioner?
The fix for an overflow that the drain pan cannot handle is a safety float switch. If the moisture begins to collect in the drainage line, a small ball valve, within the safety switch, will begin to float thus transmitting a signal to the compressor unit to turn off.

What is the use of pressure switch?
A pressure switch is a form of switch that closes an electrical contact when a certain set pressure has been reached on its input. The switch may be designed to make contact either on pressure rise or on pressure fall.

What is the level switch?
A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices.

How does an automobile coolant level sensor work?
While manufacturers use different types of coolant-level sensors, the simplest is a float that activates a switch. If the coolant drops below the designated level, the switch opens, sending a signal to the indicator light. Manufacturers install these switches either in the coolant recovery tank or in the radiator.

 

What is the use of differential pressure switch?
The Differential Pressure Switch just like the pressure switch is a simple electro- mechanical device that operates on the basic principles of Levers and opposing forces. They are mainly used for sensing a difference in pressure between two points in a plant or system.

What is the function of the limit switch?
The limit switch then regulates the electrical circuit that controls the machine and its moving parts. These switches can be used as pilot devices for magnetic starter control circuits, allowing them to start, stop, slow down, or accelerate the functions of an electric motor.

Float switch

A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices.

Float switches range from small to large and may be as simple as a mercury switch inside a hinged float or as complex as a series of optical or conductance sensors producing discrete outputs as the liquid reaches many different levels within the tank. Perhaps the most common type of float switch is simply a float raising a rod that actuates a microswitch.

 

Solid State Relays
Soft Starters
Frequency Drives
Push Buttons & Pilot Lights
Limit Switches
Motor Protection Unit
Solid State Relays Accessories
Variable Speed Drives
Electromechanical Relays
Sockets And Modules

 

Solid State Relays
A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. SSRs consist of a sensor which responds to an appropriate input (control signal), a solid-state electronic switching device which switches power to the load circuitry, and a coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

Packaged solid-state relays use power semiconductor devices such as thyristors and transistors, to switch currents up to around a hundred amperes. Solid-state relays have fast switching speeds compared with electromechanical relays, and have no physical contacts to wear out. Application of solid-state relays must consider their lower ability to withstand momentary overload, compared with electromechanical contacts, and their higher “on” state resistance. Unlike an electromechanical relay, a solid-state relay provides only limited switching arrangements (SPST switching).

Inherently smaller and slimmer profile than mechanical relay of similar specification, allowing tighter packing. (If desired may have the same “casing” form factor for interchangeability.)
Totally silent operation.
SSRs switch faster than electromechanical relays; the switching time of a typical optically coupled SSR is dependent on the time needed to power the LED on and off – of the order of microseconds to milliseconds.
Increased lifetime, even if it is activated many times, as there are no moving parts to wear and no contacts to pit or build up carbon.
Output resistance remains constant regardless of amount of use.
Clean, bounceless operation.
No sparking, allows it to be used in explosive environments, where it is critical that no spark is generated during switching.
Much less sensitive to storage and operating environment factors such as mechanical shock, vibration, humidity, and external magnetic fields.

A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. … The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. As relay diagrams show, when a relay contact is normally open (NO), there is an open contact when the relay is not energized.

A “hockey puck” SSR, so named because of its thick shape and black color. They are specifically designed to switch either AC loads or DC loads, but never both. Solid state relays (SSRs) turn on or off the power being supplied to other devices, in a similar fashion as a physical switch

Soft Starters

A motor soft starter is a device used with AC electrical motors to temporarily reduce the load and torque in the power train and electric current surge of the motor during start-up.

In dc motors the armature is generally designed to have the least resistance possible. So when starting a dc motor starter is connectedsuch that it limits the current value by being in series with armature and later seperates from the circuit. But by then back emf develops in the armature

 

Frequency Drives

A variable-frequency drive (VFD; also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.[1][2][3][4]

VFDs are used in applications ranging from small appliances to large compressors. About 25% of the world’s electrical energy is consumed by electric motors in industrial applications, which can be more efficient when using VFDs in centrifugal load service;[5] however, VFDs’ global market penetration for all applications is relatively small.

Over the last four decades, power electronics technology has reduced VFD cost and size and has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques, and control hardware and software.

VFDs are made in a number of different low- and medium-voltage AC-AC and DC-AC topologies.

 

A variable-frequency drive (VFD; also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, and inverter.

A Variable Frequency Drive is like the throttle on a car… • It adjusts the speed of an HVAC fan or pump motor, based on demand, to. save energy and prolong motor and mechanical component life. • Without a VFD, an HVAC fan or pump motor is either 100% ‘on’ or 100%

A variable-frequency drive (VFD; also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.

A variable frequency drive (VFD) refers to AC drives only and a variable speed drive (VSD) refers to either AC Drives or DC Drives. VFDs vary the speed of an AC motor by varying the frequency to the motor. VSDs referring to DC motors vary the speed by varying the voltage to the motor.

Push Buttons & Pilot Lights
A push-button (also spelled pushbutton) or simply button is a simple switch mechanism for controlling some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal.[1] The surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed or pushed. Buttons are most often biased switches, although many un-biased buttons (due to their physical nature) still require a spring to return to their un-pushed state. Different people use different terms for the “pushing” of the button, such as press, depress, mash, hit, and punch.

A pilot light is a small gas flame, usually natural gas or liquefied petroleum gas, which serves as an ignition source for a more powerful gas burner. Originally, a pilot light was kept permanently alight; however, this is wasteful of gas. Now it is more common to light a burner electrically, but gas pilot lights are still used when a high energy ignition source is necessary, as in when lighting a large burner.

The term “pilot light” is also used occasionally for an electrical indicator light that illuminates to show that electrical power is available, or that an electrical device is operating. Such indicators were originally incandescent lamps or neon lamps, but now are usually LEDs.

 

Limit Switches
In electrical engineering a limit switch is a switch operated by the motion of a machine part or presence of an object.

They are used for controlling machinery as part of a control system, as a safety interlocks, or to count objects passing a point.[1] A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.

Limit switches are used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation. They can determine the presence or absence, passing, positioning, and end of travel of an object. They were first used to define the limit of travel of an object; hence the name “Limit Switch”.

 

A limit switch with a roller-lever operator; this is installed on a gate on a canal lock, and indicates the position of a gate to a control system.
Standardized limit switches are industrial control components manufactured with a variety of operator types, including lever, roller plunger, and whisker type. Limit switches may be directly mechanically operated by the motion of the operating lever. A reed switch may be used to indicate proximity of a magnet mounted on some moving part. Proximity switches operate by the disturbance of an electromagnetic field, by capacitance, or by sensing a magnetic field.

Rarely, a final operating device such as a lamp or solenoid valve will be directly controlled by the contacts of an industrial limit switch, but more typically the limit switch will be wired through a control relay, a motor contactor control circuit, or as an input to a programmable logic controller.

Miniature snap-action switch may be used for example as components of such devices as photocopiers, computer printers, convertible tops or microwave ovens to ensure internal components are in the correct position for operation and to prevent operation when access doors are opened. A set of adjustable limit switches are installed on a garage door opener to shut off the motor when the door has reached the fully raised or fully lowered position. A numerical control machine such as a lathe will have limit switches to identify maximum limits for machine parts or to provide a known reference point for incremental motions.

Motor Protection Unit
modular electronic motor protection relay to control, monitor and meter the performances of 3-phase, constant or dual speed, AC induction motors.
In some critical applications, such as water treatment plants or power stations, it is recommended to protect the motors against malfunctions which could cause expensive downtimes. The DMPU device allows constant monitoring of the motor, reducing costs and correctly planning maintenance operations as well as increasing the lifetime of the motors.
By additional optional modules, the motor protection unit provides high protection, data logging and full variable energy measurement functions.
Furthermore, the simplified cable connection, through our split-core module, allows easy replacement and installation for enhancements and refurbishments.

Variable Speed Drives

VSD that control the speed of either the motor or the equipment driven by the motor (fan, pump, compressor, etc.). This device can be electrical or mechanical. 3. Adjustable speed drives (ASD) are devices that use both mechanical and electrical means to control the motor speed

A VSD converts the 50Hz fixed-frequency and fixed-voltage AC power supply into a DC supply, using an integrated rectifier. Integrated power electronics then convert the DC supply into a sinusoidal output with continuously variable frequency and voltage, which is used to drive the motor.

The motors on chillers, pumps, cooling towers and fans account for a significant portion of the energy consumption in HVAC system. The use of retrofit variable speed drives (VSD) is one of the most effective technologies applied in recent years.

 

A variable frequency drive (VFD) refers to AC drives only and a variable speed drive (VSD) refers to either AC Drives or DC Drives. VFDs vary the speed of an AC motor by varying the frequency to the motor. VSDs referring to DC motors vary the speed by varying the voltage to the motor.

 

Electromechanical Relays

Electromechanical relays are electrically operated switches used to isolate circuits or batteries, detect faults on transmission and distribution lines, and control a high powered circuit using a low power signa

 

A relay is a special type of switch turned on and off by an electromagnet (see the diagram of a simple relay). When a current flows through the coil an electro-magnetic field is set up. The field attracts an iron armature, whose other end pushes the contacts together, completing the circuit.

Electromechanical relays are switches that typically are used to control high power electrical devices. Electromechanical relays are used in many of today’s electrical machines when it is vital to control a circuit, either with a low power signal or when multiple circuits must be controlled by one single signal. Electromechanical relays contain electronic parts that make it possible to operate them for many different applications. They are used mostly in the general aviation, aerospace, and wireless technology industries, but they have many other applications as well. In fact, thousands of electrical devices require electromechanical relays to make them work.

An electromechanical relay, put simply, is a switch. An electrically operated switch to be exact. Relays are electrical parts that are used when a low-power signal is needed in order to control a circuit, or when a number of circuits need to be controlled by one signal. There are several different types of electromechanical relays, and which type is used depends on the specific mechanical device it is used in. Some relays require an electromagnet, or a magnet in which a magnetic field is produced by electric current, with the magnetic field disappearing when the current is switched off. (Of course, an electric current is the flow of a charge of electricity.) A relay that can control higher powered devices, such as for an electric motor, is called a ‘contactor.’

Relays are typically used when it is necessary to switch a small amount of power to a larger amount of power. Relays contain several electronic parts to make them work. These include an electromagnet, which controls opening and closing of the relay. Next is the armature, or the moving part, which is the electronic part that opens and closes. A spring is also used in a relay. This is the part that forces the relay back to its original position after each revolution. In addition, a set of electrical contacts is needed in order to transfer the power.

The point of a relay is to use a small amount of power to switch to a large amount of power. Relays typically are used in modern household appliances such as hair dryers, kitchen appliances, and lights that need to be switched on and off. They are also used in cars where things need to be turned off and on. In fact, modern car manufacturers are using relay panels in fuse boxes because they make maintenance simpler. There are a few things to think about when selecting relays for modern devices. First, you need to consider whether the contact will be normally closed (NC) or normally open (NO). Each of these situations will dictate which types of relays are needed and whether the device needs to be on all the time or needs to be toggled between the on and off positions. Another thing that must be considered is the maximum amount of voltage that the armature and its contact devices can handle. Finally, and perhaps the most important consideration, is the voltage and current that will be needed in the electronics project being undertaken because this will determine the armature activation.

Switch: Solid State Relays, Contactors, Manual Motor Starters, Soft-Starts, Electromechanical Relays, Limit Switches, Pushbutton and Pilot Lights
Fieldbus: Field and Installation Bus, Safe for Mining Systems, SBWeb Building Automation System, Parking Guidance System and Elevator Systems

Electrical Meters, Protection & Time relays, Programmable Controllers, Human Machine Interfaces, Temperature Controllers, Timers, Counters and Current Transformers.

Description

Switches

SWITCHES :- Solid State Relay (SSR), Relay, Printed Circuit Board (PCB) relays, all types of control switches.

Solid State Relays
Soft Starters
Frequency Drives
Push Buttons & Pilot Lights
Limit Switches
Motor Protection Unit
Solid State Relays Accessories
Variable Speed Drives
Electromechanical Relays
Sockets And Modules

SWITCHES :-

Solid State Relay (SSR) :-

A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. SSRs consist of a sensor which responds to an appropriate input (control signal), a solid-state electronic switching device which switches power to the load circuitry, and a coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

Packaged solid-state relays use power semiconductor devices such as thyristors and transistors, to switch currents up to around a hundred amperes. Solid-state relays have fast switching speeds compared with electromechanical relays, and have no physical contacts to wear out. Application of solid-state relays must consider their lower ability to withstand momentary overload, compared with electromechanical contacts, and their higher “on” state resistance. Unlike an electromechanical relay, a solid-state relay provides only limited switching arrangements (SPST switching).

Coupling
The control signal must be coupled to the controlled circuit in a way which provides galvanic isolation between the two circuits.

Many SSRs use optical coupling. The control voltage energizes an internal LED which illuminates and switches on a photo-sensitive diode (photo-voltaic); the diode current turns on a back-to-back thyristor, SCR, or MOSFET to switch the load. The optical coupling allows the control circuit to be electrically isolated from the load.

Most of the relative advantages of solid state and electromechanical relays are common to all solid-state as against electromechanical devices.

Slimmer profile, allowing tighter packing.
Totally silent operation.
SSRs switch faster than electromechanical relays; the switching time of a typical optically coupled SSR is dependent on the time needed to power the LED on and off – of the order of microseconds to milliseconds.
Increased lifetime, even if it is activated many times, as there are no moving parts to wear and no contacts to pit or build up carbon.
Output resistance remains constant regardless of amount of use.
Clean, bounceless operation.
No sparking, allows it to be used in explosive environments, where it is critical that no spark is generated during switching.
Inherently smaller than a mechanical relay of similar specification (if desired may have the same “casing” form factor for interchangeability).
Much less sensitive to storage and operating environment factors such as mechanical shock, vibration, humidity, and external magnetic fields.

Relay :-

Relays are used wherever it is necessary to control a high power or high voltage circuit with a low power circuit, especially when galvanic isolation is desirable. The first application of relays was in long telegraph lines, where the weak signal received at an intermediate station could control a contact, regenerating the signal for further transmission. High-voltage or high-current devices can be controlled with small, low voltage wiring and pilots switches. Operators can be isolated from the high voltage circuit. Low power devices such as microprocessors can drive relays to control electrical loads beyond their direct drive capability. In an automobile, a starter relay allows the high current of the cranking motor to be controlled with small wiring and contacts in the ignition key.

Electromechanical switching systems including Strowger and Crossbar telephone exchanges made extensive use of relays in ancillary control circuits. The Relay Automatic Telephone Company also manufactured telephone exchanges based solely on relay switching techniques designed by Gotthilf Ansgarius Betulander. The first public relay based telephone exchange in the UK was installed in Fleetwood on 15 July 1922 and remained in service until 1959.

The use of relays for the logical control of complex switching systems like telephone exchanges was studied by Claude Shannon, who formalized the application of Boolean algebra to relay circuit design in A Symbolic Analysis of Relay and Switching Circuits. Relays can perform the basic operations of Boolean combinatorial logic. For example, the boolean AND function is realised by connecting normally open relay contacts in series, the OR function by connecting normally open contacts in parallel. Inversion of a logical input can be done with a normally closed contact. Relays were used for control of automated systems for machine tools and production lines. The Ladder programming language is often used for designing relay logic networks.

Early electro-mechanical computers such as the ARRA, Harvard Mark II, Zuse Z2, and Zuse Z3 used relays for logic and working registers. However, electronic devices proved faster and easier to use.

Because relays are much more resistant than semiconductors to nuclear radiation, they are widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery. Electromechanical protective relays are used to detect overload and other faults on electrical lines by opening and closing circuit breakers.

 

Number and type of contacts – normally open, normally closed, (double-throw)
Contact sequence – “Make before Break” or “Break before Make”. For example, the old style telephone exchanges required Make-before-break so that the connection didn’t get dropped while dialing the number.
Contact current rating – small relays switch a few amperes, large contactors are rated for up to 3000 amperes, alternating or direct current
Contact voltage rating – typical control relays rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15,000 V
Operating lifetime, useful life – the number of times the relay can be expected to operate reliably. There is both a mechanical life and a contact life. The contact life is affected by the type of load switched. Breaking load current causes undesired arcing between the contacts, eventually leading to contacts that weld shut or contacts that fail due erosion by the arc.
Coil voltage – machine-tool relays usually 24 VDC, 120 or 250 VAC, relays for switchgear may have 125 V or 250 VDC coils,
Coil current – Minimum current required for reliable operation and minimum holding current, as well as, effects of power dissipation on coil temperature, at various duty cycles. “Sensitive” relays operate on a few milliamperes
Package/enclosure – open, touch-safe, double-voltage for isolation between circuits, explosion proof, outdoor, oil and splash resistant, washable for printed circuit board assembly
Operating environment – minimum and maximum operating temperature and other environmental considerations such as effects of humidity and salt
Assembly – Some relays feature a sticker that keeps the enclosure sealed to allow PCB post soldering cleaning, which is removed once assembly is complete.
Mounting – sockets, plug board, rail mount, panel mount, through-panel mount, enclosure for mounting on walls or equipment
Switching time – where high speed is required
“Dry” contacts – when switching very low level signals, special contact materials may be needed such as gold-plated contacts
Contact protection – suppress arcing in very inductive circuits
Coil protection – suppress the surge voltage produced when switching the coil current
Isolation between coil contacts
Aerospace or radiation-resistant testing, special quality assurance
Expected mechanical loads due to acceleration – some relays used in aerospace applications are designed to function in shock loads of 50 g or more
Size – smaller relays often resist mechanical vibration and shock better than larger relays, because of the lower inertia of the moving parts and the higher natural frequencies of smaller parts. Larger relays often handle higher voltage and current than smaller relays.
Accessories such as timers, auxiliary contacts, pilot lamps, and test buttons
Regulatory approvals
Stray magnetic linkage between coils of adjacent relays on a printed circuit board.

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called “protective relays”.

Magnetic latching relays require one pulse of coil power to move their contacts in one direction, and another, redirected pulse to move them back. Repeated pulses from the same input have no effect. Magnetic latching relays are useful in applications where interrupted power should not be able to transition the contacts.

Magnetic latching relays can have either single or dual coils. On a single coil device, the relay will operate in one direction when power is applied with one polarity, and will reset when the polarity is reversed. On a dual coil device, when polarized voltage is applied to the reset coil the contacts will transition. AC controlled magnetic latch relays have single coils that employ steering diodes to differentiate between operate and reset commands.

Relay types

Latching relay

A latching relay (also called “impulse”, “keep”, or “stay” relays) maintains either contact position indefinitely without power applied to the coil. The advantage is that one coil consumes power only for an instant while the relay is being switched, and the relay contacts retain this setting across a power outage. A latching relay allows remote control of building lighting without the hum that may be produced from a continuously (AC) energized coil.

A stepping relay is a specialized kind of multi-way latching relay designed for early automatic telephone exchanges.

An earth leakage circuit breaker includes a specialized latching relay.

Reed relay
A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas-filled glass tube which protects the contacts against atmospheric corrosion; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid or an external magnet.

Reed relays can switch faster than larger relays and require very little power from the control circuit. However, they have relatively low switching current and voltage ratings. Though rare, the reeds can become magnetized over time, which makes them stick ‘on’ even when no current is present; changing the orientation of the reeds with respect to the solenoid’s magnetic field can resolve this problem.

Sealed contacts with mercury-wetted contacts have longer operating lives and less contact chatter than any other kind of relay

Mercury-wetted relay
Mercury relay
Polarized relay
Machine tool relay
Coaxial relay
Time delay relay
Contactor

Solid-state relay

Solid state relay with no moving parts

25 A or 40 A solid state contactors
A solid state relay or SSR is a solid state electronic component that provides a function similar to an electromechanical relay but does not have any moving components, increasing long-term reliability. A solid-state relay uses a thyristor, TRIAC or other solid-state switching device, activated by the control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-emitting diode (LED) coupled with a photo transistor) can be used to isolate control and controlled circuits.

As every solid-state device has a small voltage drop across it, this voltage drop limits the amount of current a given SSR can handle. The minimum voltage drop for such a relay is a function of the material used to make the device. Solid-state relays rated to handle as much as 1,200 amperes have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients and in general may be susceptible to damage by extreme cosmic ray and EMP episodes.

AC Geared Motors

all types of motors

Static relay

A static relay consists of electronic circuitry to emulate all those characteristics which are achieved by moving parts in an electro-magnetic relay.

Solid state contactor relay

A solid state contactor is a heavy-duty solid state relay, including the necessary heat sink, used where frequent on/off cycles are required, such as with electric heaters, small electric motors, and lighting loads. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls.

Buchholz relay
Force-guided contacts relay

Overload protection relay

Electric motors need overcurrent protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings. The overload sensing devices are a form of heat operated relay where a coil heats a bimetallic strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized.

This thermal protection operates relatively slowly allowing the motor to draw higher starting currents before the protection relay will trip. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided.

The other common overload protection system uses an electromagnet coil in series with the motor circuit that directly operates contacts. This is similar to a control relay but requires a rather high fault current to operate the contacts. To prevent short over current spikes from causing nuisance triggering the armature movement is damped with a dashpot. The thermal and magnetic overload detections are typically used together in a motor protection relay.

Electronic overload protection relays measure motor current and can estimate motor winding temperature using a “thermal model” of the motor armature system that can be set to provide more accurate motor protection. Some motor protection relays include temperature detector inputs for direct measurement from a thermocouple or resistance thermometer sensor embedded in the winding.

Vacuum relays
A sensitive relay having its contacts mounted in a highly evacuated glass housing, to permit handling radio-frequency voltages as high as 20,000 volts without flashover between contacts even though contact spacing is but a few hundredths of an inch when open.

Safety relays
Safety relays are devices which generally implement safety functions. In the event of a hazard, the task of such a safety function is to use appropriate measures to reduce the existing risk to an acceptable level

Multi-voltage relays
Multi-voltage relays are devices designed to work for wide voltage ranges such as 24 to 240 VAC/VDC and wide frequency ranges such as 0 to 300 Hz. They are indicated for use in installations that do not have stable supply voltages.

Protective relay
For protection of electrical apparatus and transmission lines, electromechanical relays with accurate operating characteristics were used to detect overload, short-circuits, and other faults. While many such relays remain in use, digital devices now provide equivalent protective functions.

 

Railway signalling

Part of a relay interlocking using UK Q-style miniature plug-in relays.

Signalling relay and base.

Railway signalling relays are large considering the mostly small voltages (less than 120 V) and currents (perhaps 100 mA) that they switch. Contacts are widely spaced to prevent flashovers and short circuits over a lifetime that may exceed fifty years. BR930 series plug-in relaysSince rail signal circuits must be highly reliable, special techniques are used to detect and prevent failures in the relay system. To protect against false feeds, double switching relay contacts are often used on both the positive and negative side of a circuit, so that two false feeds are needed to cause a false signal. Not all relay circuits can be proved so there is reliance on construction features such as carbon to silver contacts to resist lightning induced contact welding and to provide AC immunity.

Opto-isolators are also used in some instances with railway signalling, especially where only a single contact is to be switched.

Widely used on railways following British practice. These are 120 mm high, 180 mm deep and 56 mm wide and weigh about 1400 g, and can have up to 16 separate contacts, for example, 12 make and 4 break contacts. Many of these relays come in 12V, 24V and 50V versions.

A relay is an electrically operated switch. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal.

Printed Circuit Board (PCB) relays, all types of control switches etc.,

 

Limit Switches , Limit Switch Accessories

 

How do proximity switches work?
A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor’s target. Different proximity sensor targets demand different sensors.

What is the use of proximity switch?
A proximity switch is a device which causes a switching action without physical contact. SCHMERSAL proximity switches respond to targets that come within the active range of their generated sensing fields.

 

What is NPN sensor?
The outputs of some sensors will behave like transistors, when a sensor senses an object it will trigger the transistor controlling the output (which essentially acts like a switch) and depending on its design it’ll act as an NPN or PNP type transistor. An NPN output is commonly called a “sinking” output

 

Optical Switches are usually used in optical fibers, where the electro-optic effect is used to switch one circuit to another. These switches can be implemented with, for example, microelectromechanical systems or piezoelectric systems.

 

Applications
Electro-optical sensors are used whenever light needs to be converted to energy. Because of this, electro-optical sensors can be seen almost anywhere. Common applications are smartphones where sensors are used to adjust screen brightness, and smartwatches in which sensors are used to measure the wearer’s heartbeat.

 

What is an optical switch?
In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another.

 

Float Sensor :-
A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices.

How does a float sensor work?
The purpose of a float switch is to open or close a circuit as the level of a liquid rises or falls. Most float switches are “normally closed,” meaning the two wires coming from the top of the switch complete a circuit when the float is at its low point, resting on its bottom clip (for example, when a tank is dry).

What is a liquid level sensor?
Level sensors detect the level of liquids and other fluids and fluidized solids, including slurries, granular materials, and powders that exhibit an upper free surface.

What is a float switch in an air conditioner?
The fix for an overflow that the drain pan cannot handle is a safety float switch. If the moisture begins to collect in the drainage line, a small ball valve, within the safety switch, will begin to float thus transmitting a signal to the compressor unit to turn off.

What is the use of pressure switch?
A pressure switch is a form of switch that closes an electrical contact when a certain set pressure has been reached on its input. The switch may be designed to make contact either on pressure rise or on pressure fall.

What is the level switch?
A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices.

How does an automobile coolant level sensor work?
While manufacturers use different types of coolant-level sensors, the simplest is a float that activates a switch. If the coolant drops below the designated level, the switch opens, sending a signal to the indicator light. Manufacturers install these switches either in the coolant recovery tank or in the radiator.

 

What is the use of differential pressure switch?
The Differential Pressure Switch just like the pressure switch is a simple electro- mechanical device that operates on the basic principles of Levers and opposing forces. They are mainly used for sensing a difference in pressure between two points in a plant or system.

What is the function of the limit switch?
The limit switch then regulates the electrical circuit that controls the machine and its moving parts. These switches can be used as pilot devices for magnetic starter control circuits, allowing them to start, stop, slow down, or accelerate the functions of an electric motor.

Float switch

A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices.

Float switches range from small to large and may be as simple as a mercury switch inside a hinged float or as complex as a series of optical or conductance sensors producing discrete outputs as the liquid reaches many different levels within the tank. Perhaps the most common type of float switch is simply a float raising a rod that actuates a microswitch.

 

Solid State Relays
Soft Starters
Frequency Drives
Push Buttons & Pilot Lights
Limit Switches
Motor Protection Unit
Solid State Relays Accessories
Variable Speed Drives
Electromechanical Relays
Sockets And Modules

 

Solid State Relays
A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. SSRs consist of a sensor which responds to an appropriate input (control signal), a solid-state electronic switching device which switches power to the load circuitry, and a coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

Packaged solid-state relays use power semiconductor devices such as thyristors and transistors, to switch currents up to around a hundred amperes. Solid-state relays have fast switching speeds compared with electromechanical relays, and have no physical contacts to wear out. Application of solid-state relays must consider their lower ability to withstand momentary overload, compared with electromechanical contacts, and their higher “on” state resistance. Unlike an electromechanical relay, a solid-state relay provides only limited switching arrangements (SPST switching).

Inherently smaller and slimmer profile than mechanical relay of similar specification, allowing tighter packing. (If desired may have the same “casing” form factor for interchangeability.)
Totally silent operation.
SSRs switch faster than electromechanical relays; the switching time of a typical optically coupled SSR is dependent on the time needed to power the LED on and off – of the order of microseconds to milliseconds.
Increased lifetime, even if it is activated many times, as there are no moving parts to wear and no contacts to pit or build up carbon.
Output resistance remains constant regardless of amount of use.
Clean, bounceless operation.
No sparking, allows it to be used in explosive environments, where it is critical that no spark is generated during switching.
Much less sensitive to storage and operating environment factors such as mechanical shock, vibration, humidity, and external magnetic fields.

A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. … The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. As relay diagrams show, when a relay contact is normally open (NO), there is an open contact when the relay is not energized.

A “hockey puck” SSR, so named because of its thick shape and black color. They are specifically designed to switch either AC loads or DC loads, but never both. Solid state relays (SSRs) turn on or off the power being supplied to other devices, in a similar fashion as a physical switch

Soft Starters

A motor soft starter is a device used with AC electrical motors to temporarily reduce the load and torque in the power train and electric current surge of the motor during start-up.

In dc motors the armature is generally designed to have the least resistance possible. So when starting a dc motor starter is connectedsuch that it limits the current value by being in series with armature and later seperates from the circuit. But by then back emf develops in the armature

 

Frequency Drives

A variable-frequency drive (VFD; also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.[1][2][3][4]

VFDs are used in applications ranging from small appliances to large compressors. About 25% of the world’s electrical energy is consumed by electric motors in industrial applications, which can be more efficient when using VFDs in centrifugal load service;[5] however, VFDs’ global market penetration for all applications is relatively small.

Over the last four decades, power electronics technology has reduced VFD cost and size and has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques, and control hardware and software.

VFDs are made in a number of different low- and medium-voltage AC-AC and DC-AC topologies.

 

A variable-frequency drive (VFD; also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, and inverter.

A Variable Frequency Drive is like the throttle on a car… • It adjusts the speed of an HVAC fan or pump motor, based on demand, to. save energy and prolong motor and mechanical component life. • Without a VFD, an HVAC fan or pump motor is either 100% ‘on’ or 100%

A variable-frequency drive (VFD; also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.

A variable frequency drive (VFD) refers to AC drives only and a variable speed drive (VSD) refers to either AC Drives or DC Drives. VFDs vary the speed of an AC motor by varying the frequency to the motor. VSDs referring to DC motors vary the speed by varying the voltage to the motor.

Push Buttons & Pilot Lights
A push-button (also spelled pushbutton) or simply button is a simple switch mechanism for controlling some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal.[1] The surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed or pushed. Buttons are most often biased switches, although many un-biased buttons (due to their physical nature) still require a spring to return to their un-pushed state. Different people use different terms for the “pushing” of the button, such as press, depress, mash, hit, and punch.

A pilot light is a small gas flame, usually natural gas or liquefied petroleum gas, which serves as an ignition source for a more powerful gas burner. Originally, a pilot light was kept permanently alight; however, this is wasteful of gas. Now it is more common to light a burner electrically, but gas pilot lights are still used when a high energy ignition source is necessary, as in when lighting a large burner.

The term “pilot light” is also used occasionally for an electrical indicator light that illuminates to show that electrical power is available, or that an electrical device is operating. Such indicators were originally incandescent lamps or neon lamps, but now are usually LEDs.

 

Limit Switches
In electrical engineering a limit switch is a switch operated by the motion of a machine part or presence of an object.

They are used for controlling machinery as part of a control system, as a safety interlocks, or to count objects passing a point.[1] A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.

Limit switches are used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation. They can determine the presence or absence, passing, positioning, and end of travel of an object. They were first used to define the limit of travel of an object; hence the name “Limit Switch”.

 

A limit switch with a roller-lever operator; this is installed on a gate on a canal lock, and indicates the position of a gate to a control system.
Standardized limit switches are industrial control components manufactured with a variety of operator types, including lever, roller plunger, and whisker type. Limit switches may be directly mechanically operated by the motion of the operating lever. A reed switch may be used to indicate proximity of a magnet mounted on some moving part. Proximity switches operate by the disturbance of an electromagnetic field, by capacitance, or by sensing a magnetic field.

Rarely, a final operating device such as a lamp or solenoid valve will be directly controlled by the contacts of an industrial limit switch, but more typically the limit switch will be wired through a control relay, a motor contactor control circuit, or as an input to a programmable logic controller.

Miniature snap-action switch may be used for example as components of such devices as photocopiers, computer printers, convertible tops or microwave ovens to ensure internal components are in the correct position for operation and to prevent operation when access doors are opened. A set of adjustable limit switches are installed on a garage door opener to shut off the motor when the door has reached the fully raised or fully lowered position. A numerical control machine such as a lathe will have limit switches to identify maximum limits for machine parts or to provide a known reference point for incremental motions.

Motor Protection Unit
modular electronic motor protection relay to control, monitor and meter the performances of 3-phase, constant or dual speed, AC induction motors.
In some critical applications, such as water treatment plants or power stations, it is recommended to protect the motors against malfunctions which could cause expensive downtimes. The DMPU device allows constant monitoring of the motor, reducing costs and correctly planning maintenance operations as well as increasing the lifetime of the motors.
By additional optional modules, the motor protection unit provides high protection, data logging and full variable energy measurement functions.
Furthermore, the simplified cable connection, through our split-core module, allows easy replacement and installation for enhancements and refurbishments.

Variable Speed Drives

VSD that control the speed of either the motor or the equipment driven by the motor (fan, pump, compressor, etc.). This device can be electrical or mechanical. 3. Adjustable speed drives (ASD) are devices that use both mechanical and electrical means to control the motor speed

A VSD converts the 50Hz fixed-frequency and fixed-voltage AC power supply into a DC supply, using an integrated rectifier. Integrated power electronics then convert the DC supply into a sinusoidal output with continuously variable frequency and voltage, which is used to drive the motor.

The motors on chillers, pumps, cooling towers and fans account for a significant portion of the energy consumption in HVAC system. The use of retrofit variable speed drives (VSD) is one of the most effective technologies applied in recent years.

 

A variable frequency drive (VFD) refers to AC drives only and a variable speed drive (VSD) refers to either AC Drives or DC Drives. VFDs vary the speed of an AC motor by varying the frequency to the motor. VSDs referring to DC motors vary the speed by varying the voltage to the motor.

 

Electromechanical Relays

Electromechanical relays are electrically operated switches used to isolate circuits or batteries, detect faults on transmission and distribution lines, and control a high powered circuit using a low power signa

 

A relay is a special type of switch turned on and off by an electromagnet (see the diagram of a simple relay). When a current flows through the coil an electro-magnetic field is set up. The field attracts an iron armature, whose other end pushes the contacts together, completing the circuit.

Electromechanical relays are switches that typically are used to control high power electrical devices. Electromechanical relays are used in many of today’s electrical machines when it is vital to control a circuit, either with a low power signal or when multiple circuits must be controlled by one single signal. Electromechanical relays contain electronic parts that make it possible to operate them for many different applications. They are used mostly in the general aviation, aerospace, and wireless technology industries, but they have many other applications as well. In fact, thousands of electrical devices require electromechanical relays to make them work.

An electromechanical relay, put simply, is a switch. An electrically operated switch to be exact. Relays are electrical parts that are used when a low-power signal is needed in order to control a circuit, or when a number of circuits need to be controlled by one signal. There are several different types of electromechanical relays, and which type is used depends on the specific mechanical device it is used in. Some relays require an electromagnet, or a magnet in which a magnetic field is produced by electric current, with the magnetic field disappearing when the current is switched off. (Of course, an electric current is the flow of a charge of electricity.) A relay that can control higher powered devices, such as for an electric motor, is called a ‘contactor.’

Relays are typically used when it is necessary to switch a small amount of power to a larger amount of power. Relays contain several electronic parts to make them work. These include an electromagnet, which controls opening and closing of the relay. Next is the armature, or the moving part, which is the electronic part that opens and closes. A spring is also used in a relay. This is the part that forces the relay back to its original position after each revolution. In addition, a set of electrical contacts is needed in order to transfer the power.

The point of a relay is to use a small amount of power to switch to a large amount of power. Relays typically are used in modern household appliances such as hair dryers, kitchen appliances, and lights that need to be switched on and off. They are also used in cars where things need to be turned off and on. In fact, modern car manufacturers are using relay panels in fuse boxes because they make maintenance simpler. There are a few things to think about when selecting relays for modern devices. First, you need to consider whether the contact will be normally closed (NC) or normally open (NO). Each of these situations will dictate which types of relays are needed and whether the device needs to be on all the time or needs to be toggled between the on and off positions. Another thing that must be considered is the maximum amount of voltage that the armature and its contact devices can handle. Finally, and perhaps the most important consideration, is the voltage and current that will be needed in the electronics project being undertaken because this will determine the armature activation.

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