RELAY INTERFACE MODULE:-

1 Introduction:-Now days Clear and reliable potential separation is becoming more and more

important for the reliability of industrial automation facilities. Modern relay or optocoupler interfaces fulfill the most varied tasks. Whether in production engineering, for the electrical equipping of machines or in control engineering for power distribution, building automation and materials processing - the main aim is to guarantee the exchange of signals between the process peripherals and the higher level control systems. This exchange must provide reliable operation, be floating and electrically unambiguous

Relay interface Module a hardware device used for remote device Switching. It is nothing but single or combination of multiple relay’s mounted on PCB either direct soldered or mount using relay Socket (in this case relay socket solder on PCB & relay clip in socket & use relay clip for Relay tight fitting which help working relay module to under vibration condition)

Relay interface modules must have the following characteristics:

Coupling of different signal levels Reliable electrical isolation between input and output Ease of operation. Easy mounting arrangement Independence of the type of switching current (AC and DC)

2 Application:-

Relay module used as Interfacing PLC (pro / Drive / DCS Digital Outputs to field or field devices. These will be in isolation between the I/P & O/P (Output are galvanically isolated through Relays).The relay module can be used to sense external ON/OFF conditions and to control a variety of external devices. So relay module used as

Interfacing of PLC I/Os to field Sensors & actuators Multiplication of PLC O/Ps for separately driving actuators,

annunciators & other devices. Isolation of high voltage load & input devices from sensitive

PLC electronics. Providing channel wise isolation for PLC inputs & outputs.

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3 Construction:-

Relay module is Customized product & manufacture according to the requirement so it is not easy to differentiate in number of types. But for simplicity relay module differentiate on which type relay is used, number of relay used in the module and choice of features such as with / without fuse and with / without relay mounting base.

Circuit & Mounting Arrangement

Fig 3.1.1 Schematic Circuit & Mounting diagram for 8 channel 2 changeover relay module w/o fuse

Following components are used in module1) PCB2) Relay

o Electromechanical Relayo Solid State Relay

3) Relay mounting Socket ( if require)

4) I / O terminal5) LED for indication6) Freewheeling Diode7) Mounting arrangement8) Extra Feature components

o Fuse Socket & fuse, Fuse fail Indication circuitry

o Surge protection

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RELAY INTERFACE MODULE:-

3.1 PCBA printed circuit board, or PCB, is used to mechanically support and electrically

connect the relay & I/O terminal using conductive pathways, tracks, or traces, etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board (PWB) or etched wiring board. The size of PCB depends upon the requirement & Number of used in module. Generally Single side or Double side Board is use in Relay module for more detail please click hear PCB

Leading Manufacturer:-

3.2 RelayNormally all PCB mounting type of relays are suitable for using in

Relay module. The Selection of relay is depending upon the Application & Requirement. Relay either directly soldered on PCB or mount on Relay socket.

Relay interface modules are manufacture in different channel density viz 1, 2, 4, 6, 8, 16 & 32 channels. (Also manufacture different number of channel relay module depending upon the Requirement)Number of o/p contact following number of change over Relay Interface module is available

1) One Change over Relay Interface module2) Two Change over Relay Interface module3) Four Change over Relay Interface module4) Six Change over Relay Interface module5) Only NO or NC contact type Relay Interface module

3.3 Relay Socket (if required)On module Relay either directly soldered on PCB or mount on Relay socket. In direct

soldering method relay permanently soldered on PCB. In this type there is no possibility for loose connection under any condition (unless & until relay burnt down or mechanically damaged).even though it is economical way to built the relay module but in this method if relay burnt or damaged there is no

scope for relay replacement hence not suitable. To easily maintenance Relay socket is used for mounting the relay on PCB. For tight & normal contact Relay clip is used.

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3.4 I/O Terminal

A terminal is the point at which a conductor from an

electrical device or network comes to an end and

provides a point of connection to PCB.

PCB mounted Screw or spring type Terminal used in relay module.

To reduce the relay module size often double Dekker type terminal

is used. The selection of terminal is depend on the contact rating

.

3.5 Flyback /Freewheeling Diode

A flyback diode (sometimes called a snubber diode, freewheeling diode, suppressor diode, or catch diode[) is a diode used to eliminate flyback, the sudden voltage spike seen across an inductive load when its supply voltage is suddenly reduced or removed.

Fly back /Freewheeling Diode used across the relay

3.6 LED for Indication LED is use for indication purpose. The selection of LED is important as it indicate which relay is operating/energies. Depending on Application either center glow or Diffused type of LED is used. Normally green Led is use for Relay On indication purpose. RED color LED use for power on & Fuse fails indication.

Coil

3.7 Mounting arrangement Mounting of module want to permanently fix in systems then screw mounting use (normally now days no one use this Type mounting). Otherwise din rail mounting is preferred

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3.8 Extra Feature components

3.8.1 Fuse Protection For protection from Short circuit, overload the Fuse is placed on relay contact side

Normally Glass fuse is used in Relay module. Depending upon the requirement or relay module size the Horizontal mounting or vertical mounting fuse socket is used to mount the Fuse. Some time resettable fuse is used. Red Led is used to fuse fail indication Purpose

3.8.2 Surge Protection

VaristerA varistor is an electronic component with a significant non-ohmic current–

voltage characteristic. Varistors are used to protect circuits against excessive transient voltages by incorporating them into the circuit in such a way that, when triggered, they will shunt the current created by the high voltage away from the sensitive components. A varistor is also known as Voltage Dependent Resistor or VDR. A varistor’s function is to conduct significantly increased current when voltage is excessive. A varistor remains non-conductive as a shunt mode device during normal operation when voltage remains well below its "clamping voltage". If a transient pulse (often measured in joules) is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed.

Snubber circuitSnubbers are used in electrical systems with an inductive load where the sudden interruption of current flow often leads to a sharp rise in voltage across the device creating the

interruption. This sharp rise in voltage is a transient and can damage and lead to failure of the controlling device. A spark is likely to be generated (arcing), which can cause electromagnetic interference in other circuits. The snubber prevents this undesired voltage by conducting transient current around the device

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RC snubbers

A simple snubber comprising a small resistor (R) in series with a small capacitor (C)

is used. Snubbers are used to prevent arcing across the contacts of relays and

switches and the electrical interference and welding/sticking of the contacts that can

occur. An appropriately-designed RC snubber can be used with

either DC or AC loads. This sort of snubber is commonly used with inductive loads

such as electric motors. The voltage across a capacitor cannot change

instantaneously, so a decreasing transient current will flow through it for a small

fraction of a second, allowing the voltage across the switch to increase more slowly

when the switch is opened. While the values can be optimized for the application, a

100 ohm non-inductive resistor in series with a 100 nanofarad, or larger, capacitor of

appropriate voltage rating is usually effective. Determination of voltage rating can

be difficult owing to the nature of transient waveforms; the actual rating can be

determined only by measuring temperature rise of the capacitor.

4 Types of relay module

On Types of Relay we can Differentiate Relay Interface module as Per Below1) Electromechanical Type Relay Module2) Solid State Relay Type Relay Module3) Customized (hybrid) Relay Module

4.1 Electromechanical Relay Interface module

Electromechanical relay Interface module is use in lower current switching application. Due possibility of spark at the time of relay switching hence it is not used in explosive environment.

Advantage Economical Easily available in Local market

Disadvantage Not suitable for high Switching frequency application

Not suitable for high current application Restriction due to contact life

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Sometime contact chatter Not suitable in explosive environments where a

Spark must not be generated during turn-on

4.2 Solid State Relay Module

Solid State Relay Modules deliver electrically clean, Opto isolated, noise free Output. These Modules available are for various voltage and performance levels. They are used as interface modules for matching process peripherals to control, signaling and regulation devices. SSR Type Module is used when the interface between the process peripherals and electronics is subject to the following requirements:

Low control power High switching frequencies No contact chatter Resistance to vibrations and polluted environments Long service life, independent of the number of switching operations explosive environments

Advantages Ideal for high Switching frequency application Ideal for high current application Long life as no moving or mechanical part Can be used in explosive environments where a

Spark must not be generated during turn-on Clean, bounceless operation

Disadvantages costly Not Easily available in Local market Not suitable for some application due to SSR leakage current

4.3 Customized (hybrid) Relay Module

As name suggests this Relay module is nothing but combination of SSR & Electromechanical relay as per requirement & application in Single board.

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