Interposing Relay Application, Advantages, Function, Connection

Hey, we are going to learn about a very important device which is the Interposing Relay. In this article, you will find Interposing Relay Application, Advantages, Function, Connection, and many more.
As its name suggests, the Interposing Relay is a device that is used to interpose between two different electrical circuits.

An interposing relay is also known as an interface relay or pilot relay. It is basically an electromechanical device that acts as an intermediary between different electrical circuits or systems. It is typically used in industrial control systems to provide electrical isolation, signal amplification, and voltage level conversion. The interposing relay consists of a coil, which is energized by a control signal, and one or more sets of contacts. When the coil is energized, the contacts of the interposing relay change their state (open or closed), allowing or interrupting the flow of current in the controlled circuit.

The main difference between a normal relay and an interposing relay is that the Normal relays focus on controlling the flow of current in a circuit, whereas interposing relays provide electrical isolation, signal amplification, and voltage level conversion between different circuits or systems. An interposing relay is used when two different circuits are working together but they should be separate, and highly isolated to each other. Those two circuits may have different currents and different voltages.

Interposing Relay Function

The main function of an interposing relay is to separate two circuits, provide isolation between them, put a barrier between them, and to operate one circuit with the help of another circuit. Overall, interposing relays act as an interface between different electrical systems.

In some cases, the control signal from a device, such as a programmable logic controller (PLC) or a control panel, may not be strong enough to directly operate a load or control a distant device. Interposing relays can amplify the control signal, providing the necessary power to drive larger loads or reach remote locations.

In other words, we can say the  Interposing relays can convert control signals from one voltage level to another. For example, if a control system operates on a low voltage level (e.g., 24V DC), but the load or device requires a higher voltage (e.g., 120V AC), an interposing relay can be used to bridge the voltage difference.


Let's understand with a Connection Diagram.

Interposing Relay Connection Diagram and Wiring

Suppose we want to control a high-power three-phase motor using PLC. The motor needs a 440V three-phase power supply but PLC can give a 24V DC supply. So, in this case, an Interposing Relay is needed. The coil of the interposing relay can be operated by the 24V DC supply but its contacts can handle the 440V AC supply.

In the above figure, you can see the contactor coil needs a 230V AC supply. PLC gives a 24V DC supply. So in this case, the Interposing relay interposes between 24V DC and 230V AC systems. Here, the 24V DC is fully separated and isolated from the 230V AC supply.

When PLC gives the 24V DC supply to the relay, it closes the circuit, and the 230V AC supply is applied to the contactor coil. So the contractor will be closed and the motor will start rotating.

Interposing Relay Applications

1. Interposing relays are mostly used in Industrial Automation Systems for motor control and high-power light control.

2. Interposing relay used to interpose between digital and analog circuits.

3. Interposing relay used in the digital control system as a driver such as motor driver, light driver, electrical contactor driver, etc.

4. Interposing Relay also used in industrial protection systems and switchgear systems. Such as it is used to interpose between low voltage, low current control equipment and high voltage, high current Circuit Breaker.

5. Interposing Relay is used to operate high voltage, high current isolators, actuators using low voltage, low current PLC systems, microcontrollers, etc.

Interposing Relay Advantages

1. It can provide separation and high isolation between two different circuits that's why no disturbance propagates from one circuit to another circuit. Safety and protection are also maintained.

2. It can be used in Digital Circuits also.

3. It works as a static device, so the speed of operation is higher.

4. The interposing relay does not get damaged when a digital control signal is applied to it. This makes an important advantage over a conventional contactor.



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