What is the use of interposing relays in control systems?

In order to provide electrical isolation and improve the overall reliability and functionality of the system, interposing relays, often referred to as auxiliary relays or pilot relays, are frequently used in control systems.

Why are interposing relays used?

Interposing relays are frequently used for the following purposes:


By acting as intermediary relays, weak control signals can be made more powerful to switch stronger components like motors, solenoids, or larger relays. This prevents the sensitive control circuitry from being connected directly to the control system, allowing it to manage higher loads.


Electrical isolation is provided between various control system circuits by them. The control circuit and the power circuit can be entirely divided using an interposing relay, shielding the control components from any interference or disturbances.

Logic and sequencing:

Interposing relays are frequently used in control systems to implement logic operations and complex sequencing. Specific control sequences can be achieved by connecting the contacts of several relays in various configurations, enabling complex control actions.

Fault detection and protection:

Interposing relays can be used to detect faults or other abnormal conditions in the control system, providing fault detection and protection. For instance, a relay may be set up to monitor current levels and trip or sound an alarm if the current rises above a predetermined level, signaling a defect or overload.

Signal conversion:

Interposing relays may occasionally be used to change one kind of signal into another. For instance, a relay can transform an analogue control signal (like a voltage or current) into a digital signal, allowing it to work with many control devices.

Interfacing with different voltage levels:

Interposing relays can fill the chasm between voltage-varying control signals. Interposing relays, for instance, can step up the voltage to interface with high voltage devices if the control circuit uses low voltage signals.

Interposing relays provide isolation, amplification, logical operations, fault detection, and other signal conversion capabilities, all of which are essential in control systems. They improve the control system’s dependability, adaptability, and safety by separating the delicate control circuitry from the high-power components and by making intricate control tasks easier.