Industrial Relays

What was industrial relay and how did it work?

Relays are electrical or electronically controlled remote switches. A control voltage is used to close or open a relay contact, depending on the design, or both with combined contacts at the same time. The controlled contacts switch other circuits. This switched circuit is electrically isolated from the control current.

For industrial use, precautions have been taken on these components with regard to the application environment, durability and additional electrical security. The actual relays are mostly encapsulated, whereby the housings are resistant to environmental influences, partly secure electrical protection types (IPxx) or fulfill fire protection requirements, i.e. are flame-resistant or self-extinguishing. 

In addition, there is an additional mounting environment for industrial relays – the relay socket. The base has various electrical connections for the relay control and the load circuit, for example as screw, spring or push-in contact. The connection to the actual relay contacts and the relay control is realized by plug contacts in standardized dimensions into which the relay is plugged. From there, they can be removed and replaced with a simple plug-in if necessary, without having to disconnect the wiring. The support of the relay module is ensured with a safety bracket. The base itself is suitable for mounting on different standard rails of electrical installation.

Additional components must be listed from an electrical point of view: Snubber diodes are installed to prevent damaging voltage peaks after switching inductive loads (relay coils). Further protection is offered by varistors – voltage-controlled resistors that dissipate harmful overvoltages with extremely short response times. The controlled relay contacts have a high material quality and are designed for frequent switching operations at rated voltage and current.

What types of industrial relays are there?

Many relays are designed for a control system with DC and/or AC operation. Some light emitting diodes are installed that indicate the operating status without the need for other test equipment.

Special relays have been developed for use in emergency situations. These are variants which are equipped with a manual emergency switch which can be used to carry out the actual electrical switching process in the event of failure of the control signal or the relay itself.

So-called solid state relays do not have mechanical contacts, but instead switch with electronic components such as transistors or thyristors or with a triac ("triode for alternating current", to German: "Bidirectional thyristor triode"). They work without moving parts, are therefore very durable and can be used for high switching frequencies and under adverse environmental conditions, for example in explosive environments. Galvanic isolation between the control circuit and the load to be switched is achieved by integrated optocouplers.

The available relays usually have several, partly international certifications such as VDE, UL, CSA, RINA, GOST, FI, IMQ, S, Nemko and others.