With monostable DC or AC relays, the contacts automati- cally return to the release state when the excitation current is switched off. In the case of bistable relays, the contacts remain in their present switch position when the excitation current is switched off.

What is relay and its function?

Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. When a relay contact is Normally Closed (NC), there is a closed contact when the relay is not energized.

What is bistable relay?

Bistable relays allow for two stable switch positions even when powered down. In comparison to monostable relays, just a short switching impulse of a few milliseconds is enough to switch the relay into a defined switch position. Only a low nominal power level is required. This saves energy and reduces heat generation.

What are the four functions of a relay?

If preventive relays are being used, it can detect overcurrent, overload, undercurrent, and reverse current to ensure the protection of electronic equipment. Last but not the least; it is used to heat the elements, switch on audible alarms, switch the starting coils, and pilots the lights.

What is the principle of relay?

Relay works on the principle of electromagnetic induction. When the electromagnet is applied with some current it induces a magnetic field around it.

What is an NC relay?

Normally open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. Normally closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive.

When does a monostable multivibrator switch to its unstable state?

When triggered by an input pulse, a monostable multivibrator will switch to its unstable position for a period of time, and then return to its stable state. The time period monostable multivibrator remains in unstable state is given by t = ln(2)R2C1.

What is the characteristic impedance of a relay?

The relay contacts are designed not to reflect any radio frequency power back toward the source, and to provide very high isolation between receiver and transmitter terminals. The characteristic impedance of the relay is matched to the transmission line impedance of the system, for example, 50 ohms.

What are the characteristics of a good control relay?

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.

What is the purpose of relays in circuits?

Relays are used where it is necessary to control a circuit by an independent low-power signal, or where several circuits must be controlled by one signal. Relays were first used in long-distance telegraph circuits as signal repeaters: they refresh the signal coming in from one circuit by transmitting it on another circuit.