Definitions of Basic Relay Terms and Specifications


Arc - An electric discharge between mating relay contacts when an energized circuit is interrupted.

Contact Bounce - The intermittent undesirable opening of closed contacts or closing of open contacts.

Break - The opening of closed contacts to interrupt an electrical circuit.

Voltage Breakdown - An undesirable condition of arcing within a relay due to over-voltage.

Cold - An unenergized electrical circuit.

Dielectric - An insulating medium capable of recovering, as electrical energy, all or part of the energy required to establish an electrical field (voltage stress). The field, or voltage stress, is accompanied by displacement or charging currents. A vacuum is the only perfect dielectric.

Hot - An energized electrical circuit.

Make - The closure of open contacts to complete an electrical circuit.

Peak Test Voltage - The peak AC voltage (at 60 Hz) which can be applied between external high voltage terminals or between the open terminals and ground for up to one minute with no evidence of failure. Peak test voltages must not be exceeded, even for very short pulses.

Rated Operating Voltage (kV Peak) - The voltage which can safely be applied to the relay for sustained periods of time without failure. This voltage rating decreases as AC frequency increases. Rated operating voltages approach peak test voltage only at lower frequencies.

Continuous Current, Carry - The current which flows through the closed relay contacts for sustained periods of time. This current rating is determined by the relay envelope temperature rise. A glass relay is allowed a 62 C rise, and a ceramic relay a 100 C temperature rise. Current ratings can be increased by external cooling, such as by forced air or heat sinks.

Contact Capacitance - The capacitance of the relay measured (a) between the open contact, or (b) between contact terminals and ground. Measured at 1 kHz.

Contact Resistance - The resistance between closed contacts. This measurement is made at 6.0 VDC with a 1.0 Amp RMS load.

Operate Time - The time in milliseconds between voltage being first applied to the relay coil and final closure of all normally open contacts. This time includes contact bounce.

Release Time - The time in milliseconds between removal of power from the relay coil and final closure of all normally closed contacts. This time includes contact bounce. 1 of 2 Pull-in Voltage - The minimum coil voltage required to operate a relay for all normally open contacts to close.

Dropout Voltage - The maximum coil voltage at which an operating relay releases and all normally closed contacts close.

Coil Resistance - The DC resistance of the relay coil measured at 25 C. Shock - The number of gravities (G's) a relay can sustain when tested by a 1/2 sine pulse (calibrated impact) for 11 milliseconds without the closed contacts opening or the open contacts closing. Vibration - The simple harmonic motion at rated gravities and frequency (G's/Hz) that a relay can sustain without uncontrolled opening of closed contacts or closing of open contacts.

Expected Mechanical Life - The minimum number of operations for which a relay can be expected to operate reliably. "Cold" switching applications approach this figure.

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