HTD datasheet(7/14 Pages) ETC2

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Application notes

N°102

RELAYS AND TEMPERATURE VARIATIONS

Most relay parameters are specified as maximum values over the rated temperature range of the specific relay. Users often

find that key parameters differ significantly at ambient temperature (20-25°C) and sometimes fall into the trap of specifying

their system around these ambient parameters. Additionally the actual temperature experienced by the relay can be far in

excess of existing ambient temperatures due to the heat generated by the coil current and the contact load. Figure 1 is the

summary of temperature effects on relay electrical characteristics.

Temperature

Resistance

Current

Operating

Voltage

Release

Voltage

Operate Time

Release Time

Increase

DOWN

Decrease

DOWN

Fig. 1

The following formulas are sometimes useful in calculating the effects shown above.

1. Change in coil resistance due to change of ambient temperature can be calculated by the following formula.

R = R20 [1 + .0039 (T-20)]

Where: R = Coil resistance at given temperature

R20 = Coil resistance at 20°C

T = °C Ambient temperature

"Rule of Thumb" : For each 10°C change of temperature, coil resistance will change approximately 4%.

2. High and low temperature pick up voltage:

E2 = E1K2,

Where: E2 = Pick Up Voltage at T2 temperature

E1 = Pick Up Voltage at 20°C

K2 = Coefficient of correction found on the graph in Fig. 2 at T2

Date of issue: 6/00

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