States how long a coil may be energized without overheating. The following formula is applicable:
ED % = (pulse on time/(pulse on time + pulse interval)) x 100
From this can be derived:
pulse on time = (ED %/100 - ED %) x pulse interval
pulse interval = (100 - ED %/ED %) x pulse on time
In addition to the ED % figure the listed values include an addition concerning the maximum permanent on time. Therefore a coil may only be energized by a constant current during this period and then has to be cooled off again.
At ED = 100% a limitation is not necessary as the coil will never become inadmissibly hot, even if continuously energized.
A count coil has the listed value ED = 15 %, max. 55 sec. This coil may therefore remain under constant current for max. 55 sec. After this a cooling interval of pulse interval = ((100-15)/15) x 55s = 283s is required.
The same coil is constantly receiving pulses of 40 sec. duration with a count interval of 6 min. Is this still permissible?
ED % = (40/40 + 360) x 100 = 10 %
Since the on time does not exceed 15 % these pulse-on times are permissible.
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