Document No. 1-41045473
Date Updated 07-25-2012 Date Created 09-22-2004
Document Type FAQ Related OS
Related Product PCI-1760 / PCI-1761 / PCI-1762 / PCL-725 / PCL-735 / PCM-3725
User's note of switching a inductive load
Solution :
It is caused by anti voltage. It coccurs when the relay switch a inductive load. And its amplitude(V) is relative to the induction coil(L), current variation(di) and time(dt). Formula V = -Ldi/dt.

For example, if the load is a relay-OMRON MY24NJ, its current(i)=36.9mA, inductance(L) =5.72H.operation time(t)=4ms Then, the formula is V=-Ldi/dt and get the anti voltage V= -5.72 * 36.9m/4m = -52.75V. Due to the switch time will be faster than operation time, the actual value measuring by instrument is up to -320V.

It will be over reply's specification. To solve this issue, user can add a diode in parallel to discharge this potential.people call it as freewheel diode.
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