Title: +038=360.000-OU045T_04-PCD2.m4160 PLS SBC - IO Manual.pdf
When switching off load circuits with inductive components (e.g. relay coils and magnet coils) the interruption of current results in overvoltage (standard induc- tance) at the switching contacts. This may amount to many times the operating voltage and so threaten the insulation of the load circuit. The resultant breaking spark leads to rapid wear of the relay contacts. For this reason contact protection wiring is particularly important with inductive load circuits. Values for the RC com- bination can also be determined from the adjacent diagram. However, for voltage U it is necessary to use the overvoltage arising from the interruption of current (e.g. measurable with an oscillograph). Current must be calculated from this volt- age and the known resistance, against which the voltage was measured.