The potential monitoring device PMD measures the difference of the electric potentials between two measurement points. If a pre-set value is exceeded the device is short-circuiting those two potentials temporarily.
The switching threshold can be set in one-volt steps. Direct – and alternating currents can be handled.
If the PMD shows an excessive temperature (the factory setting is 60°C) or defective contactor the device is inactive, i.e. the switching is not executed.
If the pre-set voltage level is exceeded the PMD is activated, i.e. simultaneously antiparallel connected thyristors are triggered and a contactor switched. The two contacts are short circuited.
After a pre-set specific period of time (8 to 60 seconds) the connection is cancelled.
The number of switching activities is counted. If more than five events take place in one hour an error / warning message is generated. In all other cases the counter is reset.
The following reports are generated by the PMD and are made available at potential free contacts:
Operation PMD in normal operation, open
Short-circuit PMD is closed
Error / Warning PMD has executed more than five switching activities in one hour
Excess temperature PMD interior temperature has reached threshold; device is inactive
For further information please download the datasheet: