- Three Phase AC Systems

The VMD420 is a powerful, all-in-one unit for measuring voltage and frequency stability in three-phase AC systems. Two separate alarms allow for the simultaneous measurement of overvoltage, undervoltage, overfrequency, underfrequency, phase sequence, phase loss, and asymmetry in systems up to 500 V 3AC and from 15 to 460 Hz.

Measurements taken are read as true RMS values; harmonics up to 460 Hz are taken into account. Each of the two alarms has a seperate Form C SPDT contact for use with external LEDs, contactors, PLCs, and many other applications. The two alarms may be set to any combination of the above readings. Contacts may be set for normally energized or de-energized operation.

The VMD420 has additional features for three-phase systems. In addition to reading line-to-line voltages and frequency, the VMD420 can check for load asymmetry, as well as phase sequence or loss. Any one of these settings may be configured to one of the two available alarms.

The VMD420 has three seperate, adjustable time delays (start-up, response, on release) from 0 to 99 seconds. Setpoint and hysteresis ranges allow for application-tailored sensitivity. A fault memory toggle allows alarms to either latch or auto-reset after it has cleared.

Values are read and settings are changed via a digital LCD display. Three pushbuttons allow for navigation through built-in menus. History memory stores the last received alarm. A password protection may also be set. The VMD420 is a UL listed product.

These devices are suited for installation into standard distribution panels according to DIN 43 871 and for quick assembly onto support rail according to DIN EN 50 022 or for screw mounting.