VME421H-D-2 BENDER

The voltage monitor VME421H monitors AC/DC systems in the frequency range of 
DC/15…460 Hz for undervoltage, overvoltage, underfrequency or overfrequency. 
Device variant -1 is suitable for the nominal voltage range Un = 9.6…150 V, device 
variant -2 for Un = 70…300 V. The supply voltage is taken from the nominal voltage 
being monitored Un.
In order to meet the requirements of the applicable standards, customised parameter 
settings must be made on the equipment in order to adapt it to local equipment and 
operating conditions. Please heed the limits of the range of application indicated in the 
technical data. 
Typical applications
• Voltage and frequency monitoring of single-phase machines and electrical installations
• Earth fault monitoring in medium-voltage systems via voltage transformers
• Monitoring of battery systems
• Switching machinery and equipment on and off at a certain voltage level
Function
Once the supply voltage is applied, the start-up delay “t” begins. Measured voltage and 
frequency values changing during this time do not influence the switching state of the 
alarm relays.
The devices feature two separately adjustable measuring channels (overvoltage/undervoltage).
 When the measuring quantity exceeds the response value (“Alarm 1”) or falls 
below the response value (“Alarm 2”), the time of the response delays “ton1/2” begins. 
Once the response delay has elapsed, the alarm relays switch and the alarm LEDs light 
up. When the measuring value exceeds or falls below the release value (response value 
plus hysteresis) after the alarm relays have switched, the selected release delay “toff” begins.
 When “toff” has elapsed, the alarm relays switch back to their initial position. When 
the fault memory is activated, the alarm relays remain in alarm position until the reset 
button R is pressed. Also in the event of complete power failure of the system being 
monitored, the delay times are effective during the energy backup discharging time.
Energy backup
Also in the event of complete power failure of the system being monitored, the delay times 
are effective during the energy backup time. When the fault memory is set to continuous 
mode, the alarm parameters remain stored, even on failure of the supply voltage.
Preset function
After connecting the device for the first time, the nominal system voltage will be determined
 (PrE run), and the response values for overvoltage and undervoltage as well as for 
underfrequency and overfrequency will automatically be set. When no voltage is determined
 within a nominal system voltage range (PrE run), the response values will be set to 
the minimum or maximum voltage. In this case, the message “AL not SET” appears on the 
display. As long as no button is pressed, a nominal system voltage is being searched cyclically 
(PrE run). If a button is pressed, the search will be interrupted and the message “AL not SET” 
disappears. In this case, the appropriate response values have to be set in the menu. 
When activating the frequency monitoring function, the preset frequency will automatically 
be stored.