The ISOMETER® of the IRDH375(B) series is designed to monitor the insulation resistance of
unearthed main circuits (IT systems) AC, AC/DC 0…793 V resp. DC 0…650 V.
TheAMP Plus  measuring principle meets the particular requirements of modern power supplies
which often include rectifiers, converters, thyristor-controlled DC drives and directly connected
DC components. In these systems often high leakage capacitances against earth occur due to
interference suppression measures. The IRDH375(B) automatically adapts itself to the existing
system conditions.
In combination with a coupling device, the Isometers can also be used for higher voltages. An
external supply voltage allows de-energized systems to be monitored too.

Product Details


  • Insulation monitoring for unearthed AC, AC/DC systems 0…793 V, DC 0…650 V
  • Nominal voltage extendable via coupling device
  • Two separately adjustable response values 1 kΩ…10 MΩ
  • AMP Plus  measurement method
  • Automatic adaptation to the system leakage capacitance
  • Info button to display device settings and the system leakage capacitance
  • Continuous self monitoring, with automatic alarm message
  • Automatic self test, selectable
  • Connection for external kΩ indication
  • Test and reset button
  • Connection external test and reset button
  • Two separate alarm relays with two potential-free changeover contacts
  • N/O or N/C operation
  • Alarm relay for system fault (N/C operation)
  • Backlit LC display
  • RS-485 interface
  • Plug-in terminals


  • AC, DC or AC/DC main circuits
  • AC/DC main circuits with directly connected DC components, such as rectifiers, converters, and thyristorcontrolled DC drives
  • UPS systems, battery systems
  • Heaters with phase control
  • Installations including switch-mode power supplies
  • IT systems including high leakage capacitances
  • Coupled IT systems