• Insulation monitoring device for AC and DC IT systems
  • Application main circuits with connected frequency converters
  • According to IEC 61557-8
  • Automatic adaptation to the system leakage capacitance
  • Info button to display the device setting

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. The AMPPlus 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.

  • Features
  • Applications
  • Accessories
  • Ordering information
  • Downloads
  • 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
  • AMPPlus 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


Optional accessories for ISOMETER® IRDH375

External kΩ measuring instruments (400 µA)
TypeSKMP *2)Art. No.
7204-1421120 kΩB986763
9604-1421120 kΩB986764
*2) SKMP = scale centre point

External kΩ measuring instrument 20 mA
TypeArt. No.

Transparent front plate cover IP65
TypeArt. No.
144 x 72B98060005

Coupling devices
TypeNominal system voltage UnArt. No.
AGH150W-4DC 0…1760 VB98018006
AGH204S-4AC 0…1300 V / 0…1650 VB914013
AGH520SAC 0…7200 VB913033

Variants of ISOMETER® IRDH375

TypeNominal voltage UnSupply voltage USArt. No.
IRDH375-435AC 0…793 V / DC 0…650 V*AC 88…264 V / DC 77…286 V*B91065000
IRDH375-427AC 0…793 V / DC 0…650 V*DC 19.2…72 V*B91065002
IRDH375B-435AC 0…793 V / DC 0…650 V*AC 88…264 V / DC 77…286 V*B91065004
IRDH375B-427AC 0…793 V / DC 0…650 V*DC 19.2…72 V*B91065006
* absolute values
Device “Option-W” with increased shock and vibration resistance: Indicated by the letter “W” at the end of the order number

Downloads for ISOMETER® IRDH375



Category Product Language Date Size Download