The coupling device AGH204S-4 is designed to extend the nominal voltage range of the A-ISOMETER® series described in the wiring diagram below to AC, 3(N)AC 50…400 Hz, 0…1650 / 0…1300 V. The coupling device is connected to the system to be monitored according to the wiring diagram and connected to the terminal AK of the A-ISOMETER® by means of terminal AK.