Function
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IRDH575_D00089_05_M_XXEN/01.2020
3.5 Function
The IRDH575 ISOMETER® is connected between the unearthed system and the
protective conductor (PE).
The response values and other function parameters are set via the function keys.
The parameters are indicated on the LC display and are stored in a non-vola-
tile memory (EEPROM) after the setting is completed.
A microprocessor-controlled pulsating AC measuring voltage is superimpo-
sed on the system ( measuring principle*). The measuring cycle
consists of positive and negative pulses of the same amplitude. The period de-
pends on the respective system leakage capacitances and the insulation resis-
tance of the system to be monitored.
An insulation fault between system and earth closes the measuring circuit.
From the measured current value, the microprocessor calculates the insulati-
on resistance which is indicated on the LC display or the external kΩ measu-
ring instrument.
The measuring time is determined by the system leakage capacitances, the in-
sulation resistance, and the system-related interference disturbances. System
leakage capacitances do not influence the measuring accuracy.
If the reading is below the selected response values ALARM1/ALARM2, the as-
sociated alarm relays respond and the alarm LEDs "ALARM1/2" light up and
the measuring value is indicated on the LC display (in the event of DC insula-
tion faults, the faulty supply line is indicated). The fault indication can be
stored by bridging the terminals R1/R2 (external RESET button [NC contact])
or by setting the fault memory to "Memory:on" in the "ISO SETUP" menu.
Pressing the external or internal RESET button, resets the fault message, pro-
vided that the insulation resistance is at least 25 % above the preset value.
Prevent measurement errors!
When an AC system includes galvanically connected DC
circuits, the following shall be considered:
Insulation faults in DC circuits can only be monitored
correctly when the rectifiers carry a continuous load of at
least 5…10 mA.
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