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Function
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isoLR275_D00127_00_M_XXEN/07.2018
2.4
Description of function
The isoLR275 ISOMETER® is connected between the unearthed system (IT sys-
tem) and the protective conductor (PE) using the AGH-LR coupling device.
The response values and other function parameters are set via the function
buttons. The parameters are indicated on the LC display and are stored in a
non-volatile memory (EEPROM).
A microprocessor-controlled pulsating AC measuring voltage is superimpo-
sed on the IT system to be monitored (
measurement method*).
The measuring pulse consists of positive and negative cycles of the same am-
plitude. The period depends on the respective system leakage capacitances
and the insulation resistance of the system to be monitored.
An insulation fault between system and earth closes the measuring circuit.
The evaluation circuit calculates the insulation resistance which is indicated
on the LC display or the external kW measuring instrument after the measu-
ring time has expired.
The measuring time is dependent on the selected measurement method, the
system leakage capacitance, the insulation resistance and the system-related
disturbances.
System leakage capacitances do not influence the measuring accuracy.
If the reading is below the selected response values Alarm 1/Alarm 2, the as-
sociated alarm relays respond, the LEDs "Alarm 1/2“ light up and the measu-
ring value is indicated on the LC display (in the event of DC insulation faults,
the faulty supply line is indicated). If the terminals R1/R2 are bridged (external
reset button [N/C contact] or wire jumper), the fault message will be stored.
Pressing the reset button, resets the fault message, provided that the insulati-
on resistance is at least 25 % and at least 1 kW above the actual response va-
lue. The fault memory behaviour can also be set in the "ISO SETUP“ menu, by
selecting the submenu Memory: on/off.
*)
measurement method
(Adaptive Measuring Pulse), a measurement method developed by Bender
(European Patent: EP 0 654 673 B1).
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