Function
20
IRDH275BM-7_D00123_06_M_XXEN/07.2018
An insulation fault between the IT system and earth closes the measuring cir-
cuit. From the measured current value, the microprocessor calculates the in-
sulation resistance which is indicated on the LC display or the external kΩ
measuring instrument.
The measuring time t
an
is determined by the system leakage capacitances, the
insulation resistance, and the system-related interference disturbances. Sys-
tem leakage capacitances do not influence the measuring accuracy. When vir-
tually no disturbances are caused by the operation of converters, the
measuring process takes about five minutes.
If the reading is below the selected response values Alarm 1/Alarm 2, the as-
sociated alarm relays respond and the alarm LEDs "Alarm 1/2“ light up and the
measuring 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 [NC contact] or wire bridge), the fault indication will be
stored. Pressing the RESET button, resets the insulation fault message, provid-
ed that the currently displayed insulation resistance is at least 25 % above the
actual response value when the reset is carried out. The fault memory behav-
iour can also be set in the "ISO SETUP" menu, by selecting the sub menu Mem-
ory: on/off.
The connections for an external kΩ display supplied by the current output
0(4)…20 mA at M+/M- are galvanically isolated.
*) measuring principle "adaptive measuring pulse", a measuring
principle developed by Bender (European Patent: EP 0 654 673 B1).
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