Bender A-Isometer IRDH 275, Operating Manual

Page: 15 / 76

Function
15 TGH1361en/11.2009
2.5 Additional functions IRDH275B
Current output for external measuring instrument
The current output of IRDH275B provides 0(4)...20 mA. The current output
is galvanically isolated from the device electronics and the RS485 interface.
The ISO SETUP menu, on page 43, allows to switch over between 0...20 mA
and 4...20 mA.
Real-time clock
The real-time clock serves as a time base for the memory and self test func-
tions. At first, the correct time and date must be set in the menu "ISO AD-
VANCED". If time and date are not set, a „C“ (clock) is flashing in the
standard display. In the event of a supply voltage failure, time and date will
be stored for at least thirty days.
If the 24 h test is activated in the "ISO ADVANCED" menu, a special time of
day can be selected for the execution of the self test in the menu "TEST:
12:00". Then a self test will be started automatically once a day exactly at the
preset time. If the 1 h auto test has been selected, the self test is automatically
carried out every full hour.
Interconnected IT systems
When using A-ISOMETERs® in IT systems, make sure that only one active
A-ISOMETER® is connected in each interconnected system. If IT systems are
interconnected via coupling switches, make sure that A-ISOMETERs® not
currently used are disconnected and deactivated via a control system. IT sys-
tems coupled via diodes or capacitances may also influence the insulation
monitoring process. Hence, also in this case a central control of the different
A-ISOMETERs® is required.
Function input F1/F2 for connection or disconnection of
IT systems being monitored
The A-ISOMETER® can be disconnected from the IT system and set to
STANDBY mode with the function input F1/F2. If the input F1/F2 is bridged,
the connections L1/L2 are switched off via internal coupling relays, the meas-
uring function is stopped and the message "STANDBY" appears on the dis-
play. Software version 1.4 or higher does not indicate the measured
insulation resistance during the disconnection, but indicates the value
> 10 M
Ω
. Furthermore, the alarm relays and alarm LEDs no longer provide
alarm messages. After opening the function input F1/F2, the connection to
the IT system will be restored and a completely new measuring cycle for in-