Measuring the polarization index
1. To determine the polarization index, measure the insulation resistances after one minute
and ten minutes.
2.
Express the measured values as a ratio:
PI = R
insul 10 min
/ R
insul 1 min
Many measuring devices display these values automatically following the measurement.
For insulation resistances > 5000 MΩ, the measurement of the PI is no longer meaningful and
consequently not included in the assessment.
R
(10 min)
/ R
(1 min)
Assessment
≥ 2 Insulation in good condition
< 2 Dependent on the complete diagnosis of the insulation
NOTICE
Damage to insulation
If the critical insulation resistance is reached or undershot, this can damage the insulation
and cause voltage flashovers.
●
Contact the Service Center.
●
If the measured value is close to the critical value, you must subsequently check the
insulation resistance at shorter intervals.
Limit values of the anti-condensation heating insulation resistance
The insulation
resistance of the anti-condensation heating with respect to the machine housing
should not be lower than 1 MΩ when measured at 500 V DC.
7.4 Heating in order to reach the required surface temperature
Required surface temperature
Always switch the heating on when the machine is at standstill. When the heating is switched
on for the first time (commissioning) make sure that the ambient air temperature does not fall
below the minus temperature stated in the EC type-examination certificate. Otherwise the
explosion protection is not guaranteed.
The heating is not designed to warm the machine up to the minimum permissible surface
temperature, but rather to keep the machine at the minimum surface temperature. The machine
must be operated at a surface temperature above the minus temperature stated in the EC type-
examination certificate in order to maintain the explosion protection. The machine startup or
machine commissioning can only take place once the machine has the minimum surface
temperature (see machine surface temperature during commissioning ≥ -xx° C on the
supplementary plate).
Make sure that the heating is switched off before the machine is switched on and make sure
that it is not switched on again during operation.
Start-up
7.4 Heating in order to reach the required surface temperature
LOHER CHEMSTAR 1PS2
Operating Instructions 08/2016 69
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