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 (Page 149).
● 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.
5.1.4 Preparing the mating faces
Prepare the foundation faces dependent on the machine type:
● Mounting on a foundation
– Ensure that the foundation faces are flat and free of contaminations.
– Check the dimensions of the mounting-foot holes.
● Flange connection
– Clean the flange before installation. Ensure that the flange surfaces are flat and perfectly
clean.
– Check the geometry of the flange.
● Wall mounting
– Ensure that the wall faces are flat and free of contaminations.
– Check the dimensions of the mounting-foot holes.
– Support the machine from below, e.g. using a wall bracket or by bolting it.
Assembly
5.1 Preparations for installation
SIMOTICS TN Series N-compact 1LA8
Operating Instructions 08/2017 53
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