XS series operating manual
XS user manual v0.55 - 134 -
Precautions to be observed
It is important to connect the specimen to be measured in taking care of the parasite leakages which
could be created by the measurement operating procedure.
The supplied accessories have a shielding which is connected to a guard potential, this insures a good
immunity of the measurement regarding the parasitic leakage currents and the AC residuals.
When using extending of the basic probes, take the necessary cares to avoid to introduce measurement
errors (short leads, leads not touching any metallic or insulating parts,....)
During insulation resistance measurements having high values (> 100 Gohms), the proximity of the
operator putting his hand close to the specimen under test, can alter or make unstable the
measurement. It is important to beware of Nylon blouses or of insulating material things capable of
generating by static electricity, high electrical fields which can alter the measurement of high value
resistances (100 Gohms under 100 VDC = 1 nA of measurement current).
Measurements of capacitors
We remind that a lot of recent electrical units are fitted with main line filters including capacitors for the
electromagnetic compatibility. When measuring on capacitors it is advised to select the filter mode
CAPACITOR of the SETUP menu in order to stabilize the measured values.
A) Indeed, on capacitors, the variations of the measurement power supply, even small as well as the
interferences are entirely transmitted to the input of the current measurement system which have a
very high gain, and therefore will amplify these variations. The CAPACITOR filter switches on circuits
which will limit the instability of the measurement.
B) Never perform insulation resistance measurements on capacitive specimens in reducing the
measurement voltage between each test, but always in increasing the voltage. The hysteresis and
polarization phenomena of the dielectric material will alter the results. In that case the unit indicates its
maximum value and takes a long time to come back to the real measured value.
C) The insulation resistance value of a capacitor being a function following a time exponential law, it is
important to make sense to the measured value, to indicate the duration of the measurement. The
units of the MG series allow complying with this requirement with the built-in timer, able to measure
times going from 1 second up to 16 minutes.
D) Never disconnect a capacitive specimen before switching into DISCHARGE mode and waiting the
necessary time to discharge its capacitance through the 2.2 kohms built-in resistance of the discharge
circuit (about 1 second per 100 uF).
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