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4.4 DESCRIPTION OF MEASURING LEADS
4.5 GUARD LEAD
In some cases, measurements could be affected by surface currents. By applying voltage
to an insulation to be measured, there may be two distinct currents: one flowing in the test
piece, the other flowing on its surface. In case you want to measure only the resistance
due to current Im flowing in the test piece Rx (which is the significant one), it is necessary
to absorb the surface current If using another lead.
4.6 NOTES ON THE INSULATION MEASUREMENTS
Measuring a high resistance such as the insulation resistance is very difficult as the value
of the currents considered may be very low. When measuring, to prevent making
mistakes, it is therefore necessary to take the following precautions:
• Keep the measuring leads suspended above the path or, anyway, make
sure the leads do not make contact in more of one point
• While measuring high resistances, the area around the measuring
instrument and the appliance being tested must be free. It is recommended
to use the timer function so that the operator may keep at due distance
from the leads and from the resistance to be tested
• It is recommended to use the GUARD lead to measure resistances of
some tens of G or higher
• While use the instrument with main supply, it's important to check
that the earthed resistance pole to measure is connected to the
instrument Rx+ Terminal
Fig. 2: Measuring leads
Fig. 3: Currents flowing in the test piece
EN - 7
CAPTION:
1. Hand protection
2. Safety areas
CAUTION
HT7051 - HT7051N
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