Fluke 1625-2 User Manual - Page 30

Remarks for the setting of earth spikes, pole measurement with longer earth electrode connecting leads

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1625-2 Users Manual Remarks for the setting of earth spikes: Before setting the earth spikes for probe and auxiliary earth electrode make sure that the probe is set outside the potential gradient area of earth electrode and auxiliary earth electrode. Such a condition is normally reached by allowing a distance of >20 m between the earth electrode and the earth spikes as well as of the earth spikes to each other. An accuracy test of the results is made with another measurement following repositioning of the auxiliary earth electrode or probe. If the value stays the same, the distance is sufficient. If the measured value changes, probe or auxiliary earth electrode must be repositioned until the measured value RE stays constant. Spike wires should not run too close to each other. 3-pole measurement with longer earth electrode connecting leads Use one of the accessory cable drums as earth electrode connecting lead. Spool off cable completely and compensate line resistance as described in Compensation of Earth Electrode Connecting Lead. Time average measurement: If there is a warning, MEASURED VALUE UNSTABLE, (see Table 5) after a test sequence, most likely it is caused by strong interference signals, such as unsteady noise voltage. Nevertheless, to get reliable values, the instrument offers the possibility of averaging over a longer period. 1. Select a fixed frequency (see Control Loop). 2. Keep the "START TEST" button pressed until the warning "measured value unstable" disappears. Maximum averaging time is approximately 1 minute. 22

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1625-2
Users Manual
22
Remarks for the setting of earth spikes:
Before setting the earth spikes for probe and auxiliary earth electrode make sure that the
probe is set outside the potential gradient area of earth electrode and auxiliary earth
electrode. Such a condition is normally reached by allowing a distance of >20 m between
the earth electrode and the earth spikes as well as of the earth spikes to each other.
An accuracy test of the results is made with another measurement following repositioning
of the auxiliary earth electrode or probe. If the value stays the same, the distance is
sufficient. If the measured value changes, probe or auxiliary earth electrode must be
repositioned until the measured value R
E
stays constant.
Spike wires should not run too close to each other.
3-pole measurement with longer earth electrode connecting leads
Use one of the accessory cable drums as earth electrode connecting lead. Spool off
cable completely and compensate line resistance as described in
Compensation of Earth
Electrode Connecting Lead
.
Time average measurement:
If there is a warning, MEASURED VALUE UNSTABLE, (see Table 5) after a test
sequence, most likely it is caused by strong interference signals, such as unsteady noise
voltage. Nevertheless, to get reliable values, the instrument offers the possibility of
averaging over a longer period.
1.
Select a fixed frequency (see
Control Loop
).
2.
Keep the "START TEST" button pressed until the warning "measured value unstable"
disappears. Maximum averaging time is approximately 1 minute.