Fluke 1625 User Manual page 43

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 auxil-
iary earth electrode must be repositioned until the measured value R
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 "Compen-
sation of Earth Electrode Connecting Lead".
Time average measurement:
If there is a warning "measured value unstable" (see "Procedures of Measure-
ment", "Description of display") after a test sequence, most likely it is caused
by strong interference signals (e.g. unsteady noise voltage).Nevertheless, to get
reliable values, the instrument offers the possibility of averanging over a
longer period.
1. Select a fixed frequency (see "Control loop" in "Operation")
2. Keep the "START TEST" button pressed until the warning "measured
value unstable" disappears. Max. averaging time is approx. 1 min.
Evaluation of measured value:
Figure 10 shows the maximum permissible value of the Earth resistance which
will not exceed a permissible limit value, taking into account the maximum
usage error.
10
0
5
Figure 10. Earth Resistance - Maximum Permissible Value
100
20 50
50
20
10
Procedure of Measurements
Desired Values
200
500
200
100
500
Measured Values
Earth/Ground Tester
stays
E
3000 3152
1000
1000 2000 2999
edw013.eps
35