Operating Procedure; Connections And Readings - AEMC 6250 User Manual

4.3

Operating Procedure

WARNING: Before performing the resistance test, verify that the sample
under test is not energized.
4.3.1

Connections and Readings

Clean all surfaces before connecting test leads. Verify a solid connection
between test leads and the sample. Set the range selector switch to the
desired range for the test. If the anticipated resistance is not known, begin
with the highest range (2500Ω) and successively lower the range selection
until adequate resolution is achieved. The START/STOP button will need
to be pressed each time you change ranges. The range selection may be
changed while the instrument is on.
A diagram of the measurement system is shown in Figure 4-2. The
Model 6250 generates a current (I) from the internal voltage source (V).
A voltmeter measures the voltage drop V
points to the resistance to be measured (R
measurement (R
The result is not affected by the other resistances encountered in the cur-
rent loop (R
remains below the voltage supplied by the source which is between 5 to
6V. The maximum admissible lead resistance level is R
use of Kelvin probes helps, as they eliminate the effect of the lead resis-
tance (R ).
f
R = Unit internal resistance
i
R = Lead resistance
f
28
0.561.8187
) directly using the formula R
x
, R , R ), as long as the total voltage drop induced across R
i f c
I
+
V
www.
at the Kelvin probe contact
x
) and displays the resistance
x
C1
Ri
P2
V
x
P2
C2
Figure 4-2
R = Contact resistance
c
R = Resistance to be measured
x
.com
= V / I.
x x
≈ (V- V
f
Rf
Rc
Rf
Rx
Rf
Rc
Rf
Micro-Ohmmeter Model 6250
information@itm.
x
) / I. The
x