Va t r ohm cm – Monroe Electronics Resistivity Meter - Portable - Surface - model 272A User Manual
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9
APPLICATION NOTE APNE-0002
PRACTICAL VOLUME RESISTIVITY MEASUREMENTS
with
Monroe Model 272A
Included with Model 272A is a P/N 96117-1/22A specimen support plate. This support plate
provides a durable finish on the insulated side and also provides a smooth metallic surface on
the opposite side for volume resistivity or bulk resistance measurements of materials.
The combination of this plate, the P/N 96101A-1 probe and the Model 272A instrument meets
the guidelines set forth in ASTM D-257 and IEC 93 Standards for guarded-ring testing of volume
resistivity of solid, homogeneous electrical insulating materials, generally in sheet form.
Connections for guarded measurements are shown in Figures 3 and 4.
Figure 3: Setup for Guarded Measurement of
Figure 4: Schematic Representation
Volume Resistivity
Volume resistivity,
v
, must always be calculated because the thickness of the test specimen is
one of the measurement variables. The ASTM D-257 (or IEC 93) formula for
v
is:
where: A = Effective area of measuring electrode in cm
2
t = Thickness of test specimen in cm
R
m
= Measured resistance in ohms
For the 96101A-1 probe the effective area of the measuring electrode is 7.1 cm
2
thus:
Appendix X2 in the ASTM standard further addresses the modification of the effective area of
the measuring electrode in the guarded ring configuration.
v
A
t
R ohm cm
m
v
t
R
ohm
cm
m
7
1
.
A
CASE
CKT.
COMM.
272A
96101A
INSULATED SIDE DOWN
SPECIMEN
ATTACH CLIP LEAD
SET TO INDICATE