Volume Resistivity (Pressure probe) |
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● Equipment
ⓐ Ohm-meter : Equipment having a range of 104 to 10-5 ohms with
accuracy of ±02 percent of reading.
ⓑ Thickness gauge : Equipped with .750 inch diameter foot anvil
and measuring in increments of .001 inch under 4 ounces load.
ⓒ Silver- or gold-plated electrodes : Having a contacting surface
area equal to .25 square inch (.564 inch diameter) with suitable
provisions for attaching ohm-meter leads.
ⓓ Appropriate fixture or apparatus having capabilities of supporting
silver electrodes, test specimen, and suitable means of applying
100 psi pressure across contacting surface area of specimen between
electrodes (or 25 pounds force).
NOTES;
1. Dimensions are in inches.
2. Metric equivalents (in parentheses) are given for general information
only.
● Preparation of materials for testing.
The material to be tested shall consist of;
ⓐ Test specimens with a thickness of .055 to .120 inch. Use disk
of .564±010 inch diameter.
ⓑ The surface of the material shall be clean and free of dirty,
foreign matter, and indentation.
ⓒ The specimens shall be conditioned for at least three ours at
standard temperature of 23℃±5℃ and at 45 to 75 percent RH in accordance
with MIL-STD-202.
● Preparation of testing electrodes.
ⓐ For minimal contact resistance, electrodes shall be cleaned
by wiping with alcohol prior to using.
ⓑ Electrodes must be properly aligned and contact faces must be
flat and parallel to each other.
● Test procedure.
ⓐ Measure and record thickness of material at contact areas to
be tested using thickness gauge.
ⓑ Material being tested must have sufficient area to contact entire
electrode area.
ⓒ Position material between electrodes and apply pressure of 100±5
psi across contact surface area
(25pounds load or force).
ⓓ Maintain constant pressure until electrical requirement is met
with a maximum time of two minutes.
es. Calculation. Calculate volume resistivity in ohms-cm using
the following formula:
Where:
ρ = Volume resistivity (ohm-cm)
R = Observed resistance (ohms)
A = Area of specimen (cm2)
L = Thickness of specimen (cm)
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Volume Resistivity (Surface probe) |
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The dc volume resistivity of the material shall be measured in
accordance with ASTM D991, except that the probe described herein
shall be used in conjunction with a milliohmmeter capable of measuring
to a minimum of one milliohm. The sample being measured shall be
placed on a nonconductive surface. The probe shall be placed on
actual part or a .500 inch wide by 3 inches long by .055 to .120
inch thick test sample in such a manner that the weight of the test
probe is uniformly distributed on the part or test sample. The entire
width of the part shall be in contact with each electrode. After
a 30 second stabilization period, the resistance on the ohmmeter
shall be recorded. DC volume resistivity shall be calculated in
accordance with ASTM D991 as follows:
Where:
ρ = DC volume resistivity in ohm-cm.
R = Measured resistance in ohms.
A = Smallest cross section area of part or sample between probe
electrodes (cm2).
L = Distance between two electrodes in cm, or 2.54 cm.
The test probe shall be a two-point probe as shown on figure, for
parts too small to be measured with this probe, a probe with .5
inch electrode separation may be used, but the value for L in the
equation shall be 1.27 cm. For smaller parts, the electrode’s width
and spacing should be reduced and the calculation should be on the
arc length. Each electrode should touch gasket at one point. In
the case of an actual part whose cross section configuration makes
it difficult or impossible to measure using this method, the .500
inch wide test sample described above, produced by the same process
as the actual part, shall be used.
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Inches
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mm
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NOTES |
.005
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0.13
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1. Dimensions are in inches. |
.01
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0.2
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2. Metric equivalents are given for general
information only. |
.187
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4.75
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3. Where applicable the probe will be
placed on the flat surface of the item. |
.500
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12.70
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4. Unless otherwise indicated, tolerance
is±.010 (0.25 mm). |
1.000
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25.40
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