Front Panel Operation
2-36
Cancelling test fixture leakage current
Significant leakage in the test fixture can corrupt a resistance
measurement. This leakage current can be cancelled by per-
forming a REL on the current component of the resistance
measurement. Perform the following steps to cancel leakage
current:
NOTE
The following procedure assumes that
steps 1 through 7 of the preceding resis-
tance measurement procedure has been
performed.
1. With the V-Source in standby, remove the DUT from the
test fixture.
2. Select the amps function (I) and then disable zero check.
Also make sure that REL is disabled (REL indicator
off).
3. Press OPER to source the programmed V-Source level
to the test fixture.
4. Select the lowest possible measurement range to display
the current reading. This reading is the leakage current
in the test fixture.
5. Press REL to zero the reading. This cancels the leakage
current reading.
6. Press OPER to place the V-Source in standby and enable
zero check.
7. Perform the following steps to establish the amps REL
value for the ohms function:
A. Press CONFIG and then R to display the CONFIG-
URE OHMS menu.
B. Select the AMPSREL menu item.
C. Select YES to establish the amps REL value.
D. Use the EXIT key to back out of the menu structure.
8. Re-install the DUT in the test fixture.
9. Select the ohms function (R) and proceed to step 8 of the
resistance measurement procedure.
2.7.2 Resistivity measurements
The Model 6517A can make surface resistivity measure-
ments from 10
3
to 10
17
ohms and volume resistivity mea-
surements from 10
3
to 10
18
ohm-cm.
Typical resistivity test fixtures (such as the Model 8009) use
circular electrodes. In order to use these test fixtures, the in-
sulator sample must be large enough such that all the surfac-
es of the electrodes make contact with the sample.
NOTE
When using the Model 8009 test fixture,
you do not have to make any calculations.
For volume resistivity, you only need to
know the thickness (in mm.) of the sam-
ple. The Model 6517A will automatically
perform the calculation and display the
reading.
Surface Resistivity —
Surface resistivity is defined as the
electrical resistance of the surface of an insulator material. It
is measured from electrode to electrode along the surface of
the insulator sample. Since the surface length is fixed, the
measurement is independent of the physical dimensions (i.e.
thickness and diameter) of the insulator sample.
Surface resistivity is measured by applying a voltage poten-
tial across the surface of the insulator sample and measuring
the resultant current as shown in Figure 2-33. The Model
6517A automatically performs the following calculation and
displays the surface resistivity reading:
ρ
S
= Surface resistivity (per square).
R = Measured resistance in ohms (V/I).
K
S
= P/g
where: P = The effective perimeter of the guarded electrode
(mm).
g = Distance between the guarded electrode and the
ring electrode (mm). Refer to Figure 2-34 to deter-
mine dimension g.
ρ
S
K
S
R
=
Guarded
Electrode
Sample
Top
Electrode
Ring
Electrode
Guard
6517A
V-Source
HI
LO
HI
LO
A
6517A
Picoammeter
Figure 2-33
Surface resistivity measurement technique
