NI 4070/4072 Calibration Procedure
36
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its value is
≥
10% of the higher capacitor range. For example, you can use a
1 nF verification capacitor to test both the 10 nF and 1 nF ranges.
After taking each measurement, verify that the measurement falls between
the tolerances listed in Table 24. Tolerances are provided instead of
absolute limits, because you can use capacitance verification values other
than the values suggested, or the calibrated value may differ slightly from
the nominal capacitance (for example, 272.43 pF instead of 270.00 pF).
The tolerances shown in Table 24 correspond to the NI 4072 accuracy
specifications.
The following verification procedure assumes the use of verification
capacitors with the following values: 270 pF, 1 nF, 100 nF, 10
μ
F, and
1000
μ
F.
The configuration of the cables and fixtures should be consistent
throughout each measurement. If you are using cables to connect the
verification capacitors to the NI 4072 banana plug connectors, minimize
noise by ensuring that the cables remain fixed and do not move during the
measurement.
Keep direct contact with the verification capacitors to a minimum so that
they are constantly kept at the ambient temperature. After connecting a
capacitor to the NI 4072 terminals, NI recommends waiting 30 seconds for
the capacitor temperature to stabilize.
Note
You should know the total capacitance up to the banana connectors that plug into the
NI 4072 before performing the verification procedure.
To verify the capacitance measurements of the NI 4072, complete the
following steps:
1.
Disconnect any fixtures or cables from the NI 4072.
2.
Call
niDMM_reset
to reset the NI 4070/4072 to a known state.
3.
Call
niDMM_ConfigureMeasurement
with the following
parameters:
•
Function
=
NIDMM_VAL_CAPACITANCE
•
Range
=
300e-12
•
Resolution
=
50e-15
4.
Set the number of averages of the NI 4072 to
20
by calling
niDMM_SetAttributeViInt32
with the following parameters:
•
Attribute_ID
=
NIDMM_ATTR_LC_NUMBER_MEAS_TO_AVERAGE
•
Attribute_Value
=
20
Note
This measurement corresponds to a 0 pF capacitance.
