NI 9235/9236 Calibration Procedure
4
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Test Equipment
National Instruments recommends that you use the following equipment
for calibrating the NI 9235/9236.
Test Conditions
Follow these guidelines to optimize the connections and the environment:
•
Keep connections to the device as short as possible. Long cables and
wires act as antennae, picking up extra noise that can affect
measurements.
•
Use shielded copper wire for all cable connections to the device.
Use twisted-pair wire to eliminate noise and thermal offsets.
•
Maintain an ambient temperature of 23 ±5 °C. The device temperature
will be greater than the ambient temperature.
•
Keep relative humidity below 80%.
•
Allow a warm-up time of at least 10 minutes to ensure that the
measurement circuitry is at a stable operating temperature.
Table 1.
Recommended Equipment
Equipment
Recommended Model
Requirements
Calibrator
Fluke 5500A
If this instrument is unavailable, use a calibrator with
generation of resistances in the ranges of 108
Ω
– 132
Ω
and 315
Ω
– 385
Ω
with 0.01
Ω
resolution, an accuracy
of at least 90 ppm, and automatic lead wire
compensation.
DMM
NI 4070
If this instrument is unavailable, use a multi-ranging
6 1/2 digit DMM with an accuracy of at least 40 ppm.
Chassis
NI cDAQ chassis
—
Connecting
wires
—
Connections between the module and the calibrator are
insensitive to connection resistance except between the
calibrator LO terminal and the module RC terminal. The
resistance of this connection must be less than 200 m
Ω
to
limit bridge linearity errors. The verification test limits in
Tables 5 and 6 assume this requirement is met.