3. Connect a 400Ωresistor (6 ppm accuracy) to the input and measure its
resistance. Note the average error in the measurement. Adjust the C400
parameter by subtracting the measured error. For example, if the input is
exactly 400.0000Ωand the readout shows 399.9913Ω, adjust the C400
parameter by adding 0.0087.
4. Record the date in the DATE parameter and set the DUE parameter to
the desired calibration interval.
5. Verify the accuracy at 0Ω, 25Ωor 50Ω, 100Ω, 200Ω, and 400Ωoneach
channel.
9.1.3 Thermistor Calibration ParametersThree adjustableparameters are used for calibration: C0K, C10K, and C100K.
The C0K directly affectsthe measurement at 0Ω. I t has negligibleeffect at 10
kΩbutsignificant affect at higher resistances. The C10K directly affects the
measurement at 10 kΩ. It has negligible effectat 0Ωand proportionately
greater effectthe higher the resistance. The C100K directly affects the mea-
surement at 100 kΩ. It has negligible effectat 0Ωand10kΩwithgreater effect
as the resistance increases. Each of the parameters has positiveeffect at their
primary resistances: increasing the valueof the parameter increases the mea-
sured resistance. The theoretically normalvalue for each is 0.
The calibrationparameters C0K, C10K, and C100K can be adjusted to opti-
mize the accuracy.These parameters are accessed from the CALIBRATION
function of SYSTEM menu.
9.1.4 Thermistor Calibration ProcedureCalibrationrequires adjustment of the C0K, C10K, and C100K parameters at
three specificinput resistances. If the resistances used are approximately 0Ω,
10 kΩand 100 kΩrespectivelythe adjustments are independent and the proce-
dure is simple.The order in which the adjustments are performed is important.
The adjustmentof the C100K parameter must be done last as the adjustments
of C0K and C10K affectthe measurement at 100 kΩbutC100K does not affect
the measurements at 0Ωor 10 kΩ. Each channel must be calibrated. Set the
conversiontype to RES to display resistance and set the RANGE parameter to
10KΩ. The accuracyrequired of the resistance standards is 1/4 of the instru-
ment accuracy;that is 0.12Ωat 0Ω,0.25Ω(25ppm) at 10 kΩ, and 2.5Ω(25
ppm) at 100 kΩ. The recommended procedure is as follows:
1. Connect a 0Ωresistor to the input and measure its resistance. If a short-
ing wire is used the wire should run from the C2 terminal to the C1 ter-
minal to the P1 terminal to the P2 terminal (See Figure 50 on page 128).
Note the average error in the measurement. Adjust the C0K parameter by
subtracting the measured error. For example, if the input is exactly 0.0Ω
and the readout shows –0.11Ω, adjust the C0K parameter by adding
0.11.
129
9 Calibration
PRT and Thermistor Calibration