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3.
Connect a 400Ω resistor (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 400.0000Ω and 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, 25Ω or 50Ω, 100Ω, 200Ω, and 400Ω on each
channel.
9.1.3 Thermistor Calibration Parameters
Three adjustable parameters are used for calibration: C0K, C10K, and C100K.
The C0K directly affects the measurement at 0Ω. It has negligible effect at 10
kΩ but significant affect at higher resistances. The C10K directly affects the
measurement at 10 kΩ. It has negligible effect at 0Ω and proportionately
greater effect the higher the resistance. The C100K directly affects the mea-
surement at 100 kΩ. It has negligible effect at 0Ω and10kΩ with greater effect
as the resistance increases. Each of the parameters has positive effect at their
primary resistances: increasing the value of the parameter increases the mea-
sured resistance. The theoretically normal value for each is 0.
The calibration parameters 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 Procedure
Calibration requires adjustment of the C0K, C10K, and C100K parameters at
three specific input resistances. If the resistances used are approximately 0Ω,
10 kΩ and 100 kΩ respectively the adjustments are independent and the proce
-
dure is simple. The order in which the adjustments are performed is important.
The adjustment of the C100K parameter must be done last as the adjustments
of C0K and C10K affect the measurement at 100 kΩ but C100K does not affect
the measurements at 0Ω or 10 kΩ. Each channel must be calibrated. Set the
conversion type to RES to display resistance and set the RANGE parameter to
10KΩ. The accuracy required of the resistance standards is 1/4 of the instru
-
ment accuracy; that is 0.12Ω at 0Ω,0.25Ω (25 ppm) at 10 kΩ, and 2.5Ω (25
ppm) at 100 kΩ. The recommended procedure is as follows:
1.
Connect a 0Ω resistor 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 132).
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.
133
9 Calibration
PRT and Thermistor Calibration