Wahl DSTCAL Software User Manual
9
4. CALIBRATION
– RTD Models
4.1. Theory of Calibration
With respect to calibration, the RTD thermometer can be viewed as two independent
systems with different calibration requirements.
The first system is comprised of the meter electronics. The meter calibration is
performed so that the meter will measure resistance accurately. This is accomplished
by using known, fixed resistances of a specified accuracy. Wahl recommends using
resistances with a known accuracy equal to or greater than
0.009 ohms. The
calibration routine also allows entry of the exact resistance. This will allow the
technician to enter the calibrated resistor value from a NIST traceable laboratory data
sheet or by measuring a nominal valued resistance with a precision ohmmeter, such as
an HP3458A, and entering the measured value. See
“METER CALIBRATION” below
for details.
The second system is the addition of a specific probe to the meter. Due to
manufacturing processes, there are variations in the RTD’s R0 coefficient. To increase
the total system accuracy, the electronics may be programmed with this value so that
the microprocessor can accurately calculate the actual temperature from the measured
resistance. See “PROBE CALIBRATION” below for details.
4.2. Meter Calibration
Ohm Meter Calibration Window
Selecting Resistance Screen
1. Sets R0 to 100 ohms in the event it is set otherwise.
2.
Prompts user to “Connect 50 ohm Standard Resistance to Meter Input”
(90 ohm for DST600 series), user may optionally enter exact value of
Resistance into the “Measured Resistance” box. Box will turn “red” if
value is out of acceptable range.
3.
Click “Next” to continue (Clicking “Cancel” will return to main screen).
Waiting for Stabilization Screen
4. Unit waits 10 seconds for stabilization of capacitors
Averaging Samples Screen
5. Unit takes 10 readings to average for calibration
Selecting Resistance Screen
6.
Prompts user to “Connect 280 ohm Standard Resistance to Meter
Input” (194.1 ohm for DST600 series), user may optionally enter exact
value of Resistance into the “Measured Resistance” box.
7.
Click “Next” to continue (Clicking “Cancel” will return to main screen).
Waiting for Stabilization Screen
8. Unit waits 10 seconds for stabilization of capacitors
