6
3.1 Equipment Required
•
Precision Decade Resistance Box, with 0.01 ohm resolution and
±0.02 ohm accuracy
or
•
Precision RTD Simulator, such as OMEGA CL511 Precision Calibrator
•
Precision DMM capable of measuring mA, within 0.001 mA resolution
and ±0.002 mA accuracy
3.2 Calibration Procedures
Connect the calibration equipment according to
Figure 3-1
. Standard
copper test leads are used with RTD instrumentation.
To check or adjust the calibration:
1.
Locate the Z (zero) and S (span) potentiometers.
2.
Select, from
Table 3-1
, the correct ohmic values for the Z (zero) and
S (span) adjustments that correspond to the model number.
For example, for Model TX94A-2, the Z value is 92.95 ohms, and the
S value is 135.84 ohms.
If a Thermocouple/RTD Simulator is used, such as the Model CL511
Precision Calibrator, select the Temperature Input Z (zero) and
S (span) values.
3.
Set the Decade Box to the selected Z (zero) ohmic value. Adjust the
Z potentiometer to read 4.000 mA on the monitoring instrument.
4.
Set the Decade Box to the selected S (span) ohmic value. Adjust the
S potentiometer to read 20.000 mA on the monitoring instrument.
5.
Repeat steps 3 and 4, as required, until the readings are exactly
4.000 mA and 20.000 mA. This procedure is necessary since there is
interaction between the two potentiometers.
