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Page 26 · TC-3 Temperature Controller User’s Manual
User Calibration of Resistance Sensors
In some applications, having the ability to compensate, or calibrate,
the sensor measurement is desired, such as referencing to an internal
standard or to match the readings of another instrument. This is
supported on the
TC-3 by using the Sens Cal M and Sens Cal B
menu entries to apply an offset and/or slope compensation to
thermistor or RTD readings (LM335 and AD590 sensors have separate
M and B settings).
To prevent accidental modification of the sensor calibration, the Sens
Cal M and Sens Cal B menu entries are only editable when the Edit
User Cal setting in the System sub-menu is set to Yes . By default,
Sens Cal M and Sens Cal B values are 1.000 and 0.00, respectively,
but can be adjusted to change the sensor measurement. The
calibrated measurement is computed as follows:
User calibrated reading = Sens Cal M * r Sens Cal B
Sens Cal B is displayed in kilo-ohms (kΩ) for thermistors, and ohms
(kΩ) for RTDs.
Be aware that the there is only a single set of calibration values, and
changing sensor type does not change the calibration data. Therefore,
if you will be changing between thermistor to RTD sensors, you will
need to change the calibration values as appropriate for the new
sensor setting. Changing the values back to 1.000 and 0.00 will return
the instrument to factory calibration.
Working With AD590s and LM335s
Unlike thermistors and RTDs, an AD590 or LM335 is considered an “IC”
sensor because it has an active transistor element that responds to
changes in temperature by producing a current (AD590) or voltage
(LM335).
NOTE
The calibration is applied to the resistance
measurement of the sensor, not the temperature.
To adjust the resistance-to-temperature
conversion, change the thermistor or RTD
coefficients as needed.