This section describes the calibration and adjustment sequence in more detail and describes the data the Modbus master system should exchange with the probe. A humidity and/or temperature calibrator is needed to create suitable reference conditions.
Wiring, communication settings, and Modbus implementation of the HMP Series probes and HMP110 probes are described in HMP Series User Guide (M212022EN) and HMP60 and HMP110 Series User Guide M211060EN. In addition, see Calibration-related Modbus registers and functions.
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If the probe to be calibrated is capable of sensor purge, it is recommended to perform the purge before calibration and adjustment. Write 1 in register 0x0504 to start the sensor purge.
NOTICE To prevent heat conduction during sensor purge, the probe head should not be inside a calibration chamber or be attached to anything. After the sensor purge is completed, allow the probe head to cool down completely before starting the calibration sequence. Typically this takes at least 30 minutes.
- Write the calibration passcode 1300 in register 0x2000 of the probe to unlock the calibration mode. In addition to enabling the adjustment registers and functions, this temporarily disables probe features such as condensation prevention heating that could interfere with calibration.
- Calibrate the first point:
- Insert the probe head in the reference environment for the first calibration point.
- Wait for the measurement to stabilize. Track the stabilization by reading the values for RH (0x0000) and T (0x0002). Note that the required stabilization time varies greatly depending on probe model, starting conditions, and calibration conditions.
- After the measurement is stable, write
the reference value of the environment (for example, 11.3 %RH or 23 °C) in the
appropriate register:
- 0x2100 if you are calibrating RH measurement
- 0x2200 if you are calibrating T measurement
- When the reference value is written, the probe automatically inserts the currently measured value(s) in the appropriate register(s) for the first calibration point. Read the values written by the probe and compare with the reference to determine the calibration result for the first point.
- Calibrate the second point:
- Insert the probe head in the reference environment for the second calibration point.
- Wait for the measurement to stabilize. Track the stabilization by reading the RH and T values.
- After the measurement is stable, write
the reference value of the environment (for example, 75.1 %RH or 40 °C) in the
appropriate register:
- 0x2106 if you are calibrating RH measurement
- 0x2204 if you are calibrating T measurement
- The probe automatically inserts the currently measured value(s) in the appropriate register(s) for the second calibration point. Read the values written by the probe and compare with the reference to determine the calibration result for the second point.
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If you are performing an RH calibration, you can calibrate up to 5 points using the same method. See Calibration-related Modbus registers and functions for the register addresses of the remaining points.
Note that you must write an empty (NaN) value in all fields for any unused adjustment points. This prevents any possible earlier values left in those points from affecting the current adjustment. - When you have calibrated all intended
points, activate the adjustment by writing 1 in the appropriate function register:
- 0x211E to activate RH adjustment
- 0x2208 to activate T adjustment
- If the calibration results show that no adjustment is needed, you can also exit without activating the adjustment. To exit without activating the adjustment, move directly to step 9 and close the calibration mode.
- To verify that the adjustment was successfully activated, read the return code of the adjustment function from the same register address. See Adjustment function return codes.
- Write new calibration date and information text in the appropriate registers.
- Write -32768 (0x8000) in register 0x2000 to close the calibration mode.