Calibration and adjustment sequence - HMP1 - HMP3 - HMP4 - HMP5 - HMP7 - HMP8 - HMP9 - HMPX - MMP8 - TMP1

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 are described in HMP Series User Guide (M212022EN). In addition, see Calibration-related Modbus registers and functions.

1. 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 0504_hex to start the sensor purge.

   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.

2. Write the calibration passcode 1300 in register 2000_hex 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.
3. Clear the user adjustment of the parameter to be calibrated (RH or T) by writing 1 in the appropriate function register:
   • 211F_hex to restore the factory RH adjustment
   • 2209_hex to restore the factory T adjustment
4. Calibrate the first point:
   1. Insert the probe head in the reference environment for the first calibration point.
   2. Wait for the measurement to stabilize. Track the stabilization by reading the values for RH (0000_hex) and T (0002_hex). Note that the required stabilization time varies greatly depending on probe model, starting conditions, and calibration conditions.
   3. After the measurement is stable, write the reference value of the environment (for example, 11.3 %RH or 23 °C) in the appropriate register:
      • 2100_hex if you are calibrating RH measurement
      • 2200_hex if you are calibrating T measurement
   4. 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.
5. Calibrate the second point:
   1. Insert the probe head in the reference environment for the second calibration point.
   2. Wait for the measurement to stabilize. Track the stabilization by reading the RH and T values.
   3. After the measurement is stable, write the reference value of the environment (for example, 75.1 %RH or 40 °C) in the appropriate register:
      • 2106_hex if you are calibrating RH measurement
      • 2204_hex if you are calibrating T measurement
   4. 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.

6. 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.

7. When you have calibrated all intended points, activate the adjustment by writing 1 in the appropriate function register:
   • 211E_hex to activate RH adjustment
   • 2208_hex to activate T adjustment
8. To verify that the adjustment was successfully activated, read the return code of the adjustment function from the same register address. See Table 3.
9. Write new calibration date and information text in the appropriate registers.
10. Write -32768 (8000_hex) in register 2000_hex to close the calibration mode.