2-point adjustment of RH measurement (HMP110 and HMP113) - HMP110 - HMP113 - HMP60 - HMP63

HMP60 and HMP110 Series User Guide
Document code
M211060EN
Revision
L
Language
English
Product
HMP110
HMP113
HMP60
HMP63
Document type
User guide
You can also use Vaisala Insight software for performing calibration and adjustment. See Vaisala Insight software.

To perform a 2-point adjustment to the capacitance measurement of the HMP110 or HMP113 using serial line you need:

  • Vaisala USB cable (item code 219690)
  • PC with a terminal application
  • Two humidity references. The first point requires a < 50 %RH humidity reference, the second point must be > 50 %RH. There must also be at least 30 %RH difference between the references.

The following example procedure uses the HMK15 Humidity Calibrator. LiCl salt (11.3 %RH) at 25 °C is used as the first reference point, NaCl (75.3 %RH at 25 °C) as the second.

For more information on using a humidity calibrator and salt chamber references, see Vaisala Humidity Calibrator HMK15 User Guide M210185EN.
  1. Connect the USB cable to the PC, but do not connect it to the probe yet.
  2. Remove the filter from the probe and insert the probe in the LiCl salt chamber of the humidity calibrator (11.3 %RH).
  3. Start a terminal application and set the correct connection settings. The default serial settings are 19200 8 N 1. Remember to check which COM port the USB cable is using.
  4. Wait for 20 … 40 minutes for the humidity to stabilize.
  5. Start the terminal session and connect the USB cable to the probe. If your probe is in the analog output mode, you need to press ENTER a few times to start it in RS-485 mode.
  6. Verify that the connection works by giving the ? command. 
    ?

    If the probe does not respond with device information:

    • Disconnect the USB cable from the probe and retry. If your probe is in the analog output mode, press ENTER a few times immediately after connecting the USB cable.
    • Try the ?? command in case the probe is in POLL mode, open the line using the OPEN command if necessary.
    • Check your serial line settings and cable connections.
  7. When your serial connection is working, use the L command to see the current user adjustment parameters. 
    l
  8. Use the ERRS command to see that no errors are active. 
    errs
  9. Use the SEND command to verify the currently measured RH value. 
    send
T= 22.9 'C RH= 11.1 %RH Td= -8.0 'C
  10. Give the CRH command to display the current RH measurement. Press ENTER to refresh the RH measurement to check that the measurement has stabilized. 
    crh
RH: 11.39800112 Ref1 ? 
RH: 11.38377201 Ref1 ?
RH: 11.37988329 Ref1 ?
  11. When the shown RH measurement shown is stable, enter the value of the first measurement humidity reference (11.3 %RH) and press ENTER. 
    crh
RH: 11.37988329 Ref1 11.3
Press any key when ready
>
  12. After entering the first reference point correction, press ENTER to continue to the second reference point correction.
  13. Insert the probe in the NaCl salt chamber (75.3 %RH) and wait for 20 … 40 minutes for humidity and temperature to stabilize.
  14. Press ENTER to refresh the RH measurement to check that the measurement has stabilized. 
    
RH: 74.87782214 Ref2 ?
RH: 74.89157890 Ref2 ?
RH: 74.91556023 Ref2 ?
  15. When the shown RH measurement shown is stable, enter the value of the second humidity measurement reference (75.3 %RH) and press ENTER. 
    crh
RH: 11.37988329 Ref2 75.3
Press any key when ready
>
  16. Check with the L command that the user adjustment parameters have changed.
  17. Use the SEND command to verify that the measurement is OK.
    If the entered adjustment is incorrect, you can remove the effects of RH calibration (returning the RH measurement of the probe to the factory calibrated state) with the CRHCLR command. For instructions, see Clear adjustment of RH measurement.