Vaisala DMT132 - Manual (Page 62)

USER'S GUIDE____________________________________________________________________
60 __________________________________________________________________ M211289EN-A
Capacitance Adjustment (CRH)
CAUTION Adjusting the capacitance measurement affects measurement accuracy
across the entire temperature range. This command should be used only
when the sensor has been replaced, or the measurement has drifted
significantly. After sensor change, you must perform the two-point
capacitance adjustment. For normal adjustment, use the RHCAL
command instead.
CAUTION Write down the current capacitance adjustment parameters (visible with
the L command) so that you can restore them manually if necessary.
Be aware that if you revert the transmitter to factory settings using the
FRESTORE
command, you will clear all of the user adjustment
parameters, including the capacitance offset and gain that are set by the
CRH
command. See section Restore Factory Settings on page 48.
The procedure below adjusts the capacitance measurement of the
transmitter using the serial line commands and the Vaisala Humidity
Calibrator HMK15. You can use the procedure to do a one-point
adjustment (offset) or a two-point adjustment (offset and gain).
- One-point adjustment requires a < 50 %RH reference
- Two-point adjustment requires additionally a > 50 %RH reference,
with over 30 %RH difference between the two points.
1. Disconnect the cable from connector I of the DMT132 (if
connected).
2. Connect the USB cable to connector II on the DMT132, and to a
USB port on your PC.
3. Start a terminal application and set the service port connection
settings (19200 8 N 1). Remember to check which COM port the
USB cable is using.
4. Verify that the connection works by giving the ? command:
>?
If the transmitter does not respond with device information:
- Check your serial line settings and cable connections
- Reconnect the USB cable, restart the terminal application, and
try again.