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Technical Note
Adjustment of Relative Humidity and
Temperature in HMD82M and HMW88M
The following procedure describes relative humidity (RH) and temperature (T) adjustment using serial
line commands. You can use the procedure to do a one-point adjustment (offset) or a two-point
adjustment (offset and gain).
Prerequisites
For best results, note the following recommendations:
•
For one-point humidity adjustment, a < 50 %RH reference is recommended.
•
Two-point humidity adjustment requires an additional reference, with preferably > 50 %RH value.
There should be over 30 %RH difference between the two points.
•
Two-point temperature adjustment requires a second reference point that is at least 20 °C
warmer than the first point.
As a reference instrument, you can use, for example, Vaisala Humidity Calibrator HMK15 or the Vaisala
HUMICAPâ Handheld Humidity and Temperature Meter HM70. For more information on the HMK15
and the HM70, see the respective User's Guides in www.vaisala.com.
Performing an accurate adjustment takes some time and preparation. Check the following before
starting any adjustment procedure:
•
Always wait for measurement instruments to stabilize in the ambient temperature.
Temperature differences are a major source of measurement error.
•
Check that there are no heat or moisture sources near the transmitter.
•
Check that the transmitter is not in direct sunlight or close to the discharge of the supply air
ducts.
•
Check that there is no moisture on the probe. If the sensor has become wet, you must allow it
to dry before you can measure.
List of Serial Commands
Command
Adjustment Commands
L
LI
SEND
Other Commands
ASEL
All commands can be issued either in uppercase or lowercase. In the command examples, the
keyboard input by the user is in bold type.
The notation <cr> refers to the carriage return control character, which you can send in a terminal
application by pressing enter on your keyboard. Before entering commands, send a <cr> to clear the
command buffer.
4 (8)
Description
Show current user adjustment parameters
Set user adjustment parameters
Output the measurement reading once
Show or set analog output parameters and scaling
M212167EN-A
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