Vaisala DM500 - Manual (Page 104)

User's Guide ______________________________________________________________________
102 _________________________________________________________________ M210205EN-D
The function of XTP is the same as with the command TP except that
with the command XTP the setting is valid only until power is turned
off or the command XTP is given without parameters. After this the
pressure stored with the command TP is valid again.
Adjustments
In adjustment, the reading of DM500 is changed to correspond to the
reference value. After adjustment, the original calibration certificate
shipped with the product is not valid anymore. Adjustment commands
are not affected by unit settings. Commands CDP, CTP, PCAL,
FCAL always use ºC, bar and slpm units.
CDP Adjusting Dewpoint Temperature (in 4 ... 10
points)
Syntax: CDP<cr> or CDP*<cr>
1. Turn the switch 4 (page 12, service switches) to ON-position to
enable the adjustment. After adjustment return the switch 4 to
OFF-position.
2. First, (before measuring the references), type CDPZERO to
clear the calibration coefficients.
CDPZERO<cr>
3. Take the measurements in reference conditions. Write down the
data pairs of reference value and measured value.
4. Type CDP, then give data pairs consisting of reference value
and measured value for a maximum of 10 calibration points.
Input can be terminated by pressing ENTER. After data has
been input, a confirmation is requested before previous
calibration coefficients will be overwritten.
<cr>CDP<cr>
After data has been input and confirmed, the calibration algorithm
calculates the 3rd degree polynomial to describe the measured
deviation as a function of the measured dew/frostpoint. The
polynomial is calculated from the reference value by performing a
least squares fit utilizing matrix inversion. This 3rd degree deviation
model is then used for correcting the dew/frostpoint display.