Model 106-H Ozone Monitor Manual Rev. D-2
13
The Ozone Monitor will then exit the
Menu
and return to measuring ozone.
3.11 To Change the Calibration Parameters
The instrument is calibrated at the factory where a slope (S) parameter is entered into
the instrument’s memory. This preset calibration parameter is given in the
instrument’s Birth Certificate and recorded on the calibration sticker inside the
instrument. However, the calibration parameters slope (S) and offset (Z, which in the
Model 106-H must be in units of vol%) may be changed by the user. For example, it
may be desirable to provide a positive offset by a known amount (e.g., 0.10 vol%) if
the analog output is being used for external data logging since the analog voltage
output does not go negative below zero vol%, and the current output does not go
below 4 mA. Because of noise and/or an inherent offset, some measured values will
be below zero at very low ozone concentrations or while zeroing the instrument with
zero gas. Also, the instrument zero may drift by a few hundredths of 1 vol% over time.
For this reason, zeroing of the instrument using zero gas to determine the offset is
recommended (see Section 3.10 and Section 6). Any change in the slope (gain) of
the instrument is likely due to a serious problem such as contamination, but it also can
be adjusted. Once the zero of the instrument is corrected, the slope may be adjusted
so that the instrument readout agrees with the readout from another instrument whose
calibration is considered to be accurate (see Section 5).
To change the calibration parameters, choose the
Cfg
submenu from the
Admin
Menu
and click on
Cal
to obtain the display
Cal Menu (%vol)
Z= 0.03 S= 1.012
Here Z is an applied offset (in this case 0.03 vol%) and S is the slope applied (in this
case 1.012). The value of Z will be 0.00 if you have performed the auto-zeroing
procedure described above. You can provide an offset, however, by changing the
value of Z here. When reporting ozone, the value of S is multiplied by the measured
ozone value and then the value of Z is added. During calibration, the instrument is
first auto-zeroed and checked to make sure that a reading of zero is obtained with
sampling air or oxygen containing no ozone. The value of S is set to 1.000 and ozone
having a known concentration is measured. If, for example, the instrument
consistently reads 2.5% low, the value of S is then set to 1.025. If an offset is desired
(e.g., when using an analog output to record the data), the value of Z may then be
adjusted to the value of the desired offset.
When the
Cal Menu
first appears, the
Z
will be underlined with a cursor. You may
rotate the Select switch to choose the calibration parameter
S
or
Z
. A single click on
S
or
Z
will select that parameter for change and activate a blinking cursor. Once
S
or
Z
is selected, its value can be changed by rotating the Select switch to the left or right.
After choosing the desired value, a click turns off the blinking cursor and allows you to
scroll to the other parameter or to
to exit the submenu.
Once the values of
Z
and
S
are set, clicking on
will return the display to the
Cal
menu, another click on
to the
Cfg
menu, and further clicks on
will lead back to the
Admin
and
Main
menus and
