Cambridge Sensotec Rapidox 1100L Oxygen Analyser Instruction Manual
7.5
Rapidox Calibration
Once the unit is at temperature it may be necessary to calibrate the sensor. Full
calibration is a simple procedure requiring only one or two gases. The two gas
values are user-selectable and can be changed via the front keypad (2) or the
communications software described in section 8, and the calibration values can be
stored on file for later use. It is suggested that one cal gas is set between 1000 and
10,000ppm and the other cal gas is set between 10 and 1000ppm. Below 10ppm
the sensor takes many hours to stabilise so calibration could become very slow.
Factory calibration is done at 10,000ppm and 100ppm.
The procedure is as follows:
1)
Bearing in mind the points made above, decide which two gases you are
going to use for calibration. If you are constantly working at a particular
range of compositions then it would be wise to obtain small cylinders of
calibration gas with analysis certificates. Cambridge Sensotec can supply
these. Press the ENT button on the front panel keypad (2) to access the
menu system. Using the UP and DOWN arrow buttons scroll to menu
option 1 “Calibrate” and press ENT again to enter the calibration menu.
Use the UP and DOWN arrows to select “O
2
High” or “O
2
Low” and press
ENT to proceed. The top line of the display shows the current calibration
gas stored and the bottom line of the display shows the prompts. If the gas
value is not what you require you can edit the value (in ppm scientific
notation) using the up and down and right arrows on the keypad. The
cursor flashes underneath the digit to edit. For example 1000ppm should
be entered as 1.000E+03ppm. Note that you can not go backwards to edit a
digit to the left of the cursor. Instead keep pressing the RIGHT button and
the cursor will wrap around back to the beginning. Alternatively press ESC
to start again. Press ENT when you are ready to proceed.
2)
The sensor needs to be exposed to the first calibration gas from a cylinder
of known composition. For accurate calibration it is important to allow
sufficient time to pass to flush the sensor properly. Wait for the top line of
the display (1) to become stable. The time this takes depends on the
oxygen concentration of the gas: for 1% oxygen about 5 minutes should
suffice, but for 100ppm it may be necessary to wait for about 30 minutes.
To complete the calibration press and hold the ENT button for two seconds.
During this time you will see a bar graph progress across the lower display.
The analyser will then recalibrate and display “O
2
Calibrated” and then
return to normal run mode. The display will now correctly read the value
of the first calibration gas. Note that if the ENT button is released before
two seconds have elapsed, the recalibration will be aborted and when the
analyser eventually returns to run mode it will use the existing calibration.
3)
Note that the analyser should ideally be calibrated at normal ambient
pressure and at the temperature at which it will be used. If the pressure
correction mode is set to AUTO then it is still possible to perform an
accurate calibration at pressures other than ambient. If the gas temperature
Version 1.6
7
Last printed 16/11/2011 16:59:00