Teledyne 6600 - Manual (Page 44)

3 Operation Model 6600
3-20 Part I
Teledyne Analytical Instruments
Zero off: 0.0 ppm
<ENT> to begin Zero
The offset value can be modified by using the Up/Down keys. Next section
shows how to select this value. Suffice to say that whatever value you enter, will
be automatically added to the reading. Thus, if you entered -0.1 ppm, at the end
of the zero the display will show -0.1 ppm.
Once the Enter key is pressed the instrument enters the zero mode. If you chose
AUTO zero mode, the instrument will do the work of bringing the reading back
to zero plus the offset value that was entered. If you chose MANual zero mode,
then you must enter input to the instrument as explained in the corresponding
section of the manual but with one difference: instead of bringing the display to
read zero, you must make the display read zero plus the value entered as offset.
How the offset value is selected:
To find out what the offset value should be, the intended zero calibration gas and
the a mix of the process background gas must be procured. This of course
assumes that the zero gas and the process background gas are very different and
that an offset will occur.
1. Let the intended zero calibration gas flow through the 6600 sample cell (this
assumes that you have started up you system as recommended by the manual or
technical personnel) and do a zero on the instrument. Leave the offset set to zero
value.
2. At the end of the zero function, make sure the analyser reads zero.
3. Flow the process background gas mix through the 6000 sample cell on the
Analyse mode. Wait for the reading to become stable. Write the reading down.
Change the sign of the reading: This is the offset to be entered.
4. Do a manual run to check. Reintroduce the zero calibration gas. Start a zero
on the analyser but this time enter the offset value.
5. At the end of the zero function, check that the instrument reads the entered
offset.
6. Reintroduce the process background gas mix to the 6000 sample cell in the
Analyse mode. It should read close to zero once the reading is stable (+/- 1%
error of full scale).
Spanning the 6600:
Since the instrument might be spanned with background gas the same as the
zero calibration gas, the span value to be entered should be the span
concentration plus the offset value (if the offset value has a minus sign then
algebraically it becomes a subtraction).