Teledyne 200A 9.2.9 Inability to Zero

Teledyne API Model 200A NOX Analyzer Instruction Manual, 02246, Rev. G, DCN 5247
9.2.9 Inability to Zero
If the ZERO button is not illuminated when attempting to zero, that means the reading is outside
of the software gain ranges allowed. In an analog instrument it would be the equivalent to the
zero pot hitting the rotation stop. Check the following:
Select the PMT - TEST function. With zero gas going into the instrument, the value should be
less than 150 mV, typically less than 50 mV. If you are getting a high reading, the probable
reasons are:
1. The reading may be temporarily high if the PMT has been recently exposed to room
light. If so, let the instrument run for several hours with zero gas to get the PMT accustomed
to low light levels.
2. Leak that admits gas containing NO.
3. Contaminated reaction cell. Remove and clean cell.
4. Wet (i.e., undried ambient air) air into the ozone generator. Check the PermaPure drier
and associated plumbing for leaks and correct operation.
5. Zero gas that isn't really zero. Make sure you're not trying to zero the machine with
ambient air or span gas.
6. AutoZero filter is corrupted with high readings. To clear the AutoZero filter, input zero
gas and wait for 15 minutes for the filter to clear.
9-32
PRINTED DOCUMENTS ARE UNCONTROLLED