Teledyne 200AU 9.2.9 Inability to Zero , 9.2.10 Non-Linear Response

Teledyne API Model 200AU NOX Analyzer Instruction Manual, 02293, Rev. F
9-31
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 into the reaction cell.
3. Contaminated reaction cell. Remove and clean cell.
4. Wet (i.e., undried ambient air) air in 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. Pre-reactor filter is corrupted with high readings. To clear the Pre-reactor filter, input
zero gas and wait for 15 minutes for the filter to clear.
9.2.10 Non-Linear Response
Common causes are:
1. A leak in the pneumatic system, see Section 8.7.
2. High zero background - the PMT TEST function should be near 50 mV with zero gas.
Readings above 100 mV indicate a light leak, contaminated reaction cell, bad zero gas, or
wet air coming into the ozone generator. If the reading is not less than 150 mV, the
instrument will not zero or span properly. Check Section 9.2.9.
3. Calibration device in error - re-check flowrates and concentrations, especially at low
concentrations. If you are using a Mass Flow calibrator and the flow is < 10% of the full
scale flow on either flowmeter you may need to purchase lower concentration standards.
4. The standard gasses may be mis-labeled as to type or concentration. Labeled
concentrations may be outside the certified tolerance.
5. Contamination in sample delivery system:
A. Dirt in sample lines or reaction cell
B. Contaminated cal gas source (NO2 in NO cal gas is common)
C. Dilution air contains sample or span gas