Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 172)

Instrument Maintenance Model 9110EH Instruction Manual
Figure 9-7: Critical Flow Orifice Assembly
9.3.11. Checking for Light Leaks
When re-assembled or operated improperly, the M9110EH can develop small leaks around the
PMT, which let stray light from the analyzer surrounding into the PMT housing. To find such
light leaks, follow the below procedures. CAUTION: this procedure can only be carried out
with the analyzer running and its cover removed. This procedure should only be carried out
by qualified personnel.
• Scroll the TEST functions to PMT.
• Supply zero gas to the analyzer.
• With the instrument still running, carefully remove the analyzer cover. Take extra
care not to touch any of the inside wiring with the metal cover or your body. Do not
drop screws or tools into a running analyzer!
• Shine a powerful flashlight or portable incandescent light at the inlet and outlet
fitting and at all of the joints of the reaction cell as well as around the PMT housing.
The PMT value should not respond to the light, the PMT signal should remain steady
within its usually noise.
• If there is a PMT response to the external light, symmetrically tighten the reaction
cell mounting screws or replace the 1/4” vacuum tubing with new, black PTFE tubing
(this tubing will fade with time and become transparent). Often, light leaks are also
caused by O-rings being left out of the assembly.
• Carefully replace the analyzer cover. If tubing was changed, carry out a leak check
(Section 11.5.2).
158 M9110EH Rev 0