Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 247)

Troubleshooting & Repair Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 227
surfaces. Do not exceed 15 psi when pressurizing the system.
 Turn OFF power to the instrument and remove the instrument cover.
 Install a leak checker or a tank of gas (compressed, oil-free air or nitrogen)
as described above on the sample inlet at the rear panel.
 Disconnect the pump tubing on the outside rear panel and cap the pump
port. If zero/span valves are installed, disconnect the tubing from the zero
and span gas ports and plug them (Figure 3-4). Cap the DFU particle filter
on the Perma Pure dryer (Figure 6-2).
 Pressurize the instrument with the leak checker or tank gas, allowing
enough time to fully pressurize the instrument through the critical flow
orifice. Check each tube connection (fittings, hose clamps) with soap
bubble solution, looking for fine bubbles. Once the fittings have been
wetted with soap solution, do not re-apply vacuum as it will draw soap
solution into the instrument and contaminate it. Do not exceed 15 psi
pressure.
 If the instrument has the zero and span valve option, the normally closed
ports on each valve should also be separately checked. Connect the leak
checker to the normally closed ports and check with soap bubble solution.
 Once the leak has been located and repaired, the leak-down rate of the
indicated pressure should be less than 1 in-Hg-A (0.4 psi) in 5 minutes after
the pressure is turned off.
 Clean surfaces from soap solution, re-connect the sample and pump lines
and replace the instrument cover. Restart the analyzer.
7.5.3. PERFORMING A SAMPLE FLOW CHECK
Note Use a separate, calibrated flow meter capable of measuring flows between
0 and 1000 cm³/min to measure the gas flow rate though the analyzer. Do
not use the built in flow measurement viewable from the front panel of the
instrument. This value is only calculated, not measured
Sample flow checks are useful for monitoring the actual flow of the instrument, as the
front panel display shows only a calculated value. A decreasing, actual sample flow
may point to slowly clogging pneumatic paths, most likely critical flow orifices or
sintered filters. To perform a sample flow check:
 Disconnect the sample inlet tubing from the rear panel SAMPLE port
shown in Figure 3-4.