Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 231)

Model 9110EH Instruction Manual Troubleshooting & Repair
11.5.15.1. Reaction Cell Pressure
Measure the voltage across test points TP1 and TP5. With the sample pump disconnected or
turned off, the voltage should be 4500 ± 250 mV. With the pump running, it should be 800-
1700 mV depending on the performance of the vacuum pump. The lower the reaction cell
pressure, the lower the resulting voltage is. If this voltage is significantly different, the
pressure transducer S1 or the board may be faulty. If this voltage is between 2 and 5 V, the
pump may not be performing well, check that the reaction cell pressure is less than
10 in-Hg-A (at sea level). Ensure that the tubing is connected to the upper port, which is
closer to the sensor’s contacts; the lower port does not measure pressure.
11.5.15.2. Sample Pressure
Measure the voltage across test points TP1 and TP4. With the sample pump disconnected or
turned off, this voltage should be 4500 ± 250 mV. With the pump running, it should be
about 0.2 V less as the sample pressure drops by about 1 in-Hg-A below ambient pressure.
If this voltage is significantly different, the pressure transducer S2 or the board may be
faulty. A leak in the sample system to vacuum may also cause this voltage to be between
about 0.6 and 4.5. Make sure that the front panel reading of the sample pressure is at
about 1 in-Hg-A less than ambient pressure. Ensure that the tubing is connected to the
upper port, which is closer to the sensor’s contacts; the lower port does not measure
pressure.
Figure 11-5: Pressure / Flow Sensor Assembly
M9110EH Rev 0 217