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Troubleshooting & Repair Teledyne API - Model 200EH/EM Operation Manual
264
11.5.15. PNEUMATIC SENSOR ASSEMBLY
The pressure/flow sensor circuit board, located behind the sensor assembly, can be checked with a voltmeter
using the following procedure, which assumes that the wiring is intact and that the motherboard and the power
supplies are operating properly. Refer to Figure 11- for trouble-shooting.
Measure the voltage acro
ss TP1 and TP2, it should be 10.0 0.25 V. If not, the board is fault
y. Measure the
voltage across the leads of capacitor C2. It should be 5.0 ± 0.25 V, if not, the board may be faulty.
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 11-20: Pressure / Flow Sensor Assembly
04521C (DCN5731)