User's Manual

M400E Ozone Analyzer Operator’s Manual General Troubleshooting & Repair of the M400E Analyzer

13.7.6. PHOTOMETER PRESSURE /FLOW SENSOR ASSEMBLY

This assembly is only present in analyzers with O

generator and/or photometer options installed. The

pressure/flow sensor PCA, located at the rear of the instrument between the photometer and the pump (see

Figure 3-4) can be checked with a Voltmeter. The following procedure assu

mes that the wiring is intact and that

the motherboard as well as the power supplies are operating properly:

BASIC PCA OPERATION:

 Measure the voltage across C1 it should be 5 VDC ± 0.25 VDC. If not then the board is bad

 Measure the voltage between TP2 and TP1 C1 it should be 10 VDC ± 0.25 VDC. If not then the board is

bad.

PHOTOMETER PRESSURE SENSOR:

1. Measure the pressure on the inlet side of S1 with an external pressure meter.

2. Measure the voltage across TP4 and TP1.

 The expected value for this signal should be:

EXAMPLE: If the measured pressure is 20 Hg-in-A, the expected voltage level between TP4 and

TP1 would be between 2870 mVDC and 3510 mVDC.

EXAMPLE: If the measured pressure is 25 Hg-in-A, the expected voltage level between TP4 and

TP1 would be between 3533 mVDC and 4318 mVDC.

 If this voltage is out of range, then either pressure transducer S1 is bad, the board is bad or there is a

pneumatic failure preventing the pressure transducer from sensing the absorption cell pressure

properly.

PHOTOMETER FLOW SENSOR

 Measure the voltage across TP3 and TP1.

 With proper flow (800 cc

/min through the photometer), this should be approximately 4.5V (this

voltage will vary with altitude).

 With flow stopped (photometer inlet disconnected or pump turned OFF) the voltage should be

approximately 1V.

 If the voltage is incorrect, the flow sensor S3 is bad, the board is bad or there is a leak upstream of

the sensor.

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