Procedure
1. Open - Main Menu Analyser State Menu Pressure & Flow Menu.
2. Turn off the vacuum pump and allow the analyser to return to ambient.
3. Disconnect all external tubing connected to the rear ports of the instrument except for the AUX
in Port and AUX Out Port (for the external converter).
4. After two-five minutes observe the pressure readings: ambient, cell and manifold. Ensure that
they are reading the same ±3 torr (±0.4 kPa).
5. If the readings are outside this level, perform a pressure calibration (refer to Section 5.2).
If the calibration fails, the instrument may have a hardware fault. The cell pressure PCA and the
manifold pressure PCA have test points. To determine if the pressure sensor is faulty simply measure
the voltage on the test points shown in the photos. The voltage measured across the test point is
proportional to the pressure measured by the sensor, so if the sensor is exposed to ambient pressure
at sea level then the voltage will be around 4 volts but if the sensor is under vacuum the voltage will
be low (for example, 0.5 volts). If the test point measures zero or negative voltage the assembly is
most likely faulty and will need to be replaced.
Figure 61 – Test Point Location
Figure 62 – Typical Test Point Reading of Cell Pressure with Vacuum Connected to Exhaust Port
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