5.33
5.3.3 Setting Mechanical Zero
See Figure 6.2.
1. Power up the analyser
2. Pass a zero gas (e.g. Nitrogen) though at a sample rate of 100-200 ml/min (150 ml/min
max for 313 and 324 cells).
3. Turn the zero screw (9) anticlockwise until the photo cell assembly (24) reaches limit, then
turn the screw clockwise to the limit, counting the number of turns (between 4 and 6).
Adjust the screw to its mid position.
4. Display parameter 14, the uncorrected oxygen reading (or on separated systems, connect
a volt meter to the photocells in the transducer unit. See Section 5.2.1., test 6).
5. Slacken coarse mechanical zero screw (25), M4 socket head screw (3mm allen key).
6. Slide photo-cells along the slot until a reading between ±3% is obtained for parameter 14,
(allow for delay on display) or, if using a voltmeter, a reading between ±10.0mV.
7. Re-clamp screw. Check zero position is within limits.
8. Adjust zero screw (9) until a reading of between ±0.05% O
2
is obtained for parameter 14.
(±5.0mV if using a voltmeter).
9. Replace front of Inner Box (1).
10. Replace foam insulator.
11. Replace front cover.
12. Allow the analyser to warm up for 12 hours and then re-calibrate. See section 3.6.
Note: It is possible that the coarse span resistors may require adjusting, See Section 5.3.6.10.
5.3.4 Leak Testing
1. Common the ‘Sample In’ and ‘Sample Out’ gas connections and connect a water
manometer to the junction.
2. Pressurize the sample system to 500mm w.g. and measure the rate of pressure loss on
the manometer. It should be less than 1mm w.g. / 2min.
3. If the leak rate exceeds this value, check analyser pipework for leaks using a solution of
a neutral wetting agent. (Include the cell and its window).
4. Rectify leaks and recheck.
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