M&C TechGroup PMA 50 EEX Operator's manual - Manual (Page 33)

33
Gas sampling and gas conditioning technology 9-3.15-ME
23.2 MECHANICAL ZERO POINT ADJUSTMENT
The mechanical zero point adjustment has to be done as described in the following.
1 IR LED 5 Heater element
2 Temperature cut out (72°C) 6 Adjustment screw photocell
3 Sample gas heating coil 7 Measuring cell
4 Fastening screw photocell 8 Photocell
Figure 8 Schematic view of the transmitter unit

Before switching on the analyser, set the range selector to 30%. Control the zero point of the analogue
display and adjust it if necessary to 0% via the adjustment screw below the digital display;

Switch on the analyser via the external switch. Normally, the analogue display will indicate a value of
21% oxygen because the cell is filled with ambient air;

The warming up is indicated by the permanently beaming LED in the front plate of the analyser; after
approx. 30 minutes, the flashing display signalizes that the required operating temperature has been
reached;

Set the potentiometer for zero point and span value in the mid position; you can do this by turning the
potentiometer with a screw driver fully to the left and then turn it five turns back to the right;

Charge the analyser with a zero gas volume flow of approx. 40 l/h;

With a precise adjustment of the zero point, the analogue display should indicate 0.0 Vol.% oxygen;
If this does not happen, please execute the following steps:

Open the housing of the analyser (see 23.1);

Remove carefully the isolating cap of the transmitter unit; now, all screws of the photocell fixing are
visible (see figure 8);

Set the range switch to 3%;

Turn the adjustment screw 6 (see figure 8) of the photocell as long clockwise or anticlockwise as on
the display appears a value of nearly 0,0 Vol.% oxygen;

After the mechanical zero point adjustment, the fixing screw of the photocell fixing 4 must be screwed
down again;

Now, the zero point adjustment has been done;

Place carefully the isolating cap on the analyser and close it according to 23.1.