Figure 1. Field check adapter
2. Connect the tubing to the bottom port of the adapter ((2) in Figure 1).
3. Connect the adapter with the tubing to the flow meter, the pressure regulator and further to the low-end reference
gas bottle. The side port of the adapter is left open for gas outflow.
4. Let the low end reference gas flow and stabilize with a flow rate of about 0.6 l/min. Follow the reading of GM70
and wait until the reading has fully stabilized.
5. Take out the screw from the GM70 probe handle to expose the adjustment button (see Figure 1). Press the
button with a small screwdriver. When pressing the button, the indicator turns to adjusting mode.
6. Press OK to confirm that you are making an adjustment.
7. Select CO2 and press Select.
8. Press Yes to give the ambient pressure and temperature values. To continue adjusting, press Exit.
9. The adjustment mode is now active. Press Graph to confirm that the readings have stabilized. Go back and
press Adjust to select the adjustment method.
10. Select 2-point adjustment and press Select. Press Ready with the stabilized reading in the lower reference
concentration.
11. Give the lower reference concentration value by using the arrow buttons (for example, if you are using pure
nitrogen, enter value 0 ppm). Take care that you give the correct value in correct units, as you cannot revert the
earlier values after accepting the new values. Press OK.
This step completes the low-end adjustment: next, move on to the adjustment at the second (high-
end) reference point.
12. Take out the tubing from the low-end gas bottle and connect it to the high-end gas bottle.
13. Let the high end reference gas flow and stabilize with a flow rate of 0.6 l/min. Follow the reading of GM70 and
wait until the reading has fully stabilized.
14. Press Ready with the stabilized reading in the higher reference concentration.
15. Give the high-end reference concentration value by using the arrow buttons. The analyzed CO
2
concentration of
the reference gas is typically printed on the bottle. Take care that you give the correct value in correct units, as
you cannot revert the earlier values after accepting the new values. Press OK.
16. Confirm the adjustment by pressing Yes. If you press No, you return to the adjustment mode display and
changes are canceled.
17. The adjustment is complete. Press Back and Exit to return to the basic display.
18. Shut off the gas flow.
19. Replace the screw onto the adjusting button.
Making a 1-point adjustment
CAUTION! Make sure to check the following when carrying out the adjustment:
Give the correct reference concentrations in the correct units
Wait until the reading has fully stabilized before accepting the reading.
CAUTION! Reverting to factory settings is not possible after the adjustment.
See also Field Check Adapter 26150GM Quick Reference Guide (M210450EN), available at
www.vaisala.com/gm70.
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