Making a 2-point adjustment - GM70

GM70 User Guide
Product status
Discontinued product
Document code
M010139EN
Revision
H
ft:locale
en-US
Product
GM70
Document type
User guide
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.

The difference between the 2 references must be at least 20 % of the measuring range of the probe.

See also Field Check Adapter 26150GM Quick Reference Guide (M210450EN), available at www.vaisala.com/gm70.
  1. Insert the probe into the field check adapter until the perforated filter is covered ((1) in Figure 1).
    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 CO2 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.