Aalborg DFM 26 Operating Manual page 29

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Note: Before performing Zero Calibration make sure the device is
powered up for at least 30 minutes and absolute no flow condition
is established.
Shut off the flow of gas into the Digital Mass Flow Meter. To ensure that no seep-
age or leak occurs into the meter, it is good practice to temporarily disconnect the
gas source. From the Main Menu, the user would traverse the menu tree until
reaching the "Zero Calibration" menu. The following screen will appear:
The user must acknowledge the warning that the Auto Zero procedure is about to
be started and there is absolutely zero flow thru the meter. Selecting YES confirms
that user has taken the necessary precautions and starts Auto Zero algorithm.
Selecting NO aborts the Auto Zero procedure.
To start Auto Zero use (p) or (q) buttons to highlight "Yes" option and press the
(u) [Enter] button. The following screen will appear:
The Auto Zero procedure normally takes 2 - 3 minutes during which Zero and
Sensor reading will be changed approximately every 4 seconds. The nominal value
for fully balanced sensor is 120 Counts. If the DFM's digital signal processor was
able to adjust the Sensor reading within 120 ± 2 counts, then Auto Zero is con-
sidered as successful and the screen below will appear:
Figure b-18, Zero Calibration (Start)
Figure b-19, Zero Calibration (In progress)
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