EC900 Series Operation Manual V4.7
13.3 Automatic Calibration option
Automatic calibration can be initiated in two different ways. Either automatically after a pre-
determined interval, or initiated by a control signal.
1. Connect the certified gas to the ‘cal gas’ connection on the rear panel of the analyzer or
appropriate valve connection if using remote Autocal. Ensure the pressure is set to the same
pressure as the sample gas to obtain the same flow rate.
2. Set ACAL in the main menu to the oxygen value of the certified gas.
3. Set Acd in the main menu to the desired interval, in hours, for Auto-calibration. If Auto-
calibration is to be initiated via a control signal then Acd should be set to zero.
4. To initiate Auto-calibration from a control signal. Referring to the diagram below, the
connection on pin 17 should be shorted to ground momentarily.
A control signal provided by two volt free relay contacts on the rear of the instrument is available to
indicate that there is an Auto-calibration in progress. This is between connections on 15 and 16.
These will be a short circuit while Cal is in progress.
When automatic calibration is activated the instrument will sample the certified gas for 30 minutes
before performing the calibration. During this time the display will read the currently measured value
of the certified gas.
The settling time can be modified via the USB connection using the command CALTIM= (See section
14, USB Comms Port).
Following auto-calibration a fault alarm will appear if the measured value of oxygen does not achieve
a certain band around the ACAL value within the settling time allowed. The acceptable band can also
be modified using USB comms with the command CALBAND=x, where x=0 to 999 (default 100)
expressed as a percentage of the ACAL value.
NOTE
Great care should be taken not to allow air to enter the analyzer. If the certified gas contains low ppm
levels and air has entered the system, it could take several hours for the oxygen value to equilibrate.
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