Advanced Instruments Inc.
Sensor
Recovery from Calibration
In-service Calibration Recovery
PPM Fuel
Cell
Air to 0.1% < 30 seconds
Air to 0.01% <2 min
2 minute exposure to
Air to 10 PPM < 60 min
Similar
Less than 30 min
The above times assume the introduction of a zero gas (low level of oxygen in nitrogen) after span calibration.
When purging the analyzer to lower ranges and calibrating with a span gas, observe the following guideline.
If the oxygen reading reaches less than 2% of the intended calibration range, enter the value of the span gas. If the
oxygen reading is greater than 2% of the calibration range, add the O2 reading to the value of the span gas (the
impact of the offset on accuracy is minor but the addition allows the oxygen sensor to continue to purge down and
avoid negative readings after calibration).
Zero Calibration
Typical offset from a PPM analyzer is less than 0.5 PPM. Therefore, for most applications, a Zero calibration is not
required. However, ZERO calibration option has been provided to allow the user to measure oxygen concentration at
the very low levels (less than 0.5 PPM) with great precision. As described below, accomplishing either objective places
a degree of responsibility on the user.
Determining the true offset requires the user to wait (see Online Recovery Time section) until the analyzer reading is
no longer trending downward (best evidenced by a constant horizontal trend on an external recording device.
The zero offset adjustment is limited to 50% of the most sensitive range of the analyzer. At the factory,
each analyzer is QC tested to confirm that the maximum offset is less than 50% of the most sensitive range available.
Should you observe a zero offset more than 50% of the lowest range, check the sample system for any possible leaks,
integrity of the zero gas and, assure that the analyzer has been given enough time to stabilize on zero gas before
initiating the “ZERO CALIBRATION”.
Caution: If adequate time is not allowed for the analyzer to establish the true baseline and a ZERO calibration is
performed, the analyzer will in all probability display a negative reading in the sample mode after a certain period of
time. If a negative reading is seen, perform ZERO calibration again.
Zero Calibration Procedure
Zero calibration should carried out after the span calibration and once performed should not have to be repeated with
subsequent span calibrations. Normally, zero calibrations are performed when a new sensor is installed or changes are
made in the sample system connections.
The maximum zero calibration adjustment permitted is 50% of the lowest full scale analysis range available.
Accordingly, the analyzer’s ZERO has not been adjusted prior to shipment because the factory conditions are different
from the application condition at the user’s installation.
1.
Access the MAIN MENU by pressing the MENU key.
2.
Advance the reverse shade cursor using the ARROW keys to highlight CALIBRATION.
3.
Press the ENTER key to select the highlighted menu option.
The following displays appear:
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