Appendix E – Calibration
96
• If the sensor responds quickly enough, check that within another 3 minutes the
current reading has fallen to virtually zero (less than 5µA).
• If the current reading is greater than 5µA, select the “Zero Cal” function form
the main menu, or from the calibration menu. Press the “ENTER” key and the
unit will correct the 0% saturation point to the current input at this point.
Span Calibration in Free Air
• The frequency of this check depends upon the application, but should be made
generally once a month.
• Wash off any process chemicals or water from the sensor. Use de-mineralised
water or follow the manufacturers cleaning instructions as necessary.
• Set the instrument to read Current. Select % saturation as the secondary
reading.
• Stabilise the sensor by leaving it in the process solution for up to 10 minutes.
This will allow the temperature compensator networks to reach equilibrium.
• Lift the sensor so that it is just above the process solution, and therefore as
close to the temperature of that solution as possible. Observe the instrument
readings and wait until the output stabilises. If necessary enable the sensor
filter to obtain a stable reading.
• If necessary check and set the calibration level (100%) in the “Calibration”
Menu.
• Select the “Span Cal” function from the main menu, or from the calibration
menu. Press the “ENTER” key and the unit will correct the 100% saturation
point to the current input at this point.
• Enter the Pressure level at the span calibration from within the calibration
menu. It is important to have the sensor pressure level correctly entered,
especially when the sensor is measuring in a system where pressure can vary
over a wide range. If automatic Temperature compensation is selected the unit
will automatically store the measured temperature at the instance of the 100%
span calibration. If, however, the Temperature compensation is “Manual”, the
user will need to ensure that the “fixed” temperature input is set to the
temperature the sensor is experiencing at the instance of calibration, as this will
be taken as the calibration temperature.
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