user manual

Input Calibration
172 UDA2182 Universal Dual Analyzer Product Manual January 2009
Step Action Screen
4
Press
Enter
Follow the prompts at the top
and bottom of the screen.
“Pressure Sensor Cal”
Display shows the barometric
pressure value in mm Hg.
“Press Enter when stable”
5
Once the reading is stable,
press
Enter
Change to sample value”
Use the arrow keys to change
the displayed value until the
displayed pressure in mmHg
agrees with the known pressure.
“Enter to save, Exit to cancel”
6 “ Cal Complete”
This screen gives you an option
to exit or recalibrate.
Press ENTER to recalibrate.
Press EXIT to return to Input Cal
Screen.
7
If the calibration fails, an error
message will be displayed
across the bottom stripe of the
screen.
Make necessary adjustments
and re-calibrate.
Error Messages:
See Table 12-2.
Running a Probe Bias Scan
Introduction
The dissolved oxygen probe is an electrochemical cell, which produces an electric current
that is directly proportional to the concentration of oxygen dissolved in the sample in
which the probe tip is immersed. (When the probe is in air, the current is identical to that
produced when the probe is in air-saturated water.) This current is a direct measurement of
oxygen level. Usually, the probe is operated at -0.55V with respect to a reference electrode
within the probe.
(The minus sign is omitted from the screen as well as from the
following discussion.)
However, in some applications, the performance of the DO probe
can be enhanced by using other bias voltages. The purpose of this test is to evaluate
whether the probe bias voltage should be adjusted. Possible interference with probe
performance may also be inferred from the Probe Bias Test (PBT).
Test initiation
When the test is initiated, the bias voltage is adjusted down from its original value (usually
0.55V) at 25mV/sec until 0V is reached. Then the bias voltage is driven up to 1.0 V at
25mV/sec and finally, it is driven down again until it has returned to the value it had just