Operation LXT-220 DO
Teledyne Analytical Instruments 48
3. For diagnostic reasons note the DO and mV/FS values from the
prior calibration.
4. Press both horizontal CALIBRATE keys simultaneously to enter
the calibrate mode. Observe the diagnostic value on the bottom
line becomes a real-time value and that the term "CAL" has
disappeared.
5. To change the buffer point, position the cursor under the desired
digit using the left-hand CALIBRATE key.
6. Increase or decrease the value by pressing the appropriate
vertical CALIBRATE key.
7. Wait for the real-time mV value to stabilize.
8. To file the calibration and exit the calibrate mode, press either
MENU SELECTION key.
A perfect electrode slope (efficiency) is typically greater than -
150.0 mV/FS. If the value falls below -100.0 mV/FS, the electrode
should be serviced or replaced.
IMPORTANT: If a flashing asterisk appears during or after
calibration, the electrode may require service, or
the buffer solution may be contaminated.
Note: Comparing the millivolt values before and after the
calibration provides a valuable diagnostic tool in
determining the degradation of the electrode. Large
differences between calibrations may indicate coating or
damage to the measurement half-cell.
3.4.2.4 CALIBRATION USING A GRAB SAMPLE AS A STANDARD
The LXT-220 allows easy standardization to a grab sample value
by placing the process value into the first calibration point.
Procedure:
1. Record the O2 value of the process when the sample is extracted.
2. Record the O2 value of the grab sample.
3. Calculate the difference between the two values as follows:
(Grab sample value) - (Displayed value) = differential