Hach-Lange ORBISPHERE Model 51x User Manual - Manual (Page 66)

64
Calibration menu
7.4 Calibration errors (EC and TC sensors)
7.5 Interference calibration (EC sensor)
Calibration results A calibration screen will be displayed showing current measurement data
which is continually refreshed.
The value “% ideal current” is a percentage of the current against the ideal
current for the membrane type selected. If this percentage is not within the
accepted range, an error message is displayed and the calibration process
fails (see
Calibration errors (EC and TC sensors) on page 64 ). A warning
message can be displayed when this value is close to the boundaries, but
when calibration can be accepted.
The message is first displayed in the result box. The dialog box with the
error message or the warning is displayed when the finish button is pressed.
The value “% last calibration” shows the ratio between the current
measurement and the previous sensor calibration.
The value “% variation” indicates the variation during the last 3
measurements, which is the stability of the measurements. A variation as
low as possible is needed for a precise calibration.
The display shows the actual calibration parameters, and the actual
readings (temperature, barometer, current).
Note:
In case of calibration failure, consider replacing the membrane. See
the sensor maintenance manual for details.
Verification Similar to the calibration procedure, but for verification of the actual
calibration values. The result of the measurements made during the
verification is not stored and the actual calibration data is not modified.
Calibration errors (EC and TC sensors)
The calibration is not possible in the following circumstances:
•
When the "ratio ideal current" is greater than 170% or smaller than 30%
• When the sensor cannot measure (thermal cut off, sensor out, etc.)
• When the "ratio ideal current" is greater than 150% or smaller than 50%, a warning is displayed but
the calibration is valid.
Interference calibration (EC sensor)
The hydrogen interference calibration is available for EC sensors measuring O
2
concentrations, and is
required when H
2
interference has been enabled (see Interferences configuration on page 55 ). The
lower part of the screen displays the actual measurement.
•
Enter in the upper box the purity of the hydrogen that is used for this calibration. A reasonably pure
(e.g. 99.8% or better) hydrogen source and an accurate pressure gauge are needed.
• Hold during calibration : Selected by default, this holds the measurement sequence to avoid storing
invalid values.
Instructions Using a flow chamber, expose the sensor to the H
2
source at the same
barometric pressure that is shown on the display. Press Start to initiate the
H
2
interference calibration.