Hach-Lange ORBISPHERE 3650 - Manual (Page 44)

42
Calibrations
6.4 Sensor calibration
When delivered, the sensor is pre-calibrated. However, it should be re-calibrated on site, when
being used for the first time, and always after a membrane change. If you have just replaced the
membrane, allow at least half an hour for the membrane to settle before attempting to calibrate.
If you want to verify the accuracy of the calibration, place the analyzer back in measurement
mode and compare your displayed gas concentration against the value in the appropriate tables
found in the accompanying Calibration Tables booklet.
Your calibration is stored internally and is valid for the life of the sensor's membrane, thus it is
not necessary to repeat the calibration procedure until after the next membrane change.
The sensor can be calibrated either by using a span gas or directly in line in a liquid sample.
Additionally, oxygen sensors can be calibrated in air. The mode of calibration may be selected
using the WinLog97 program or directly from the instrument (see
Selecting type of calibration on
page 38 for more details).
6.4.1 Calibration in a span gas
The span gas calibration procedure may be used if you have a supply of gas with a known
concentration in %units (use O
2
for oxygen sensors or H
2
for hydrogen sensors). To perform
this type of calibration, the instrument must be set for calibration In a Span Gas. The WinLog97
program also must be used in this procedure to set the gas concentration parameter.
Switch on the instrument, if necessary, and wait a minute or so for the displayed measurement
to settle. Then expose the sensor to a span gas sample with a known gas concentration. Enter
the percentage of gas in the span gas using the WinLog97 program (see
Entering a span gas
value on page 39 ).
1. Press the CAL button. Remember, this button may have been
locked out to prevent an accidental reset (see Locking out the
instrument’s CAL button on page 39 for details).
2. A brief clearing [---] message appears.
3. Press CAL again within a 3 second period.
4. The percentage of the measured current to the ideal one is
displayed.
5. When the reading is stable, press CAL again.
If the new calibration current is within 25% to 175% of the ideal
current, the instrument displays CAL and returns to the
measurement mode. Calibration is now complete, the sensor is
calibrated, and you can proceed with your measurements.
If the new calibration current is not within this range, the
instrument displays Err and returns to measurement mode. The
system will not calibrate, and it is likely that a sensor service will
be required.