
7.1.6 Incorrect calibration
1.
The device checks the validity of the calibration. Only valid
calibrations are saved for use.
A3423
Fig. 47: Error message / last valid calibration
2.
An error message is displayed if calibration fails. Press EXIT
to confirm the message.
3.
The device reverts to the last valid calibration. Check the
standard solutions and recalibrate them.
4.
The failed calibration is discarded, but a record of the failed
calibration is saved with the time and date.
7.1.7 Setting the offset
n
Chapter 6.5.6 ‘Setting the OFFSET’ on page 38
n
It is possible to use an offset factor in the device instead of car‐
rying out a physical calibration.
n
This procedure is not recommended as an alternative to cali‐
bration. However, the process can be used to match the
sensor to another device
n
The use of an offset means that the device is only precise with
turbidity values in the immediate vicinity of the setpoint, but not
across the entire measuring range of the device.
n
Make sure that the OFFSET symbol always lights up when an
offset is used. The maximum deviation is ± 1.00 NTU.
n
A complete calibration is needed if the deviation of the device
is greater than 1 NTU.
1.
Note the measured value recorded by the sensor.
2.
Take a sample of the process water being monitored by the
sensor. Use a laboratory turbidity measuring device to
measure the turbidity.
3.
Compare the turbidity recorded by the sensor with the tur‐
bidity determined in the laboratory. If the measured values
are very close to each other then there is no need to set the
offset or perform calibration. The process can be terminated
at this point. However, continue with this process should the
measured values differ significantly from each other, but less
than 1 NTU. Use the offset option to improve the turbidity
measured value of the sensor so that the turbidity measured
value of the sensor matches the turbidity recorded in the lab‐
oratory up to the next calibration.
4.
Select the offset function of the sensor by pressing the
DOWN key until the arrow lights up beside
‘CONFIG’ on the
display and then press the EXIT key.
5.
Press the right arrow key until OFST is displayed in the
bottom row of the display.
The process for setting the offset is
described below:
Operation
54