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7.3 Calibrate the sensor
7.3.1 About sensor calibration
The sensor characteristics slowly shift over time and cause the sensor to lose accuracy. The sensor
must be calibrated regularly to maintain accuracy. The calibration frequency varies with the
application and is best determined by experience.
7.3.2 Temperature calibration
It is recommended to calibrate the temperature sensor once a year. Calibrate the temperature sensor
before calibrating the measurement sensor.
1. Put the sensor in a container of water that is at a known temperature. Under agitation, measure
the temperature of the water with an accurate thermometer or independent instrument.
2. Push the menu key and select SENSOR SETUP>CALIBRATE.
3. If the pass code is enabled in the security menu for the controller, enter the pass code.
4. Select 1 PT TEMP CAL and push enter .
5. The raw temperature value is displayed. Push enter .
6. Enter the correct value if different from that displayed and push enter .
7. Push enter to confirm the calibration. The temperature offset is displayed.
7.3.3 Zero calibration
Because of the stability of the electrode, for most applications this calibration is not required but can
be used to define the unique zero point of the sensor.
1. Remove the sensor from the process and rinse in distilled water.
2. Push the menu key and select SENSOR SETUP>CALIBRATE.
3. If the pass code is enabled in the security menu for the controller, enter the pass code.
4. Select ZERO CAL and push enter .
5. Select the option for the output signal during calibration:
Option Description
ACTIVE The instrument sends the current measured output value during the calibration procedure.
HOLD The sensor output value is held at the current measured value during the calibration procedure.
TRANSFER A preset output value is sent during calibration. Refer to the controller user manual to change
the preset value.
6. Place the clean sensor in a zero concentration solution, push enter .
7. Wait for up to one hour for the value to stabilize and push enter .
8. Review the calibration result:
• PASS—the sensor is calibrated and the offset is displayed.
• FAIL—the calibration is outside of accepted limits. Clean the sensor and retry with a fresh
reference solution. Refer to Troubleshooting on page 17 for more information.
9. If the calibration passed, push enter to continue.
10. If the option for operator ID is set to YES in the CAL OPTIONS menu, enter an operator ID. Refer
to
Change calibration options on page 13.
11. On the NEW SENSOR screen, select whether the sensor is new:
Option Description
YES The sensor was not calibrated previously with this controller. The days of operation and previous
calibration curves for the sensor are reset.
NO The sensor was calibrated previously with this controller.
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