pH ARC Sensors Modbus RTU Programmer’s Manual (EPHUM011)
Perform the following steps to do a standard calibration at CP1 and CP2:
Step1: Select the desired set of calibration standards (see chapter 2.7.11)
Step 2: Immerse the sensor into one of the calibration standards available in the selected set
Attention:
It is important that the pH ARC Sensor is immersed in a defined calibration standard at least 3 minutes BEFORE the calibration is started.
Step 3: Choose one of the calibration points CP1 or CP2.
Attention:
The assignment of both CP1 and CP2 to the same pH value is rejected.
Try to avoid the following situations:
For example, the sensor was calibrated earlier at pH 4 (CP1) and at pH 7 (CP2):
You want to perform a new calibration at CP1: it is possible to assign CP1 to pH 4 or to pH 10, but not to pH 7 (already used for CP2).
You want to perform a new calibration at CP2: it is possible to assign CP2 to pH 7 or pH 10, but not to pH 4 (already used for CP1).
If you calibrate now CP1 at pH 10, pH 4 will later be free for selection at CP2. In this case you can calibrate CP2 at pH 4 or pH 7, but not at pH 10 (CP1).
Step 4: Start the calibration (automatic recognition or manual selection)
The calibration is initiated at CP1 by writing to register 5162 or at CP2 by writing to register 5194.
Start | Number of | Reg1 / Reg2 | Modbus | Read | Write |
register | registers |
| function code | access | access |
5162 | 2 | pH value at CP1 (unit is always pH) | 16 | none | A/S |
5194 | 2 | pH value at CP2 (unit is always pH) | 16 | none | A/S |
Figure 2.7.3.1.3: Definition of register 5162 and 5194. You have two options to enter the pH value: Automatic recognition: pH value=0: the sensor tries to assign the measured electrical potential to
one of the calibration standards available for automatic calibration.
Manual selection: enter the actual pH value at 25°C (the value must be within the tolerance range of the nominal value of one of the calibration standards available for manual selection)
Step 5: Read the calibration status (see chapter 2.7.4)
Step 6: Check the pH ARC Sensor’s quality indicator
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