pH ARC Sensors Modbus RTU Programmer’s Manual (EPHUM011)
Standard Calibration with Automatic Recognition of the Standard
Prior to calibration, the specialist selects - for each set of calibration standards - a list of calibration standards allowed for automatic recognition (register 9530).
When the calibration is initiated, the sensor screens this list of allowed calibration standards and checks if the currently measured electrical potential is within the allowed range of electrical potentials, defined for the individual calibration standards in this list.
If the sensor does find a corresponding calibration standard, the nominal pH value of the specific calibration standard is assigned to the currently measured electrical potential. The temperature dependency of the calibration standard is considered during the assignment.
Temperatue dependency of Hamilton pH buffer solutions
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Temperature [°C]
Figure 2.7.3.1.2: Temperature dependency of the pH value of HAMILTON DURACAL calibration standards.
If the sensor does not find any corresponding calibration standard, the bit representing the corresponding status “no matching calibration standard”is set in the calibration status register.
Note that only the nominal value of the calibration standard is used for calibration. The actual value of the calibration solution, which may deviate from the nominal value, is not taken into account and cannot be set by the operator.
Standard Calibration with Manual Selection of the Calibration Standard
If the operator knows in what calibration standard the sensor is immersed, he can initiate the calibration procedure by means of setting the pH value to the actual value of the calibration standard. The sensor now screens the list of calibration standards that are allowed for manual selection (register 9530). If the pH value entered by the operator fits in the allowed pH range of one of the allowed calibration standards, the entered pH value is assigned to the currently measured electrical potential. The temperature dependency of the calibration standard is considered during the assignment.
If the sensor does not find any corresponding calibration standard, the bit representing the corresponding status “no matching calibration standard”is set in the calibration status register.
Note: using manual selection only, the actual pH value of the calibration standard can be set. However, the actual value must be within the given tolerance of the standard in use.
624300/01 | page 36 / 67 |
