MODEL 54e pH/ORP | SECTION 7.0 |
| SPECIAL PROCEDURES AND FEATURES |
7.3 SOLUTION TEMPERATURE COMPENSATION
Security Temperature Coeff Temperature sensor
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Temp coeff: +.000
Operate iso: +07.00 pH
Sensor iso: 07.00 pH
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This section is for advanced users only.
It explains how to input values for:
•the isopotential pH and
•the temperature coefficient for solution temperature compensation.
1.Beginning from the main menu, move the cursor down to "Program" and press Enter (F4). From the program menu, move the cursor down using the arrow key to highlight "Configure" and press Enter (F4).
Use the arrow key again to highlight "Temperature Coeff" (as shown on the left) and press Enter (F4) .
The Controller can compensate for two different temperature effects on the measured pH: the temperature effect on the pH sensor and the tem- perature effect on the actual pH of the process solution.
Sensor Temperature Compensation. The millivolt output of a pH sen- sor changes with temperature, which in turn, changes the measured pH value. The Sensor Isopotential pH (Sensor ISO) is the pH where the pH sensor's output does not change with temperature. The Controller uses the Sensor Isopotential pH value to correct for the temperature effect on the pH sensor. Except in rare instances (antimony or glass on metal elec- trode systems), the Sensor Isopotential pH is always 7.0 pH.
Solution Temperature Compensation. The actual pH of a solution can sometimes noticeably change with temperature. This can occur in solu- tions with a pH above 6.5 pH and in solutions containing weak acids, bases, and their salts. This effect can be compensated for by entering a Temperature Coefficient (Temperature Coeff) which is the change in solu- tion pH per degree centigrade (°C). If there is no noticeable solution pH change with temperature, or solution temperature compensation is not desired, the Temperature Coefficient (Temperature Coeff) should be set to 0.00.
Operating Isopotential pH. The Operating Isopotential pH (Operate ISO) is the Isopotential pH, which the Controller is using for overall tem- perature compensation. It represents a combination of both the sensor and the solution temperature compensations.
If no solution temperature compensation is being used (Temperature Coeff = 0), the Operating Isopotential pH (Operate ISO) is equal to the Sensor Isopotential pH (Sensor ISO).
If there is a
Operate ISO = Sensor Iso - (Temperature Coeff) X (298.16)
Conversely, if an Operating Isopotential pH is known for a particular solu- tion, the Controller will automatically calculate the corresponding Temperature Coefficient.
Example: High Purity water with Ammonia, being measured with a normal pH sensor (Sensor Isopotential pH of 7.0 pH), has a Temperature Coefficient of
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