MODEL | SECTION 10.0 |
| CALIBRATION – PH |
10.4 PROCEDURE — STANDARDIZATION
1.The pH measured by the transmitter can be changed to match the reading from a second or referee instru- ment. The process of making the two readings agree is called standardization.
2.During standardization, the difference between the two values is converted to the equivalent voltage. The volt- age, called the reference offset, is added to all subsequent measured cell voltages before they are converted to pH. If after standardization the sensor is placed in a buffer solution, the measured pH will differ from the buffer pH by an amount equivalent to the standardization offset.
3.Install the pH sensor in the process liquid.
4.Once readings are stable, measure the pH of the liquid using a referee instrument.
5.Because the pH of the process liquid may change if the temperature changes, measure the pH of the grab sample immediately after taking it.
6.For poorly buffered samples, it is best to determine the pH of a continuously flowing sample from a point as close as possible to the sensor.
7.Press MENU. The main menu appears. Choose Calibrate.
8.Choose pH.
9.Choose Standardize.
10.The top line shows the present reading. Use the arrow keys to change the pH reading in the second line to match the pH reading from the referee instrument.
11.The screen at left appears if the entered pH was greater than 14.00 or if the mV offset calculated by the trans- mitter during standardization exceeds the reference offset limit programmed into the transmitter. The display then returns to step 10. Repeat the standardization. To change the reference offset from the default value (60 mV), see section 8.4.
12.If the entry was accepted the display returns to step 9.
13.To return to the main display, press MENU then EXIT.
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