MODEL 3081 pH/ORP | SECTION 7.0 |
| CALIBRATION OF pH MEASUREMENTS |
CALIBRATE
Std
EXIT NEXT ENTER
CALIBRATE
Std |
| 08 | .00 |
EXIT | NEXT ENTER | ||
CALIBRATE
SLOPE |
| 5 | 9.00 |
EXIT | NEXT ENTER | ||
NOTE
A transmitter adjacent to the one being calibrated may pick up signals from the IRC. To avoid accidentally changing settings, use a different security code for each near- by transmitter. See Section 5.7, Security.
7.7.3 Procedure
1.Enter the CALIBRATE menu by pressing CAL on the IRC. The CALibrAtE
2. At the CALibrAtE
3. With the Std
4.Be sure that the process pH and temperature are stable or, at worst, slowly drifting. Take a grab sample from the process stream or sample line at a point as close as possible to the pH sensor. Note the transmitter reading (pHtrans) at the time the sample was taken.
5.Measure the pH of the sample (pHstd) using the second pH meter. For best results make the measurement at the same temperature as the process.
6.Note the current process reading (pHcurr). Calculate the corrected reading from the equa- tion:
pHcorr = pHcurr + (pHstd - pHtrans)
where pHcorr is the corrected pH value, pHcurr is the current process reading, pHstd is the pH measured using the standard instrument, and pHtrans is the pH measured by the trans- mitter when the sample was taken. Use the editing keys to change the flashing display to pHcorr calculated above. Press ENTER to save the corrected pH.
7.The transmitter converts the difference between pHcorr and pHcurr into mV and com- pares the result with the value programmed for rOFFSt in Section 8.4, Diagnostic Parameters. If the difference exceeds the value for rOFFSt, the transmitter will not accept the data and will not update the display to the corrected pH. The message StD Err will appear.
8. If the corrected pH value is acceptable, the display will change to look like the screen at the left. The slope displayed is the current electrode slope. If the slope is incorrect and the correct value is known, use the editing keys to change the slope to the desired value. Press ENTER to save the value. To leave the slope unchanged, press EXIT .
9. To leave the CALIBRATE menu, press EXIT .
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