Standardization - Emerson Rosemount Analytical HART 5081-A-HT Instruction Manual

MODEL 5081-A

13.4 STANDARDIzATION

1. The pH measured by the transmitter can be changed to match the reading from a second or reference instru-
ment. The process of making the two readings agree is called standardization, or one-point calibration.
2. During standardization, the difference between the two pH values is converted to the equivalent voltage. The
voltage, called the reference offset, is added to all subsequent measured cell voltages before they are con-
verted to pH. If a sensor that has been calibrated with buffers is then standardized and placed back in a buffer,
the measured pH will differ from the buffer pH by an amount equivalent to the standardization offset.
3. Install the sensor in the process liquid. Once readings are stable, measure the pH of the liquid using a refer-
ence instrument. Normally, it is acceptable to test a grab sample. Because the pH of the process liquid may
change if the temperature changes, measure the pH immediately after taking the grab sample. For poorly
buffered samples, it is best to determine the pH of a continuously flowing sample from a point as close as pos-
sible to the process sensor.
CALIBRATE
PH CAL
EXIT NEXT ENTER
CALIBRATE
Std PH
EXIT NEXT ENTER
CALIBRATE
Std
07 . 00
EXIT ENTER
4. Press CAL on the remote controller.
5. Press NEXT until the PH CAL submenu appears. Press ENTER.
6. Press NEXT until the Std PH submenu appears. Press ENTER.
7. Be sure the process pH and temperature are stable. Measure the pH of
the process liquid using the reference instrument. Use the arrow keys
to change the flashing display to match the reading from the reference
meter. Press ENTER to save.
8. Press RESET to return to the main display.
SECTION 13.0
CALIBRATION - pH
71