Specifications

MI 611-211 – October 2005 3. Operation
32
and selects the first one for which this pH is within 0.5 pH of the average pH for the buffer. If this
pH is not within 0.5 pH unit of any buffer table, a CAL ERROR message is displayed and no
buffer is selected.
To perform an automatic calibration:
1. Press ENTER at the prompt CAL AUTO.
2. At the prompt IMMERSE IN BUF 1, immerse your sensor in the first buffer solution
and press ENTER after you have done so.
3. If stability parameters were configured ON, the display READING XX.XX pH will
flash until stability is achieved and then alternate with the message ENTER TO
CONTINUE
. Wait for this message and then press ENTER again. If stability
parameters were configured OFF, watch for the measurement to stabilize before
proceeding to press ENTER. The instrument will then find the nearest buffer value
and display that value on the display under the heading BUF 1 IS. Press ENTER if
acceptable.
4. Wait for the first calibration to be completed. At the prompt IMMERSE IN BUF 2,
immerse your sensor in the second solution and repeat the procedure just completed
for BUF 1. Completion will be indicated with the display CAL COMPLETE.
Documentation of Calibration Procedure
Next, optionally follow the prompts to enter the calibration date, and name of the calibrator. The
date should be in the form mm/dd/yy. The name of the calibrator can contain up to six
characters.
NOTE
Invensys Foxboro recommends keeping a record of your calibrations. Recording the
mV values and slope can help you establish maintenance and replacement
information on your sensors. See Table 12 to calculate the expected mV value
generated by a sensor in contact with a buffer of known pH value. Slope and mV
values together provide useful data for troubleshooting the pH sensor.
Electronic Calibration
This calibration procedure can be used to verify the calibration of the transmitter. It is not
required at startup or for routine sensor/transmitter loop calibration. This procedure is
recommended for troubleshooting a measurement loop to isolate a problem to the transmitter or
eliminate the transmitter as a source of a problem. A millivolt source is used to supply theoretical
millivolt inputs in place of the sensor.
1. Disconnect all sensor leads from your transmitter.
2. Connect a millivolt source between sensor input terminals as follows: positive to
terminal 3 and negative to terminal 4. Jumper terminals 4 and 5.
3. In Configuration mode, go to
CONFIG TEMP and set the temperature in MANUAL
to 25
°C or 77°F.
4. Go to Calibration mode. In
CAL MANUAL, specify SINGLEPT or TWO PT
calibration.
SINGLEPT must be used for ORP.