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7.5.4 Procedure
1. Refer to Section 8.7, Buffer Calibration Parameters. Verify that auto calibration is activated. Identify
the buffers being used and set the stability limits.
2. Enter the CALIBRATE menu by pressing CAL on the IRC. The CALIbrAtE sub-menu appears (pic-
tured above left).
3. At the CALIbrAtE sub-menu, press ENTER . The CAL bF1 prompt appears.
4. Rinse the sensor and place it in the first buffer. Be sure the glass bulb and the temperature element
are completely submerged. Keep the sensor tip at least three inches below the liquid level. Do not
let the weight of the sensor rest on the glass bulb. Swirl the sensor to dislodge trapped bubbles. The
main display will show the measured pH based on the previous calibration.
5. Press ENTER . bF1 flashes until the measured pH meets the programmed stability limits. If the pH
reading is not stable after 20 minutes, the transmitter automatically leaves the CALIBRATE menu
and returns to the process mode. If this happens, consult Section 12.5, Troubleshooting, for assis-
tance. Once the reading is stable, the display changes to look like the figure at the left. The flashing
number is the nominal pH, that is, the pH of the buffer at 25°C. If the flashing number does not match
the nominal pH, press
Ï or
Ð
until the correct pH appears. Press ENTER to save the first
calibration point.
6. The CAL bF2 prompt appears.
7. At the CAL bF2 prompt, remove the sensor from the first buffer. Rinse the sensor and place it in the sec-
ond buffer. Be sure the glass bulb and the temperature element are completely submerged. Keep the
sensor tip at least three inches below the liquid level. Do not let the weight of the sensor rest on the
glass bulb. Swirl the sensor to dislodge trapped bubbles. The main display will show the measured pH
of the buffer based on the previous calibration.
8. Press ENTER . bF2 flashes until the pH reading is stable. If the pH reading is not stable after 20
minutes, the transmitter automatically leaves the CALIBRATE menu and returns to process mode.
If this happens, consult Section 12.5, Troubleshooting, for assistance. Once the reading is stable,
the display changes to look like the figure at the left. The flashing number is the nominal pH, that is,
the pH of the buffer at 25°C. If the flashing number does not match the nominal pH, press
Ï or
Ð
until the correct pH appears. Press ENTER to save the second calibration point.
9. The calibration is complete, but the transmitter remains in the CALIbrAtE sub-menu for two minutes
after ENTER is pressed.
10. Remove the sensor from the buffer and return it to the process. If the transmitter was in hold during
calibration, wait until readings have stabilized before taking the transmitter out of hold. See Section
7.3, Using the Hold Function.
11. The transmitter uses the calibration data to calculate a new slope. Refer to Section 13.7, Buffers and
Calibration, for more details. If the slope is unacceptable, the calibration will not be updated, and the
transmitter will display a SLOPE Err HI or SLOPE Err LO error message. Refer to Section 12.5,
Troubleshooting, for assistance.
12. To leave the CALIBRATE menu, press EXIT .
13. For quality control and troubleshooting, it is helpful to know the electrode slope. To display the slope,
press CAL on the IRC. The CALIbrAtE sub-menu will appear. Press NEXT . The Std sub-menu
appears. Press ENTER . The Std prompt appears. Press ENTER again and SLOPE xx.xx will
appear in the display. The four digit number is the electrode slope. For a good sensor, the slope is
between 50 and 60.
CALIBRATE
bF 22
EXIT ENTER
10.00
MODEL 3081 pH/ORP SECTION 7.0
CALIBRATION OF pH MEASUREMENTS
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 nearby transmitter. See Section 5.7, Security.
NOTE
During calibration, the sensor may be exposed to solutions having pH outside
the normal range of the process. To prevent false alarms and possible unde-
sired operation of chemical dosing pumps, place the analyzer in hold during
calibration. See Section 7.3, Using the Hold Function, for details.
CALIBRATE
CAL bbF 11
EXIT NEXT ENTER
CALIBRATE
CAL bbF 22
EXIT ENTER
CALIBRATE
bF 11
EXIT ENTER
4.00
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