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MODEL 3081 pH/ORP SECTION 7.0
CALIBRATION OF pH MEASUREMENTS
CALIBRATE
Std
EXIT NEXT ENTER
CALIBRATE
SLOPE
EXIT NEXT ENTER
CALIBRATE
Std
EXIT NEXT ENTER
08.00
5
9.00
7.7.3 Procedure
1. Enter the CALIBRATE menu by pressing CAL on the IRC. The CALibrAtE sub-menu
appears (pictured above left).
2. At the CALibrAtE sub-menu, press NEXT . The Std sub-menu appears.
3. With the Std sub-menu displayed, press ENTER . The Std prompt appears.
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 (pH
trans
) at the time the sample was taken.
5. Measure the pH of the sample (pH
std
) using the second pH meter. For best results make
the measurement at the same temperature as the process.
6. Note the current process reading (pH
curr
). Calculate the corrected reading from the equa-
tion:
pH
corr
= pH
curr
+ (pH
std
- pH
trans
)
where pH
corr
is the corrected pH value, pH
curr
is the current process reading, pH
std
is the
pH measured using the standard instrument, and pH
trans
is the pH measured by the trans-
mitter when the sample was taken. Use the editing keys to change the flashing display to
pH
corr
calculated above. Press ENTER to save the corrected pH.
7. The transmitter converts the difference between pH
corr
and pH
curr
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 .
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.