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PART THREE - OPERATION
SECTION 6 - pH CALIBRATION
Rev. 9-898
Model 692P
-37-
calibration procedure requires a clean sensor and two fresh,
accurate pH buffers (or known process solutions) that have
the same values as the two preset calibration points.
1. Place clean sensor, with protective caps removed
, in the
lower value buffer
.
NOTE
: If a pH combination electrode is used with an
external temperature sensor, place the tem-
perature sensor in the buffer along with the
electrode during this step and step 4. If an ex-
ternal resistor is used for fixed temperature
compensation (Table A on page 14), it is rec-
ommended to bring the temperature of buffer
used in this step and step 4 to the fixed com-
pensation temperature for best accuracy.
2. With display in pH measuring mode, press
BEGIN CAL
key (display indicates one of the preset values
“LO
CAL VALUE” or “HI CAL VALUE”). If display indicates
the higher value, press
BEGIN CAL
key again to display
lower value.
After pressing
BEGIN CAL
, you have 30 minutes to com-
plete the calibration of this point. During the routine,
another 30 minutes can be added by pressing any key
except
END CAL
.
The instrument checks the stability of the pH and tempera-
ture inputs. As each input changes, the respective pH
and
°
C (or
°
F) indicator flashes. When each input is sta-
ble, the respective indicator stops flashing and remains
on.
When the pH and
°
C (or
°
F) indicators are both on (not
flashing), press recessed
END CAL
button using a slen-
der tool. The instrument checks that:
n
The pH input has a slope between 51 and 62 mV/pH.
If not, the display flashes “HI/LO SLOPE ERROR.”
n
The pH input offset is within
±
1.50 pH of the entry
value. If not, the display flashes “HI/LO ERROR.”
n
This calibration point is at least 2.00 pH away from
the other calibration point. If not, the display flashes
“BUFFER VALUE ERROR.”
When these conditions are met, the display flashes “OK”