Rosemount SOLU COMP II, Инструкция по эксплуатации

Страница: 50 / 61

MODEL SOLU COMP II SECTION 8.0
TROUBLESHOOTING
8.3.2 Calibration Error During Two-Point Calibration
Once the two-point (manual or automatic) calibration is complete, the Solu Comp II automatically calculates the
sensor slope (at 25°). If the slope is greater than 60 mV/pH or less than 45 mV/pH, the analyzer displays the
Calibration Error screen and does not update the calibration. Check the following:
A. Are the buffers accurate? Inspect the buffers for obvious signs of deterioration, such as turbidity or mold
growth. Neutral and slightly acidic buffers are highly susceptible to molds. Alkaline buffers (pH 9 and greater),
if they have been exposed to air for long periods, may also be inaccurate. Alkaline buffers absorb carbon diox-
ide from the atmosphere, which lowers the pH. If a high pH buffer was used in the failed calibration, repeat the
calibration using a fresh buffer. If fresh buffer is not available, use a lower pH buffer. For example, use pH 4
and 7 buffer instead of pH 7 and 10 buffer.
B. Was adequate time allowed for temperature equilibration? If the sensor was in a process substantially hotter
or colder than the buffer, place it in a container of water at ambient temperature for at least 20 minutes before
starting the calibration. Using auto calibration avoids calibration errors caused by temperature drift. The ana-
lyzer will not update readings until the drift is less than 0.02 pH over 10 seconds.
C. Were correct pH values entered during manual calibration? Using auto calibration eliminates errors caused by
improperly entering data.
D. Is the sensor properly wired to the analyzer? Check the sensor wiring including any connections in a junction
box. See Section 3.0.
E. Is the sensor dirty or coated? See the sensor instruction manual for cleaning instructions.
F. Is the sensor faulty? With the main display showing, use
"
or
'
to scroll through
the information screens until the electrode impedance screen (at left) is displayed.
Refer to the table for an interpretation of the impedance readings.
Another way of checking for a faulty sensor is to replace it with a new one. If the new sensor can be calibrat-
ed, the old sensor has failed.
G. Is the analyzer faulty? The best way to check for a faulty analyzer is to simulate pH and temperature inputs.
See Section 8.4.
8.3.3 Calibration Error during Standardization.
During standardization, the millivolt signal from the pH cell is increased or decreased to force it to agree with the
pH reading from a referee instrument. A unit change in pH requires an offset of about 59 mV. The Solu Comp II
limits the offset to ±1400 mV. If the standardization causes an offset greater than ±1400 mV, the analyzer will dis-
play the Calibration Error screen. The standardization will not be updated. Check the following:
A. Is the referee pH meter working and properly calibrated? Check the response of the referee sensor in buffers.
B. Is the process sensor working properly? Check the process sensor in buffers.
C. Is the sensor fully immersed in the process liquid? If the sensor is not completely submerged, it may be meas-
uring the pH of the liquid film covering the glass bulb and reference element. The pH of this film may be dif-
ferent from the pH of the bulk liquid.
SRef Imp 123k^
Glass Imp 123M^
REFERENCE IMPEDANCE (Ref Imp)
less than 40 k
Ω
Normal reading, reference junction is clean.
between 40 and 140 k
Ω
Reference junction is fouled or dirty.
greater than 140 k
Ω
Reference junction is blocked or electrolyte is depleted. Sensor has failed.
GLASS IMPEDANCE (Glass Imp)
less than 10 M
Ω
Glass bulb is cracked or broken. Sensor has failed.
between 10 and 1000 M
Ω
Normal reading.
greater than 1000 M
Ω
pH sensor may be nearing the end of its service life.
43