Instruction manual

93
MODEL Xmt-P SECTION 10.0
TROUBLESHOOTING
10.5.1 Warning or error message during two-point calibration.
Once the two-point (manual or automatic) calibration is complete, the transmitter automatically calculates the sensor slope
(at 25°C). If the slope is less than 45 mV/pH, the transmitter displays a "Slope error low" message. If the slope is greater
than 60 mV/pH, the transmitter displays a "Slope error high" message. The transmitter will 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 dioxide 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 pH 7 buffer instead of pH 7 and pH
10 buffer.
B. Was adequate time allowed for temperature equilibration? If the sensor was in a process liquid 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.
C. Were correct pH values entered during manual calibration? Using auto calibration eliminates error caused by improp-
erly entered values.
D. Is the sensor properly wired to the analyzer? Check sensor wiring including any connections in a junction box. See
Section 3.3.
E. Is the sensor dirty or coated? See the sensor instruction sheet for cleaning instructions.
F. Is the sensor faulty? Check the glass impedance. From the main display, press the ê key until the "Glass imped"
screen is showing. Refer to the table for an interpretation of the glass impedance value.
G. Is the transmitter faulty? The best way to check for a faulty transmitter is to simulate pH inputs. See Section 15.13.
10.5.2 Warning or error message during standardization.
During standardization, the millivolt signal from the pH cell is increased or decreased until it agrees with the pH reading
from a reference instrument. A unit change in pH requires an offset of about 59 mV. The controller limits the offset to ±1400
mV. If the standardization causes an offset greater than ±1400 mV, the analyzer will display 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.
less than 10 MΩ Glass bulb is cracked or broken. Sensor has failed.
between 10 MΩ and 1000 MΩ Normal reading
greater than 1000 MΩ pH sensor may be nearing the end of its service life.
Problem Action
Incorrect current output 1. Verify that output load is within the values shown in Figure 2.5.
2. For minor errors, trim the output (see Section 7.3.6)
Display too light or too dark Change contrast (see Section 7.10)
“Enter Security Code” shown in display Transmitter has password protection
(see Sections 5.4 and 7.6)
“Hold” showing in display Transmitter is in hold (see Section 5.5)
“Current Output for Test:” showing in display Transmitter is simulating outputs (see Section 7.3.5)