Emerson Rosemount5081 - Advanced pH and Sensor Troubleshooting

2. Low readings can be caused by zeroing the sensor before the residual current has
reached a stable minimum value. Residual current is the current the sensor
generates even when no ozone is in the sample. Because the residual current is
subtracted from subsequent measured currents, zeroing before the current is a
minimum can lead to low results. See Oxygen readings too low for more information.
3. Sensor response depends on flow. If the flow is too low, readings will be low and flow
sensitive. Verify that the flow past the sensor equals or exceeds the minimum value.
See the sensor instruction manual for recommended flows.
8.4.8 pH measurement and calibration problems
Problem See Section
SLOPE HI or SLOPE LO message is
showing.
pH SLOPE HI or SLOPE LO
-0- OFFSEt message is showing. pH -0- OFFSEt message
Transmitter will not accept man-
ual slope.
Transmitter not accepting manual slope
Sensor does not respond to known
pH changes.
Sensor not responding to pH changes
Process pH is slightly different
from the expected value.
Process pH slightly different
Process pH reading changes when
flow changes.
Process pH reading changes with flow
Process pH is grossly wrong and/or
noisy.
Process pH grossly wrong or noisy
Process readings are noisy. Process readings noisy
pH SLOPE HI or SLOPE LO
Refer to SLOPE HI or SLOPE LO for assistance.
pH -0- OFFSEt message
Refer to -0- OFFSEt for assistance.
Transmitter not accepting manual slope
If the sensor slope is known from other sources, it can be entered directly into the
transmitter.
The transmitter will not accept a slope (at 25 ° (77 °F)) outside the range 45 to 60 mV/pH. If
you attempt to enter a slope less than 45 mV/pH, the transmitter will automatically
change the entry to 45. If you attempt to enter a slope greater than 60 mV/pH, the
transmitter will change the entry to 60 mV/pH.
Diagnostics and troubleshooting
Instruction Manual 109