Emerson Rosemount 56, Инструкция по эксплуатации

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108 Profibus Communications
Section 12: Profibus Communications Instruction Manual
April 2017 LIQ-MAN-56
Table 12-14. Signal Board Diagnostic Bits – continued
pH / ISE Faults and Warnings
Signal
Board 1 / 2
GSD Descriptor Help
51 / 83 SN 1/2 Ref Z Too
High (Fault)
The impedance of the reference junction is too high.
1. Confirm that the sensor is fully immersed in the process liquid.
2. High reference impedance implies the reference junction is fouled or depleted.
Replace the sensor.
3. Some sensors are designed to have high reference impedance. If this is the case,
change the reference impedance setting (in the measurement menu) to high.
52 / 84 SN 1/2 Glass Z Too
High (Fault)
The sensing element in a pH sensor is a thin glass membrane. Normally, the im-
pedance of the membrane is 80 – 100 megohm. As the glass ages, impedance in-
creases. A large increase in impedance implies the sensor is near the end of its
useful life. Certain ion selective electrodes (fluoride, ammonia, and ammonium)
also have high impedance sensing elements.
1. Confirm that the sensor is fully immersed in the process liquid.
2. If sensor performance in buffers and the process is acceptable, increase the im-
pedance limit.
3. Replace the sensor.
53 / 85 SN 1/2 Broken
Glass Fault (Fault)
The sensing element in a pH sensor is a thin glass membrane. In a good sensor,
the glass impedance is very high. If the glass bulb breaks or cracks, the impedance
drops to a very low value, and the broken glass fault appears. Certain ion selective
electrodes (fluoride, ammonia, and ammonium) also have high impedance sens-
ing elements.
1. Inspect the sensor for obvious damage.
2. Check the sensor in buffers. If the sensor does not respond to pH changes, the
glass is broken.
3. Replace the sensor.
108 / 140 SN 1/2 Out Of
Range pH Brd
(Warning)
The pH input is outside the range -750 mV to +750 mV or the ORP or ISE input is
outside the range -1500 mV to +1500 mV.
Check sensor wiring.
Replace sensor.
111 / 143 SN 1/2 No
Solution Gnd
(Warning)
The sensor is not properly wired. Check wiring.
115 / 147 SN 1/2 Broken
Glass Disabled
(Warning)
The impedance of the sensing glass in a pH sensor is a strong function of tempera-
ture. For the impedance to be a useful indicator that the sensing glass is cracked
or broken, it must be corrected for temperature. If the process temperature ex-
ceeds the correction cut-off temperature, the broken glass fault is automatically
disabled. The analyzer recalculates the cut-off temperature every time the sensor
is calibrated. The cutoff temperature is about 115 °C.