ABB FEX300, Operating Instruction

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Extended diagnostic functions
OI/FEX300/FEX500-EN FEX300, FEX500 131
8.1.5 Electrode impedance monitoring
1)
The impedance between the electrode and ground is monitored by using a minimum/maximum
limit value. This enables the transmitter to detect an electrode fine short or leakage.
When the value falls below or exceeds the set limit value, an alarm is tripped via the
programmable digital output, depending on the configuration.
Conditions for using the function:
• This function is available in the nominal diameter range
2)
of DN 10 … 300 (3/8 “ ... 12 “).
• The signal cable length of the external transmitter must not exceed a maximum value of
50 m (164 ft) .
• For this function, the conductivity of the fluid must be in the range
20 μ S/cm ... 20,000 μ S/cm.
Additional installation conditions:
• When using plastic tubes, install a grounding plate at the front and back of the device.
• There must not be any deposits on the measuring electrodes.
• The measuring tube must always be completely full, and the fluid must feature only minor
conductivity variations.
8.1.6 Sensor measurements
This function includes the monitoring of the sensor temperature and the monitoring of the
resistance of the flowmeter sensor's coils.
8.1.6.1 Sensor temperature monitoring
The temperature of the coils in the flowmeter sensor can be monitored by using adjustable
minimum/maximum limit values. When a set limit value is exceeded, an alarm is tripped via the
programmable digital output, depending on the configuration.
The coil temperature is a factor of the ambient and fluid temperatures. The measurement can,
e.g., be used to monitor overtemperature due to the fluid. The coil temperature is measured
indirectly via the coil DC resistance (ABB patent GB 2 348 011).
8.1.6.2 Monitoring of the sensor coil resistance
The coils in the flowmeter sensor can be monitored by using adjustable minimum/maximum limit
values for the coil resistance. When a set limit value is exceeded, an alarm is tripped via the
programmable digital output, depending on the configuration.
1) At present, the function is only available for devices without explosion protection or with explosion protection for
Zone 2 / Div. 2. For devices in Zone 1 / Div. 1 this function is under preparation (the function is already implemented
in the software, but cannot be used for devices in Zone 1 / Div. 1).
2) The specified nominal diameter range is valid for ProcessMaster, only. The nominal diameter range valid for
HygienicMaster is DN 10 … 100 (3/8 “ ... 4 “).