Endress+Hauser iTEMP TMT85, Руководство по эксплуатации

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iTEMP TMT85
Operation via FOUNDATION Fieldbus TM
Hauser 77
14.3.7 Transducer Blocks "Sensor 1 and 2"
The "Sensor 1 and 2" Transducer Blocks evaluate the signals of both sensors from a
metrological perspective and display them as a physical variable (value, measured value
status and unit). Two physical measured values and an additional primary value, which is
mathematically calculated from the sensor values (the PRIMARY_VALUE), are available in
each Sensor Transducer Block:
• The sensor value (SENSOR_VALUE) and its unit (SENSOR_RANGE -> UNITS_INDEX)
• The value of the internal temperature measurement of the device (DEVTEMP_VALUE)
and its unit (DEVTEMP_UNIT)
• The primary value (PRIMARY_VALUE -> VALUE) and its unit (PRIMARY_
VALUE_UNIT)
The internal temperature measurement of the reference junction is in both Transducer
Blocks but both values are identical. A third value in the Block, the PRIMARY_VALUE, is
calculated mathematically from the sensor values.
The rule for forming the PRIMARY_VALUE can be selected in the
PRIMARY_VALUE_TYPE parameter. The sensor value can be mapped unchanged in the
PRIMARY_VALUE but it is also possible to calculate the differential value or mean value
for both sensor values. Furthermore, various additional functions for connecting the two
sensors are also available. These can help increase process safety, like the backup function
or sensor drift detection.
• Backup function:
If a sensor fails, the system automatically switches to the remaining sensor and a
diagnostic message is generated in the device. The backup function ensures that the
process is not interrupted by the failure of an individual sensor and that maximum safety
and availability is achieved.
• Sensor drift detection:
If 2 sensors are connected and the measured values differ by a specified value, a
diagnostic message is generated in the device. The drift detection function can be used to
verify the correctness of the measured values and for mutual monitoring of the
connected sensors. Sensor drift detection is configured in the "Advanced Diagnostic"
Transducer Block, →  84.
The electronics can be configured for various sensors and measured variables via the
SENSOR_TYPE parameter.
If resistance thermometers or resistance transmitters are connected, the type of
connection can be selected via the SENSOR_CONNECTION parameter. If the "2-wire"
connection type is used, the TWO_WIRE_COMPENSATION parameter is available. The
resistance value of the sensor connection cables is stored in this parameter.
The resistance value can be calculated as follows:
• Total cable length: 100 m
• Conductor cross-section: 0.5 mm 2
• Conductor material: copper
• Resistivity of Cu: 0.0178 Ω * mm 2 /m
R = 0.0178 Ω * mm 2 /m * (2 * 100 m)/0.5 mm 2 = 7.12 Ω
Resulting measured error = 7.12 Ω / 0.385 Ω/K = 18.5 K
The Transducer Blocks for sensor 1 and 2 have a wizard (configuration assistant) for
calculating the resistance of sensor cables with different material properties, cross-
sections and lengths.
When measuring temperature with thermocouples, the type of reference junction
compensation is specified in the RJ_TYPE parameter. The internal terminal temperature
measurement of the device (INTERNAL) or a fixed value (EXTERNAL) can be specified for
the compensation. This value must be entered in the RJ_EXTERNAL_VALUE parameter.