Function description
Operating Manual PSSu E S 2AI RTD(-T)
22017-EN-07
14
4.3.2
Connection type
The measuring circuits for the temperature measurements may be configured per input:
}
2-wire measurement
}
3-wire measurement (default)
}
Connection for 4-wire sensor
The module will detect an open circuit on the measuring lines. Should an open circuit occur,
the module will output 7FFF as the measured value. If resistance measurement is con-
figured, the module will output FFFF in the case of an open circuit. With a 4-wire sensor
connection, an open circuit on an individual measuring line will not be detected; con-
sequently, the measurement result will be corrupted.
4.3.3
Range monitoring
You can deactivate range monitoring for each input. Range monitoring refers to the meas-
uring range of the sensor which is configured for the input. This option is activated in the
default configuration. The module writes the result of range monitoring as follows:
}
System environment A:
In the status byte (see
PSSu assignment in system environment A [
20]
)
}
System environment B:
in the I/O data element "Overrange" or "Underrange" (see
PSSu assignment in system
environment B [
21]
)
The module behaves as follows, irrespective of the range monitoring configuration:
}
If the value falls
below
the range, the temperature value stops. The temperature value
corresponding to the lower limit of the measuring range is output.
}
If the range is
exceeded
, the temperature value continues. The module extrapolates
the temperature value linearly.
4.3.4
Offset for the 2-wire measurement
In the case of 2-wire measurement, the line resistance influences the measurement as a
matter or principle, corrupting the result. The module allows you to take the value for the
line resistance into account and to compensate for it when determining the temperature.
You can calculate the line resistance (feed and return line), measure it directly using a
meter or define it via the module.
To use the module to define the measuring line resistance, follow the instructions below:
}
Short out the temperature sensor. The short circuit should be as close as possible to
the temperature sensor.
}
Connect the PSSuniversal system to the system software.
}
Call up the module configuration.
– Deactivate "Manufacturer scaling" and "User scaling".
– Select the resistance measurement ("0.0 ... 4000.0") under "Measuring range".
– Select 2-wire measurement under "Connection type".
– Enter zero under "2-wire measurement offset".
