Pilz PSSu E S 2AI RTD - Manual (Page 14)

Function description
Operating Manual PSSu E S 2AI RTD(­T)
22017­EN­06 14
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.
4.2.4 Offset for the 2­wire measurement
In the case of 2­wire 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 2­wire measurement under "Connection type".
– Enter zero under "2­wire measurement offset".
} Start the PSSuniversal system. Measurement of the line resistance will start.
– The measurement will be more accurate if the line temperature is the same during
measurement as it is during operation.
} In the system's PII (system environment A) or in the I/O data element "Data" (system
environment B), the measurement value appears as a hexadecimal value. Convert this
value into a decimal figure and note down the decimal value. This decimal value is the
measuring line resistance in 1/16 Ohm.
To account for the line resistance within the configuration, follow the instructions below:
} Call up the module configuration in the system software.