Siemens sitrans tr200, Operating Instructions Manual

Page: 47 / 78

Functions
8.15 Special characteristic curve
SITRANS TR200/TR300
Operating Instructions, 04/2007, A5E01071992-01
47
8.15 Special characteristic curve
The transmitter offers the facility for connecting multiple sensors to the device. Sensor
characteristic curves valid for these sensors are already programmed into the device.
There are however sensors (e.g. Cu100) for which this device does not offer sensor
linearization as standard. In this case, however, it is possible to store a customer-specific
special characteristic curve in the device. The sensor characteristic curve is then corrected
by scaling the measured value output.
The transmitter requires pairs of values (x-values, y-values) for customer-specific
characteristic curve correction. These pairs of values form sampling points and the output
characteristic curve is generated in between these points by linear interpolation from the
input characteristic curve. The maximum number of sampling points is restricted to 30 pairs
of values. The individual pairs of values are entered as a percentage of the set measuring
span.
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Figure 8-4 Principle of customer-specific characteristic correction
Instructions on parameterization
Then assigning parameters to customer-specific characteristic curves, the following
instructions apply. These instructions apply irrespective of which parameterization software
is used, and apply to both transmitter device versions.
●
The start point for characteristic curve correction is:
–
the resistance-type transmitter sensor class for the desired special resistance
thermometer
– the mV transmitter sensor class for the desired special thermocouple.
The sensor characteristic curve for the resistance-type transmitter or mV transmitter
forms the basis (0 to 100 %) of the subsequent characteristic curve correction.
● Always enter the individual pairs of values in the unit % of the set measuring span.
● The first pair of values is always (X = 0 %; Y = 0 %). The last pair of values is always (X =
100%; Y = 100%). The first and last pairs of values are specified by the parameter
assignment software and cannot be changed. Correction of the first and last pairs of
values can be performed only by means of a two point trim of the sensor.