ABB REF 54 Series Technical Reference Manual page 48

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Technical Reference Manual, General
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The measuring signal level of each transducer is constantly supervised. If the
measured signal falls more than 4% below or rises more than 4% over the specified
input signal range of a particular channel, the transducer or the transducer wiring is
considered to be faulty and the channel-specific invalid signal is immediately
activated. The invalid signal is deactivated as soon as the transducer signal is within
the valid range.
When necessary, the valid measuring range may be narrower than the default
-4..104% of the selected measuring range. A narrower range can be defined by
means of the parameters "Input high limit" and "Input low limit" that can be found
in the menu Configuration/RTD1/Input # .
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Input low limit -4...104 %
Input high limit -4...104 %
When an input is configured for resistance or temperature measurement, the internal
excitation current generator forces a current pulse through the measuring circuit
when the input is sampled. If the actual current level does not match the programmed
level due to too high impedance in the circuit, the invalid signal is immediately
activated. The invalid signal is deactivated as soon as the circuit resistance is low
enough.
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Short disturbances on an input are eliminated by signal filtering. The filter time,
which defines the step response time, is set for each transducer input of the feeder
terminal by the "Filter time" parameters in the menu Configuration/RTD1/
Input # . The filtering algorithm is a so-called median filter which shows no
reaction to interference spikes but levels out directly on permanent changes.
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Filter time 0 = 0.4 s
1 = 1 s
2 = 2 s
3 = 3 s
4 = 4 s
5 = 5 s
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The user can scale each RTD/analogue input linearly or non-linearly by constructing
a separate linearization curve for each input. The name implies the typical use, i.e.
the linearization of not directly supported non-linear sensors. The curve consists of
at least two (for linear scaling) and up to ten points, where the x-axis of the curve is
0 to 1000 per mille of the range selected for the input and the y-axis is the scaled
1. Not supported yet
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-4 %
104 %
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5 s

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