ABB Industrial IT enabled REX 521 Technical Reference Manual, General page 18

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Technical Reference Manual, General
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Amplitude error at the whole measuring range
(e = error in per cent)
Phase displacement error at the whole
measuring range
(e = error in degrees)
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The digital inputs of the protection relay are voltage-controlled and optically
isolated. For technical data of the digital inputs, refer to Table 4.2.1-3 on page 37.
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The filter time eliminates debounces and short disturbances on digital inputs. The
filter time may be set individually for each input.
t
0
Input
Filter
Filtered Input
Filter Time
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The figure above illustrates the input filtering. At the beginning, the input signal is
at high state, the first low state is filtered and no input status change is detected. The
second low state is longer than the set filter time, thus detected as a change and
attached with the time tag t
filter time, the state is accepted and attached with the time tag t
Each digital input has a filter time parameter Input # filter
(Configuration\Digital inputs\Input filtering), where # is the
number of the input.
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Input # filter 1...65535 ms
A risk for debounces and short disturbances on digital inputs grows if the input filter
time is changed to less than the default value.
Amplitude correction factor
= 1/(1+ e/100)
Phase displacement error = - e
t
1
Filter Time
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.When the input signal returns to high state, after the
0
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5 ms
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