Function blocks
Function blocks for TwinSAFE logic components 139
3.20 The function block COMPARE
3.20.1 Functional description
The FB COMPARE checks the 2-5 analog inputs CompIn1 to CompIn5 for equality within a time and
value tolerance window. The input data types INT16, INT32, UINT16 and UINT32 are permitted. The
output CompOut must be selected to match the input types. The Architecture option field can be used to
select how many inputs are to be evaluated. The parameter Allowed Deviation and Tolerance Time (ms)
can be used to specify which deviations between the input values are permitted during which interval. The
IsValid output returns a logical 1 if the comparison has a positive result.
The CompOut output contains the first analog value that meets the comparison criteria.
The ERROR state is assumed if an overflow or underflow occurs. In this case the CompOut and IsValid
outputs are set to 0 and the Error output to 1.
Description of the Architecture option field
1oo2:
The two input values are compared for equality. If an error is detected, the FB outputs CompOut and
IsValid are set to 0.
2oo3:
The 3 input signals are compared, and the majority result is used (2 out of 3). If all values outside the
defined limits are different, the CompOut FB output is set to 0 and the IsValid output is reset.
3oo5:
The 5 input signals are compared, and the majority result is used (3 out of 5). If fewer than 3 values within
the defined limits are equal, the FB output CompOut is set to 0 and the output IsValid is reset.
Figure 3-84: Function block COMPARE
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