Allen-Bradley ProcessLogix 1756-IA16, Reference Manual, Page: 90 / 120

Publication 1757-RM810A-EN-P - May 2002
3-50 Functional Blocks
Inputs Required number of inputs is determined by this block’s mode:
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If Mode = Cascade, 2 inputs are required – X1 and RT. Both must come from other function blocks.
•
If Mode = Auto or Man, only X1 is required. X1 must come from another function block; an operator cannot set it.
•
Both X1 and RT are initializable inputs. So, this block may have one or two primaries, depending upon whether RT
input is used or not.
•
If mode = Auto, an operator or user program can set the RT value.
Input Ranges
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XEUHI and XEULO define the full range of X1 inputs in engineering units. This block applies no range checking,
since it assumes that X1 is within XEUHI and XEULO.
– XEUHI represents the 100% of full scale value.
– XEULO represents the 0% of full scale value.
•
RTHILM and RTLOLM define the ratio limits for RT inputs in engineering units. An operator is prevented from
setting an RT value that is outside these limits. If the RT value from a function block or user program is outside
these limits, this block clamps the value to the appropriate limit and sets RT primary windup status.
– RTHILM represents high ratio limit value.
– RTLOLM represents low ratio limit value.
Outputs Block has following initializable outputs:
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OP = Calculated output in percent.
•
OPEU = Calculated output in engineering units
Note that the default OP connection pin is exposed on the blocks and the implicit/hidden connection function
automatically makes the appropriate value/status parameter (OPX/OPEUX) connection when required.
Output Ranges CVEUHI and CVEULO define the full range of CV in engineering units.
If this block has a secondary, it uses the secondary’s input range through BACKCALC to set its CV range. If it does not
have a secondary, its CV range tracks its own input range (XEUHI and XEULO).
•
OPHILM and OPLOLM define normal high and low limits for OP as a percent of the CV range (user-specified
values).
– OP clamps to these limits if algorithm's calculated result (CV) exceeds them or another block or user program
attempts to store OP value exceeding them.
– Operator may store OP value outside these limits.
•
OPEXHILM and OPEXLOLM define the extended high and low limits for OP as a percent of the CV range
(user-specified values).
– Operator is prevented from storing an OP value that exceeds these limits.
Parameters on following page