Allen-Bradley ProcessLogix 1756-IA16, Reference Manual, Page: 60 / 120

Publication 1757-RM810A-EN-P - May 2002
3-20 Functional Blocks
LIMIT
LT (Less Than)
MAX
Description Provides a 3-input limit function, meaning that it provides an output that is maintained within a specified range as
defined by user-specified minimum and maximum values.
Function Provides an output that is maintained within a specified range as follows:
•
MIN <= OUT <= MAX
•
If IN = NaN, then, OUT = NaN
Inputs IN = real number
Outputs OUT = real number maintained within a specified range
Parameters IN
MAX
MIN ORDERINCM
OUT
Description Provides a 1- or 2-input Compare Less Than (with deadband) function, meaning that it checks to see if one designated
input (IN [1]) is less than either a second input (IN [2]) or, for single input, a designated trip point parameter (TP).
Function Turns the digital output (OUT) ON only when one designated input (IN [1]) is less than a second input (IN [2]) or, for
single input, a designated trip point parameter (TP) as follows:
•
If IN [1] < IN [2], then: OUT = ON.
•
If IN [1] >= (IN [2] + DEADBAND), then: OUT = OFF.
•
If IN [2] <= IN [1] < (IN [2] + DEADBAND), then: OUT is not changed.
Inputs IN [1..2] = Real numbers
If only one input connection is configured, an input port is displayed for parameter TP and the value of TP is used
instead of IN [2].
If IN [1] and/or IN [2] are NaN (Not a Number), OUT is not changed.
DEADBAND and TP have the same data type as that of the inputs.
Outputs OUT = Boolean value controlled by the status of the input signals.
Comparison blocks should set their outputs to Off if any of the inputs are NaN. This “fail safe” behavior is consistent
with the IEEE 754 floating point standard.
Parameters DEADBAND
IN [0..2]
NUMOFINPUTS ORDERINCM
OUT
TP
Description Provides an 8-input MAX function, meaning that it provides an output that is the maximum value of eight inputs.
Function Used to isolate the highest value of multiple input values and use it as a designated output value. This block ignores
NaN inputs.
Inputs IN [1..8] = Real numbers
Outputs OUT = Real number
Parameters EUDESC
HIALM
IN [1..8]
INPTINVSTS [1..8] NUMOFINPUTS
ORDERINCM
OUT