Limit instruction in a plc help to limits the value to within maximum and minimum range of values. limit instruction output is depend on maximum and minimum value if the input value between minimum to maximum range then output is equal to input value. if input value is greater than maximum value then output is equal to maximum value and if value is less then minimum value then output of limit instruction is minimum value. You can use this limit instruction to select a value within a maximum and minimum range. In this article we see how to use limit instruction in program like c, ladder and structured text.

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What is Limit Instruction in PLC ?

PLC LIMIT Instruction Is A Three Input Variable Type Instruction Where First Input Is Maximum limit of value, Third Input Is minimum limit of value And Second Input Is A Value Which Compared With Upper And Lower Limit. Output Of This Instruction Is Depend On Upper And Lower Limit. Output Value Always With In Range Of Upper Limit And Lower Limit. If Second Input Value Not Less then Lower Limit And Not Greater Then Upper Limit So Output Is Equal To Second Input Value.

B&R Automation Studio LIMIT Instruction Blocks in Ladder Programming

ladder programming select Limit function from function library and limit instruction on rung. Following is the input and output parameter of limit instruction.

input parameter
• MN: minimum value to limit the output
• IN: input value of limit instruction. limit operation perform on this value.
• MX: Maximum value to limit the output
output parameter
• Output: output of limit instruction.

above is the example of B&R Automation Studio LIMIT Instruction Blocks in Ladder Programming. if the input value within the range of maximum and minimum range then output is equal to input value. for example if the maximum value is 123 and minimum value is 10 so output of limit instruction is not greater then 123 and not less then 10. if the input value is greater then 123 then output is 123 and if the input value is less then 10 so the output is set to 10.

B&R Automation Studio LIMIT Instruction Blocks in Structured Text

in structured text we use limit instruction as function. in a bracket we first declare minimum range then input value then maximum value. output of the limit instruction is same as above explanation. you can declare constant value or variable for minimum and maximum value instruction. Above example of B&R Automation Studio LIMIT Instruction Blocks in Structured Text first statement use variable for limit instruction and second instruction use constant value for limit function.