PLC Programming LES GRT Compare Instructions - Greater Less Than Instruction RSLogix Studio 5000

PLC Programming LES GRT Compare Instructions - Greater Less Than Instruction RSLogix Studio 5000

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The LES, also known as the Less Than, is an instruction used to compare two values against each other. The instruction takes two integers, floats or constants and will return TRUE if the value specified in “Source A” is less than the one in “Source B”. The “Source B” operand must be strictly less than the one specified in “Source A”. In other words, the instruction will return FALSE if they are equal.

This instruction can be used to test for an upper limit for an analog sensor and reliably notify the programmer should the value be exceeded.

In RSLogix 500, you may not compare two constants; this restriction is not present in RSLogix 5000 as well as Studio 5000. This is also the case for all comparison instructions.

The GRT, also known as the Greater Than, is an instruction which compares two operands and evaluates if the value stored in “Source A” is greater than the value stored in “Source B”. If that’s the case, the instruction will evaluate to TRUE and allow the rest of the rung to execute. The GRT instruction may take integers, floats or constants as operands.

A typical use for this instruction would be a lower limit of a temperature sensor. Should the limit value be greater than the current temperature, the programmer will know immediately that there’s an issue.

This instruction is very commonly used within a ladder logic environment as it’s one of the simplest ways to compare two distinct values against each other.

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