Compare (input instruction)
LIM: Limit Test
Passes power while the test value sits between the low and high limits, inclusive.
Also called: within range, band check, in range.
LIM(low, test, high)What it does
LIM is two comparisons in one instruction: low is less than or equal to test, and test is less than or equal to high. It reads better than the pair it replaces and it keeps both limits in one place, which matters when someone later has to change the band.
It is the natural instruction for a good-part window, an in-tolerance check, or a temperature band that a process must stay inside.
A rung you can run
A good-part weight window
[object Object]
LIM(980,Part_Weight,1020)XIC(Weigh_Complete)OTE(Part_Good)
XIO(Part_Good)XIC(Weigh_Complete)OTE(Reject_Push)Anything from 980 to 1020 inclusive passes. Everything else is pushed off the line.
Run this rung in the simulatorWhat it is called on other controllers
| Platform | Equivalent |
|---|---|
| Rockwell (Studio 5000) | LIM |
| Siemens (TIA Portal) | Two comparisons in series |
| CODESYS and IEC 61131-3 | Two comparisons, or LIMIT for clamping |
Common mistakes
- Writing the limits the wrong way round. The low argument comes first, and swapping them gives a test that is never true.
- Using LIM on a value that has not been scaled yet. Compare engineering units against engineering-unit limits, not raw counts against numbers someone worked out for a different card.