Limit

[PEERPSI]

Looking to set a limit in my logic that returns a bit if my process value falls between the lower and upper limit values. Looking at LMT(680) but it does not appear that it switches a bit just passes the value through.

Any ideas?

[PEERPSI]

The instruction information for LMT mentions flags that are turned on for > and < conditions. Where do these appear and are they single bits?

[Michael Walsh]

You can take the = out of the instruction names if you don't want to include the limit itself.

[BITS N BYTES]

1 minute ago, PEERPSI said:

The instruction information for LMT mentions flags that are turned on for > and < conditions. Where do these appear and are they single bits?

The LMT instructions uses a group of boolean "condition flags". These change state immediately after the instruction is applied.

Read section 1-2-1 in the manual W451-E1-03 for an explanation of how Condition Flags are used.

[Michael Walsh]

Yes, my post was really answering the first question.  A simple way to do what @PEERPSI wanted to do.  The condition flags (when monitored in CX-Programmer) will show the state they were in according to the last instruction that used them in the ladder.  They can mislead the programmer if you do not understand what is going on.  It is important to look at the coil after the flag to see if the flag was on when the rung in question was executed.  For instance, it is possible that the contact for one of these flags looks off, but the following coil is on.  This is due to the fact that when that rung executed the condition flag was indeed on, but another instruction used the flags as well and turned the condition flag off later in the the code.

[PEERPSI]

This is really testing my AB minded way of doing things!

I've used the > and < instructions and have achieved my goal.

[BITS N BYTES]

This isn't an AB test of how they DO THINGS.

Rather OMRON has a unique [yet different approach]. IMHO much easier to use.

For example:- A simple oneshot up differentiation condition requires NO stupid extra bits to manage, just a change in the examination of the bit with an upward symbol.

See here:- http://www.plctalk.net/qanda/showthread.php?p=620324#post620324