Step 5

Hi Guys,
Some years ago I installed a 95U and to date it has been completely troublefree, but i've recently experienced the following problem.

Within the program, The flag F73.6 is being used and despite it's operating parameters being in order, the flag remains high !! no matter the state of the operating inputs.
___________
--I80.0| & |
-------| & |
F104.2 | & |
------o| & |---- F73.6
______|___|

With I80.0 low, and with F104.2 low, output F73.6 is high.

I've tried an altenative Flag F74.4 but the result is the same.

I suspect a problem within the RAM, does anyone have any thoughts on a way round this ? apart from replacing the plc, which I am loath to do.

Thanks guys,

Regards Norm

I can't tell the logic (use STL), but try changing the input if you have another spare... it could be going true then back off, your PC would not see it (just show off) but the PLC would see it...

Or

Try using set/reset in your program and see if that holds it off,

Norm Bourne said:

Hi Guys,
Some years ago I installed a 95U and to date it has been completely troublefree, but i've recently experienced the following problem.

Within the program, The flag F73.6 is being used and despite it's operating parameters being in order, the flag remains high !! no matter the state of the operating inputs.
___________
--I80.0| & |
-------| & |
F104.2 | & |
------o| & |---- F73.6
______|___|

With I80.0 low, and with F104.2 low, output F73.6 is high.

I've tried an altenative Flag F74.4 but the result is the same.

I suspect a problem within the RAM, does anyone have any thoughts on a way round this ? apart from replacing the plc, which I am loath to do.

Thanks guys,

Regards Norm

Click to expand...

I have seen something similiar once on an S5-95u years ago. We had one section of code that was not operating properly , eventhough logically it should be.

We program in STL and we resolved the issue by inserting one more line of blank code , a NOP, just before the offendending code and the issue went away.

Since you are programming in LAD, insert a blank segment just before this code and see what happens

Thanks guys,
The STL code is :O I80.0
:ON F104.2
:= F73.6
With the offending Flag remaining on (high) in spite of the input status.


I've tried stopping the program and putting it back into run, to no avail.

Anyway lads, I,ll carry out your suggestions, the problem is the installation is 150 Miles north of here,

Thanks again

Norm

Are you sure that you don't have FW72 or FY73 being written to somewhere else in the code????

Yes, I have checked the relevant FW's & FB's And I dont appear to have a prob. in that regard.

The relevant area of code deals with the input from an Air Flow switch, (I80.0) which replaced a pressure switch, which was giving problems in that being a blower, the pressure, when the blower was operational , varied by lesss than 1 lb, with the result that there was little resolution, between go & no go.

Accordingly, I fitted an air flow switch, but the point being that no problems were experienced with the PLC code, prior, other than than the uncertain nature of the operation of the pressure switch.

But theres no doubt it guys, youve certainly given me food for thought.

Many thanks,

Best regards,

Norm

Not sure I am remembering correctly or not, but I do not beleive you can use a OR statment as your fist statment in STL or you will get a RLO result of 1. Not sure if it hold true to ladder or not. It you have it programmed in STL you may try changing the the OR to a AND which will give you the same result logicly, but will make sure if the RLO is a 1 from the previous operation you will not get a high flag.

"Thanks guys,
The STL code is
:O I80.0
:ON F104.2
:= F73.6
With the offending Flag remaining on (high) in spite of the
input status."



:A I80.0
:ON F104.2
:= F73.6


Hope this helps.

Larry