313C with Step7 PID / analog out

I have an analog input that is used as the PV to a PID.

The PID controls an analog out.

The analog out is connected to a transducer.

The PID is reading the input at just above zero and has ramped up the output to 100% .

The transducer does not respond. (the whole loop worked perfectly Friday. I do not think I made any changes today that would affect this loop.

The analog output connected to the analog out is supplying 4.8mA DC as indicated by a FLuke DMM in series with the output.

I don't see how this is possible unless the analog out malfunctioned over the weekend while it was off.

I will switch to the other analog out as a test.

As confirmation , the gauges and general obsevation agree that the output is not on.

I switched to the other analog out.

The only program change is PQW752 to PQW 754.

Works just like it did before.

What could have happened to take out the first output? Everything is still functional, nothing is shorted out, there has been no release of magic smoke.

Maybe it is just one of those things, but at this level in my S7 game , I always suspect that the problem is more likely something I did.

I don't see how programing could cause an analog out to fail though, it wasn't even on.

All PLC hardware in this example is only a few weeks old and has less than 20 hours run time on it. In the lab, 75 deg F, regulated 24 volt DC power supply.

I wonder if this is common with the 313C?

This will not be good if they fail so easily.

Well, it seems it is possible to latch the analog out.

During my tests I discovered when I switched the output , all seemed to work , so I went back to the edits I had been doing when it failed.

And it failed again.

Hmmmmmm, prolly not hardware.

I must have been writting over the output somewhere.

Not sure where.

The big negative to the FC and FB structure is, when you discover one little error , you spend a long time saving and re entering all the variables to every instance of every effected block. And then the block that it is used in.

Not likin that bit.

dahnuguy said:

The big negative to the FC and FB structure is, when you discover one little error , you spend a long time saving and re entering all the variables to every instance of every effected block. And then the block that it is used in.

Not likin that bit.

Click to expand...

You don't need to do that. I'm not sure what you mean by "one little error", but if you are talking about adding or removing parameters, you can just right click on the call and select "Update Block Call". Or, to do everything at once, you can do a block consistency check (Blocks>ConsistencyCheck>CompileAll).

But I'm not sure what you're doing. The whole point of using FCs and FBs is so you don't have to go back and change every one.

S7Guy said:

You don't need to do that. I'm not sure what you mean by "one little error", but if you are talking about adding or removing parameters, you can just right click on the call and select "Update Block Call". Or, to do everything at once, you can do a block consistency check (Blocks>ConsistencyCheck>CompileAll).

But I'm not sure what you're doing. The whole point of using FCs and FBs is so you don't have to go back and change every one.

Click to expand...

ah Ha...........

I thought it should be that easy.

Now it is much better than before.

"What I was / am doing" is this:

I write a FC and or a FB and then call said FB from OB1.

Then several days later, I get new information that makes a change in the original FB or FC necessary.

SO I edit the FC or FB and save it.

Then when I save OB1 the block(that has just been edited) is red.

Then I go to the new block and install the new block in the old blocks place and move all the external parameters over.

Now I have only had to do this a couple times, but it is anouying.

I thought there was a better way............just wasn't sure where or what it was and didn't want to stop to ask at that moment.

Thanks,