RSLogix AVE

KLemas16! · Feb 2, 2017

Hello again,

Looking to use an AVE block in ladder to calculate the average of 7 temperature elements in the foundation of an LNG tank. My issue is the AVE block only executes once when the rung is initiated but I want this to be continuous. Am I using the right block for my situation? If so, what would be a simple way to make this block work each scan?

I've attached an image of code. Thanks in advance for any help.

widelto · Feb 2, 2017

Is Foundation_Temperatures an array ?, Is Foundation_Temp_Ave a DINT or a real ?

Mike_RH · Feb 2, 2017

Unlatch the ControlAVE.EN bit after the AVE instruction is executed.

Jsu0234m · Feb 2, 2017

You could use a timer with a preset of 50 that would just keep resetting itself.

robertmee · Feb 2, 2017

widelto said:
Is Foundation_Temperatures an array ?, Is Foundation_Temp_Ave a DINT or a real ?

You can tell by Rung #2 Foundation_Temperatures is an array of at least 7 elements....assuming the unshown prior rungs populate Foundation_Temperatures[0] to [5] in similar fashion.

But I agree....It looks like the AVE tag is a DINT...should be a REAL.

KLemas16! · Feb 2, 2017

So I move the scaled value of each temperature into Foundation_Temperatures which is DINT[7] data type. for example:

A temperature into Foundation_Temperature[0]
B temperature into Foundation_Temperature[1]
.........
.........
G temperature into Foundation_Temperature[6]

I then use the AVE on this array Foundation_Temperature.

I added an OTU on the next rung to ControlAVE.EN but it doesn't seem to work.

Still on a learning curve coming from the DCS world. Thank you all.

Mike_RH · Feb 2, 2017

This will do it:

robertmee · Feb 2, 2017

Don't know if it's an issue, but every AVE I've ever done, I specify the Array as MyTag[0], not MyTag as you have shown. If you read the help on the AVE instruction, it specifically says "specify the first element of the group of elements to average". Since it compiles without it, though, I don't know.

Also, you might have to clear the Ctrl_AVE.POS, or at least clear the .DN bit. Not sure just clearing the .EN bit will reset the block. But the easiest is just to generate a 50ms timer and use the DN bit to reset the timer and fire the AVE block.

Mike_RH · Feb 2, 2017

The ave instruction requires a false to true transition of the rung to trigger its operation.
The instruction determines this by the state of the EN of the control block.
Unlatching the EN bit forces the next execution of the instruction to behave like it has had a false to true transition. I think the same effect could be had by doing a RES on the control block.

rdrast · Feb 3, 2017

Or just roll your averaging routine into a statement list routine and let it execute every scan.

I really prefer Statement List for any kind of math. And then, the sources of data do not have to be consecutively in an array as well.

You could even just create an AOI with the logic in statement if you like.

KLemas16! · Feb 3, 2017

With the unlatch function, it looks like both the .EN and .DN needed to be reset. Now the block is working perfectly. Thank you all for the support.

On to the next challenge

Ken

daba · Feb 3, 2017

KLemas16! said:
With the unlatch function, it looks like both the .EN and .DN needed to be reset. Now the block is working perfectly. Thank you all for the support.

On to the next challenge

Ken

Replace the two unlatches with a single RES of the AVE control tag. This will handle all eventualities, (although I very much doubt you will ever generate the .ER bit, since your input array is DINTs, and your destination is a REAL), and it ensures the AVE instruction executes on every scan.

RSLogix AVE

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