RSLogix Correct Length for AVE

logix_mind · Dec 1, 2022

I have a furnace and I'm wanting to calculate the average metal temp at which the furnace is tapped each day. There's no set number on the amount of taps that I will see each day. It could vary between 8, to 24, to 13, to whatever.

Every time that the furnace is tapped I'm shooting the temp into a FFL. At 11:58PM I'm wanting to calculate the average metal temp at tap for that day and at 11:59 I am clearing out my array.

My issue is in my AVE instruction...how can I set the correct length (i.e. taps per day)? It won't let me enter in a tag in the length block. Is there any way to have a length in this instruction that will be dynamic like what I have?

dmroeder · Dec 1, 2022

Add a separate rung to MOV a value into AvgMetalTemp_AVE_Control.LEN

logix_mind · Dec 1, 2022

dmroeder said:
Add a separate rung to MOV a value into AvgMetalTemp_AVE_Control.LEN

Thank you so much! That's exactly what I needed!

dmroeder · Dec 1, 2022

As you now see, the value for length and position come from the control tag, that is why you can't put a tag in its place. An instruction like COP, which has a length property, doesn't have a control tag, that is why you can use a tag or a constant.

logix_mind · Dec 1, 2022

dmroeder said:
As you now see, the value for length and position come from the control tag, that is why you can't put a tag in its place. An instruction like COP, which has a length property, doesn't have a control tag, that is why you can use a tag or a constant.

I was unaware that the control tag had properties like that which I could use so that will be very helpful in the future.

Whenever I go to unload the array, is there a way for me to unload the entire array at one time or does it have to be toggled one by one until empty?

dmroeder · Dec 1, 2022

Well a RES addressed to the control tag will reset the FFL/FFU position to 0, probably clears any bits that might be on. The data will still be in the array, so you would have to clear the data out of your FIFO array. You can use a FLL for that. Source 0, destination FIFO tag, length=size of array.

logix_mind · Dec 1, 2022

dmroeder said:
Well a RES addressed to the control tag will reset the FFL/FFU position to 0, probably clears any bits that might be on. The data will still be in the array, so you would have to clear the data out of your FIFO array. You can use a FLL for that. Source 0, destination FIFO tag, length=size of array.

So if I do that, I won't have anything toggling the FFU, right? It will just all be done through the FLL and RES?

dmroeder · Dec 1, 2022

Correct. the FLL will populate the array of data with zeros, the RES will reset your FFL/FFU to the state that it is in the screenshot (position and EM).

logix_mind · Dec 1, 2022

Yup, that seems to work quite well. Thank you for the help!

drbitboy · Dec 1, 2022

The FLL is unnecessary. The reset of the .LEN parameter to 0 essentially makes all values in the array invisible, and each value is overwritten at the next tap when .POS equal that value's offset (index) in the array.

Also, the code should not RESet the FIFO control structure until and unless that control structure's .EN bit is 0, otherwise there will be a spurious entry into the FIFO.

Finally, I think the MOV instruction should use the FIFO .POS parameter as its source; that is the number of elements in the FIFO array to be averaged.

[Edit: MOV fifoctl.POS avectl.LEN i.e. use FIFO .POS, not .LEN, as MOV source]

joseph_e2 · Dec 1, 2022

drbitboy said:
...

Also, the code should not RESet the FIFO control structure until and unless that control structure's .EN bit is 0, otherwise there will be a spurious entry into the FIFO.

...

By the way, this also applies to CTU/CTD instructions. If the rung EN is true when the RES is called, the instruction will execute again. For that reason, I've seen an ONS/OSR placed before the CTU/CTD instruction. An alternative here is to write a 0 to the ACC register.

drbitboy · Dec 1, 2022

joseph_e2 said:
An alternative here is to write a 0 to the ACC register.

+1, CLR count_ctl.ACC FTW!

Or put an XIO count_ctl.EN in front of the CLR.

RSLogix Correct Length for AVE

logix_mind

Member

dmroeder

Lifetime Supporting Member

logix_mind

Member

dmroeder

Lifetime Supporting Member

logix_mind

Member

dmroeder

Lifetime Supporting Member

logix_mind

Member

dmroeder

Lifetime Supporting Member

logix_mind

Member

drbitboy

Lifetime Supporting Member

joseph_e2

Member

drbitboy

Lifetime Supporting Member

Similar Topics