Trying to get a Voltage Out from PID prog.

[Mickey]

Power comes from bus connection

 

[MikeLB56]

I'm sorry Mickey, I don't quite understand what you mean by bus. But from the screen shot you posted, are you saying that I need to take my scaled value(4455), put it in N7:1 and then move it to my output which will give me a relative voltage output? I have tried doing it the other way.
I was putting the input into a move command, moving it to N7:1 and made my input on my SPC block N7:1. Was this wrong or is it essentially the same thing that you did in the above program just reversed?

 

[Mickey]

Your output card is going to give an output of 0 volts with a value of
0 moved to O:1.0. It will give an output of 10.5 volts with a value of 32760
moved to O:1.0. The reason for this is because you configured the card for Raw/Proportional, 0-10 volts.

My post #11 would also work.

The Bus connector see pic:

 

[jwright]

Clarification Request.

Hi Mickey,

So if I understand you correctly, one would need to use a MOV command/block to place the 0-32760 values to the Output. This will equate to 0-10VDC on the analog module. 0 = 0 and 32,760 = 10.5VDC.

My question is - why won't an SCP command do this? Or will it if the Min=0 and the Max=32760? I see that Mike's post used two SCP blocks. The second one placed the output to O:1.0

Thanks for the clarification - I'm learning too.

John

 

[Mickey]

Yes the SCP will do this. Have look at post #11.
What Mike realy wants is to control a temperature thru a PID instruction.
But he cannot get to output to work so he is focused on that problem for now.

User manual
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1762-in005_-en-p.pdf

 

[jwright]

thanks!

Yes - I see post #11 now. Thanks! It looks like Mike was thinking he needed to add an external 10VDC power supply to the module. As I understand you, this is not so. The Bus grabs the voltage from the 1200 unit.

John

 

[kupeyy]

Ok, a few things: No external power supply is needed and I think your problem is in software.



Your scale block is taking an integer, and scaling it as Min 0 and Max 10. But if you look in the documentation on the analog output module, it accepts a range of 0 to 32760 (or 0 to 16380) to give a voltage of 0 to 10 volts. Scaling the value from 0 to 10 would yield an output of approximately zero. In mikes code, the integer N7:1 (which is scaled from the input) can be used as the output word. As said in previous posts with a Move command.



I would recommend testing configuration/hardware setup to confirm all problems are in software. One easy way to do this is to open the Output Data file, change the radix to decimal and click the number next to O:1.0. Enter 32760 in that address. Put any simple program into the PLC and go online. As long as the program isn’t changing that address, it should keep writing that value to the output and thus give a voltage. Manually changing that number should change the voltage.



That should confirm everything is working correctly. As for the PID block, it seems you can scale the input as you are doing and you should do that first in a rung above the PID block. Then use that Integer as your process variable and then your control variable will be a different integer. That integer should be able to be moved to the output address with no scaling because it should be in the right format. But if you had to scale it do so from 0 to 32760 or 16380 based on your configurations. If the manual method of inserting values worked, then moving that control value into the output address should also work to give you a voltage.



I have never done this or tested it so these things are confident assumptions. If anyone sees things inaccuracies in anything I have said, please point it out.





JK