using ladder logic what do I use to control a power supply output voltage up and down. I have a 1756OF8

I am not sure I understand your question. Are you trying to control a remote power supply or are you just asking how to change the output signal level (ie, make it go from 4-20 ma or 0-10 VDC)? If you are controlling a remote power supply, you will need to give me some info on the power supply itself.

Russell

Russell I guess I'm asking (1st time user) what do I use in the ladder logic a counter, timer, ? to control the analog module, to control the power supply , I will also need it to go up in voltage, but when run is interupted I will need the power supply to be set back to a lower lower voltage then where it was at when it got interuped. I hope this is alittle clearer. Thank you

Ok, if I understand this correctly, I would not term what you are trying to do to be controlling the power supply. A better way to put it is that you are wondering how to control the output level of a channel on the output card. Let me know if I am wrong.

If that is what you are trying to do, then the answer is much bigger than the question implies. You really need to spend some time in the manual for the OF8 and understand fully how to configure the card. You should have already added the card into your program configuration. If not right click on I/O configuration and select add I/O module. Make sure you know the information about your module and select the appropriate module from the list. Once the module is added, you can double click on the module in the list to setup the card ranges, alarming, fault interactions, etc. This is what you need to read the manual about to fully understand. After you have configured the module, you will need to understand where to send your command word to in order to get the card to work. You need to look in your controller tags for the tags that start with 'Local.' Those are the tags that are directly tied to the I/O modules in your rack. They are ordered and named according to the slot location of the card. So a card in slot 7 would be Local:7:O. You will find three categories for your card Local:7:C, Local:7:I, Local:7:O that store your configuration information, your card status information and your output information respectively. You can expand those items by clicking the plus sign. You should see (again using our slot 7 example) "Local:7:O.Ch0Data" for channel 0 and the other 7 channels. That is where you need to move your value to control the output. You will wire to the specific channel you are using and the data words here will correspond to that physical output wiring. Again check the manual. If you need help getting the manual, I have put together a video on AB's web site that will help you to go there and find the literature you need. It's in the AB/Rockwell videos under Other.

You should do some additional work to make things easier to follow and modify in the future. Make sure you are on the 'edit' tab in your controller tags and right click on the output data channel you want to use. Click to create an alias. this will allow you to create a tag that can better describe what you are controlling. Also if you need to move the card or output to a different channel in the future, this will allow you to keep all your programming associated with the alias the same and to just change its tie to the Local address.

Once you have created your alias, then you can use a mov instruction to move a value into that register. Or if you want to manual "play" with the output to get a feel for how it works, you can plug values into the register directly while online and monitor the output to understand how you are affecting it. You will need to scale value you plop into the output register according to your required output levels and how you configured the card.

There is a lot to this so let me know if you have additional questions.

I will go through your answers line by line and I know I have a long way to go. This project was just dumped on to me and I have NO PLC experience, but at least I have work. Thanks again