Created Date: May 07,2019

Created by: e2dad

Hello folks! I am a self learner PLC noob! On my own I have learned PLC programming except analog portion. Do more software for me has been thus far very intuitive!

Goal: I am trying to "regulate " a pneumatic braking system. I want to SET a certain tension/force on a line using a Load cell that put outs 0-10VDC signal. When the tension/force is set, the brake will maintain it by controlling a pneumatic solenoid valve (0-10VDC input). Assume the winch or pull force initiator will be manually controlled for safety!

How would I correlate volts to force in the program. Not sure how I would start. Your help is much appreciated!

Created Date: May 07,2019

Created by: Garry

Here is a post on the analog in/out of the Do-More BRX.

https://accautomation.ca/brx-plc-analog-io-system-configuration/

https://youtu.be/WmdbalWwO6E

You will see that you can scale the input/output to the units that you want.

What I would do is measure the analog input and chart the characteristics. If it is linear then great, just do the scaling in the card.

This should get you started.

Regards,

Garry

PS The entire series of the BRX can be found here.

https://accautomation.ca/series/brx-do-more-plc/

Created Date: May 07,2019

Created by: e2dad

Please provide a link to specifications for the pneumatic valve.

Its a 4-20mA controlled I/P proportional pnuematic solenoid valve (only one direct automation sells). Can I use have a 0-10 volt analog input and control a 4-20mA output (pneumatic valve) using a PLC? The PLC I intend to use is from the BRX family (automation Direct) which supports both analog input/output types.

Created Date: May 08,2019

Created by: Alexandru

the input from the load cell will be a 0 to 100%. The program gives you a percent representing the percent of your analog input signal. For example, 10% would be 1V, 100% would be 10V coming from load cell to the plc.

with the output is the same.

At the plc side:

for the 0-10v analog input you need a 0-10v analog input port.

for the 4-20mA output you need a 4-20mA output port.

Created Date: May 08,2019

Created by: Tinker

I'd think one would want either PID or filtering (possibly both?). As for "how to use " I have no experience with Do-More PID but have generally found the help system pretty good. Emphasis on "generally " , for PID the "Contents " page is the best place to start. But for some topics the contents doesn't help so I tend to start at the "index " (a mistake with PID) on the version I have installed (not 100% certain it is the latest) the first instance of "PID " in the index is useless, scroll down a bit to "PID Closed loop controller " then after clicking that, scroll (again) down to "PID closed loop controller ". Don't let the large number of topics your scrolled past give you the wrong idea about how complicated it is (it's probably even worse than you think:))

Again having no experience I may not know what I'm talking about, but, considering the elasticity of compressed air and finite response time of your pressure transducer I personally wouldn't bet a lot on auto tuning working really well (but what do I know) however, the "PID View " looks like it could be very useful for manual tuning.

Created Date: May 08,2019

Created by: ControlsGuy

Since my tensions fluctuate quite a bit within 2 seconds... how can I set my adjustment so that the plc is not adjusting everytime? Would I use comparator contacts? Is it better if I is PID function for smoother regulation? If so, how do I use PID function?

Even if you use PID, if your PV is noisy I'd filter it.

Secondly, what about something that will allow a little displacement with minimal change in tension and hopefully minimal to no inertia, like a pneumatic counterbalance for example? Works like an accumulator in a pressure system, to absorb some of the process shock, so the controls don't have to either ignore it or try to fix it.