proportional valve and load cell

Hello,

I am working on designing a test stand that needs to apply a controllable force using a pneumatic cylinder. The plan is to use a load cell and proportional valve with a PID loop. The stand will be a labview stand, but I do not want to run the PID loop in labview for timing issues. I am looking for some sort of hardware controller that will interface with the proportional valve and load cell. Something that I can send a desired force to and it will open the valve until that desired force is acheived. Does anybody know of a controller that can do this?

Thanks, Bryan

Tee hee hee. I suspect you meant "open the valve" and not "open the load cell" . . . .

yes, it would be hard to open the load cell

Hmmm... You may want to look at an electronic pressure regulator. They respond quite fast and you send them a 4-20mA or +/-10VDC signal to set the downstream air pressure which would regulate the force on the load cell. If you know what force you want before this is applied this may work better.

Have used this in the past to set grinding force compliance for a robot. Mounted the complete stand grinder on a linear rail with a pneumatic cyclinder and set the pressure on the cylinder with an electronic regulator. Works well.

Some brands are Proprtion Air and Burkurt. There are others, I am just drawing a blank.

Darren

We recently introduced a strain gage input PID module for our Modular Controller series: http://www.redlion.net/Products/ProcessControl/ModularController.html

If you go with one of the enhanced masters you could use its web server, virtual HMI, as the interface. If you must use LabView as the front end, you could communicate to any of the masters via a Modbus connection (RS232, RS845/422, or Ethernet). You could also use OPC if you choose one of the enhanced masters, although this would also incur the cost of our OPC server.

Regards,

How quickly will the pressure change?

If this is just a go to a pressure and hold it then you should be able to get by with a small PLC and pressure regulator. Many commanies have pressure regulating valves that will provide stable pressure. I used a couple MAC valves for pressure regulation on either side of the piston once. They work pretty well and reduce the need for a fancy controller. You would still need the load cell to provide the actual applied force feedback though. You should realize that is is hard to control force when the forces get to be lower than that of the static friction.

I would consider a DL06 with ethernet so you can communicate with the NI Labview.

If you need something that needs to something more than just hold a pressure let us know. There are some pretty fancy controllers out there that are designed to do this type of work and can easily interface to lab view.

The stand will allow the user to select or define a load profile in labview, this load profile can be composed of a series of increasing or decreasing load and dwell periods where the cylinder will hold a load.
I am looking for something, like a stand alone red lion meter, that will control this. I do not want to add a plc to do this and I am trying not to have this control running in labview.
What fancy controllers are you talking about Peter?

Did something similar using a KEB servo drive driving down onto a press on load cells. It was extremeluy fast and the PID was built into the KEB drive.

The resultant load was fed back into a scada system which plotted graphs of the force per run. The scada system was also used to set targets for the desired force.

I would presume other makes of drive as well as KEB would have built in PID control.

The cost of using a servo would be too high for this application, another engineer at my company has done a similar system with a danaher servo and a torque transducer. The danaher servo had PID control built in as well.

Ok, I found something that does exactly what i am lookin for. A company called Enfield Technologies makes a controller and proportional valve that interface with a load cell. All I need to do is give it a desire load and it will set the cylinder to that load.
Their website is: http://www.enfieldtech.com/

Bryan