sensing the speed of piston in a hydraulic cylinder

Hello control engineers,

I am looking for help!

I have to sense the speed of the piston moving in a hydraulic cylinder to provide feedback to a controller that is controlling a proportional solenoid. Does anyone know if this has been done? If yes, how? Many thanks for your help.

Simplelogix

Try here for control
http://www.deltacompsys.com/

You can buy linear feedback devices for many different manufacturers

http://www.balluff.com is one.

I am using one from http://www.ametek.com along with the delta controller to convert a hydraulic slide to a peck feed.

I always use Temposonics for this.

http://www.products.mtslinearsensors.com/

More info and maybe more resolution required.

The speed can be sense easily by taking the difference in position over 1 scan time. The problem is that the Temposonic Rods usually have a resolution just a little better that .001 inch. This means a cylinder moving 10 inches per second will see a position change of about 10 counts each milliseconds. However, because each Temposonic rod is different and not calibrate for exactly 1 counter per .001 inches the motion controller will see the counts change between 10 and 11 each millisecond. A change of 1 count in 1 millisecond is about a 1 inches per second change.

To reduce this 'noise' due to quantizing error, two things can be done:
1. The motion controller should have a low pass filter to filter out the sampling/quantizing noise. The bad part about the filter is that it introduces phase delay. Most use just a simple low pass filter which has been explained on this forum many time. Coming soon are 4 pole Butterworth filters which really smooth out the velocities.
2. Use a SSI Temposonic rod. SSI rods can provide position with resolutions down to 1 micron or about .000039 inches which is about 40 times the resolution. This reduces the sampling/quantising noise by 40 too.

So what is the application and how fine must the velocity feed back be?

Hi Rick Densing, RussB & Peter Nachtwey,

Many thanks for your help guys. Much appreciated.

Peter, the application is to provide speed control to hydraulically powered arms of a delivery vehicle. The finer details are yet to be worked out but to start with any sort of control is better than nothing. Their main criteria are that the operating environment is very harsh and the hydraulics cannot be taken apart.

I will be a frequent visitor here for your help so please do look in regularly if you are already not doing so.

Thank you all once again
simplelogix

Check this one they have speed transducer. We use their transducer for injection ram control.


http://www.transtekinc.com