Position Transducers for Hydraulic Motion Control

I'm looking for some clarification about position transducers. I'm currently working on a hydraulic motion control system that requires position feed back. I've decided on putting a transducer into the hydraulic cylinder.

I'm going to use digital SSI style probe but I am unclear on the exact difference between binary and gray encoding and if one method has any significant advantages over the other.

Gray code only requires one bit to change states per increment.Here is a link that contains a good explanation of it:


http://www.opticalencoder.com/pdf/introduction.pdf

What motion control will you be using? Most controllers will work with either but you may want to make sure. I use MTS Temposonics type R for the most part. I have also used a few Balluff. If you set the controller up for the wrong one it will give you counts but they will jump around and give you very bad results. It is my understanding that gray code is faster because it only changes one bit at a time but I don't think this would be enough to say its better.

A more important question

There is no advantage using one over the other. As pointed out above the better motion controllers will handle both binary or gray scale. I recommend 24 bit binary rods. There is no point if buying a 25 bit.

The update rate is dependent on internal electronics and delays caused by waiting for the return pulse.

Now here is the question that isn't asked but should be. Is the MDT rod data synchronous to the motion conroller. MTS rods are. I think you must still specify if the Balluff rods must be synchronous to the motion controller.

SSI rods that aren't synchronous to the motion will cause glitches in the velocity and the results will look like this.
ftp://ftp.deltacompsys.com/public/jpg/reference encoder roller.gif

Contact
http://www.pqsystemsltd.com/
They can supply the right rod.

Thanks

Thanks fellas and thanks for the heads up about the synchronous rod issue Peter. I am in fact using a Delta Controller for this project and was planning on getting in touch with Chris at PQSystems in the morning. I guess my instincts were correct even if my knowledge is lacking.

On another matter I plan to connect my RMC75E controller to a RedLion G310 HMI panel via ethernet. Do you know who can give me some guidance on how to setup the communications?

drawson said:

On another matter I plan to connect my RMC75E controller to a RedLion G310 HMI panel via ethernet. Do you know who can give me some guidance on how to setup the communications?

Click to expand...

Never mind Peter. I came upon the samples posted on your website. Thanks.

The R-Series MTS Temposonic can be reprogrammed if you don't like the output you are getting. If you need help with this let me know. I repair and sell MTS transducers.

[email protected] 208-773-4731

Drawson,

One other concern with putting the transducer into the cylinder is that you are actually measuring the position of the piston in the cylinder (where the magnet is) and not necessarily the load that you are trying to position.

We had an instance where the customer would set up the machine in the morning and all was well. It was a spotface application with a tight tolerance on the spotface depth. As the day progressed, the measured spotface depth got larger and larger until it went out of specifications. All the while, the motion controller is reporting that it is dead on position!

We scratched our heads for a while until we realized that the oil was cold in the morning and warmed up with time. The growth in the cylinder rod was enough to push the spotface out of tolerance. The magnet was exactly where it was supposed to be so the motion controller was happy. What was amazing was that when we went to the handbook and looked up the temperature coefficient of steel and did the calculations they were right in line with what we were seeing in the spotface.

We could have added a temperature transducer to the system and done the compensation but decided to change to an external transducer.

If the cylinder rod is short (ours was about 28"), or you control the oil temperature or your tolerances are not that tight then it doesn't matter. But if you have tight tolerances and don't control the oil temperature, you should do the calculation and see if you have an issue with rod expansion.

Norm, check the date.

Old thread alert. We had a bunch of old threads dredged up all at once by a poster who sells and repairs MTS transducers.

Well maybe someone will learn something today and not have to figure it out the hard way like I did...

Steve, maybe you should put a 3 month limit on what you reply to?...

Yeah I got it figured out. Thanks for the update.

By the way, Welcome to the forum Steve.

For this kind,

batter use sony. It is perfect

Nec