There are alternatives to slip-ring.
Can you tell me more about your problem ?

<nbucska@pcperipherals.com>

I have a rotating piece of equipment with about 200 I/O signals total. I was preparing to mount the PLC onto the rotating table, pass power and PC interface to it via a slip ring (fewer pass through connections this way).

I'm not really sure about wireless, due to a significant amount of noise already in existance.

What did you have in mind??

What kind of bandwith do you need for communication between the rotating PLC and the outside ?

Power you can filter or xmit through a rotating xformer.
Is the signal bidirectional ?

<nbucska@pcperipherals.com>

don't know yet on the bandwidth...

bi-directional would be a definate.

How would I go about picking a transformer?? I'm pretty good with basic electrical and electronic stuff, just not very familiar with basic technology available to know how to apply it.

You can xmit power and superimposed power in one direction with a rotating XFORMER : Two pot-ferrite cores with the primery/secondary (i.e with E-xsection)are concentricly mounted, one on the rotor axis the other one is static

The other way you may use concentric IR link.

<nbucska@pcperipherals.com>

Several years ago, I successfully mounted a remote I/O rack on an unwind turret and passed the power and communications through slip rings.  In my application I was able to setup the processor to ignor temporary signal loss from the remote rack.  Obviously none of my remote I/O were process critical nor was there any sort of safety monitoring being done there.  Additionally we chose to install new slip rings with silver (I think) contacts for longer life and less skipping.

If you are dealing with process critical or safety related I/O, I would not recommend this method.  In that case, I would agree that wireless is probably the best bet.

Schick,

Consider MERCOTAC mercury-wetted slip rings (available in McMaster-Carr!) and multiplexing your I/O before & after the slip ring.  Power should be conditioned on the receiving end of a more standard copper/graphite or silver based ring set (which would surround the MERCOTAC).  This was used successfully in a specialty theater crane which carried live performers overhead at the MGM/RIO Casino in Las Vegas, Nevada.

--Steve

Hi Boothby:

What do you do about the Hg. vapor ?

<nbucska@pcperipherals.com>

Boothby-

Thanks for the idea...
Unfortunately this will be used in food processing and those darn FDA people have a problem with Hg...

If you need more help than generalities, you have to give us more data -- enough to design the %^&#$ thing.

You have to understand the problem completly, before you can really suggest a solution.

<nbucska@pcperipherals.com>

A few years ago I did a project that had a PLC with about 120 I/O mounted in a continuosly rotating table. The slip ring provided power, about 12 I/O, and communications connection for PLC programming (9600 baud). Never had any problems.

Hi, you should be able to use slip rigs for power and serial data without any problem.Keep the baud rate as low as you can tolerate, or you could use error correcting protocals if you are still unsure.

what is a remote rack

You might want to look at ethernet wireless, opto 22 as well as many others have products that would work well. http://www.opto22.com/products/snap_wlanio.asp
They also had a web based control demo (real time) at there web site. If noise is really bad you may be able to run the transmition signal thru the slip ring assembly via suitable wire and bring it right to the area of other transceiver or possibly direct link them.

Hi Schick:

What is the rotational speed, what is the input/output
requirement, if the controller is on the rotor ?
What is the number of inputs/outputs and what is
their speed?

Does the interface must work before it is spinning ?

<nbucska@pcperipherals.com>

Has anyone used inductive coupling devices like the INPUD system available from MESA Systems Co.?

UPDATE on the project requirements...

After speaking with a couple of EE's who have worked with the older technology of the machine I'm designing, we've come up with the solution that we need to supply power to PLC's on board, making them slaves, and have an additional PLC located elsewhere to control the rest of the machine and interact with the rest of the production line.

Back to the original question...
I am looking to you all for your experiences utilizing PLC's and slip rings. Although I am leaning towards AB for PLC's, nothing's written in stone.

There are quite a number of manufacturer's out there. I was looking for proven combinations.

Sorry if we got off track back in the beginning.

An alternative to a slip ring is the roll ring.  Unlike the slip ring where there are wires sliding on a rotating interface that create wear, noise, and debris.  The roll ring has a rolling flexure that makes the electrical contact between the rotor and stator.  Because the contact is rolling there is virtually no wear, low noise, and no debris.
The roll ring easily handles currents to 10 amps per circuit or if using multiple flexures in each circuit higher currents can be achieved.  It has resistance noise less than 5 milliamps and lasts for a long time without maintenance.  In addition, multiple flexures can be inserted into the circuit to further reduce the noise.  The roll ring can be tailored to your application by stacking circuits and using more than 1 rolling flexure per circuit.

At  work we use three methods. We have fiber-optics in the traveling cable feeding the dockside gantry. Current/power is transmited thru copper/graphite sliprings, while data is transmited thru the fiber-optics via mirrors mounted on the rotating shaft of the slipring.this is done with Ge Fanuc plcs. The second method is thru radio modems at 900 mhz. connected to allen bradley plcs with windows software. For the third method we use Linux and breezecom 2.4 ghz radio links (strickly operator information data). All methods appear to be highly reliable, although none are used directly for machine control, we have been succsesfull with program changes and forcing from remote computers. If you require more info let me know.

I think that you can find a good answer at:
 Pasavant,Prussag Noel.
they have good expereince with PLC,Analog-Digital signals
in rotating machines.(water treatment plants)

Hire an expert and sue them when you don't get the results you are looking for.

Anyway In the wire and cable industry we have had experience with data communication (AB PLC's) transferring critical information at 800 RPM and no we did not utelize RF.

Rick Nieuwnhuysen]
Engineering Manager

Rewire-

Whose slip ring did you use? AB recommends 2 mfr's, but I'm not sure they have what I'm looking for.

schick

extremely interesting thread...