PLC to I/O communications


Thread Starter

Sam Robinson

I'm building a 16' indexing table with 36 I/O points. I need a way for a PLC that is mounted in the base of the machine to communicate with the I/O that is on the moving table. Does anyone have any ideas how this can be accomplished without a physical connection between the PLC and its I/O.

Thank you,
Sam Robinson
Industry Products Co.
I can think of modems, infrared modems, and the new bluetooth standard come to mind. 900 mHz Ethernet modems are available from several sources...Data-Link is one.

Walt Boyes

Walt Boyes--MarketingPractice Consultants
21118 SE 278th Place - Maple Valley, WA 98038
425-432-8262 home office - 253-709-5046 cellphone
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Michael Griffin

At 16:23 17/08/00 -0400, Sam Robinson wrote:
>I'm building a 16' indexing table with 36 I/O points. I need a way for
>a PLC that is mounted in the base of the machine to communicate
>with the I/O that is on the moving table. Does anyone have any
>ideas how this can be accomplished without a physical connection
>between the PLC and its I/O.
I can make several possible suggestions:

1) Slip rings. This is a lot of slip rings though.

2) Some sort of device bus (e.g. ASI) via slip rings or some sort of transformer or optically coupled "slip ring" equivalent (the optical coupling would be for data only - power would still have to go through regular slip rings). The difference between this option and the previous one is that this requires only two or four wires, rather than several dozen. I can't recommend any slip rings for this application, but the device bus vendor may be able to.

3) For inputs, Baluff (I think) has a sort of inductively coupled proximity sensor line which allows a signal to cross a very short gap
without a direct connection. This consists of two halves, a fixed cable and "receiver", and the moving "transmitter" - sensor pair (which are joined together by another cable). This moving part is self contained and does not require a separate power source. The fixed and moving portions would line up at each index position, with the moving part lining up with a different
"receiver" at each index position. I believe this product was originally intended for use in stamping dies to avoid having to join up cables for die sensors at each die change.

4) We have so far managed to avoid slip rings etc. in our own index table applications. We view them as potentially quite troublesome. What we have done in several applications is the following.
- For inputs, we have sensors fixed at certain positions around the table (in fixed locations - not on the table), at the points where they are actually needed. We use optical through beams or inductive sensors as appropriate.
- For outputs we have pneumatic valves mounted directly on the rotating table. However, these are not solenoid operated valves, but
actually small "manual" push button detented valves. At various locations around the table, small pneumatic cylinders operate from above or below to actuate the push-button type table mounted valves to clamp or unclamp tooling, rotate nests, etc. Air is supplied to the table through a single swivel coupling.
I won't claim this method is perfect, but these devices are probably some of the least troublesome parts of these machines. The small "push button" valves have metal operators (buttons). I haven't looked them up in the catalogue so I don't know if they are actually intended for this application. I have been told though that they are lasting much longer than
we expected.

Michael Griffin
London, Ont. Canada
[email protected]

Robert McDonald

We have done this type of thing before using sliprings.

However we have mounted the PLC on the turntable and only the power and communications have travelled through the sliprings.

Perhaps you could look at RS485 type I/O for the machine.

Robert McDonald.

Dean Kindrai

Check out the Balluff "High Power Remote System". It can be used to transfer I/O signals across an air gap. It's not designed as a system to transmit for long distances, but if you can wire the I/O to a location that is fixed, but across an air gap, it will work great for you.

For information, call Balluff at 1-800-543-8390,

Dean Kindrai
Neff Engineering of Wisconsin
(262) 834-6300
Wireless would appear to be a solution. There are a large number of wireless providers. One that I know that has worked with PLCs is:

The Data Linc Group at:

You can also call Jim Steffey @ 425-882-2206 at Data Linc.

William(Bill) L. Mostia, Jr. PE
Principal Engineer
WLM Engineering Co
Independent I&E Consultant
P.O. Box 1129
Kemah, TX 77565 USA
E-Mail: [email protected]

These opinions are my own and are offered on the basis of Caveat Emptor

Kenny Hartman

Sam -

Check out We've done many applications similar to yours with this type of device.

- Kenny Hartman
A.W. Schultz Inc.