Communication protocol question

[psm007]

I have been asked to design a control system of which will have 24 winder stations. Each winder station will have its own control system of wich will have field i/o, vfd and servo drive all communicating back to a main plc or plc's. To limit the amount of wiring going back to the main cabinet, i have been asked to use a communication protocol such as ethernet/ip or other protocol.

My issue is these winder stations and thier dedicated control system will be mobile and can be moved anywhere on a 24 slot frame.so i can move the winder station and its controls out of one slot and place it in another. I have been asked to detect what location it has been moved to for alarming purposes. Is there a communication protocol that would allow me to do this? Would can bus work?

 

[Saffa]

There is no modern protocol that I know of which has any concept of physical location, or location on a daisy chained bus.

If i understand you correctly, the whole control panel / station moves, then you hook up power (and comms?) When it's coupled into a particular location?

I'd add one more plug for position sensing. You can do this two ways depending on whether you have free analogs or digital inputs.

Using 5 digital inputs, you can bridge the contacts in the plug to give you a unique combination per location ( 2 ^ 5 = 32 combinations). The PLC reads this and changes location accordingly.

Using a voltage input, you could fit a small multi-turn pot in each plug. Set correct value during commissioning, and lock in place with a drop of varnish. Have a tolerance in the PLC code to account for a bit of drift over its life.

 

[Ken Roach]

Welcome to the PLCTalk forum community !

One method would be to use a managed Ethernet switch that reports the MAC ID's that are connected to each port. Each "winder module" will have unique MAC IDs for the VFD, Servo, and I/O devices.

Or, you could do as Saffa recommends and make something else unique about the plug-in location that the I/O devices could detect. It would simply need enough distinct bits or difference to be distinguishable. A discrete I/O module connected to a handful of jumpers would be a simple way to do it.

Once upon I time I did something similar with 1-Wire protocol and a little "memory button" device. When you plugged in a cartridge that had power and I/O devices, you also connected a 1-Wire device with a unique ID number, so a 1-Wire reader could tell which cartridge was in place. The cartridges had unique histories of duty cycle and wear between rebuilds and even super-precise timing information that let us tune their cutter heads based on how much friction and stiction each particular assembly had. At the time, we built a costly custom ProfiNet to 1-Wire multi-channel interface board.

If I had to do that again today I would probably use IO-Link or a short-range RFID device instead of 1-Wire.

 

[Winklehoffen]

We do something very similar to this with EtherCAT. We used to use Interbus but that is now gone the way of the Dodo and EtherCAT was recommended to us as a replacement. Works well.



Unfortunately I can't give you the specifics as I didn't do the code.

 

[LadderLogic]

Yes, Beckhoff offers an option to use “hot connect” feature over EtherCAT fieldbus.

https://www.beckhoff.com/en-us/search-results/?q=hot connect

If this sounds like something of interest to you, contact your local Beckhoff office, I’m sure they will be happy to help.

 

[ck8177]

Another option to consider may be RFID. You could place an RFID reader on each movable station and a programmed RFID tag on each possible location, in such a way that the reader will read the tag and act accordingly when moved. Something like this:

56RF High-Frequency RFID

I'm sure there are cheaper options available, but we have had decent luck with this one. Plus, if you are using AB PLC's than there are already AOP's/AOI's available to make programming these guys easier.

 

[Puddle]

Using a voltage input, you could fit a small multi-turn pot in each plug. Set correct value during commissioning, and lock in place with a drop of varnish. Have a tolerance in the PLC code to account for a bit of drift over its life.

Digital display pots for best results. Good for applications with ham-fisted operators too.

https://uk.rs-online.com/web/p/potentiometers/2486759

 

[mk42]

If you use Ethernet, you could have a different Ethernet cable running to each "slot", and then read which PLC is connected to which Port via SNMP. Siemens has an SNMP library available from the support site, other brands may have support as well.


If the comms are wireless, location will be very difficult, unless the "slots" are so big you have a different AP for each, and even then, you can't be sure.



If you are looking for a different alternative, RTLS systems exist to find the location of a device in space, but in this case I agree with CK8177 that RFID would be more straightforward.

 

[psm007]

I would like too thank everyone for your input. It is greatly appreciated.