1 msec data transfer between two PROFINET slaves

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Jan 2007
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Vancouver, WA
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I need to get data from an MTS temposonics multi-magnet transducer to my motion controller. I think the best option, given the communications capabilities of each, is PROFINET. Both devices are slaves. I would like the data transfer rate to be 2 msec, preferably 1 msec. I need some PROFINET master to read from the sensor and write to the motion controller at this rate. Any suggestions on the most cost-effective product for doing this? I assume it will require a PLC that is not doing much else so the scan time can be fast enough.
EtherNet/IP may also work.
 
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I'm not sure who has cheapish PN controllers besides Siemens. Note that you theoretically would need programming software in addition to these, which very well may cost more than the PLC. It does have a fully functional 21 day trial, which may be helpful in this case.

An S7-1200 (around a few hundred dollars) supports 1 ms update rates, and if the only program is copying data from one to the other, I can't imagine that taking more than 1ms. However, that means 1ms from transducer, 1ms processing, 1ms send to motion controller, which puts you in a 3ms time range, at best case. You could use a cyclic interrupt to call it at a specific interval (fastest is 1ms), or just let the main program cycle as fast as it can.

A slightly more expensive PLC, like a 1510sp or 1511 (probably around 1k) would support faster bus speeds, Profinet IRT, and isochonous processing. Isochronous processing means that you could set it up where the PLC reads its inputs, does its processing (block moves), and then sends its outputs, all synchronized to the bus cycle (as fast as .25ms). The fastest cyclic task here, if you aren't synching to the bus, is .5ms.

However, one important question is what is the fastest update rate your devices support? Do they support Profinet IRT? Do they support isochronous processing? What profinet class are they certified as?

Long term, the best method would be for the motion controller to be a Profinet controller directly, and supporting I-Device to simultaneously act as a device to other controllers. That doesn't help you right now, though.
 
My device supports 1msec and no IRT. Eventually, the motion controller will support PROFINET or EtherNet/IP as a master, but for now I am stuck with a separate master. This application is slow-speed, so I can probably live with a 3msec delay.
The S7-1200 is about as cheap as I could expect, aside from the software cost.
Looks like EtherNet/IP will work, possibly opening up the options. My CompactLogix can talk EtherNet/IP to two devices and transfer the data with an insignificant scan time (0.07 msec), it just costs more the $1k. I know many other manufacturers have been adding EtherNet/IP, maybe there are some low-cost ones?
 
insignificant scan time (0.07 msec)

For the record, the 1200 is very probably in the same ballpark, data copies take almost no time at all. I was putting 1ms as the worst case processing time.

The 1200 programming software (Step 7 Basic) is much cheaper than the Professional version that is used for the other PLCs (300/400/1500), but with the same look and feel. Both combined would probably be under 1k.

Can't help you on the EIP side, though. GE also has PN controllers, I think, although know almost nothing about them.
 

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