thatcadguy
Posts: 9
Joined: Tue May 24, 2016 3:12 pm

PLC / Industrial I/O "shield" for any of the RPi's?

Thu Jun 02, 2016 11:33 pm

I (like many others) want to use the RPi3 (or any of them really) in an industrial automation environment. I see that there are a lot of hardware projects out there along these lines (UniPi, etc.) but so far none that I've seen are really up to the task. Most of them have analog voltage I/O (not 4-20mA current), and only 1-2 of each (need much more, like 4+ of each). Some of them don't have RS485 serial ports either (need this for Modbus RTU), or Ethernet ports (kind of pointless without this).

I don't care about ladder logic or IEC 61131-3 languages, just usable, proper I/O. Thanks for any responses.

EMT
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Location: Wiltshire, UK
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Re: PLC / Industrial I/O "shield" for any of the RPi's?

Wed Jun 08, 2016 4:22 pm


thatcadguy
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Re: PLC / Industrial I/O "shield" for any of the RPi's?

Wed Jun 08, 2016 6:05 pm

Thanks for the link. Hopefully they add a DAC card though and get UL certs so I can use it.

Also ran across this the other day: http://hackerboards.com/rpi-industrial- ... nd-1-wire/
But as stated before, too few analog signals, 0-10V output only (no current)

Just for clarity, I should add that it wouldn't be hard to add what I need myself with my own boards, but the thing is that the device needs UL approval, so it has to be complete or otherwise I'd have to get the whole connected thing approved AFAICT.

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jasonclark
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Re: PLC / Industrial I/O "shield" for any of the RPi's?

Wed Jun 08, 2016 7:35 pm

If possible, use the Pi as a ModBUS master (TCP or RS485), then use Remote GPIO modules.
This pretty much means you just need to connect it to the control network and configure the Pi firewall to only allow traffic on Port 502 (default ModBUS port), or get a UART to 485/422 driver.

Going TCP would mean levering the PI existing UL/CE(?) compliance without spending ££££/$$$$ on further tests.

Otherwise, a SPI based GPIO Expander can get you easily 32 GPIO the other requirements (ADC/DAQ) need more thought.
Pt100 interfaces can be fairly simple (AD7794 is perfect for the job with build in current generator and 24bit ADC) Plugable modules (as per many PLCs) will be tricky.

So..my suggestion is to use the PI as a machine controller but not the hardware interface. Get 3rd party boards to do this - less risk, probably a better job (more immune to noise etc).
But, it'll depend on the application. If it's commercial and a 1-off, I'd think hard about putting a Pi in. Those 3am Sunday calls are not worth the cost saving.
If it's for brewing beer or managing a wine cellar... definitely chuck a Pi in :-)

thatcadguy
Posts: 9
Joined: Tue May 24, 2016 3:12 pm

Re: PLC / Industrial I/O "shield" for any of the RPi's?

Wed Jun 08, 2016 8:17 pm

Thanks Jason. That was the original idea, unfortunately, cost. Most UL approved remote I/O modules are astronomical in price (to my cheapskate mind), e.g. 4 analog inputs for $200+ alone. Original idea was to use it as a TCP master with something like the Red Lion E3 I/O module (which has everything, but is also around $1000). Basically, using the Pi or any other SBC for that matter is only worthwhile for my application if it can be mated with something else that is also low-cost. Otherwise I might as well just buy a $400 UL approved embedded PC.

The requirement for UL approval is really a thorn in my side. I breadboarded together my own I/O solution for less than $200.

boyoh
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Joined: Fri Nov 23, 2012 3:30 pm
Location: Selby. North Yorkshire .UK

Re: PLC / Industrial I/O "shield" for any of the RPi's?

Wed Jun 08, 2016 9:27 pm

thatcadguy wrote:I (like many others) want to use the RPi3 (or any of them really) in an industrial automation environment. I see that there are a lot of hardware projects out there along these lines (UniPi, etc.) but so far none that I've seen are really up to the task. Most of them have analog voltage I/O (not 4-20mA current), and only 1-2 of each (need much more, like 4+ of each). Some of them don't have RS485 serial ports either (need this for Modbus RTU), or Ethernet ports (kind of pointless without this).

I don't care about ladder logic or IEC 61131-3 languages, just usable, proper I/O. Thanks for any responses.
Using the Pi in a industrial application is a very tall order. To compete against the PLC sequencer
Using Ladder logic, Production lines need fast repair , with off the shelf spares , and easy programming
In your programming you must have a high safety factor , All isolating must be don in open loop Manual.

Easy fault finding , and program checking is a must AND ALL PROGRAMING MUST BE FAIL TO SAFE
The PLC will integrate with all other sensors and MIcrocontrollers signals , 4/20ma & 0/10v are common
Industrial sensor signals to interface with the PLC in/put modules.

One last point ,a industrial environment is a very noisy( electrical) place, So a very high noise rejection
System is needed, The PLC is well suited to this
BoyOh ( Selby, North Yorkshire.UK)
Some Times Right Some Times Wrong

thatcadguy
Posts: 9
Joined: Tue May 24, 2016 3:12 pm

Re: PLC / Industrial I/O "shield" for any of the RPi's?

Wed Jun 08, 2016 9:37 pm

Thanks for the concern, but this is for an OEM application, not something I'm going to sell to others (it's just me programming it). It's also not a time-critical or safety-critical application.

We've done the same application with an AB MicroLogix comfortably, which uses an old, slow 16-bit processor of some kind. A modern computer running Python could outperform it.

EDIT: additionally, the PLC actually isn't too well suited to this application because we need the flexibility of a regular Linux system to do more advanced math and data analysis on our process data. This is why we're looking in this direction.

J1pp
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Joined: Mon Mar 07, 2016 10:06 pm

Re: PLC / Industrial I/O "shield" for any of the RPi's?

Wed Jun 08, 2016 11:27 pm

Some interesting products.

https://www.ereshop.com/shop/index.php? ... cts_id=805

looks like someone has looked at it in the past

viewtopic.php?f=44&t=75582

thatcadguy
Posts: 9
Joined: Tue May 24, 2016 3:12 pm

Re: PLC / Industrial I/O "shield" for any of the RPi's?

Thu Jun 09, 2016 5:56 am

J1pp wrote:Some interesting products.

https://www.ereshop.com/shop/index.php? ... cts_id=805

looks like someone has looked at it in the past

viewtopic.php?f=44&t=75582
Thank you! Wasn't exactly what I was looking for, but good enough, I could use quite a few things from that site.

J1pp
Posts: 17
Joined: Mon Mar 07, 2016 10:06 pm

Re: PLC / Industrial I/O "shield" for any of the RPi's?

Fri Jun 10, 2016 7:14 pm

https://www.indiegogo.com/projects/mona ... erry-pi--2#/

Interesting indiegogo item for industrial applications. Saw this in pi weekly



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