Remote/field I/O.

Elcan

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Apr 2008
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NC
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Hello all,
I'm designing a project where I need to use remote or field I/O. This would be my first time with remote I/Os. Excuse my ignorance!

I'll offer basically 2 options for the PLC brand: Allen Bradley (CompactLogix) and AutomationDirect (Productivity 2000).

For the AutomationDirect option, I was thinking about using either a master and a remote P2000, or even 2 processors P2-550, since the price difference is not that much, and I could use the remote PLC to take over the control of remote I/Os if the local PLC dies. Any comments here?

For the Allen Bradley option, I noticed that the remote I/Os (either Flex or Point) are very expensive. Can I use a 3rd party remote I/O? Recommendations?
What if I use a P200 as a remote of the CompactLogix. Is it too complicated to make them talk?

Thank you!
 
If the processes can stand alone, or at least partially do so, then a 2nd CPU makes sense.

I have read some threads about getting A/B to talk to PxK, but have not tried it myself. I think the folks who have tried it have succeeded, but I don't know the details. I do have both types of PLCs on my test bench at the moment, but have not had time to try this. If I get some free time before we have to install the Logix system, I will try it...

I have not personally used any 3rd party EthernetIP I/O but have read many threads about a handful of different brands. So I'll let others with real experience chime in on them.
 
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If you are communicating between PLC's then you could also use the Productivity 1000 PLC. It can support up to 128 discrete I/O points or 32 analog I/O channels total and has all of the communication ports built into the unit. 2 serial (RS232 and RS485) USB port for programming and Ethernet port.
https://www.automationdirect.com/productivity/p1000/index

If you use a CompactLogix, it will communicate Modbus RTU. This may be a good option.
https://theautomationblog.com/which-compactlogix-models-support-modbus/

Just some thoughts.
Regards,
 
Have you considered giving the client the price of the full Rockwell experience?

I believe Wago did IO that would work on EthernetIP... though I am not sure about the price for their stuff, but doubt that is more expensive than Rockwell's.
 
Have you considered giving the client the price of the full Rockwell experience?
I warned him that AutomationDirect is a fraction of the price of Rockwell, but I think some people is still afraid of moving away from the Allen Bradley (or Siemens) world.
I haven't had a single issue with AutomationDirect so far, and several with AB over the years. To be fair, I have much more ABs in the field than ADs.
 
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I have a system that has a P2K main rack and then using Opto22 Snapio as remote io, i'm using Ethernet/IP to commuicate to the Snapio and it is working excellently.
 
I use POINT I/O on my CompactLogix systems. It costs a little more than the B&R X20 I/O assemblies my colleagues use.

Every time they want to modify a module setting, they get out the B&R utility, then make the change, then export a file, then import that file into Studio 5000, then do a download.

I click on a menu and a drop-down, then click Apply and keep on working.

In addition, when I'm using the smaller 1769-L16 and -L18 controllers, my local I/O has exactly the same resolution, configuration, and data types as my field I/O. I don't have to scale or copy or compare or document any differences.

If I was going to build a dozen machines, I'd consider using the B&R as well. But I value the time I save on troubleshooting and editing more than I value the money I save on hardware.
 
I don't hardly ever use A/B gear, but I can offer my thoughts on the P2K based system, which I use daily.

If you're going to do remote I/O with P2K, get one CPU and the rest of the racks will have P2-RS modules. While you can use multiple P2K CPU's, it's not ANYWHERE as easy to program as a P2K CPU + P2-RS modules.

When you use the RS slave racks, they program as if it's directly connected to the main rack. No special instructions, no MODBUS addressing, nothing. It. Just. Works. I recently did a P2K master with P1K slave units and while it wasn't horrible, I spent a LOT of extra time doing all of the tag conversion \ management in the RX and WX instructions (which are proprietary to PxK Suite). I spent more time in labor doing the programming the the small bump in hardware cost (between a P1K and a P2-RS system) would have cost.

I HIGHLY recommend the P2K + P2-RS system if you need to do remote I/O. It's just so stupid simple.
 
The first thing to evaluate to choose a remote I/O system is the response time required, it is not the same to need that a motor stops almost immediately when an object reaches a position detector or instead you only have to know the temperature of a process , if a door is open or a heater is on.

In the first case we need a bus with low latency, which normally works through the publisher-subscriber system, examples are Ethernet/IP for AB, DeviceNet for Omron, CC-Link for Mitsubishi, etc. they normally are configured with the same PLC programming software and then the refresh of the remote data is automatic.

In the second case in which latencies of some tenths of a second would be admissible, more economic modules could be used using request-response messages, for example those that use Modbus RTU or Modbus TCP ... but usually they may require more programming work due it's you PLC program that it has to send the messages and get the responses.
 
Automation Direct has just introduced its line of Remote IO for Modbus RTU and Modbus TCP.

Here is the link to the information:
https://www.automationdirect.com/adc/Shopping/Catalog/Programmable_Controllers/Do-more_Series_(BRX,_H2,_T1H)_PLCs_(Micro_Modular_-a-_Stackable)/BRX_Series_PLCs_(Stackable_Micro_Brick)/Ethernet_Remote_I-z-O#start=0&Port_Protocol_L_s_R__ms=%22Modbus%20TCP/IP%22

Manual:
https://cdn.automationdirect.com/static/manuals/brxuserm/ch15.pdf

This is part of the Do-More Series but they have examples of the remote I/O being used on the Productivity Series.

Regards,
 
I've used AB PointIO in many of my projects. In fact, it's a standard at the plant I'm currently working on. My opinion is that you don't pick AB for cost savings & it makes no sense to save on remote IO if you decided to go with AB processors. If cost is an issue, I would just stick to a different platform. However, if you decide to get AB controllers, it would make sense to keep the system compatible with the same remote io.

Cheers,
Vlad
 

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