Old MB+ network with ProSoft

ds7891

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Sep 2016
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Hey guys, I have a system that utilizes Modbus Plus. It consist of 4 PLC processors, and 2 PC's where the PC's are connected to the MB+ network via PC cards.

Similar to how the PC's are connected to the MB+ string so that data can be read/written to each PLC from the SCADA system running on the PC's, I would like to do the same with some newer PLC hardware.

Basically, we need to expand the plant and the newer hardware will be Allen Bradley. But I need data out of the MB+ network and be able to put data into the network. All the existing PLC's are Modicon compacts.

(Yes, I am pushing the customer to upgrade the MB+ network after the plant expansions. Plant expansion has to happen first. :) ).

I found ProSoft makes a device that looks like what I need:
https://www.prosoft-technology.com/...bus-Plus/Modbus-Plus-to-Modbus-TCP-IP-Gateway

I talked to them the other day, and it definetly sounds like what I need.

My BIGGEST fear....is breaking into the MB+ network. It has been close to 20 years since someone has taken apart the MB+ network wiring. I see the Phoenix Contact sells Taps. I have a location where I am ready to break in. I understand the terminating resistor's. I understand that devices must be Node set.

What else am I missing, and what are the biggest concerns?


What are the chances, after cutting in my new tap and something goes wrong, I can't get the MB+ network back up and running?
 
If I read you correctly, you just need data out of it for display or archiving?

I had only one encounter with MB+ and it was not a good one. The name Modbus Plus is completely misleading. It's more like a old 10Base 2 physical layout with token passing. That reminds me, I better remind the plant to rip that thing out and set it on fire.

back on the topic, because it's token passing, adding another master might not be as easy as it sounds. Can you take the data out the PLC instead of breaking in the MB+ network? That's what I would try to do instead of adding a tap in there.

eta: MB+ is peer to peer instead of master/slave. So, don't listen to me but still, I would try talk through the PLC instead.
 
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I used to work at a site with an extensive Modicon install base, all on MB+, and an extensive Compact/Control Logix install base on Ethernet. The exact module you've linked is what they used to bridge the two networks. They were pretty much rock steady, the only problem we ever had was when we started to hit the limits of the device and data transfer slowed down, so we bought a second one and split them into Line 1 and Line 2. I *think* I might even have updated the configuration on one to add some more data at one point. I don't have any real specific memories of it, which means it was probably a fairly uneventful and painless process.


As far as the physical side of MB+, that stuff is pretty much bulletproof. TBH I think you could probably use wire nuts and orange circ and you'd still get it to work over a short-medium distance. If you get the proper tees and some good meaty STP cable you should have no dramas. As long as you terminate neatly at the tee, worst case you can unplug your converter box and I'd be 99.9% confident that the rest of the network will be quite OK.
 
I used to work at a site with an extensive Modicon install base, all on MB+, and an extensive Compact/Control Logix install base on Ethernet. The exact module you've linked is what they used to bridge the two networks. They were pretty much rock steady, the only problem we ever had was when we started to hit the limits of the device and data transfer slowed down.

Thanks for the info!

Any chance you could describe the install where you used the gateway?

Roughly how many points of data do you think you were passing through the gateway?

Other than the MB+ hardware concern (which you instilled some confidence in above. Thanks), my next concern was the capabilities of the gateway. I have upwards of 2000 tags I need to pass through the ProSoft.
 
I honestly couldn't even hazard a guess as to the tag count. There were probably 15-25 modicon PLC's on the MB+ network, and the plant SCADA had to communicate via those gateways. The plant SCADA didn't have any real control over those machines (all pushbutton controls from that era) but there was a decent amount of monitoring. Does that help give you an idea of scale?
 
I honestly couldn't even hazard a guess as to the tag count. There were probably 15-25 modicon PLC's on the MB+ network, and the plant SCADA had to communicate via those gateways. The plant SCADA didn't have any real control over those machines (all pushbutton controls from that era) but there was a decent amount of monitoring. Does that help give you an idea of scale?

Do you remember what size the average rack was?
 

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