Devicenet Question - how do you connect to an existing network?

[**Bolty**]

Evening All,

Little bit of background - Last week I'm asked to attend a "plc fault" with one of the techs - usual story of very little info given. On arrival we find the devicenet network down to 2 parts of the plant. Both the 1747-SDN scanners in the rack are showing error 91 but thankfully a reset of the 24vdc supply seemed to cure the issue and the fault cleared and comms came back. (it appears to be noise generated by a large vsd that tripped at the same time according to the scada)

If it had been the scanner module that had failed then we would have been in a bad situation as no-one has the configs for the scanner modules!.

Not ever dealing with devicenet before it's been a mad rush to download manuals and understand the basics. I've since found a 1770-KFD convertor hidden away and am happy with RSnetworx for devicenet but cannot fathom the best way to connect to the network and then get the all important configs. It seems the AB 1787-PCABL probe lead is obsolete (since 2013) and tracking one down is proving difficult to say the least so how do you connect?. Is it connect to an existing devicenet connector and run a flying lead? (this means disturbing the network) or is there an equivalent to the 1787-PCABL which is a little less intrusive?. I'm aware there's a pass thru option (dependant on firmware version etc) but all the reports on this seem a little negative.

Any replies or pointers are greatfully received.

Bolty.

 

[Logix_Stef]

I seem to remember that you can 'tap in' at any point odf the network to go online. You need to have RSLinx running and RSNetworx, 1770-KFD adaptor a 96881702 lead to tap into the network and a serial lead to connect the adaptor to the laptop. If the scanner configuration is lost, it is possible to rebuild it with all the devices on the network working OK.
I think this is called 'map in' the scan list into the scanner. Was a long time ago though. I still have the leads and the adaptor but no software.

 

[ddnnis]

I’ve done a lot of projects that use the 1769-SDN scanner; I believe it works the same way.
· I typically hooked up to the screw terminal on the scanner to establish communication with the network. But as mentioned by the gentlemen earlier you can typically tap into the network at any convenient terminal.
· Make sure you see the network on RSLinx before proceeding to RSNetWorx.
· When you configure the RSLinx Driver for 1770-KFD convertor, make sure to set the correct baud rate in the driver. The choices are 125K, 250K and 500K. Since you don’t have the Devicenet files, you may have to try each baud rate until you establish communications with the scanner.
· Once you see the network on RSLinx your next step is to open RSNetWorx.
· In RSNetWorx select Network/Online. If all’s good you should see the entire DeviceNet network. Once you see the network select the Network tab and select Upload from Network. Once the upload is done save the uploaded file.

 

[**Bolty**]

Thanks for the replies - much appreciated.

It's the hooking up to the devicenet terminal on the SDN module that is causing the issue as this means I've now got to disturb the network to connect into the existing wiring with a flying lead to allow connection to my 1770-KFD - not good on a live plant (and asking for a short shutdown ).
If I had the 1787-PCABL (96881702 lead) that plugs directly into the terminal, I would be fine, but this lead is obsolete and there appears to be no equivalent made by Allen Bradley or indeed not even a third party vendor.
hmm.. I need to go back and have a better look at the devicenet network when I get a chance and look more closely at how its connected instead of a passing glance.

Thanks again,

Bolty.

 

[alan_505]

Have a look at all the connection points on all the modules as maybe one of them has a double connector that is only using one side of it.


Alan

 

[JohnCalderwood]

Bolty,

where are you?

I managed to get a cable from Scattergoods a couple of years ago
http://www.scatts.co.uk/list.aspx?f...Lines&catid=26&catdesc=Clearance+Lines&page=1

although I do not see it listed - give them a try?
Or Lektronix?

 

[**Bolty**]

Afternoon John, I'm in Scotland, a wee bit further north than you but not by much .

I tried Scattergood and plc center but no joy. I'm waiting for Lektronix to get back to me. I've also got the feelers out through another company we use who are keeping their eyes open.
In the meantime, it turns out a couple of the guys in another area have this mystical PCABL lead so i'll borrow it from them so all is not lost!

I went back today to the plant in question and found one of the devicenets is daisy chained from one panel to another through weidmuller terminals and from these terminals a small drop cable is also then ran to a devicenet interface for the micrologix (1781-net-dni). I could potentially run a temp drop cable in this fashion to my 1770-KFD and get the all important configs.

Every days a school day.

Thanks for everyones replies -

Bolty.

 

[JohnCalderwood]

I was going to say, if not that far, then I could loan you the cable and USB interface unit.....depends what company you are with!

But you seem to have a cable available for loan purposes.....

I got told about these cables by a colleague in the US as I had the same issue, how to get the configuration from some of our PLC5 racks and SDN cards, maybe just got lucky with scatts, but hopefully Carron at Lektronix can help - think I paid under £100 for the cable.

 

[**Bolty**]

Thanks for the offer of a loan of the cable

It turns out another collegue has one of these leads locked away but didn't really understand what it was for....typical!.

Carron from Lektronix got back to me but they couldn't lay their hands on one either so make sure you look after yours as they are like hens' teeth.

Anyhoo, looks like I'm ok now so devicenet configs - here we come!

Bolty.

 

[Ken Roach]

I dislike the "probe cables" a lot. They always got damaged, and they tended to pull on the connector, and the little alignment "ears" broke right away.

Because DeviceNet (and really and CAN bus network) that allows very flexible drop cable architectures, I always wired in a programming drop cable at the PLC scanner, that would just stay in the cabinet and allow me to connect a 1770-KFD or 1784-PCD or 1784-U2DN.

 

[**Bolty**]

The whole reason for chasing one of the probe cables is to allow me to get the configs out without disturbing the existing network but seems like it isn't without it's own problems - just as you described.

The more I look at this, the best approach does seems to be running a permanent drop cable on each of my devicenet networks but can I do this anywhere on the networks?.
The drop cable at each of the SDN scanners make sense as you can see what's going on at the same time, but my hands may be tied as taking either of the networks off line may be a hassle - not impossible, just needs planned in.
I can tap into either network elsewhere by piggybacking into existing terminals that would worst case cause 1 node to drop out and not the whole network.

Ahh.. decisions - decisions. Pity the pass thru driver option isn't a bit better

Bolty.

 

[Ken Roach]

It's true that "tapping into" any network is risky if you haven't provisioned for it ahead of time. Some DeviceNet networks are built with no way to plug in at all, but most have at least a 10-pole connector or a non-critical device you can un-plug.

Droplines, even unused ones, can be anywhere in the network. They don't have to be at the PLC end, or near a terminating resistor.

A dropline can be up to 6 meters long, as long as you aren't on the edge of the network's dropline budget. Most aren't.