AS-interface and 1756 ControlLogix

RonJohn

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We are looking at some new equipment at our plant and the supplier is quoting us valves with AS-interface (ASi) control in a ControlLogix package. ASi is a new & foreign concept to me, so I'm looking for some insights. Searching this site, I found some old posts that spoke favorably but none of them were recent.
New/additional communication protocols typically mean increased headaches so I want to prevent as many as possible.

First off, what is actually gained by using ASi as opposed to digital I/O?

I found some info on the web (again, more than a couple years old) regarding ASi cards for the 1756 rack as well as stand alone Ethernet/IP to ASi gateways. Can any one enlighten me as to pros/cons of each?

My main concern is that our plant runs 24/7/365 so if adding/modifying/deleting any nodes require a PLC program download, it becomes a major ordeal. Not sure if this is the case with all, some or none of these type devices.

My other concern is how the system responds to a cable issue. If the valves are all direct wired and a cable gets sliced, I lose one valve. What happens if a branch cable gets sliced with this protocol?

Lastly, if there are any PDFs that you can recommend for understanding ASi better, please advise. Thanks in advance.
 
ASI (Actuator Sensor Interface) is a two wire reasonable speed communications. This reduces wiring, easy to program ASI interfaces i.e. valves, sensors etc. there are a number of versions over the last few years (I used the 32 way ASI A version but I believe there is now 64 version.
The nodes are programmed with an ASI programmer i.e. 1 to 31 (or 1-64) for each ASI Card. The system I did had 12 cards on one plc and 8 other plc's with at least one card. There is a couple of downfalls, 1 it depends on the PLC how you get at the data this can be a little confusing as some plc's were available before ASI so it has been a retrofit card and I/O is transferred to internal bits or words. 2 If a node goes down then although there are error bits that can be programmed to generate an alarm this can affect some or all of the nodes on the card (particularly prone to this on processes where things get very wet) so it could be you have all nodes reporting errors or maybe 3-4 even though there is only 1, This can take some finding but unplugging each in turn usually finds the one causing the problem. 3 Most new ASI modules come programmed for address 0 and if replaced without programming then using functions on the PLC ASI card it will program it with the correct address, however be warned that if there is more than one in error this can cause the wrong address to be allocated. Once you get used to it it's not too bad but I have known some people that have been on the verge of a breakdown trying to find a fault.
Hope this gives you some insight and I have not used some of the later generation and obviously only on certain PLC's.
Note: Each ASI loop can be no more than a 100m this applies if daisy chained or starred or a mix. the total length of 1 loop can only be 100m after this you have to use ASI extenders so for example if a loop contains 20 nodes and the first 10 are loop in / out then the other 10 are starred the total amount of cable when added up must be less than 100m or you could start to suffer from node dropouts. Also make sure you use proper ASI power supplies to power the loop as these will shut down on over current without damaging the PSU and as soon as the short has cleared they resume.
 
Thanks widelto, I did see this product in my web search. Not sure what they mean by "complete set" as they have another module that appears exactly the same as the BW1611, sans those two words.
 
Thanks for the insights parky. This sounds a lot like DeviceNet, which I dabbled with back in the early 2000's during my integrator days. That stuff worked great when it worked but was a bear to design properly for one off projects and a pain to troubleshoot under certain circumstances.

This equipment will be in a wash down environment, so stuff will get wet. So what does one gain using ASi vs. quick connect cables ran back to digital I/O?
 
Most ASI based equipment I have used has been quite hardy, for example APV Valves, IFM ASI Sensors and ASI Interfaces (8-16 I/O) and the obvious is the reduced cables, remember it's easy to replace an ASI Cable and most ASI connections are pretty waterproof. so not much to choose regarding both, the only thing is some installers will use multicores from PLC I/O to adaptable boxes and these can be a problem with water ingress and corrosion having to replace complete installations, ASI on the other hand might have less interface boxes but depends on the installation. Note: you do not have to use ASI cable just something like SY (braided pvc/pvc) but some valves with ASI heads have special glands for the yellow ASI cable and only needs clamping to make connection. The last installation I used to look after only used a small amount of ASI cable & lots of SY.
You do not have to download anything provided you leave spares on each ASI Card, these are programmed on the card very often just using two buttons to scan any extra nodes and The ASI nodes just require an ASI programmer terminal like IFM. however, if you put the card into programme mode you may loose the I/O on that card while in program mode but PLC will continue to run (well on Mitsubishi Q & FX series), so never had to shut down the PLC.
 
I'll just run an example by you to give an idea of the benefits of ASi bus,


On one PLC I have 128 valves (Definox mix proof valves), each valve has three pilot solenoids plus two position switches, this would require a 7 core cable to each valve a total of 896 cores of wire to connect and route, with ASi bus I have 4 channels giving me 128 nodes - which means I have to connect 8 cores and route 4 cables - absolutely no contest


Steve
 
We are looking at some new equipment at our plant and the supplier is quoting us valves with AS-interface (ASi) control in a ControlLogix package.

Sounds like you were talking to me! Haha, probably not, I'm working on a project on the East Coast using ASi and ControlLogix.

Sounds like food & beverage and you are getting various valves including mixproof. As others have mentioned, those valves have a lot of IO! If you get a valve manifold with 30 valves, and have to run discrete wiring to each, you won't have much fun at all.

ASi reduces installation foot prints, commissioning time and provides you the value of feedback IO. The increase in cost due to ASi valve heads and ASi Masters is offset by the reduced installation costs, reduced control panel size, and reduced amount of traditional IO hardware.

Programming of the valve head is simple, just make sure they provide a GOOD ASI mapping reference, and/or put the asi address right on the head so if you need to replace it you have what you need on the valve.

ASi or DeviceNet Valves do the same thing, I think ASi is far easier to design, integrate and manage than then DeviceNet (yuck).
 
Last edited:
Thanks folks for the feedback!

Paul, I don't know specifics at this time but mixproof valves are a possibility. Your mapping/device ID suggestion is GOLD! Care to enlighten me on any master/gateway you recommend for/against?
 
I agree IFM for discrete's or use modules, as for valves I have used APV in one installation it contained nearly 400 valves (mix proof & others), the heads are easy to replace just un-screw the cover, either replace the ASI module or the complete head, I have done this many times while system live the electronics are extremely hardy only thing to watch is safety as the valve or process may operate once re-connected. As the system was completely enclosed from personnel or isolated where there was a possibility of harm and any fault would hold the process until re-started. there was never a problem due to our working practices and safety controls in place. (just in case the health & safety conscious out there want to rant).
 

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