Modbus with SLC5/04 and PanelView 1000

Jimmie_Ohio

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Aug 2005
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Cleveland
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After viewing the posts of others and helping whenever I could, it's time for me to post a topic and get some free advice. But then again, you get what you pay for...

I have a project to design that is similar to another one that I did a few years ago without any problems.

On the new project, I am proposing the PLC to be a SLC5/04 (catalog # 1747-L542). I am also using a PanelView 1000 color (catalog # 2711-K10C8). My old project was the same processor, except I used a smaller, monochrome PV550 (catalog # 2711-B5A8).

I'm not sure how far away these will be from each other yet. (I'm questioning the customer, but it shouldn't be more than 100' apart.) Last time I hooked these up via DH+ (blue hose) on CH0, the PLC was probably only 40-50 feet away from the PanelView. I'd like to do the same on the new project.

Now to the part in which I'm not completely sure... (DISCLAIMER: I know nothing about Modbus).

The project's specification wanted Modbus communication available to tie in to "the plant DCS" (distributed control system). To satisfy that specification at the quoting stage, I "googled" the topic, found a ProSoft InRax MVI46-MCM Modbus Communications Interface Module for SLC, and figured on throwing it in my SLC chassis. The rest of the modules are digital I/O, all local.

As happens to all bad quotes, this became an order last week. Now I must put it all together. Getting the PLC to do what I want with the PanelView is not an issue at all. Also, I will not "see" any hardware for months, until the whole project is approved "for construction".

I have downloaded the MVI46-MCM data sheet and manual and plan on reading it in detail over the next several days. Here are my questions:

1) I do not need this module to "control" anything in my scope. It is simply for the customer's interface. Do I need to do anything more than configure the M1 file in the RS Logix 500 software? In other words, can I trust the vendor's sales brochure's claim of simplicity? Or is this an unexpected, painful, time-consuming task?

2) Do I need to map any bits into any special register for him to pick up over Modbus? Or is this the responsibility of the DCS programmer? After all, it's his interface. I just don't know who picks up where.

3) Are there any odd hardware restrictions or other anomalies of the MVI46-MCM of which I should be aware? For example, it looks like I can put this in any available single slot.

4) What questions should I be asking the customer, if any, so my design and implementation goes smoothly?

As I said above, I will find out a lot more after reading up on the Modbus module, so please don't tell me to read the manual.

I'm really looking for very general advice and things to watch out for from those of you who have actually used this Modbus module in the past. I have described the whole project in case you have any other communication suggestions or ways to do it better or cleaner. Since I'm just starting to sketch the design out and prepare my ACAD drawing package, now was a good time to seek suggestions for a better system.

REMEMBER: I know how to program the PLC and build PanelView screens. I know how to get these to "talk" to each other. Although not to sound ungrateful, please don't waste your time on making suggestions that don't apply to how Modbus affects the project's scope.

Lastly, money is no object on this control project. Percentage-wise, my controls are about 2-3% of the overall project's budget, so a thousand here or there is meaningless. And by the way, I'm controlling a process (conveyors and other simple on-off devices) at a power plant.

Thanks in advance for any productive replies!!!
 
just a guess

I would suspect that you will have to map the PLC registers to the ProSoft card, and provide documentation on what is located where. Then the DCS programmer will read the data from the prosoft card. In my experience the DCS is usually the master and the plc will be a slave. I don't think it will be very difficult.

Ken
 
Jimmie,

I haven't used the SLC version, but I did use the ControlLogix version MVI56-MCM. In my case the Prosoft card was the modbus master. I agree with what Ken had to say.

What I can tell you is that I used the sample program provided by Prosoft with very little modification. (I tweaked the size of the transfer between the module and the controller) I had to set up a command list in the controller to read each device and that was a bit ugly, but if the DCS is the master, you will probably not have to deal with that. The good news is that while the manual is going to be really dense, the tech support at Prosoft is very good. I suggest you discuss your application with them and verify that it is as straight forward as it seems. Then when you get your hardware set up, let them walk you through the checkout. They were very helpful to me.

Good luck,

Mike Ellis
 
Ken & Mike,

Thanks for the positive input. This was EXACTLY what I was looking for. I just needed to get a warm feeling about what to expect.

My biggest problem when these type of things happen is that I only see the control panel for a few days to program and simulate the operation. If I have a problem at the system integrator's plant (not the end user), I only have these options:

1) Figure it out fast (best option, of course)
2) Ship it, then get answers by the time the plant starts up, usually in three months. (potential with this to look like a fool)

I'm pretty resourceful, so I'll read the manual and stay armed with Prosoft's Tech support number. Realistically, I can probably defer problems to the DCS guys at the plant who spec-ed this.

Thanks again!
 
Instead of the in-rack Pro-Soft card, I suggest you take a look at the Prosoft 4102 stand alone unit. The in-rack units require some block transfers to get data into it. The stand alone unit reads the PLC and then copies the data into registers. A very simple set-up procedure takes care of the configuration. Then I give the SCADA supplier a spreadsheet or CSV file with the addresses he needs, the descriptions, and the engineering units and range of any analog data.

I usually use a separate file (File 90 is common) for data that is accessed by SCADA systems. That lets me copy the appropriate data into a contiguous block for efficient reading by SCADA, and lets me control how the data written by SCADA is used by my program. That also mimimizes the access of my normal program registers by a programmer of unkown competence.
 

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