PLC logic and Scada Control

Hi I'm new here. Setting up plc control and interfacing via scada .
Most basic scada packages for the pc are not recommended for critical or complex control , I have many questions in this area, one is how do I go about interfacing a basic plc via a VB6 SCADA (to be written by myself when i learn how ) to update the set point of a pid loop , put the loop in manual and back to automatic mode ? My thinking is that a basic old plc like a hitachi 200 series would be difficult to achieve this from a vb6 self written scada interface. By the way even the simple routine to update a digital output seems difficult to me as the plc also controls the same output what is the mechanism exactly one could use to achieve "seemless" transition of logic wether it be induced by the plc code itself or the vb 6 scada code.
I am thinking to get an off the shelf scada package, but the same issue will be present that way too, as i would still need to know how to transfer setpoint settings, auto manual etc without upsets , has anybody done this with vb and a basic plc.
thanks so much in advance for help on this.

If you want to Use VB6 to develop a SCADA software you will have to think about the communication between Your software and the PLC

For me :
I use an OPC server and OPC clinet to handle the communication ..
and yes It is Expensive , but not in the big projetcs .

I did that with Siemens S5 928-135u

And if the points that will be read from the PLC are not too much , you may search for a plc that can send/recieve simple ascii characters and use it ti send/recieve your set points and instructions to/from the PLC

I know two PLCs that can do this :
1- NAIS (i forgot the series name)
2- triLogi PLC ( www.tri-plc.com )
the last one is cheap and very useful and supports Modbus Protocol.

best regards

Do a search for SCADA, OPC, and VB on this forum. Should be lots of info.

Basically you have to write your plc code with an HMI in mind, ie
you have a rung where input-1 energizes output-1. If you wanted to be able to engergize output-1 from HMI, you would have to add a jumper around input-1, and use "bit-1" to engergize the output also.

input-1                          output-1

----|  |------------------|------------(  )-

                          |        

              bit-1       |   

  ------------|   |-------|

Why re-invent the wheel? There are so many SCADA systems out there that it is not funny. Most of them can communicate with almost anything.

As you are in Ozz, have a talk to Citect and perhaps Automation Systems. They both have offices in Melbourne and would be able to help.

I have used Citect with networked Omron, Siemens, Hitachi PLCs and Modbus to Wormald fire panels and BACnet to Alerton BMS systems. Have written to all of these with Citect, although it is not cheap.

If you are looking for a cheaper solution, Automation Systems could sell you Omron PLCs and Omron CX-Supervisor. You buy the development package once and then only have to buy a run time licence each time you use it. Works out quite cheaply that way.

Just bear in mind it is not a Citect and no where near the price but has unlimited tags and supports OPC to anthing else that can support OPC.

You also have a choice of using CX-Supervisor script language or VB in the project.

Hope this helps.

DIY SCADA

If you want to do your own SCADA system try DELPHI, it is a lot easier than VB and I use the AB ethernet TCP activeX control from these people Automated solutions

I have written several applications from a HMI to a SCADA program that is licence free and portable to any desktop PC on our network.

Well, yes it is true that developing a SCADA system Using a programming language is more Difficult than Packages and may require more time BUT:

If you are already a visual basic programmer (intermediate is OK)so why not ?
Use your skills to save many hundreds (may be thousands) of dollars -especially when you are going to design a SCADA system for a small project - and save your time as you already know how to write a program in VB.

That's my openion

I don't understand why so many guys want to roll their own SCADA. I did it many years ago (DOS and Q-Basic) and it is a daunting task. When I did it I was just starting my business, had lots of time and no money, and the only packages available were several times the price that SCADA packages are now. Operator expectations then were low, so I got by with character based "graphics" and no trending and very little archiving data.

I'm still not convinced it was the right decision. At the time I thought I could use the same system over and over, but technology changes and needs change and I only got three plants out of the system, and each of them required a lot of modifications.

If you figure $30 per hour and you can purchase a SCADA package for $2,000 (at AutomationDirect.com Lookout Direct is priced less than that) you have a week and a half to write your comm drivers, write your application, test it, debug it, and get it operational. That is a tall order, particularly since Windows is harder to work in and expectations for graphics and data display are much more sophisticated.

If you buy an ActiveX or OPC comm driver your development time goes down, but your price goes up.

True, you have to spend time configuring SCADA screens, but with a good package you can do a lot of configuration in a few days.

Unless you have a lot of identical systems or you work for free it just doesn't make sense to me to develop your own application nowadays.

Tom Jenkins said:

Unless you have a lot of identical systems or you work for free it just doesn't make sense to me to develop your own application nowadays.

Click to expand...

I agree 100% with Tom. I'm a firm believer that if an off-the shelf package has the functionality that you want, you won't be able to "roll your own" with nearly the same completeness and/or capabilities. I also believe that whatever you do make will cost you more in labor costs than the purchase cost of the off-the-shelf package.

Unless you have time to kill, you can use the system MANY times over, or the functionality that you want doesn't exist, it will cost you more in development labor than any SCADA package will cost you to buy outright.

Marc


PS: If you propose to develop the SCADA for outside use, don't forget to factor in liability and/or support costs too!

To add a little more, Tom mentioned the price of the Automation Direct package. This would equate to about $4000.00 AUS.

Omrom CX-Supervisor, with unlimited tage, costs about $3500 AUS for the development package. Each runtime is about $1500.00.

If you wish to fiddle about with VB then you can within the package. BUT, the basis is there and will save a lot of time. Trending is not as good as Citect, the best trends in the business, but is fairly complete.

I have used it for collecting and trending data for generators, mains power, water usage etc etc. The first time is a little tricky, as with most packages, but support is excellent from Automation Systems and they were able to help me out a lot. The clients are happy, that is the main thing.

The last one I did had an Omron CJ1 PLC collecting data from a Si-TEC CGC generator controller and an IME power monitor by way of Modbus RTU, water meter pulses and flow rates via digital and analogue inputs. Modbus is very easy with CX-Protocol, as are all serial interfaces. The SCADA then collected from the PLC. SMS messaging was also implemented from the PLC serial port using a Falcom GSM modem. Works a treat.

Maybe i will recognize this fact when i become older, as Tom said : (( I did it many years ago (DOS and Q-Basic) and it is a daunting task. When I did it I was just starting my business, had lots of time and no money... ))

but i think that the capabilties that i can get from VB is more than packages (Am i right?)

And aslo i can write (modules) and (functions) in VB that i can use from now and ever beside that i use active x controls for trending and visulaizing the processes (pipes,tanks,pumps...etc)
So with these active x controls the life is so easy.

And i think that you all agree with me that developing your own SCADA is the best choice when you are in small projects.

Ayman

I fail to understand how you can think that you can get more capabilities by using VB than companies who have numerous people doing nothing but write code for upgrades to SCADA systems.

For example, a company may have two or three people doing nothing but write drivers for different things.

When the Citect driver for Omron FINS Gateway first came out, I was a beta tester for that driver. I was having all sorts of problems with incorrect data being returned etc etc. the other beta testers were not having a problem. It turned out that they only had very small projects. I had a project with 8 networked PLCs all over a large office block with thousands of tags. The end result was that the Omron FINS Gateway software was not returning the data in the same order as the requests were sent from Citect and this was causing the problem. They had to place a header on all messages to identify the replies. I can understand this as there were different distances, some quite long, to the PLCs. Also, Omron Controller Link is a very reliable and robust token ring network. A request can only receive a reply when the device being addressed has the token. I doubt very much that you would have the time or resources to address a problem of this nature.

When you consider my premise that the Omron CX-Supervisor package has unlimited tags, OPC to everything and is very inexpensive, I doubt very much that, if you look at it realistically, you could develop a package with the capabilities of that, or any other SCADA system, at anywhere near the cost of them. If you require a special driver for an existing package you would be looking at a high cost just to have ot written for you.

There are other low cost packages around as well.

BobB:

As i said before, maybe when i have less time and become a big Sy$tem integrator i'll leave this choice.

But i think that there are some points that must be cleared, When Iam saying that using VB or SCADA is better than using packages :

1- I didnot mean that iam goning to write the harware driver, of course not , this seams like a nightmare to me.
I use an OPC server and OPC client active X control for communication handling.

2- all thr major functions that SCADA system must provide i purchase active X controls for it, such as Trending, visualizing (pipes,tanks,pumps .. etc)
Expet the Alarming and historical data functionalty, I build this from the scratch ONCE and i used it over and over again.

3- I donot have to pay a per installion fees for VB (only paying for OPC server and some runtime lisences for Active X controls)

4- Coding is very simple, Yes it is large
(for example i wrote 15,000 lines of code for a 400 point project)

BUT It is identical and similar.

You kno what :
when Iam writing these post i think that you are right ( i mean 15,000 lines of code for 400 point is a very big disadvatge that cannot be neglgable !!)

and of course time = money.

May be i have to look -deaply- in SCADA packages.

Thanks for replies.

especially when you are going to design a SCADA system for a small project - and save your time as you already know how to write a program in VB.

Ayman
I agree with you ,4 years ago when we decide to build our own SCADA in one of our small projects we saved a lot of money,We wee have the OPC client/Server and hire a part time programmer to write the code.we spend alot of time to draw the screens but we saved about 2500$ in this project

Unless you have a lot of identical systems or you work for free it just doesn't make sense to me to develop your own application nowadays.
Nowadays and after about 10 Own scada we have built in this period ,it's very easy for us we build also our own controls & Trends ,the hired programmer in our first project is now our IT manager and i didn't take more than 3 to 4 days to buuild our own tested SCADA.
I think nowadays it's better for us to build our own SCADA system it saves money and time.
Best of luck.

(Alsalam alikom) hesham,

Iam glad because iam hearing from you..

And yes you are right,

Customized SCADA system is the best choice for small projects if and only if you already KNOW HOW to do it.

Thank you all of making this subject reach of ideas.

ayman metwally said:

Customized SCADA system is the best choice for small projects if and only if you already KNOW HOW to do it.

Click to expand...

I don't agree with this as written. I stand by my earlier statement (whether you "know how to do it" or not)

Unless you have time to kill, you can use the system MANY times over, or the functionality that you want doesn't exist, it will cost you more in development labor than any SCADA package will cost you to buy outright.

Click to expand...

Marc