I just started to evaluate some control systems for water distribution and water treatment systems. After my information the best way to control water treatment systems is to use PLCs and HMI like Wonderware. But to control distribution areas, it is better to use RTUs and SCADA Systems.

Is there anybody that can give me some information about the two combinations?

- Advantages and disadvantages about the combination of PLC’s and HMI.

- Advantages and disadvantages about the combination of RTU and SCADA Systems.

 

There is really very little differnce in the two methods. outside of having a local HMI at a pump station or small water treatment plant, depending on the brand of RTU you use (Motorola Moscad's are true PLC and RTU systems), you may only save money. I personally use Moscads, they are very relaible, and in a large 5 pump application a Redlion HMI is a great combination.

A tank would only require a level sensor and a simple PLC, but consider the cost of maintaining multiple manufacture's equipment in the field, simpler to go with one brand all around. In the system I help put in across Vail/Eagle Valley here in Colo. Motorola everywhere. In 4+ years, not one major RTU failure anywhere, great tech support, very robust, reliable operation and so many different methods to transmit data that it is really hard to beat. (UHF, 900MHz spread spectrum, fiber, RS232, RS485, trunked radio, VHF, satellite, TCP/IP, 900MHz MAS, dial up) you can put multiple CPUs at any RTU, distributed or simplex control, very powerful math functions built into every CPU.

It comes down to money and the investment the customer is willing to make for the long term.

In either case your customer is probably going to want a SCADA front end (Wonderware, IFix) so they can manage their system, collect data, perform alarming functions, trending, historicals and such. there is nothing that says you have to use HMIs and PLCs or SCADA and RTUs, you can easily mix and match as you please, an RTU here with an HMI, and a connection to a SCADA system, a PLC with a SCADA system connection there, or a PLC which communicates with an RTU that communicates with the SCADA, or a completely standalone system, no SCADA, just a hand full of PLC or RTUs and one or two HMIs. (did a system in southern Colo, that had 3 tanks, 1 well/pump site, there were 4 RTUs, and 1 HMI to run the entire system - has been up for 5 years, no failures or problems - all done over a VHF link).

Spend the time to understand your customer's needs, now and in the future, don't try to sell them something they don't want and install solid equipment. Back it up with rock solid technical/field support.

Matt Hyatt
Technical Consultants
[email protected]

 

Try Google. This was one of the first results.

http://www.synchrony.com/trends_SCADA.pdf

 

Keep in mind that HMI and SCADA are the same thing and a RTU is generally a PLC with a radio, land line or some other communication interface.

regards

 

Why not do as I normally do. Use a combination of PLCs, HMIs and SCADA systems. The best of both worlds. RTUs are generally not robust enough for industrial applications. PLCs are designed for the job.

Try http://www.citect.com. Excellent SCADA system that is used regularly in Australia with Omron PLCs (http://www.omron.com)for water and sewage systems. There are many very large system around here.

 

I disagree with the statement that RTU's are not robust enough for the job.. I have replaced more PLC's with Motorola Moscad (L and M products as well as straight Moscad's) in all types of applications in all types of environments. These are very robust pieces of equpiment. One water plant in Castle PInes took a direct hit (10 feet from the door of the plant) The only gear that was still functional was all of the Motorola equpiment. Enought said.

Matt

 

I agree with the fact that RTUs are robust enough. However i don't see what the big fuss is all about with the Motorola Moscad RTUs. I found them to be quite cruddy really. They felt cheap, sucked a lot of power for what they were doing, the software toolbox was awkward and the list goes on. I must admit this was quite some time ago and things may be better now but i was mainly unimpressed by them.

 

Well, like I said, I have put in more Moscad (Motorola gear) as replacements to all other PLC products out there. But to each their own. Oh, and Motorola has been making Moscad related gear for about 30 to 35 years. I don't think any other manufacture can make a statement like that in terms of longevity. The products have come a long way and with the superb computing power of a solid processor built in, well, just does not get any better. Plus they have the Full sized Moscad, Moscad-L and Moscad-M. The first two you can pick and chose modules for, the later is a smaller, light weight, predefined package, utilizing C based graphical programming structure.

Enough said - to each their own.

MJH