I need to design a data acquisition system for a ground fault detector. Does anyone have experience working with the SCADAPack series RTUs/PLCs from a company called Control Microsystems? Several RTU/PCL units will measure electric currents and alert operators in the event of a problem. Communications between master and slave will be acomplished using RF or cellular radios.

Any recomendations on what sort of technology/equipment/manufacturer to use?


Thanks,
William Sanchez

 

They appear to be quality equipment that is competitively priced. I have not used it myself, but have seen it and have had several good
reports on it from trusted users.

I have used RTU's from a company called Rugid Computer in Olympia WA that I have found hard to beat for the price. I like National Instruments Lookout, Intellution Fix, TA Engineering AIMAX, CiTech and Green Leaf Systems Harmony for SCADA software. I like MDS for radios, but have also had pretty good results from EF Johnson and Motorola.

 

I have used Control Micro with great results. Equipment is rated up to 158 F and boards are sealed to prevent H2S or othe gases from
attacking the boards. Programming is ladder logic based on Modbus or Allen Bradley protocol.

 

William,

We are using the SCADAPack units here as RTUs at our wastewater pumping stations. We use the Modbus protocol to talk back to the Intellution Paradym-31 PCs. We are using store and forward on 450 MHz frequency to update info and provide control when necessary. The PLCs work are realiable and we are capable of remote downloads from the plant.

I can give you more details directly if you want them.


Thanks,

Robert J. Dusza, Jr.
Treatment Manager
(V) 1-860-647-3219
(F) 1-860-647-3150
E-mail - [email protected]
Manchester Water & Sewer Dept.
125 Spring St. P.O. Box 191
Manchester, CT 06045-0191

 

Will,

I've used their products for a number of years and have been very pleased. Very reliable.

In addition to ladder logic, the Scadapack can execute custom C programs concurrently. The required compiler is a significant extra cost but allows you to do almost anything with the unit. In my case, I used it to replace the standard Modbus protocol on one of the comms ports in order to interrogate another serial device.

One thing I really appreciate is their programming software Telepace (for ladder logic). Since it also uses Modbus, you can use the same
communication link to make program changes without visiting the site. (This includes monitoring rung execution online) The beauty of this can be seen in the following.

I had developed a program to monitor a sewage lift station. Wetwell level changes and pump drawdown rates were used to calculate an inflow rate and accumulate flow totals. This was somewhat difficult since I only had integer instructions to use (or so I thought) and accuracy was not what I would have liked. I ran into a Control Microsystems rep. at an ISA show and lamented the lack of floating point instructions. He looked surprised, handed me a new version of Telepace and said to use the online
documentation for the new features. (Thanks Alan)

That afternoon, I was able to call the host system (NT running Lookout for an HMI) with PcAnywhere, load the new version of Telepace and edit the Scadapack program online to use floating point instructions. The entire process took less than an hour including learning curve and on line
monitoring and testing. Both the host and remote sites are a 3 hour drive from my location. Any mechanism that reduces what we've come to call
'windshield time' is very, very beneficial.

As far as communications are concerned, the 3rd port can be set up as a dial up and init. strings supplied, so cell shouldn't be a problem. We've
also had success with spread spectrum modems from Freewave (Boulder Colorado) if distances are moderate.

As for your specific application I'm not sure what you need. I don't really know what monitoring devices might be available today. Many years ago we needed to maintain a common logic ground reference to all mainframe computer components separate from frame grounds. (ground loops and all that). The technique for detecting a short between frame and logic grounds within a cabinet involved injecting a low voltage AC current with a frequency unlikely to be present in the system on a ground connector (ie 59 Hz or may 39Hz. ??) A clamp on meter was used with a filter tuned to that frequency to detect the presence of that signal elsewhere in the system.
Basically, all the current you inject goes somewhere. If you don't have any current at your test point, you don't have a path. If you don't see all the current at your test point you have multiple paths.

As I recall the equipment was quite simple considering it was in pre- integrated circuit days.

Regards,

Bob Lockert
Blocke Communications
Calgary, Canada