Values into logic from a SCADA system

saultgeorge

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Jul 2015
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Detroit
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535
Hi
I'm not busy enough here at my work, so I have time to write programs to keep myself up to speed. So I wrote a rather complex (I think, anyway) traffic light program from scratch in RS 5000 v.20.04. It has crosswalks, vehicle counts, left turn lanes, SCADA, faults and some other stuff. Now before all of you folks start hammering on me about no longer using PLC's in traffic control, I was wondering how back in the day or even now that timing presets, event programming sequencing, and receiving and clearing faults could be accomplished from a central SCADA headquarters. Would there have been a phone line? Co-ax cable? Ethernet? Radio? We had radio to our sites when I worked at a water utility, but it went into an RTU unit.

Lastly, if one wanted to send say a value of 20000 from SCADA to a specific controller, how would that value get written into a tag that would be moved into the preset of a timer in logic for example? Would there be an interface module from SCADA in the PLC rack? I think one could convert it then. I know all you folks are busier than I am, but unless I get more breakdowns, I have to keep busy. Thanks for any replies. :sleep:
 
Firstly, I envy your position. I'll send you some of my work!

I'm not sure how remote comms is done with real world traffic lights. Never seems like any intelligence is adjusting the timing here at least.

We do this in the water utility space using Ethernet and serial radio though. Typically there is a central master PLC that is polled for data by the SCADA. This PLC then uses timed standard message blocks to send and receive data at intervals ranging from every few seconds to every 15 or 30 minutes. For us The central PLCs are compactlogix and The remotes are micrologix 1100 and 1400s. For most of our sites we just reserve blocks of 50 words in and out. The radio networks can get quite complex as well deepening on terrain.

For systems using RTUs the methodology is similar, except the protocols used generally mean less programming is required to get communications working. E.g. DNP3 protocol, where the master is often a software application which can communicate directly with the field RTU without needing a hardware based master.
 
Not sure about other countries but in the UK most traffic light systems use a combination i.e. Induction loops, Sensors & cameras for controlling the traffic flow. Induction loops are most prevalent and can alter the timing based on traffic flow at junctions, there is also a time function I believe that during certain times of the day the timing changes i.e. 6:00-9:00 probably the busiest for traffic to enter towns & cities so the timing may be altered to keep the traffic flow going I think also these were built in but some could be altered remotely. I know in the old days many traffic control had telephone & modem interfaces so I suspect modern ones may use RF. It is unlikely that the majority of traffic lights are connected to allow adjustment as they are probably old, however, a friend of mine who worked on them told me there were some coming on the market that used sensors to detect if the bulbs failed (I think he meant if it was energised and no light then alarm). This I believe was used to send information back to central control.
The thing that really surprised me was the half sized cray computer that seemed to be used for a simple crossroads.
Not sure what you mean by interface module apart from some communications but most nowadays would probably use the in-built coms on the processor. As for timer changes there is no reason why the values could not be pushed directly into a tag used on the timer in the time format.
 
Saffra
Hi, thanks for the reply. I've always wanted to go to New Zealand and Australia. Send me an application ha ha! I noticed that you work at a water utility--I worked as an industrial electrician/PLC programmer for the Las Vegas Valley Water District from 2000 to 2010. Their SCADA used a radio signal, a "maintained call" as it were from operations to a particular site, and it went into an RTU unit through a Bristol-Babcock DPC 550 processor which sent a digital signal out to a relay in the cabinet and the contact closure sent an input to the PLC 5 that we used. I'm not sure how it did analog, but in operations they had a huge screen with all the sites showing level, flow and pressure, along with other statuses and disinfection info. Thanks for your reply.


Parky
I don't know why I didn't think of this: I could use the system clock to do exactly what you were talking about in your reply. Duh. And I already have induction loop inputs along with open sensor faults and such in my program. I know they use cameras in some of the cities out west; I know they did at the bigger intersections in Vegas. I'm sure now that you mentioned it the systems around here in the outlying areas of Detroit use a time-of-day based sequencing for inbound and outbound traffic flow on some of the major arterials. I did an extra credit study on traffic flow in university years ago. Not too much on controls for the hardware, but mostly inbound and outbound flows. I've gone "with the flow" around here to some customer sites and it works pretty good.


I really appreciate you two gentlemen replying to my question, seeing as how you're probably busier than me and you took the time to respond. I've got some more ideas now that I can implement when things are running good and I have time on my hands.
 
I have just retired and should have more time, however, the other half (AKA the wife), compiles a list of jobs for the day so no peace for me :rolleyes:
 

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