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Should I use a PLC for this? I want to install a simple valve regulating system for a fuel oil purifier. I'd like to install 3 valves-one for throughput, and one each to discharge to each of 2 diesel day tanks. Throughput is the amount of fuel going through the purifier. I can use the day tank electronic level gauge signals for inputs and I want to regulate and control the amount of fuel both going through the purifier and to keep the tanks at the same level regardless of what equipment is being used (boilers, generators, main engines etc.) Currently the oilers are always fiddling with these 3 valves and I was wondering if a simple PLC with programming would be the way to go. Advice?

anonymous said:

Should I use a PLC for this?

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Perhaps your question should be "could I use a PLC for this?" rather than should, because the answer to the 'should' question is "that's up to you"

Now, the answer to 'could you use a PLC for this' is yes, of course you can.

A small brick type PLC will probably suit this application, (I won't recommend a brand or type as that will open up the debate to "so and so's PLC are better than that PLC").

Originally posted by anonymous
I was wondering if a simple PLC with programming would be the way to go

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As far as I am concerned (others may have different views) automating any process is the way to go, that's what keeps me employed!

Paul

I guess I should've asked if there was an easier way to control a simple process such as this. If I buy a little PLC (brick, as you called it), I would need to buy programming and analog input and output accessories etc. I think I saw something in a class one time that was like a PID? controller or something. I'm a real novice at this stuff, but am hoping to learn something and in the meantime avoid this little chore of constantly regulating these 3 valves. I would also like to hear anyone's advice on what a good, cheap PLC would be for this job. We have a SLC504/c for propulsion control on here and some Siemens S7 PLC's for our telegraph commands and logging. These, of course, are way expensive and overkill for the small job I'm talking about. I see in my Newark catalog several types but have no idea which one to choose or which is easiest to write a simple program for.

Since this is a small scale project, AND you're new to programming, you might want to look into a programmable relay. Newark sells the Moeller 'EASY' (though you can get 'em cheaper than Newark's selling 'em for). HERE'S a link to the EASY overview page. You can download the manual for the EASY HERE to see what you're getting into.

You don't realy need software for these. You can program them right on the front panel. I used one not too long ago as a simple shift register, and it was quite simple (er, I mean 'Easy'!) to use.

Sound like a 'real' PLC would be overkill for you application, but it's up to you...

beerchug

-Eric

Thanks, Eric.
I read thru the Moeller info quickly. Wouldn't I need to be able to position the valves with analog output signals. It didn't look like the Moeller Easy Relay had analog output as an option. I'm looking for something that can adjust valves over a wide range of operating conditions, depending on fuel usage. I found some valves that would work in a Johnson Controls catalog that are positioned with either 0-10 VDC or 4-20 mA. Is there a way to get an output relay to step the valve open or closed in small increments.
I also see a thing made by Newport that's called a PID Controller that has optional analog outputs. Maybe that would be a way to accomplish this little job?

You could accomplish this with the PID controller and a few relays. In fact, it might be less expensive than a PLC the first time around. However, any changes or upgrades would require re-building the panel and would probably be more expensive. I think a small PLC like the AuomationDirect.com (ADC) DL-05 or an Allen Bradley MicroLogix would be a better way to go. The ADC has PID capabilities if you need it for the valve control - some MicroLogix's do too. You can even add a simple inexpensive operator interface and get a lot of diagnostics info that you can't get with a controller and relays.

Thanks Tom, that's the best constructive advice I've gotten so far. I'll probably go with the Micrologix stuff as I've had a little experience with it at a programming course on the SLC 500 stuff. I'm familiar with RSLogix, and I would guess all the A/B stuff can be programmed with that, which we already own a copy.

Hi anomynous,

You are saying that you already have several PLC's (SLC504/c, Siemens S7). Why don't you use one of those PLC's and integrate that small piece of code into one of them?
You only got a small amount of I/O, only the distance from the PLC to the tanks could be a problem.
Otherwise Siemens have a small PLC S7-200 and they sell it as a starterkit. It's rather cheap and the programming software is included. Just a thought.

Kind regards

Hi anomynous,

as Tom Jenkins said you can use PID controller for this process many process controller manufacture have a special version for valve control with selectable analog output and position feedback inputs .here is a link for such controllershttp://www.gefranonline.com/ing/prodotti/strumenti.html

Thanks to everyone for your help. This site is awesome...I had no idea that I would get helpful responses from all over the world. My background is in marine engineering and most of the time I'm doing more mundane things like rebuilding a diesel or welding or fitting pipe etc. etc. Most of my electrical experience is with 480 VAC 3 phase motor controllers and 1000 volt DC motors and 500 VDC generators. Electronics, PLC's and all are a little intimidating to most of us on ships, so I appreciate you all being patient with me. We always try to go by the KISS philosophy (keep it simple stupid), so I wanted to do this with the easiest method and the PID controller will do just fine from what I've read. The fellow from Belgium is right in that we could use one of the other PLCs to handle this job, but we are on Coast Guard inspected vessels and if you alter the propulsion program, you better have a damn good reason for it, especially if you screw something up--so I'm not going to mess with either the telegraph/throttle plc or propulsion plc programs. Thanks again...I'll be spending more time on this site trying to get more comfortable with these magic little boxes.

anonymous,

I agree with Tom Jenkins. For your fuel valve regulating system, I highly reccommend the Automation Direct DL-06 (about $200 depending on which model (AC, DC, etc) that you buy). It has 4 add-on slots, for which you can get analog input and output cards. There are different analog cards available, but a 2-In, 2-Out sells for $149. So for about $500 in hardware, software, and cables, you could do your project and learn some stuff to boot, and have the software left over for future changes or other projects!