Learn PLC Programming

www.tryplc.com is your home for find solid information to teach you everything you need to know about PLC .And if that wasn't enough we offer educational materials, articles and tips for the novice to the advanced programmer.

 

Useful link, but if I'm putting a computer anywhere near a boat I'll be using something a lot more powerfuil than a plc.

Tim B.

 

PLC Use on a Boat

Tim B,
PLC's come in such a vast range of capability and I/O count that they're both much more "powerful" than any other form of digital device FOR CONTROL; AND- there's a model for "every" application.

They can be conformal coated, potted, "hardened", enclosed in compact submersible environments and PLC's happen to 'run' every new propulsion engine sold, outside of China, in the last decade or so.

Tiny, ten I/O 'smart relays', as small as a PDA, costing a few hundred dollars can monitor simple systems at extremely low energy while the boat is moored or on the hook and you're away- and activate a dial-out or siren& lights for intruders or bilge alarms. These micro PLC's are an example of the huge number of products there are in the digital control marketplace.

Larger PLC's systems easily sequence large hp engines up through pre-lube and cold roll on past ignition, warm-up and ready to load states. Heck, our Ford SUV has a PLC that auto starts with a radio signal from inside the house and sequences the engine up and this New Years Day ('07) in Alaska its not warm. After run up and monitoring engine conditions this PLC keeps the engine revved or idled to optimize EGT, lube pressure, block temp and so on.

"Power" in a digital control, at least to me, means the speed with which an environmental event can be recorded, decided, and responded too- by the device. Interface or Human Machine Interface (HMI) is just screen ware- keeping the humans informed. Today's PLC's can scan several k input count along with accompanying logic in parts of a millisecond. No other digital controller is so 'unburdened' by conflicting priorities; so other types of computing devices can't compete for 'power' or control.

What won't happen from the very nice web page linked above is that anyone will be able to apply a PLC to their boat. That site focuses on control routine instruction, sometimes called programming, not system design.

The weak link in current knowledge is the I/O or sensors needed to let the PLC "what's happening" and correlating that suite of sensors and machine events into logic. That is why people don't buy new PLC's and apply them to engines monitoring systems, stability control systems, navigation or steerage aids, or safety systems: because the programming is the least of the knowledge gap.

I agree that PLC's won't be widely applied to small marine projects by non-production builders anytime soon, but its not because they aren't "perfect" for the many jobs on aboard. The reason is the education and experience required to apply them makes other methods more affordable, but eventually the embedded PLC will run the entire boat.

They (PLC's) will be networked as witnessed by the increasing use of marine on-board LAN's for all new 'smart' equipment. (Where the word smart simply means addressable on the network AND the ability to carry out the internal PLC's command structures) Eventually the engine will 'talk' to the fuel system, which will 'talk' to the nav system, and so forth. There will also be a screen(s) to keep the humans up to speed, but the PLC will be the basis for the entire system.

The networked organization will follow the industrial model of graceful degradation where the various nodes or PLC CPU's can fail without stopping the entire system and then redundant controllers will hot swap between clock scans.

All this improvement is following the industrial/military model of control growth and maturity of design reliability. All of it will be based on the vast number of models of a PLC just like it has in the cars we drive, the heating in our homes the telephone switches that control our communications, the commercial planes that fly us around, and defend the airspace, and the ships that haul goods around the globe and the plants that refine the products that define our civilization and built the computer on which we're discussing whether PLC's are "powerful" enough.

I know** PLC's are as powerful as needed, but I'm also aware that selecting the correct PLC for any give job is not simple given the huge number of choices available.

[**FULL DISCLOSURE: I design, build, and maintain PLC based control systems for oil and gas production automation, including digital control of anti-surge on gas turbine compressors where fractional millisecond controls response time is required.]

Cheers,
Kmorin

 

For monitoring and control, they're great. I need a computer that can do sums and display the answer graphically (with a great amount of detail). It also needs to run code that's scalable to a much larger system which may double as an entertainment system. A Linux-based computer is the obviuos solution. The smallest useful units I've found are at http://www.embeddedarm.com

Tim B.

 

Thanks Nuttaphong I'll check that site out later, had a quick look.

Boats normally run on a 12 volt system, PLCs (from my limited experience) 24 volt is the industry standard, although I have been told they will run on 12 volts but may not be reliable.

Also because 24 volts is standard, 24 volt solenoid controlled equipment is a lot cheaper that 12 volt, that's if it's available.

However Nuttaphong didn't mention using PLCs on boats anyway.

Carefull kmorin you could end up getting too many questions from yours truly about PLC programming.

 

PLC's and PC's and C's

Interesting discussion. Certainly PLC's have the reputation for solid big-job control. I've been out of the field for about 5 years, but even then there was a serious convergence going on in the PCL-PC area. Modern PLC's are typically a modern microcomputer with PLC software in ROM. And ladder-logic programming capability done in a graphics-intensive environment on a personal computer.

Since the area I worked in (Semiconductor manufacturing) was so data-intensive, lots of stuff moved to PC's pretty early.

But most big-ship propulsion and steering systems are PLC based.

The interesting question to me, with 'small' < 100 foot boats and small and home builders, is how to effectively combine these control and monitoring tasks (and human interface/display) in a modern onboard PC. It obviously CAN be done, but what's a GOOD way is a big question...

I'm glad to see someone talking about (Computer NOT CAD) here for a change!

I built quite a few control system using all relays, in the past (I'm Old!) and I still have a certain respect for the reliability of something built with a dozen or more relays, lights and buttons! And then there's all those relays in boxes in my cellar in Vermont...

I have a thread just started over in Collaborations on PC-based boat control panels, if you're interested...