Proportional LP gas valve

[sea330]

This sound very interesting a LP gas valve 4 to 20 ma or 0 to 5 volts dc. model EPV-500B the only thing is if you order you need to specify nitrile O rings for LP gas. $ 400.00 seems reasonable to get the gas control we need for a gas fired roaster. Been looking for something like this for some time and not pay a $1000 bucks. Rich 
http://www.hassmfg.com/search.pl/1213638750-2927?keyword=1167
 

[Ascholten]

That is a typical 4-20 mA valve.
Price is pretty high.
Look at Emerson Controls.  They might have something like that for you a lot cheaper.  Many other companies as well.

You still need something to 'put' the 4-20 to it.  A PID,
I like Yokogawa, I know the guy and he gives me good deals on them since we order a lot of them at work.
You don't have to get a full blown PID you can get just a temperature control device.  Ohmega I think is a brand, im trying to remember the cheap ones we use at work, not cheap as in crap but cheap as in simple and not the 800 dollar full blown programmable etc etc.
still need an RTD too to drive the PID to drive the valve.
Also you will need a power supply for this thing, 12V or 24V, even though they say it is dampened and filtered.  Using a crappy power supply is going to cause you a ton of grief with noise in the long run, so no a battery charger is probably a BAD idea... another 70 bucks.

At 4 ma it will be 'off' (or 20 depending on how you set it up) that would put your flame out so you will need to 'tune' it or have some kind of pilot light port on it.  First time it over runs on temp poof you will be relighting it.  Not something you want to fiddle with in the middle of a roast.

Finally BTW,  4-20 mA becomes 1-5V with the addition of a resistor  if it is a hastle to 'swap' it once you get it.

You are still spending probably 600 bucks or so when you take all this in.

Aaron

[jano]

Couldn't you just hook up a strong servo to a manual valve? That should do the trick...  And then, in line, you can put a little pressure sensor inline, and create a circuit to get the limits of the pressure and convert to voltage range of your data logger.  Ooooo.

[sea330]

Don't think I would care to go that route, i would prefer to get a valve designed for controlling gas flow. My Watlow pid temperature controller has 4-20 ma output and 0-5 volt dc output, it would be easy for me to calibrate the valve. I run a 2 kilo Ozturk roaster all manual, it would be sweet to have temperature/gas flow feedback control system.

I have been retired for almost 10 years from a Airspace company up in Seattle as a process control tech, specialized working on precision controlled autoclaves and ovens. Thank god I kept most of my documentation and training aids from all the schools I went to.

Rich 

[Ascholten]

If you are I and C then the 'tuning loop' thing is old hat to you, I will not go further into it.

Just a friendly reminder though to set your 4mA or 20 if you are reverse acting with enough 'open' on the valve to keep the pilot lit.  This won't be the full on full off we are used to when calibrating positioners.  Oh and if you are getting really geeky, it's gas / fluid flow don't forget to root it if you are going to go that extreme route.. ok ill shut up.   Have fun! 

Aaron

P.S.  The Watlow PID's are pretty easy to set up and tune.  the 93's are pretty good base units to start with.

Aaron

[sea330]

Most of the stuff I have worked with is Maxitrol, Barber Colman, Honeywell, Watlow, and Allen Bradly, Honeywell PLCs, really high end stuff. Started out in the ET shop repairing Motorola radios after about a year an opening came up in the process control world,  loved it, found my calling. Hated to retire but the golden hand shake thing made it impossible to turn it down. 

[Ascholten]

We use a lot of the allen bradley stuff at work.  SLC 500 mostly but trainsitioning to the newer stuff which means they are essentially throwing away the old stuff.  I already got a bead on that!!

For positioners the Siemens PS2 is good too.  I like them at least.

Watlows are good.

Motorola Radios, oh don't remind me of those thing, give me nightmares.  Ill stick with my yaesu thank you

Aaron

[sea330]

I loved to work on the old Motorola analogs, they were fun to work on, at least you could repair them board level, the newer ones all you could do is replace mother boards, plug them into a programmer, you were done, no challenge there. Ah PLC5s and slick100s and 500s they were cool, spent many weeks in schools, a couple analog modules, some I/O you could do almost anything, very slow scan times but reliable as hell.     

[Ascholten]

Yah, we have the digital motorola's  they suck.  I loved the analog ones as you said, built like a tank and you could 'tweak' them very easily to do what you wanted.    The SLC's not too slow, well compared to today's world I guess you could call them slow but work horses for sure, when you consider you could take just about any type of input you can think of, 'ladder logic' it into anything you needed basically and go out with it.  Rugged unless you done something stupid like short circuited across a 120V output card or something, then you burned the dry contacts and had to replace the card.

We are going to the newer siemens PLC's which are ok but not as I guess you could say 'open' as the SLC's were, so can't play as much.

We had an 'alarm' hooked up on one circuit I remember, a photo snesor down the path way that if it was broken it would turn on a fan, a loud fan.  When the boss came creeping up the fan would come on.  (for obvious reasons a normal alarm would not do, it'd be like WTF is that for?)  ahh those were the days.

Aaron