mreed

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I am looking at building a brew system and have been reading quite a bit about the different PID Controllers. I would like to use gas for the system, just my preference.
I have seen a lot of home brew systems built that use a PID controller with a gas valve. But if I understand correctly from what I have been reading, using a PID controller with a gas valve the controller has to be in the ON/OFF mode therefore only getting the benefit of the P in the PID. It will keep the temp close but always fluctuate a few degrees high and low depending on the width of the dead band.
The only way to get better control i.e. PI is by using a heat source that is variable like an electric element or a modulated gas valve.
Any comments would be appreciated.

Suthrncomfrt1884

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Because of the thermal mass in your mash tun, you really don't need to worry about temp fluccuations much. My PID kicks off at the exact moment it hits my set temp, but because of residual heat, the temp still reads higher for a few more degrees. It will kick back on as soon as I drop a degree below my set temp. Even though it may read 2 degrees high or low at any given time, the mash is always constant. It won't lose heat fast enough to make a difference.

Add in circulation, and you'll be fine. I monitor my temps through my PID, analog thermometers on my kettles, and a digital thermometer every 10-15 minutes. Other than my PID, everything reads exactly where it should be.

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Texan

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To "properly" take advantage of a PID loop to the application you are talking about you will need a modulating valve to give you a varying orfice for the gas to flow through.

The valves are not cheap.

The pricing for most of these I have worked with are way out of the budget for most home brewers, when a simple on off control will suffice as a much cheaper solution.

mreed

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Thanks very much to the two of you for your reply.

wubears71

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I'm starting to put together my all grain setup and this is one of my options I'm looking at. By the way I'm a chemical engineer who does automation and systems integration for a living. If I come up with something I'll let you know.

kenmunkholm

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If your PID has an analog output, like 4-20mA or 0-10VDC, you can do down the Maxitrol route.

The M4xx series valves are reasonable and then use a signal conditioner like an SC11-B.

This valve is not a shutoff valve, it goes downstream of a combination gas valve and has adjustments for minimum and maximum fire.

Check out pexsupply dot com for pricing.
I haven't purchased there, just using them for a price yardstick

bob12

Recipes 

See this post: http://www.homebrewtalk.com/f235/simular-solution-temperature-controller-proportional-valve-gas-369786/#post4617760