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PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
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Discussions > Espresso > Machines > PID versus HX...  
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calblacksmith
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Posted Fri Jan 6, 2012, 6:52am
Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
 

JGG Said:

I welcome correction on this, but I think you actually want the temperature probe in the steam.  The heat transfer characteristics of steam are superior to liquid water, so the probe reacts more quickly to changes when it is "embedded" in the steam.

Jim

Posted January 5, 2012 link

Interesting comment Jim, I had not thought of it quite like that. It is something to think about when I rework a HX machine I have in my shop that needs a Pstat (a personal machine and it has been sitting for over a year now, who knows when I will get to it LOL)

It has a horizontal boiler with removable side plates. I just may drill and tap a hole for a temp probe that I have which is based on a 1/4" pipe fitting and is a one piece SS waterproof unit. It should be able to withstand the pressure in the boiler. The only reason I am even considering this PID mod is because I already have the temp probe (I was going to make a chocolate tempering machine using a water bath) and the PID unit, and SSr, thus saving me the cost of buying a new Sarai Pstat.

So by placing the temp probe in the saturated steam, it will respond quicker than in the water but I suspect, not quite as quickly as a Pstat which senses pressure but I could be wrong on the idea of response time.

 
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Coffeenoobie
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Coffeenoobie
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Posted Thu May 10, 2012, 12:39pm
Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
 

frcn Said:

The PID would control the temperature of the boiler water in a HX machine. But the water in the HX is indirectly heated by the boiler water, and the group s located remotely from the boiler (particularly win regards to thermosyphon machines), the benefit of the PID in a HX machine is minimal. It would give more precise stability of the water in the boiler which may or may not translate to better control of brew temp, at least at the beginning of the extraction, but the benefit there would be minimal, and controlled to a great extent by the machine's design and engineering. Te major benefit is the elimination of the arcing contacts of the pressurestat, but that can be done by adding an SSR between the pressurestat and the heating element anyway.

The difference in operation is that the pressurestat has a range of operation heating for a period until the pressure rises to a predetermined point, then when the element is de-energized, cooling through the dead band to repeat again. A PID can hold a given, preset pressure, and thus temperature. But again, the benefit at the coffee is minimal if not questionable.

And, technically, HX machines usually have a pressurestat and not a thermostat (See THIS article).

Posted January 3, 2012 link


What is an SSR?

 
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wsikes
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Posted Thu May 10, 2012, 1:04pm
Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
 

Hello Helen... I wondered the same thing for a while... SSR=Solid State Relay
I hope you don't feel as stupid as I did when I found out what it was... lol.

 
Bill
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Coffeenoobie
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Posted Thu May 10, 2012, 1:20pm
Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
 

Yes I do feel stupid that I did not guess.  But I have no idea what relay that would be and if it is a cheap part I might do it when I next tinker with my Oscar.  Hopefully soon - I want to add the vacuum breaker.

I was taught in school to spell something out the first time then after that you can shorten it.

 
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wsikes
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wsikes
Joined: 3 Oct 2011
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Location: West Virginia
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Grinder: Promac MD-64 AT
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Roaster: Behmor
Posted Thu May 10, 2012, 1:29pm
Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
 

I'm thinking about adding a PID to my little old Saeco Aroma... it's working so well I hate to get rid of it so soon.  May or may not do the mod... just in the thinking stage right now.

 
Bill
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Coffeenoobie
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Coffeenoobie
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Espresso: N S Oscar
Grinder: K30 & Vario W
Posted Thu May 10, 2012, 1:39pm
Subject: Re: PID versus HX Machine Temp Management- Shouldn't End Result Be The Same?
 

I was only thinking about it because I thought my pstat was going out and I thought about getting one with another input that would let me see the group head temp.  Turned out it was a plastic safety valve that was faulty so I am not doing it right now.  I am still  thinking of doing the musica restricters but I have not found anyone to be able to explain to me how it will affect my espresso other than to shorten the cooling flush and flatten out the temps on the pull.  I am not expert enough to know what that will do to the taste of what I am getting now.  The parts are cheap so I might do it anyway, I can always pull them off if I don't like it.

 
Coffeenoobie

Buying advice: GRINDER GRINDER GRINDER. Don't cheap out on the grinder.

My coffee treasure map...
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Oscar trick out: http://s156.photobucket.com/user/GandBteam/story/14231
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