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Brews & Views Bulletin Board Service * Brews and Views Archive 2004 * January 29, 2004 * PID questions < Previous Next >

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Belly Buster Bob (142.177.84.205)
Posted on Monday, January 12, 2004 - 08:44 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

recent surfing on HERMS systems has convinced me I want one.
I have decided to adapt the idea off this site
http://sdcollins.home.mindspring.com/index.html

my question is regarding PID's is there any one unit better than the other? (for brewing) and what type of thermocouple works best?
Thanks for any help
 

Marlon Lang (68.218.229.99)
Posted on Monday, January 12, 2004 - 11:08 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

BBB,
In general, no one controller is "better" for brewing. It's like buying an automobile - they all get you home, but some do with in more style. In general, I would recommend one with a solid-state output for a solid state relay and one that accepts a thermocouple input. Usually, they will accept several flavors of thermocouple, but if you have to choose, go with ISA Type "K", Chromel-Alumel. Both alloys are based on chrome and are thus somewhat corrosion resistant.
 

Joe Sandlin (66.207.81.26)
Posted on Monday, January 12, 2004 - 11:57 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

BBB, I recently upgraded my HERMS from the simple RANCO on-off controller operating my solenoid to PID. I agree with Marlon, they all will get you there, but get the controller that you want, then buy the sensor to match it. I ended up with a RTD sensor and a relay output, but my valve only draws 20 watts, so relay arcing is not an issue. I just wanted the multiple ramp soaks so that I could setup a step mash/mashout and forget it for a couple of hours. When I automate my HLT, I'll not worry about those features, but will want alarms for in case the ignition fails, and SSR control. So just look for the features that you want for your application.
 

Marlon Lang (68.218.229.99)
Posted on Tuesday, January 13, 2004 - 02:58 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

An additional comment: I usually recommend thermocouples because they be cheap. You can get 50 feet of t/c wire for $20 on e-bay, then make a whole bunch of T/Cs to measure temperature all over your rig. But, if the controller of your dreams wants an RTD or thermsitor input, it boils down to the usual $$$ decision.
 

Walt Fischer (24.221.196.114)
Posted on Tuesday, January 13, 2004 - 03:05 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I agree...
I use a K style thermocouple in a 6 inch SS probe.
My PID is much more then needed, a $270 Omron....But since i stole it offa ebay for 80 bucks, it was the right price for me :)

Go for it!
Walt
 

Joe Sandlin (66.207.81.26)
Posted on Tuesday, January 13, 2004 - 11:35 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Marlon, how do you switch between your various thermocouples? I thought that TC's had to run directly to the controller, because dissimilar metals (like switches) threw them off. Not true?
 

Belly Buster Bob (142.177.81.11)
Posted on Tuesday, January 13, 2004 - 01:08 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I'm a bit lost on the thermocouples, Are they not probe style? How do you make your own?
I've searched the web and can't seem to find much relevent material on PID hookup for temp controlling.
 

TexanBrewer (63.174.45.1)
Posted on Tuesday, January 13, 2004 - 01:47 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

BBB,

Thermocouples are really the junction of two dissimilar metals. After buying bulk type-K thermocouple wire from e-bay, I made my thermocouples by striping a bit from the ends of the wires and twisting them together.

The other ends of the thermocouple wire are hooked up to the PID or reader. You do need to ensure that the wire is hooked up the correct way -- in the US, the red wire is negative.

---
Scott
http://texanbrew.com
 

Belly Buster Bob (142.177.105.225)
Posted on Tuesday, January 13, 2004 - 04:21 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

thanks folks, I use thermocouples all the time in aircraft engines but I really never knew much about them. I wasn't aware you could just twist Therm. wire together and Voila! How long will that last in immersed in wort?
 

TexanBrewer (198.64.161.66)
Posted on Wednesday, January 14, 2004 - 03:54 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I'd have to check my notes but I've been using the same twisted-pair thermocouple in the wort for about a year now.

---
Scott
http://texanbrew.com
 

Belly Buster Bob (142.177.105.243)
Posted on Wednesday, January 14, 2004 - 02:03 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

I knew I saw another seperate heat exchanger system somewhere. I want to build mine quite similar to yours Texan. I got the bug from another system, he really has some good arguments about the seperate heat exchanger. I read his article and immediately set out to start "The Scrounge". I 3 days or so I have my container, coil, heater element and a bunch of fittings. Amazing how the bug takes ahold of you.
Thanks for all I shall now go read you site entirely
 

Belly Buster Bob (142.177.8.96)
Posted on Wednesday, January 14, 2004 - 03:37 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Texan.....do you control the temp of your wort or the temp of your heat exchanger? I would like to control the temp of the wort exiting my heat exchanger. ...I think....maybe. Ebay seems to be the place for PID's
 

TexanBrewer (63.174.45.1)
Posted on Wednesday, January 14, 2004 - 04:02 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Ebay is the place for PIDs. Those little devices are very expensive new. You may also get lucky enough to find some thermocouple readers fairly cheaply. These little boxes are like thermometers that read the thermocouple input.

I control the water in the exchanger. I see about a six degree differential between the water in the the exchanger and the liquor at the mash return. The thermocouple from the PID goes into the exchanger water.

I've another thermocouple at the output of the return manifold reading the temperature of the mash liquor. This mash temperature reader does not control anything; it just gives me a visual confirmation of temperature transfer.

I would think your idea better -- put the PID's thermocouple at the point where the liquor exits the coils. (Oh man, here comes that whole argument again!) A PID is designed to do all the fancy calculus, etc. to control the temperature of the liquid it is monitoring. I'm kinda throwing away the PID's functionality by using it the way I am. Someday I may get motivated to change my ways but for not it works for me.

Hope this helps.

---
Scott
http://texanbrew.com
 

Belly Buster Bob (142.177.80.147)
Posted on Wednesday, January 14, 2004 - 05:44 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Thanks Scott, I've been reading alot on PID's and think they may actually be able to learn the ramp times and adjust so no overshoot if the therm. is in the wort output. I've a way to go yet but we'll see. I've created a monster, my wife once again thinks I'm over the edge.
Thanks for all the help, I'll be back for more I'm sure
 

Walt Fischer (24.221.196.114)
Posted on Wednesday, January 14, 2004 - 08:00 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Yea.. some pids use fuzzy logic to figure this out BBB...
Mine does :)

Walt
 

TexanBrewer (63.174.45.1)
Posted on Wednesday, January 14, 2004 - 08:04 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

After one of your Goldens, I imagine everything is fuzzy, Walt. :)

---
Scott
http://texanbrew.com
 

Belly Buster Bob (142.177.84.212)
Posted on Wednesday, January 14, 2004 - 08:32 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

hehe
 

Joe Sandlin (66.207.81.26)
Posted on Thursday, January 15, 2004 - 12:04 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

BBB, my PID was dumb as a box of rocks when it came out of the box. It didn't know if I was using a BIC lighter as a heat source, or a nuclear reactor. It didn't know whether I was trying to heat a cupful of liquid or a bathtub full. It was a failure trying to use it on my first brew, and I had to go to manual. That's where the tune function comes in. I tuned using the spent grains after the mash, and it learned what thermal mass it was trying to heat, and what BTU's it had available. After that, life was good...
 

Marlon Lang (68.218.228.105)
Posted on Thursday, January 15, 2004 - 12:41 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Joe,
Sorry about the tardy reply. There is a thing called the "law of intermediate metals". Suppose you connected the Chromel wire to a copper wire, and the Alumel wire to a copper wire, then used the copper wires in some sort of switching scheme. As long as the Cu-CH and Cu-AL junctions are at the SAME TEMPERATURE (e.g. ambient), there is no error introduced. This means you can mosey down to Radio Shack (NAYY), buy a bunch of SPST switches and rig up a multi-point system.

BBB: I've used a stripped/twisted-together T/C for several years. Works fine, looks great.

Please forgive the blatent self-promotion, but in the Sept-Oct issue of BYO, I wrote an article on PID tuning. I would greatly appreciate any feedback you fellows can provide.
 

Joe Sandlin (66.207.81.26)
Posted on Thursday, January 15, 2004 - 01:07 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Marlon, is the same thing true of my RTC sensor? Is the error negated with a purely resistive three wire sensor as it is with a TC? I don't know how much error is introduced with switching stuff from Radio Shack...
 

Marlon Lang (68.18.112.162)
Posted on Thursday, January 15, 2004 - 11:30 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Joe,
No problem with adding longer copperleads to your RTD. If your sensor is three wire, run one lead from the red and one from each white. If you sensor has only two leads, run one from the red and TWO from the white. Your controller should have three terminals for the RTD input. Clear as mud?
 

Belly Buster Bob (142.177.103.193)
Posted on Friday, January 16, 2004 - 07:12 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

sorry to keep going on but does type k wire have properties that make it better than "j" or "t"
 

Marlon Lang (68.18.104.56)
Posted on Saturday, January 17, 2004 - 12:07 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

BBB,
It depends on how you define "better". "K" uses chrome alloys so the wires tend to be corrosion resistant. Also, it is commonly available. On the down side, it has a lower mv/degree change. (Your controller won't care, though.) "J" uses one iron wire - it will rust and tends to be brittle. But, it has a higher mv/degree change. "T" is OK, but harder to find and usually more costly. All life is compromize.
 

Belly Buster Bob (142.177.105.229)
Posted on Saturday, January 17, 2004 - 12:26 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Thanks Marlon, just checking out my options. I've found some different sources for surplus wire and "K" seems to be the hardest to get.
 

Marlon Lang (68.18.104.56)
Posted on Saturday, January 17, 2004 - 12:54 am:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

BBB,
If you found "T" (Copper/constantan), that would be a good choice as far as corrosion resistance. I once found a 50 spool of "K" on e-bay for $29, but I just checked and the lunch box is empty.
 

Belly Buster Bob (142.177.95.216)
Posted on Saturday, January 17, 2004 - 03:16 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

Thanks for all your help folks. My PID is on the way (Ebay) and I have found a source for "K" wire,
$20 CDN for 25'
I'm on my way to HERMSVILLE!!!!
 

Jeff Chapman (148.64.20.135)
Posted on Saturday, January 17, 2004 - 04:20 pm:   Edit Post Delete Post View Post/Check IP    Ban Poster IP (Moderator/Admin only)

If your looking for assembled sensors reasonably priced, try Chris Cooley at CWC2337@aol.com or 321-453-0540. He's very knowledgable and prices are great. I got a Type J thermocouple with 1/4" x 6" Stainless Steel end for around $15. He also carries contactors, which I used instead of SSR's on my HERMS. NAYY

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