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10/18/2020 3:27 PM
How was the Uganda Bugisu Ken?

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Lets Talk Thermocouples
jkoll42
I wanted to see what people are using for TC's. I've been using TT-K-24 wire (24 AWG Type K PFA insulated) for many years because it was easily routable and rated to 500F so I didn't have to worry about contact w/ a fully heated chamber. I've done a simple end twist and mechanically crimped the twist. It has an extremely fast response rate.

My issue has been that over time they fail either at the bend taking the stress from the beans or at the twist end from constant bean battering. Of course the failure happens out of the blue in the middle of the roast like last night.

My thought was to switch over to a K type probe style - anyone have any thoughts or experience? The last time I ran a probe was when I first started roasting with the Poppery I probably 20 years ago and it was analog! I'm OK with losing some response time and was also thinking it might smooth out the ROR readings.

Jon
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
renatoa
Confused, not sure what you are actually using... TT-K-24 wire for what ?
Wires are just wires, their purpose is to connect or extend, don't measure temperatures by themselves... you should have a junction inside roast chamber somewhere.
A Junction, inside a sheath, connected to wires, is what you are calling "K type probe style", so switch over from what ?
renatoa
Back to your original question: I am using exclusively naked thermocouples, like this:
https://www.amazon.co.uk/sourcingmapÂ...B005DJRAYC
...just junction and wires into glass fiber cloth.
No metalic shielded cables for me, too many issues with TC shielding over the years.
All sheath are custom for my setups, those of retail TC don't give good results.
They aren't bad, simply they aren't for the task of the actual setup I am building.
That's because the sheath is a very underrated part of the TC, while it is the most important, ensuring the proper heat transfer from measured environment to the junction.
There are a lot of coffee roasting writings about the importance of probe diameter, when actually they should be instead about how to (not) choose the right sheath for the right job.
Just an example, check attached picture. This was tube of a standard sheath for the chinese TC sold everywhere, as a combo with a PID controller and a SSR.
When used for air measurement at the exit of a hotgun, I can't get more than 220C degrees when unmodified. After cutting the slots you see in the picture I can finally read the 300 C degrees proper and real temperature.
That's because an air probe sheath should look as below:
https://www.tegam.com/wp-content/uplo...-Probe.jpg
renatoa attached the following image:
cust_sheath.jpg
jkoll42

Quote

renatoa wrote:

Confused, not sure what you are actually using... TT-K-24 wire for what ?
Wires are just wires, their purpose is to connect or extend, don't measure temperatures by themselves... you should have a junction inside roast chamber somewhere.
A Junction, inside a sheath, connected to wires, is what you are calling "K type probe style", so switch over from what ?


It's Chromel/Alumel TC wire. The "junction" in the RC is the twisting and pressing of the two stripped ends. You can also high current weld them to produce a bead weld. That produces what you described as a "Naked Thermocouple" but out of much higher quality wire and sheathing than the amazon link. Also you can make it to whatever length you want. I would link the Omega link for the wire and stress relief connector but their site is down.
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
renatoa
Got it ! DIY thermocouple Grin

If you think this solution is better than the commercial factory built, then why switch ?
allenb
Hi Jkoll, hope things are going well with you and family.
So, you've been using what I typically use, a twist your own TC without a weld which has served me well for many years but you're right that they can be a pain if they are bobbled around a lot by the beans and break during a roast. Shock

I tend to agree that using a factory made TC with as small a diameter sheath as possible for keeping lag time small is a better option since as you stated, it prevents non-relevant RoR readings from being read. Unfortunately, it's such a zoo out there with zillions of possible options, not sure I'd be able to make a selection without drinking lots of cups of coffee. Just be sure to keep the sheath long enough to prevent outside ambient temperature conduction false reads.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
jkoll42
So I took a chance on the below linked one on Amazon since I had the same thoughts you did Alan. It's 3mm and has a pretty neat setup where you can adjust the position of the 1/8 male NPT anywhere along the probe. Figure I will just attach a 1/8 brass FIP coupler to the outside of the RC and can mess with how far I extend into the bean bed.

I think it should be a good unit since it's using actual nice connectors, wire and one reviewer said it was showing +/- .1C from a calibrated TC they had access to.

Should be here this weekend so we shall see!

https://www.amazon.com/gp/product/B07...&psc=1
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
CK

Quote

jkoll42 wrote:

It's Chromel/Alumel TC wire. The "junction" in the RC is the twisting and pressing of the two stripped ends.


This is a great idea for a quicker response to my ET thermocouple. There's no issue with beans bothering it in the hot air inlet pipe.

I have some Chromel/Alumel leftover from cutting a k-type thermocouple lead wire to a shorter length... happy to have kept it instead of tossing it.

Any tips on how many twists, or how long of a bare section? When pressing the stripped ends how did you do it ... a vice, pliers or something else? Any images?
renatoa
quicker response could become annoying... what do you think about being able to see the on-off pulses of the SSR ? Check attached clip Grin
renatoa attached the following file:
whatsapp_video_2020-09-20_at_132552.zip [2.88MB / 25 Downloads]
CK

Quote

renatoa wrote:

quicker response could become annoying... what do you think about being able to see the on-off pulses of the SSR ?


No doubt about it, that is a very fast TC read! I may research this on the Transparent roaster just for fun anyway.
jkoll42

Quote

CK wrote:

Quote

jkoll42 wrote:

It's Chromel/Alumel TC wire. The "junction" in the RC is the twisting and pressing of the two stripped ends.


This is a great idea for a quicker response to my ET thermocouple. There's no issue with beans bothering it in the hot air inlet pipe.

I have some Chromel/Alumel leftover from cutting a k-type thermocouple lead wire to a shorter length... happy to have kept it instead of tossing it.

Any tips on how many twists, or how long of a bare section? When pressing the stripped ends how did you do it ... a vice, pliers or something else? Any images?


I usually do 3 or 4 twists and just give it a little crimp with pliers. Your temp measurement is coming from the differential in voltage across the wires so it's actually reading at the base of the twist. The twist and crimp is just to keep the junction as solid as possible if you aren't doing a bead weld. The response is so fast because there is absolutely nothing to act as a heat sync between the wires. I'll get a pic up today of an example
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
jkoll42

Quote

CK wrote:

Quote

renatoa wrote:

quicker response could become annoying... what do you think about being able to see the on-off pulses of the SSR ?


No doubt about it, that is a very fast TC read! I may research this on the Transparent roaster just for fun anyway.


Yes, with literally no thermal mass across the wires it's as close to instant as realistically possible. I imagine you could custom tune response rates by crimping various metals/thicknesses of metal over the twisted pair but I've never tried that - might be fun for someone to experiment with
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
renatoa
Yep, I did this by doing a sandwich made from copper/alu adhesive tape and kapton, with the junction inside.
Like this: https://www.prosensor.fr/upload/photo.../tpl_i.jpg
The goal was to increase beans contact area, not response rate.
jkoll42
I'll post roaster specific in the roaster thread but the probe style TC ended up working quite nicely and the ability to easily change how far it was in the rotating bean mass also worked out perfect to tune it in. The first one arrived bent and damaged but the replacement was great. My reference point of 400F for 1C with the bare TC hit exactly the same at 400F with the probe.
-Jon
Honey badger 1k, Bunn LPG-2E, Technivorm, Cimbali Max Hybrid, Vibiemme Double Domo V3
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