[Homeroast] Blue plastic on thermometer melts

Rich rich-mail at octoxol.com
Sat Mar 12 18:12:35 CST 2011


All Type K thermocouples have the same range.  The difference is the 
insulation and the sheath material if any.

Type K (chromel{90 percent nickel and 10 percent 
chromium}–alumel)(Alumel consisting of 95% nickel, 2% manganese, 2% 
aluminium and 1% silicon) is the most common general purpose 
thermocouple with a sensitivity of approximately 41 µV/°C, chromel 
positive relative to alumel.[7] It is inexpensive, and a wide variety of 
probes are available in its −200 °C to +1350 °C / -328 °F to +2462 °F 
range. Type K was specified at a time when metallurgy was less advanced 
than it is today, and consequently characteristics vary considerably 
between samples. One of the constituent metals, nickel, is magnetic; a 
characteristic of thermocouples made with magnetic material is that they 
undergo a step change in output when the magnetic material reaches its 
Curie point (around 354 °C for type K thermocouples).

On 03/12/2011 05:48 PM, Dean wrote:
> While I don't >personally< have any concerns with PTFE (Teflon) family
> at roasting temps (some have expressed these in the past), I would
> probably stay with the Glass/Glass wires. If size is not a problem and
> stiffness is an advantage, get a probe with a stainless sheath. then no
> insulation in the beans. Maybe a little less responsive, but repeatable.
> Google found me some in the past. Omega can be kinda high-end......
>
> Dean
> In da weeds. (and the mud......)
>
> On 3/12/2011 4:30 PM, Coffee wrote:
>> Brian,
>>
>> I actually think that the plastic is heat resistant for 'normal' temps
>> like boiling or whatever, but at the 400 degree plus stage, you get
>> 'blue beans'. (ok, all you folks get your minds out of the gutters) ;)
>>
>> And yes, I carefully scraped the rest of the blue plastic off and
>> continued to use the TC. Be sure not to cut into the insulation as you
>> clean it up. You can get replacement K Type TCs at
>> http://www.omega.com/pptst/5TC.html and I use the 5TC-TT-K-30-36 with
>> a max temp of 500f for use in my iRoasts. They work just fine, with no
>> melting. :)
>>
>> Best Regards,
>> Ken B
>>
>> On 3/12/2011 2:58 PM, Brian Kamnetz wrote:
>>> Ken,
>>>
>>> Thanks for your response. You are correct, and you have answered my
>>> questions.
>>>
>>> I wasn't sure how to use the thermometer and it sat for a couple
>>> years. Recently I asked a guy with some engineering background for
>>> assistance and he described what I had and how I should use it. His
>>> only error was mistaking the blue plastic for insulation, which he
>>> then assumed would be ok in the beans while they were roasting.
>>>
>>> Before I roast next time I will carefully remove the remainder of the
>>> blue material.
>>>
>>> Tom, safe travels to and from Guatemala.
>>>
>>> Brian
>>>
>>>
>>>
>>> On Sat, Mar 12, 2011 at 12:01 PM, Coffee<coffee at onlykenssite.com> wrote:
>>>> Tom, I think the thing he is talking about is the end of the TC that
>>>> came
>>>> with the electronic thermometer you sold 2-3 years ago. I also ruined a
>>>> couple of roasts by not knowing to remove it before use, and think I
>>>> even
>>>> said something on the list about it. It was a blue plastic (?)
>>>> sleeve that
>>>> was not heat resistant to the temps we roast at. New TC's purchased
>>>> from
>>>> Omega did not have it. I have not purchased another thermometer,
>>>> because
>>>> the one I originally bought still works fine, so I do not know if
>>>> that is
>>>> still the case or not.
>>>>
>>>> The original Thermometer I bought through SM was a CircuitSolutions.com
>>>> K-Type MS6500.
>>>>
>>>> Hope that clears up the confusion. :)
>>>>
>>>> Best Regards,
>>>> Ken B
>>>>
>>>> On 3/12/2011 10:00 AM, Tom& Maria - Sweet Maria's Coffee wrote:
>>>>> I am confused because all the thermocouples I have used from out stock
>>>>> (quite a few) have bare ends and then woven fiberglass (or frankly,
>>>>> I am not
>>>>> sure what the material is exactly) that has proved very heat
>>>>> resistant. I
>>>>> don't remember seeing plastic on the sensor end. Am I confused?
>>>>>
>>>>> Tom
>>>>>
>>>>> PS- Off to Guatemala in a couple hours so might not see replies for
>>>>> a bit.
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> I tried to search for this in "http://themeyers.org/HomeRoast/". The
>>>>>> search came up with threads, but the threads wouldn't open.
>>>>>>
>>>>>> A couple years ago I got a digital thermometer from SM, and used it
>>>>>> for the first time today. The probe had a blue end about 3/4 inch
>>>>>> long. I roast with a heatgun, and put the beans in a colander that I
>>>>>> place in a stainless steel bowl. I threaded the blue plastic end of
>>>>>> the sensor into the colander and roasted a pound of Jimma. When the
>>>>>> roast ended the blue end was melted.
>>>>>>
>>>>>> What should I do next?
>>>>>>
>>>>>> Thanks for any help.
>>>>>>
>>>>>> Brian
>>>>>>
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