Hello,

I have a questions; and I think this might just very well be the sort of place I could find answers.

I am currently in the process of devising a method to log my roasts on an Electric Probat sample roaster type BRZ 2, I've read up on the posts pertaining to data logging a roaster on home-barista and if I've missed an answer adequate to my question I do apologise in advance.

I have chosen to use Artisan and an Omega HH806AU http://www.omega.co.uk/ppt/pptsc.asp?ref=hh806

However I am at a road block and I'm finding it quiet frustrating, I have been in communication with Omega UK all day and they seem to know less than me on the subject and I know very little.

I am trying to find a thermocouple suitable, I've narrowed down the type to K and most other parameters except being able to find the answer to 1)whether or not you can bend the sheaths without hampering their effectiveness, I wish to enter the probe via the current probat probes entrance point however it requires being bent into a curve in order to reach inside the bean mass on the other side, I tell you what I'll attach some images to clarify my predicament, all the photos in this flickr account are of the Probat sample roaster http://www.flickr.com/photos/42975540@N...hotostream

It has been suggested I use these probes here: http://www.omega.co.uk/ppt/pptsc.asp?re...03&clear=1 except I'm not sure if you can bend them

and I have been told that the thermometer comes with two of these as standard not that they look very useful for my intentions http://www.omega.co.uk/ppt/pptsc.asp?re...v=&clear=1

2) The second image on the above linked flickr account is of the exhaust pipe and I was wondering as my second question whether or not it would be suitable to measure environmental temperature through piercing this pipe just enough to rest the thermocouple inside, this sounds dumb in my mind but yet I question if it could really be that simple.

I realise I am new to this forum and have literally joined to ask a question but I have a very passionate and professional background in coffee, and I'm sure over time I will contribute in answers to others questions.

It would be really lovely if someone would reply linking me to a suitable thermocouple that I could bend and order tomorrow then life would be well again, I've really gotten myself into a muddle with all this.

Thank you
Stephen

Of importance would be the diameter and length of the existing probe, i.e. how far inside the drum does it extend.

Yes, the great majority of thermocouples can be bent but some rules to follow would be to shape the thermocouple bend using a mandrel and to NOT make the bend radius less than 3 times the diameter of the sheath. For a mandrel to use with the 1/8" thermocouple I list below, you should use a 3/4" pipe in a vise or a tube bender.

For example, say you chose a ~3 mm diameter thermocouple such as this:
http://www.omega.co.uk/ppt/pptsc.asp?ref=TJ36-XCiB_chb&Nav=tema07 . The proper part number would be TJ36-CASS-18G-6-CC-XCIB. In the US, we would add "-SMPW-M" to the part number as that would get us a cable termination with a sub-miniature male plug to fit the HH806AU.

The existing probe is 8cm inside the drum and removed and measured taking into account of its curve a full 14.5cm in total, not entirely sure on the diameter however 3mm would fit well. Thats a very useful guideline in regards to the bend, I shall have to look into the best place to get hold of a tube bender.

Would I be right in thinking that this code to follow would provide me with a 1/8 inch diameter 6 inch long ungrounded type K thermocouple with a sub-miniature male plug matching the appearance of the thermocouple in the image?
TJ36-CASS-18U-6-CC-XCIB-SMPW-M

My only concern now is the length beyond the probe which is thicker and quiet long as the space between where the probe enters the drum and the cog which rotates the drum are quiet close, is there another option with less of a solid and seemingly large end to the probe that you know of?

Thank you for your help

Would I be right in thinking . . . ?

Yes.

Probes can always be ordered in custom lengths, so order one about 0.6" longer and bend it using a mandrel. Since the dimensions are apparently very close, practice some bends with hardware store metal tubing or similar.

Thank you for your help so far! I wonder if you have an opinion on this thermocouple http://www.omega.co.uk/ppt/pptsc.asp?re...Nav=tema07

In particular it peaked my interest from the description "The semi-rigid MI sheath can be formed to suit many applications" I believe I read somewhere it is minerally insulated (whatever that means)

I'm thinking possibly going with TJ1-CASS-IM30U-150-SMPW-M

I'm thinking possibly going with TJ1-CASS-IM30U-150-SMPW-M

Looks fine to me. I question why you are using an ungrounded thermocouple as all of the ones I have sold are "grounded" and I have sold a lot.

I was under the impression that grounded thermocouples could pick up electrical signals and mislead the temperature readings and that ungrounded was slower to react yet unlikely to suffer this same fate? I'd love for you to tell me thats not the case as speed and accuracy are obviously very important. The problem I find when searching for information on the internet is how conflicting different sources can be, I also seem to remember it being said to have an effect if you were connecting the thermometer via USB or/and if it was plugged into mains power and there being a difference between if you were in the UK or USA (I'm in the UK)

I'd also be interested to hear your opinion on the best variant of thermocouple for measuring exhaust air temperature, perhaps exposed tip?

Sorry for being such a novice I'm regards to thermometry.

I was under the impression that grounded thermocouples could pick up electrical signals and mislead the temperature readings and that ungrounded was slower to react yet unlikely to suffer this same fate?

I can only quote Omega's words as regards this situation. Going beyond that is not within my capability.

A grounded junction provides a fast response time but it is most susceptible to electrical ground loops. In ungrounded junctions, the thermocouple is separated from the sheath wall by a layer of insulation.

For the exhaust, a smaller diameter (~1/16") thermocouple of the same type as you are choosing for BT would be a good choice.

I do not claim to be an expert, but this is what I've observed when using grounded thermocouples in roasters and espresso machines:

• Measuring instruments that are battery-powered do not seem to have any issues with grounded thermocouples. This includes USB-powered devices (see below) when the laptop is on battery power (i.e. no charger).
• The PID controllers I've used (Watlow, Cal, Fuji, Delta) are powered from mains, so seemingly could be susceptible to ground loop problems. Apparently, though, the input circuitry has been well-isolated because I have not observed any issues with ground loops when using those controllers.
• USB-powered instruments (like TC4/Arduino, etc) are susceptible to ground loop problems in some situations. I ran into problems when using laptop chargers with 2-prong plugs because of differences between USB V- and roaster ground. The solutions that worked for me were to add a wire between USB V- and roaster ground or use chargers with 3-prong plugs. (So far I haven't fried any desktop or laptop computers by tying USB V- to earth ground).
• Similarly, TC4/Arduino systems that are powered from 2-prong wall wart PSU's can experience ground loop problems with grounded TC's. Forcing the roaster frame and PSU V- to be at the same potential by running a wire between them has always solved any problems for me.

FWIW, I exclusively use grounded probes for the improved response time. I haven't encountered any ground loop problems yet that are not fairly easily solved.

The other thing I will mention is that I can tell when ground loops are present because temperature readings seem to run around 20F lower than they should be.

JIm

Thank you Erics I will take that on board in regards to using the same type yet smaller diameter probe for the exhaust.

And thank you JimG for your overlay in regards to ungrounded/grounded potential scenarios, solutions and symptoms.

I feel much more confident in my purchasing decisions now and I'll be ordering it tomorrow, I'll be sure to post roast logs and any pertinent observations as a result of logging.