Bad Thermocouple?

[cgriffith]

My problem started abruptly during my last roasting session.  Just before TP, the ET and BT temps started jumping around making readings impossible.  I mean I was roasting blind.  Luckily I had some experience to know what to do up to DE.  I finally figured out around 170 deg C that if I unplugged the ET from Center 301, that BT was normal.  I continued roasting using just BT.

Does this sound like typical behavior of a failing thermocouple or Center 301?

Is there something I can try to troubleshoot before wholesale replacement of TC?

[SusanJoM]

So this is a continuation of the problem you had here?:
https://www.hukyforum.com/index.php/topic,682.msg14489.html#msg14489

Have you had this problem ever since you started trying to plug your HUKY in to your Center?
And have you done all of the grounding stuff that has been suggested to folks having spiking issues???
Are you using the thermocouples and connectors just as they came from Mr. Li?
Does your Center have settings to chose different kinds of T/Cs or is it just for K types?

I'm just fishin' here....

[cgriffith]

I would say this is a continuation of issue posted on May 22nd.  This is the first roast I have done since that time.  I have not had any disruptive spikes before May 22nd post.  These are the stock TC that come from Mr. Li.

I have not researched extensively the grounding issue/solutions as this has just developed and I don't think is a grounding issue.  It is only related to the ET thermocouple.  If I unplug the BT TC and only plug in ET, the issue still exists.  If I unplug the ET TC the BT TC reads fine.  If I move TC around in Center, issue still exists.

I approve the fishing expedition, but still wonder what the lifespan is of these TC and what failure looks like typically.

[SusanJoM]

How frustrating....

I don't remember anyone saying their T/C supplied from Mr. Li has failed, but hat doesn't mean it hasn't.

Try Googling 'troubleshooting a thermocouple' and see if you come up with anything there. 

And/or maybe/hopefully someone who knows more will chime in here. 

[edtbjon]

I've had the BT probe exchanged twice. That's the one probe that takes any beating. The symptoms in my case were erratic readings. The good news are that I could simply swap the BT and MET TCs and the old BT did behave nicely in its new protected MET position. (The second time I exchanged the BT TC for a new one...)
An extra TC is possibly the only "needed" spare part that I recommend buying. It's $19 (I think) and the BT is quite important for most of us.
But there are quite a few links in the chain. The crazy readings for the OP may well be some kind of grounding issue, which is more likely than a broken TC. The annoying nature of these issues are that they often are not repeatable...  I made some 100 or so roasts with the Center 301 before getting me a Phidget, and I do think the Phidget is a more stable platform (but I've had similar issues with the Phidget too...).

[cgriffith]

Does anyone have the specs on the TC used?

[cgriffith]

Well, I grounded my Huky yet I had another horrendous roasting session due to this TC issue.  Does anyone know the specs on these TC so I can order a new one?

[SusanJoM]

Why don't you just order one from Mr. Li?
Seems to me he might just replace the one you have if you explain to him.
If not, he will send you the correct one.

[cgriffith]

I prefer to source and supply these things from US.

[hankua]

Try taking it over to Home Depot and measuring the thread pattern, Omega should be able to match it.

http://www.omega.com/guides/thermocouples.html?gclid=CPaQ8bvRwtQCFc9Zhgodb9kLoA

[cgriffith]

Well I am hoping I found the issue with my TC instability...

The other day I removed my ET probe and performed boiling point/freezing point check and all was fine as well as clean.  I went back to the idea of some kind of voltage interference.  I cooked up a much nicer ground wire.  I roasted tonight.  Early in warmup, the probes started going crazy again.  I systematically started looking at electronic things plugged into my power strip; unplugging and plugging back in to see if temps stabilized.  Then I remembered reading somewhere about this issue with a mac laptop not being plugged in during roast.  So I unplugged my netbook and temps immediately stabilized.  So, I roasted on battery power, and had no issues.

Fingers crossed this is it.  If so, then USB voltage instability can make its way back to Center 301.  I wonder if running Center 301 on AC power would help vs. 9v battery.

Anyways, hope this is helpful, and thanks all how answered my questions.