HeatSnob - Grounding errors with non-supplied probes

[prloring]

My HeatSnob seems to be giving much more noise in the readings, the general trend line is right but the RoR is now unreliable as after first crack it's jumping around all over the place between -2 and+12, the resulting curve still looks like a +5deg RoR but the numbers don't read that way. What's strange is that up until about 150deg it reads just like the old meter. I can't test the supplied probe in situ as it's too short. My current probe (a fairly recent purchase) appears identical to the new shorter one and is, I believe, isolated from the roaster itself... It's held in place by PTFE plumber tape wrapped dozens of times around the shaft of the probe (poor mans PTFE tubing). I'm using a laptop constantly plugged in (battery is dead).

Any ideas or help would be appreciated.

[Dimal]

A short length of PTFE Tubing would be better to use than silicone tubing for that purpose.
Lots available from Ozzie suppliers on the Bay...

Mal.

[MrFreddofrog]

Hi Gazza

I had a grounded thermocouple (not a beanbay one) and it drove me crazy. It would work fine but once connected to the laptop it would create a ground loop and all the readings would fail. Eventually I had an ungrounded MIMS one fabricated (mineral insulated metal sheath) and it works now.

If you want to persist with your ground thermocouple easiest solution should be operating the laptop on battery power. Without a power plug there is no ground loop. If you're using a desktop then you'll need to electrically isolate the probe from the entire roaster. Some silicon has a 240C continuous rating so that might be an option. I'm using normal rubber grommets in the outer left wall but if you could find silicon grommets or tubing for the inner wall that might be another option.

But first you might want to check what temp you need to withstand. Where Andy recommends to install the short heatsnob probe, I get 150C max but you may get different temps depending on your roast profile.

Anyway, that was my experience. Hope that helps.

[oliverm]

Can you check if it the thermocouple is isolated from the probe case or is connected to it ??

I'm away for a week or so but can check when I get home if you're still having troubles.

[gazza]

The long probe I bought from bean bay works

Can you check if it the thermocouple is isolated from the probe case or is connected to it ??

[oliverm]

The long probe I bought from bean bay works with my heatsnob.

[gazza]

From Roastmonitor, with the polarity swapped it counts down for an increase in temperature and when the probe case is connected to ground it stops counting and I get same error.

Looking at the output of HIDTester2 I can see the "short to ground" data change.

The short probe supplied is fully isolated, are you likely to get more stock of long probes in Beanbay (that work) or do I look elswhere ??


Gary

[Andy]

I'm glad the supplied one works!

Optic makes sense be sheeze, it gave us a lot of grief too... one bit of chaff and people screamed. ;-)

As for the old ones, I don't know, they should work though.
One of the gotcha's with thermocouples is that the transpose the red/black sometimes. As some specifications show red as earth!

Try swapping the polarity and see what happens

[gazza]

Just received my Heatsnob and it works fine with the supplied short probe but will not work in my roaster with either of the long probes that were purchased from beanbay (yellow cable or meal braid).

I get this error in Roastmonitor: "19:03:04 meter 1: Thermocouple shorted to ground "

There seems to be a compatibility issue with the type of thermocouple used with it, the new probe is isolated from the probe case and the others are not and in my roaster the case of the probe is tied to ground. I suppose that is one advantage of the old meter being optically isolated from the PC.



Gary