View Thread

lmclaren wrote:
Hi Ben, It is unclear from the photos, but where the thermocouples attach to the board, are you extending the cables to a socket on the back? If so, you will loose the cold end reference, the thermocouple wire / thermocouple socket should be directly attached the the board. Note sure if it would make that much difference though.

Have you tried putting both thermocouples together and immersing in boiling water and ice water to see if they agree with each other?

I had real problem with one of my thermocouples when I let the metal probe touch the metal of my roaster, the readings where all over the place. I ended up replacing the probe with a bead so it remained isolated from the metal work, it is now totally stable.

best regards

Lee

It is correct to say that a grounded thermocouple takes its reading from the outer casing of the probe and not just the tip?

lmclaren wrote:

No, the temp is measured at the TC junction, probably at the tip of the probe, the problem is that the TC wires are not insulated from the metal enclosure which means that any earth potential will also flow into the TC signal. TC signals are very very small.

I expect in commercial equipment the TC interfaces are floating and do not have the same problem, commercial interfaces are expensive to buy.

I think it will work well if you keep the probe away from metal.

Lee

Thanks! Excuse the ignorance but when you say any "earth potential" are you referring to loose voltage trying to ground itself? If all the electrical equipment used in my roaster are grounded then why would there be any loose voltage? Or is there always fly aways!

JackH wrote:
Ben, I had similar issues with grounded type metal sheath probes. JimG said it might be a ground loop problem like you were describing. It is especially a problem with the two prong power packs we use to power the TC4 and the metal roasting pot.

My solution was to change the BT probe to a bead type. The response is much faster with the open bead too. My only concern is contamination of the probe from the oils and other stuff. I guess they are cheap enough to get spares.

He also suggested that you could also run a ground wire from a good ground to the TC4's ground pin.

jedovaty wrote:
Ben - I got the same ROR graph like you, with the up/down/up/down, try to adjust the filter setting in the code -- I forget exactly where it is, either in the pBourbon or aBourbon, but if you increase the number from the default of 85, it'll smoothen out (but add a bit of lag). I'm at 92 or 93, but think I need to go higher.{/quote}

Thanks I will look into it.

[quote}
What TO do you have, what kind of wattage is it?

I'm getting the same bean temp stalling you are at what seems like FC. I'm running more tests, but I theorize if we want to stick below 500 ET, either we need more heat intensity (e.g. another heating element), or move the bean mass closer to the heat source, or combine one of these with a different amount of beans. Think of it like heating up a cup of water with ice cubes. The temp of the water will not change until all the ice cubes melt.

I want to go as far as saying that the variac is causing this (like my router control), you'd be better off with something like the SSR with potentiometer, as it will provide the full heat source to help raise the BT while keeping ET right. However, I see others using variacs with similar setups succesfully, so I don't know what's we're doing different.

jedovaty wrote:
Hi Ben, take with a metric cube of salt with my no-experience.

I do 400g batches, which are ~50g off yours, not that much difference. I use 24ga for ET and BT: http://www.omega....t/5TC.html They're not very expensive.

Also, how are you making the connection between TC and the Arduino? Are you using all the TC wiring, or do you have any "normal" wires in the mix?