Thermocouple

[PiRoDa]

I want to add some thermocouples to my oven, but was wondering if anyone got some solid experience with them?

- Are they long lasting, or do you need to make them removable?
- If placing them in the dome, do the wires need to run over the thermo blanket, or can they just run over the brick dome?
- How do you read-out temperatures? With a normal off-the-shelf thermo couple reader?

[BenKeith]

Between coffee roasting for 20 years and building race engines for 50 years, I have tons of experience with them but first let me say, once you learn how to read your oven, you will probably find it's not needed. If you just want to check, get one of those hand held infrared guns. I installed thermocouple in my oven when I first built it. After about a dozen times cooking in it, I haven't used it since. When I'm cooking bread in it, I will shoot the back of the oven with an IR just to make sure it's about the right temp.

However, to answer your question, you will want to get a K type thermocouple. You will want the solid stainless steel shell, and not an exposed bead. The exposed bead respond quicker but damage to easily. You will need to make sure the probe is long enough to reach inside the oven and possibly make a 90 degree bend outside, depending on how you mount it. They make a 90 degree mounting enclosure for them with a cover you can take off that will let you replace the probe if it goes bad. My oven was 3" of refractory, 4" of insulation, 1/4" exposed in oven and 2" for the 90 degree bend (remember, there has to be a radius) and you can see it takes a fairly long probe. You can order them with the radius pre bent and just give the measurement you need beyond the radius. I wanted the radius to lock it in place so I didn't have to worry about the probe moving in or out on me. To bend your own radius, use a small tubing bender. Doing it by hand could crimp the shield and damage the wire inside.
I would recommend a probe with the stainless steel braided shield over the wire and make sure it has a long enough lead to reach from where you want to mount it and to where you want your read-out. The cheap Chinese probes have very light gauge wire, I won't use those. Omega is a good source probes. Good probes with good wire are not cheap. If using a portable, handheld readout, you will want the K type plug to go on the end of the wire. For outdoors, I would recommend one of the two channel, hand held K type readers, they are not expensive and you don't need an enclosure to protect it. If you want a permanent mount, those readouts generally have screws to connect the cable so you don't need the plug. The bi-metal cables are polarity sensitive so make sure the wires are on the proper terminal.
As far as where to mount the probe, I mounted mine about 6" off the floor and to one side. I wanted it close to what temp would be for the top of a loaf of bread, but I think the recommend spot is in the back of the oven.

I ran mine over the blanket but under the stucco because I didn't want that housing sticking out of the side of my dome, Like anything, they can fail, so buy quality because if it does fail, being embedded like that, there is no replacing it, although I've never had but one to fail and that was one of those cheap Chinese ones I tried in one of my coffee roaster.
One thing I didn't mention, if you don't want to expose the tip into the oven, I exposed mine about 1/4", and just want to drill within about a, 1/8 - 1/4 inch of the inside, you will want to use some type of thermal joint compound to go in the bottom of the hole that can withstand the heat or it probably won't give you the proper reading.
Also. make sure you get a probe that has an upper limit of over 1,200 degrees F. Mine will easily reach that during initial firing. and heat up.

Hope this helps you out.

[spoink47]

Between coffee roasting for 20 years and building race engines for 50 years, I have tons of experience with them but first let me say, once you learn how to read your oven, you will probably find it's not needed. If you just want to check, get one of those hand held infrared guns. I installed thermocouple in my oven when I first built it. After about a dozen times cooking in it, I haven't used it since. When I'm cooking bread in it, I will shoot the back of the oven with an IR just to make sure it's about the right temp.

...

That's a cool story! May I ask where did you work? 20 years of coffee roasting seems pretty solid. I'm also into coffee, but I'm more of an amateur. Started with a simple Ninja coffee maker (and even wrote some articles about it, like this one). And now I'm a chief barista at a coffee house, huh

and what about race engines? That just sounds incredible! I'm very curious

[BenKeith]

Sorry for the big delay, didn't see this until I was deleting old emails.
Coffee roasting is home roasting. Started in 2000 after buying a good espresso machine and living in the middle where there is no such thing as fresh beans without buying mail order. me being an anal perfectionist, that soon led to building my own air and drum roaster. I'm very mechanically smart and have a degree in electronics, so that was an easy process. Again seeking perfection, that included making them computer controlled with the use of thermocouples and controllers I built.

As for engines, I started racing go carts back in the early 60's, building and modifying my own engines then. Late 60's I was drag racing and boat racing, again with my own modified engines. Early 70's I was into dirt track and modified sportsman circle track. I was building engines for a number of other racers also then. That led me into building blown (super charged)engines for several guys in the truck and tractor pulling leagues. One of my engines was used by the guy that won the two wheel drive class, winter nationals in the 80's. Also built a lot of 2 stroke outboard racing engines. Taking 200hp motors and getting over 450hp out of them. My heavy, 20' bass boat would run almost 90 mph loaded with two people and gear. So, like I said, I have a little experience