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Topic: Recommendations for a ~50-300+C Temp sensor (Read 7893 times) previous topic - next topic

phibes4000

Hi,

I don't know much about temp sensors, have done a lot of searching with no conclusive result, so thought I'd ask here.  I want to monitor a coffee roasting oven, eventually with multiple probes.  

I don't need extreme accuracy, and would prefer something reasonably cheap that I could attach a thermocouple to.

Is there an IC and thermocouple combo that anyone can recommend? Most of the solutions I've seen are not high temperature; or are stand-alone industrial solutions for more extreme applications...

Thanks in advance,

Lee

Senso

Search for PT100 temperature sensors, they are a bit non-linear, but some software can take care of that and they have very wide temperature ranges.

phibes4000

Thanks - they look OK, but a bit $ for anything with a probe (unless I don't understand what I'm looking at).  

What I want is a long probe (eventually several) on a lead that I can insert into areas like an oven, coffee bean mass, etc; and then have these connected to the arduino without transferring heat.  Ideally would be $10-30 per probe.

Is there anything else I should consider?

Thanks

anachrocomputer

Don't forget that with a thermocouple, you'll need a thermocouple amplifier such as the Analog Devices AD595. The output from the AD595 would then go to the Arduino's analog input pin. Do make sure that the 10-bit resolution of the Arduino's ADC is sufficient for your application!

phibes4000

Thanks for the amplifier tip.  Are there any example projects/circuits I can refer to?  Every one that I can find seems to be low-temp.  Because my electronics knowledge is basic (trying to remedy that), I would like to find something I can at least use as a reference point.

kg4wsv

Maxim has the MAX6674 and 6675.  IIRC, one is high resolution and goes up to ~128C; the other is lower resolution but goes to around 1024C.  Both are for K-type thermocouples.  There has been code posted that worked for me.

The devices are fully integrated - there are leads for the t-couple on the analog side and SPI on the digital side.

-j

phibes4000

Brilliant! The MAX6675 is just what I was looking for.  Thanks.

phibes4000

One more thing on this; slightly off topic...

I want to be able to drill holes in things like ovens/roasters and slide the probes in and out.  But have the holes covered when not in use.

In the past, I vaguely recall seeing ports like this on an oven, with an interference fit.  But I can't find anything googling.  Does anyone know the right terminology for such?...

pwillard

#8
Apr 06, 2010, 12:35 am Last Edit: Apr 06, 2010, 12:37 am by pwillard Reason: 1
You could use a Stainless Steel small diameter tube to hold the probe using ceramic tubes to insulate the probe wires somewhat.

 See: http://www.earthwaterfire.com/furnace_tubes.htm for what I'm talking about.

Then use a ceramic plug to close off the tube when the probe is not used.

This is what I do with my 900C degree KILN.

rocketgeek

You can use stainless steel sheathed TC probes and drilled-out compression fittings. If you use a teflon ferrule in the compression fitting, you can adjust the probe location. When you want to cap it, remove the probe, nut, and ferrule and replace them with a cap. I've had good luck with Swagelok fittings in this kind of application.

pwillard

I also have these on my thermocouple for the wires that reach inside my kiln:

http://www.omega.com/pptst/ORX_INSULATORS.html

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