Comments on: Meat thermometer using predictive filtering

By: Canbot

Canbot — Sat, 20 Jun 2009 14:58:51 +0000

@fuzzmaster

Inferred thermometers take surface measurements, the point of a meat thermometer is to take the temperature at the core of the meat because that is what you need to know to properly cook meat.

By: fuzzmaster

fuzzmaster — Fri, 19 Jun 2009 21:01:23 +0000

Great video quality and explanation on what was done. Personally, I’d spend $8(at max for the intended use) and get something that handles the processing, filtering, and communication on its own: http://www.melexis.com/Sensor_ICs_Infrared_and_Optical/Infrared/MLX90614_615.aspx
…but that’s just me I guess

By: leblanc meneses

leblanc meneses — Fri, 19 Jun 2009 13:38:58 +0000

> Um… how do you do derivatives in programming?
> Posted at 6:19 am on Jun 18th, 2009 by Andrew

Odin84gk gives a simple example of the concept.

however in animations of physical models the popular methods are:
http://en.wikipedia.org/wiki/Euler%27s_method
http://en.wikipedia.org/wiki/Runge-Kutta

which is the standard.

By: Nate

Nate — Fri, 19 Jun 2009 12:14:38 +0000

Nice job. I hadn’t heard of predictive filtering. Seems like it should be called compensation filtering, since you really are not predicting (estimating future world state) as much as compensating for the transfer function of the sensor, which is very common in control applications. The term seems to appear in a decent number of papers, surprised nobody has written the Wikipedia page yet. Thanks for putting that together.

By: andrew

andrew — Fri, 19 Jun 2009 05:08:07 +0000

@jack:

i don’t think so. i’ve been using lm335′s in a project of mine (same as the lm34 here, except calibrated for the kelvin scale) and they do the same thing regardless of how they are mounted. it might be because the sensors are manufactured with a plastic case, which is not very thermally conductive.

By: war6763

war6763 — Fri, 19 Jun 2009 00:33:04 +0000

Not sure how 5 minute epoxy will react (or what chemicals will be transferred to the food) when heat is applied…

Also, even lead-free solder has impurities which are toxic… I would dissect a stainless steel thermometer and fill it in with a sensor in order to be certain that no contaminants enter the food.

Otherwise, good work! The presentation was explained well, although it would have been useful to compare the output to something else such as a capacitor in practice so that the portion of the audience which is not as skilled in mathematics would be able to relate. A simple breadboard example would suffice, and would not even require extra hardware or programming changes, as long as proper values were chosen.

By: jack

jack — Thu, 18 Jun 2009 21:43:52 +0000

I’d imagine the response is so slow because of the huge length of copper they’re using.

By: will d.

will d. — Thu, 18 Jun 2009 18:41:03 +0000

this is the best narrated student video i have ever seen. excellent job!

By: Odin84gk

Odin84gk — Thu, 18 Jun 2009 18:07:48 +0000

@andrew
Lets say you are sampling the AtoD converter every 1mS and you get S1 and S2. A very simple derivative would be (S2-S1)/1mS.

By: uncivlengr

uncivlengr — Thu, 18 Jun 2009 14:51:24 +0000

I would imagine the predicted values would be much more accurate than they appeared to be in the video if the tip was held stationary in the hot water – by letting it bob up and down, he’s changing the distance the heat has to flow along the wire, which affects the rate of heat transfer to the sensor.

By: Andrew

Andrew — Thu, 18 Jun 2009 13:19:12 +0000

Um… how do you do derivatives in programming?

By: Foxy

Foxy — Thu, 18 Jun 2009 13:18:33 +0000

This looks like a project for a signal processing class. I always thought you could do something like this, I just never took the time to do the math/ prove it with an experiment. Very nice video.

/whips out old thermodynamics and signal processng books.

Laplace ftw!

By: Tilman

Tilman — Thu, 18 Jun 2009 10:42:46 +0000

@:d
No, this won’t work, because you are proposing to model the temperature curve by a parabola which it obviously isn’t.

@myself: i talked to a biochemist and she told me copper wasn’t so critical and the traces were so small that it’s probably no problem… But clean it in order to remove lead and so on which might still stick on it from the wire insulation you might have peeled off.

By: :D

:D — Thu, 18 Jun 2009 10:20:41 +0000

why using all that math shouldnt this work x=x0+vt+1/2at^2?
x0=actual temperature
v=x0 to x1 velocity
t=chip delay? how much time does the chip takes to get the right temp
a=acceleration

By: Tilman

Tilman — Thu, 18 Jun 2009 08:31:53 +0000

Even though copper has very good heat conductivity, I would not recommend to stick a copper wire into food: It will get corroded by the acids in the food, leaving back traces of copper salts which are toxic.
A possibility around this would be to use a copper tip covered by some protective layer (e.g. gold). Also, the tip from the mechanical meat thermometer shown in the beginning of the video might work well.