Temperature Task

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Temperature Task

Post by Jim_R » September 3rd, 2010, 1:21 pm

Discussion for the Temperature task.
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Re: Temperature Task

Post by haven chuck » September 20th, 2010, 3:29 pm

Does anyone have any ideas on how to do this task?
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Re: Temperature Task

Post by Primate » September 20th, 2010, 3:43 pm

haven chuck wrote:Does anyone have any ideas on how to do this task?
Not a clue. I was thinking some sort of thermistor and a chemical reaction, but I haven't gotten any farther than that.
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Re: Temperature Task

Post by Flavorflav » September 21st, 2010, 10:00 am

Without knowing much about the active temperature range of commonly available thermistors, my hunch is that you would be better off with a bimetallic strip.

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Re: Temperature Task

Post by Dark Sabre » September 21st, 2010, 3:44 pm

Primate wrote:
haven chuck wrote:Does anyone have any ideas on how to do this task?
Not a clue. I was thinking some sort of thermistor and a chemical reaction, but I haven't gotten any farther than that.
You could totally use a thermistor...wouldn't be very different from the photo-resistor type setups people used last year. Chemical endothermic kind of reactions have been some of the less time-predictable transfers I've done. Your mileage may vary.

You might also want to consider a thermal limit switch. Since they are switches, you have a lot more options with what your next step is.
I bought these from American Science and Surplus ages ago and played around with them. I think they would work pretty handily for a task like this. Was glad to see they still offered them. You can buy (or find) thermal limit switches lots of other places though if NO@cold, closed at >135 doesn't strike your fancy. Ovens often have one somewhere around the main cavity (though I wouldn't remove one from your every day oven, haha...they are important safety features), but those might trip at too high of a temperature to be useful. Hair dryers and toasters usually have thermal fuses, which don't do you any good.

Bimetallic strips are definitely an option too. I used one, which I assume you have seen on the wiki.

I'd also heard words like "peltier cooler" tossed around. Might be something to look into. Not a sensing device, but a way to electrically cool something, which is convenient.

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Re: Temperature Task

Post by Primate » September 21st, 2010, 5:06 pm

Dark Sabre, that's genius. I've been thinking specifically solely of decreasing the temperature, but heating up a bimetallic strip and then letting it curl back up would be perfect. How reliable did you find that to be?

(Also, I was thinking of hooking up the thermistor with a relay to create a switch, but calibration would be an absolute nightmare.)
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Re: Temperature Task

Post by Paradox21 » September 21st, 2010, 5:14 pm

What is the easiest (and cheapest) way to get a bimetallic strip? My trusty surplus store didn't have any.
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Re: Temperature Task

Post by Dark Sabre » September 21st, 2010, 5:27 pm

Paradox21 wrote:What is the easiest (and cheapest) way to get a bimetallic strip? My trusty surplus store didn't have any.
I got mine from the cheapest outdoor dial thermometer I could find. Analog thermostats may have them too.
Primate wrote:Dark Sabre, that's genius. I've been thinking specifically solely of decreasing the temperature, but heating up a bimetallic strip and then letting it curl back up would be perfect. How reliable did you find that to be?

(Also, I was thinking of hooking up the thermistor with a relay to create a switch, but calibration would be an absolute nightmare.)
I never had any trouble with it, either from a timing or just working perspective. I would note that what I was doing was designed to satisfy both an Increasing Heat and Decreasing Heat bonus, so doing it exactly like that probably isn't necessary. The way mine was set up, the previous transfer turned the nichrome on, which curled the bimetallic to hit a switch. That switch was connected to an RCX, which turned off the power to the nichrome, and the bimetallic cooled down and hit the same switch, triggering the next transfer. Since you can't use logic or anything, you'll have to figure out your own switch setup.

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Re: Temperature Task

Post by Primate » September 22nd, 2010, 3:56 am

Dark Sabre wrote:I never had any trouble with it, either from a timing or just working perspective. I would note that what I was doing was designed to satisfy both an Increasing Heat and Decreasing Heat bonus, so doing it exactly like that probably isn't necessary. The way mine was set up, the previous transfer turned the nichrome on, which curled the bimetallic to hit a switch. That switch was connected to an RCX, which turned off the power to the nichrome, and the bimetallic cooled down and hit the same switch, triggering the next transfer. Since you can't use logic or anything, you'll have to figure out your own switch setup.
Yeah, I saw that in your description on the wiki. I might end up just doing the same thing, though, since trying to keep nichrome running would eat up batteries like none other. I can't just make it the first transfer, since we had some issues at our state competition last year. There was a two- to three- minute interval between getting everything all set up, after which point you couldn't touch anything, and actually running the thing, so you had to cross your fingers and pray that those batteries had enough juice.
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Re: Temperature Task

Post by Uncle Fester » September 22nd, 2010, 11:45 am

A Peltier cooler moves heat from one side to the other. If you MECHANICALLY (absolutely NOT electrically) reverse one, it's a heater. Seriously-- one side gets hotter, one side gets cooler. The side you "get the temperature" from determines if it's heating or cooling.

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