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Old 04-24-2013, 07:53 PM   #11
bobotwf
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Wouldn't mind knowing the answer to this too. I have a rock bottom ebay PT100 in my smoker and it is rubbish. But the alternatives seem way more expensive.
What about them was rubbish? Mine all worked exactly the way I'd expect. Am I lucky or are we expecting different things?

 
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Old 04-25-2013, 12:51 AM   #12
alien
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The calibration was off by 1 at 0C and 7 at 100C, compared to a thermapen.

 
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Old 04-25-2013, 06:13 PM   #13
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DS18B20s are great for microcontroller builds but you can't use them with off the shelf PIDs.
Uh, why not? Unless you mean just buying the device doesn't work off the shelf - they are just a three-wire RTD. All the eBay sellers I see put them in a sheath with some conductivity paste and some pigtails. Should work fine, at least I'm willing to invest $5 to find out.
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Old 04-26-2013, 03:43 PM   #14
bobotwf
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Uh, why not? Unless you mean just buying the device doesn't work off the shelf - they are just a three-wire RTD. All the eBay sellers I see put them in a sheath with some conductivity paste and some pigtails. Should work fine, at least I'm willing to invest $5 to find out.
The DS18B20s aren't RTDs. They're ICs that use the 1 wire protocol. Each chip has a separate address and they're all connected to the same data pin on your microcontroller. They don't provide a change in voltage or resistance or anything with temperature. I use them and highly recommend them, they're easy to work with and mine were very accurate.

 
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Old 04-27-2013, 11:36 AM   #15
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Originally Posted by bobotwf View Post
The DS18B20s aren't RTDs. They're ICs that use the 1 wire protocol. Each chip has a separate address and they're all connected to the same data pin on your microcontroller. They don't provide a change in voltage or resistance or anything with temperature. I use them and highly recommend them, they're easy to work with and mine were very accurate.
Huh, well that would definitely prevent them from working as I intended. I did purchase a few different ones from eBay for under what I would have spent on one from one of the automation companies so hopefully I end up with one that will work for me.

All I really want to do is use this Pilsener yeast I have in the fridge!
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Old 05-05-2013, 12:50 PM   #16
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Originally Posted by bobotwf View Post
The DS18B20s aren't RTDs. They're ICs that use the 1 wire protocol. Each chip has a separate address and they're all connected to the same data pin on your microcontroller. They don't provide a change in voltage or resistance or anything with temperature. I use them and highly recommend them, they're easy to work with and mine were very accurate.
Yep, you wuz right. I know you know you were right, but you know how men are.

The other one I bought was the proper one and all is well now. I'm in $10 for two sensors, one of them worked. so not too bad. Here's what I ended up getting:

Probes Unlimited Pt100 Temperature Sensor RTD Automation Controller Teflon Probe





This shows it as a two-wire but it is a three wire so .. not sure but whatever it works and is within a couple tenths of matching a calibrated sensor setup so all is well in the world. Excellent service from this company, very fast shipping if anyone else has the need.

I used to do building controls but have been out for a long time having decided to stay with just the IT side of the house. My brew buddy is still in controls thankfully so he was able to get me straightened out.
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Old 05-06-2013, 03:20 PM   #17
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Yep, you wuz right. I know you know you were right, but you know how men are.
Heh, hopefully it'll come in handy later, it's not wasted money it a future partially funded project.

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This shows it as a two-wire but it is a three wire so .. not sure but whatever it works and is within a couple tenths of matching a calibrated sensor setup so all is well in the world.
The picture shows two red wires that are equivalent. That's so you can detect the inherent resistance in the wires in your circuit and subtract it from the observed resistance the RTD circuits reports. If you don't do that you'll be off by a tiny little bit.

 
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Old 05-06-2013, 03:36 PM   #18
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Oh! Okay that makes sense. I'll let my buddy know and he can go do. Thanks.
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