Hi,
I'm trying to locate a suitable temperature sensor for a coffee group handle:
Happy to work with RTD's or thermistors. Thermocouples aren't accurate for this.
Many thanks for any suggestions. I'm a bit stuck browsing through digikey. I've spent a few hours trying to find a suitable part.
The DS18B20 is a good choice.
Examples for the DS18B20 and a thermistor can be found at Adafruit.
I have never seen a DS18B20 suitable for operating in these conditions, I therefore think it is a dumb choice, and you are right to be thinking in terms of an RTD.
Having said that, I believe these are usually about 100mm long, although I don't think this is down to some physical limitation and you may find shorter versions are available.
A wet PT100 in a small-bore pipe can go in a T-piece. Failing that you might compromise and use a DS18B20 dry in a thermowell, but I'm not aware of these off the shelf.
Pic shows a PT100 in a T at bottom right. At top left is a dry DS18B20 in a custom-made thermowell.
The DS18B20 can go up to 125 degrees Celsius. That 125 degrees is also the maximum storage temperature.
For example the sous vide by Adafruit uses it.
For a boiler or water cooker it is not often used. When the water cooker is without water, the 125 degrees is reached very quick, destroying the sensor.
The advantage is its high accuracy and digital interface. So for a range of 85 to 100 degrees Celsius, it could be used.
headingwest:
- Watertight as it will be operating in water to 12 bars
Erdin:
The DS18B20 can go up to 125 degrees Celsius. So for a range of 85 to 100 degrees Celsius, it could be used.
My previous may have been a bit cryptic, but the operating range is barely relevant. The real problem is the operating environment.
For the metrically-challenged, 12 bars would be about 170 psi i.e. what you might get in your city water supply, which indeed may be the OP's intent. It is possible to install the abovementioned waterproof DS18B20 against such a pressure, I have done it with glass thermometers, but you only need it to fail once to be convinced that using a device better-suited to the purpose is a really good idea, and something with a tapered screw thread springs to mind quite quickly.
Screw-in RTDs are commonplace. OTOH, I have never found a screw-in DS18B20, but I eagerly await the day when one turns up.
Or just epoxy an LM35 or TMP36 in a pipe thread fitting?
If response time is not an issue, and if it's a one-off, that might work.
This is going to be a commercial product, I already have a couple of temperature related products using thermocouples. This new product will be around $500 (gasp) so accuracy and a quality build is important.
Would a thermistor be more accurate than an RTD in the 90 celcius region?
I think screw in is required due to the pressure, I'm looking at this one:
http://www.omega.com/pptst/TH-44000-NPT.html
Any other screw in recommendations??? Actually finding a suitable off the shelf product is surprisingly hard.
Thanks for your suggestions and help.
cptdondo:
Or just epoxy an LM35 or TMP36 in a pipe thread fitting?If response time is not an issue, and if it's a one-off, that might work.
If response time was not an issue, he could epoxy the sensor to the outside of the pipe, thereby saving time, money, and a lot of worry.
headingwest:
Would a thermistor be more accurate than an RTD in the 90 celcius region?
I understand that thermistors are OK within a narrow range but I get the impression RTDs are so much more useful and reliable that industry is heading that way irrespective of the real technical need. I have never seen a screw-in thermistor probe and I don't know anything about thermocouples.
I think screw in is required due to the pressure, I'm looking at this one:
http://www.omega.com/pptst/TH-44000-NPT.html
It looks like just what is needed! The price is a bit eye-watering compared with the RTDs I got from eBay but not that surprising.
A raft of information is available here.
After reading everything, I changed my mind.
A DS18B20 or TMP36 is not the best option.
So a screw-in NTC or that RTD is better.
That link is for an industrial RTD, there are my household items with such a sensor. So there must be reliable and cheaper ones.
I found such a temperature sensor in a bread baking machine.
