PDA

View Full Version : Temperature sensor for grill/smoker



Chuck Rice
05-17-2008, 12:26 AM
I am looking for a temperature sensor to measure from outside temp to 1000 degrees (I guess that a grill can get that hot), but with the best resolution at around the 100..250 degree range. I want to have the propeller measure the temp, then either send me a message to add more coals, or adjust the gas jet if I am cooking with propane (I often use both to smoke briskets). But all I am finding are room temperature sensors in plastic cases that would melt if the smoker got too hot.

Has anyone happened on a sensor with the propper range?

Ken Peterson
05-17-2008, 12:49 AM
Digikey has a bunch of thermistors. You would have to rig up a circuit to produce a voltage and do the calibration yourself. You would also need an A/D, but the delta/sigma approach should work.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

Chuck Rice
05-17-2008, 01:08 AM
I thought that they were also low temperature devices.


http://www.omega.com/prodinfo/thermistor.html said...
Accuracy
Thermistors are one of the most accurate types of temperature sensors. OMEGA thermistors have an accuracy of 0.1C or 0.2C depending on the particular thermistor model. However thermistors are fairly limited in their temperature range, working only over a nominal range of 0C to 100C .


Grills can be more extreme than this.

Ken Peterson
05-17-2008, 01:14 AM
Digikey has some in the 300C range

If you are willing to rig up an op-amp circuit, you can also try using a thermocouple. This is basically two pieces of wire, made from different metals, soldered together at one end. Some of them can get REALLY hot.

http://en.wikipedia.org/wiki/Thermocouple

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


Post Edited (Ken Peterson) : 5/16/2008 5:24:31 PM GMT

Bean
05-17-2008, 01:34 AM
I would suggest using a thermocouple for temperatures that hot.
Parallax sells a thermocouple kit using the DS2760. Search of DS2760 on the Parallax website.

Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Did you know that 111,111,111 multiplied by 111,111,111 equals 12345678987654321 ?

www.iElectronicDesigns.com (http://www.iElectronicDesigns.com)


Rayman
05-17-2008, 01:48 AM
There are also optical temperature sensors that would work, but that's probably a more expensive route...

You might look at the Omega website for more options...

Ken Peterson
05-17-2008, 02:42 AM
Wow...I didn't realize Parallax had a thermocouple kit. There you go, Chuck!

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

tripp
05-17-2008, 04:29 AM
I use max6675 for tck sparkfun have them...

Timothy D. Swieter
05-17-2008, 06:00 PM
I was just thinking about this earlier today. I got the thermocouple kit for christmas and I have a couple other uses in mind as well, but a "smoker" is one idea I was toying with this morning because I would love some serious BBQ.

The smoker I was thinking about making was going to use an electric hot plate like in Good Eats (Alton Brown's Show) titled Q. My thoughts was to use a uOLED-PROP and the uOLED-IOC for a control and display. A user interface would be provided with buttons to start a timer and set the desired termperature. The thermocouple would provide feedback about internal temperature. An appropriate output circuit (relay or solid state or similar) would be provided to turn on/off the electric plate. I think the first revision would just turn the plate on/off instead of trying to regulate it. That needs more thought though.

Good luck with your project Chuck.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter

www.brilldea.com (http://www.brilldea.com)- check out the uOLED-IOC, an I/O expansion for the uOLED-96-PROP
www.tdswieter.com (http://www.tdswieter.com)
------------------------------------------------------------
One little spark of imagination is all it takes for an idea to explode

Chuck Rice
05-31-2008, 02:03 PM
Got the Thermocouple/Max6675 working tonight. Other than the surface mount soldering (which was not too bad) it was an easy project. I still need to find a Propane Solenoid Valve that does not cost an arm and a leg.

Attached is the project. Feel free to use and abuse it. And enjoy a slow cooked brisket!

StefanL38
05-31-2008, 05:44 PM
Hello Chuck,

just a quick idea as posted out on a brainstroming,

how about using a small motor with a gear mechanical connected to a standard handdriven propane-valve?

best regards

Stefan

Chuck Rice
06-01-2008, 12:18 AM
StefanL38 said...

how about using a small motor with a gear mechanical connected to a standard handdriven propane-valve?
Stefan


Yes, I have been thinking about that, but it would need to be failsafe. If something went wrong and it lost power, it would need to close the gas off. That means a strong spring and a strong motor. So I am still thinking about ways to do it.

StefanL38
06-01-2008, 04:42 AM
hello Chuck,

as there is everytime a border where human beeing starts to be responsible. (which camping-gas-installation that uses rubbertubes
is automatic secured against cutting the rubbertube with a knife or disconnecting the grill from the tube ?)

I like to suggest more ideas. If the ideas are not useful themselves maybe they can be inspiration for new and better ideas.

How about a emergencybattery that delievers electricity for 10 Minutes to close the valve. And giving alarm about normal power failure
from one of these superloud beepers of a smokedetektor ?
The propeller could watch for battery-voltage still OK and normal powersupply OK. In case of a failure a normal relay as an "OPENER" contact that closes on
lost of power connects the battery to the beeper.

How about using a servo to have enough force to turn the valve ?

Camping-gas cooking stoves have a temperature sensor that has to be hot to keep a valve opend (by heatextension of a closed gasvolume)
If you heat this sensor electrically from the same powerline as the propeller-powersupply and the propeller drives a normal relay "opener"-contact
in serial to the electrical heating of the sensor. The sensors would become cold if the software fails and/or if the power gets lost.

I don't know the prices of these sensors maybe this is a cheaper way to do it.

Or a complete different way http://forums.parallax.com/images/smilies/wink.gif, http://forums.parallax.com/images/smilies/wink.gif how about selling grilled meat one day in the city to earn the money for a professional propan-solenoid-valve? (LOL)

cheers

Stefan

Chuck Rice
06-01-2008, 06:36 AM
Found an inexpensive valve at this web site: www.propane-generators.com/rsk-hp.htm (http://www.propane-generators.com/rsk-hp.htm)


http://www.propane-generators.com/rsk-hp.htm said...

Propane High Pressure Shutoff Valve
Features:
1/4" Male x Female NPT Brass Body
Rated for gas pressure up to 250 psi
12V Low 8 Watt Power Consumption
UL Listed Fuel Valve
Normally Closed (requires 12V to open)

Part Number Price
Valve-14-12SS $17.60



although the price is really 22.60 when you put it in your cart.

This looks like it would work. It is a high pressure valve, but I
assume that it would also work at low pressure. Does anyone
know more about Propane connections and safety? I do not
really want to earn a Darwin Award.

Timothy D. Swieter
06-01-2008, 02:44 PM
Chuck -

Flames and gas and electrical safety design is a big deal and very involved. I hope you don't earn a Darwin award either! The vavle you metnoiend, it looks to be on or off, not analog. To control the flame you can control the gas but also the oxygen.

I want to do a project similar to yours, but I am going to use electrical heating elements because they are easier to control. I watched a Good Eats episode once on the Food Network. This is Alton Brown's show. The episode was called Q and it was about BBQ (of course). Alton made a BBQ smoker out of flower pots and an electrical hot plate. There have been several peopel on-line who have also made similar devices, here is one: http://www.ntscblog.com/2005/07/little-brown-egg-i-condo-q.html

I thoguht I would use a uOLED-IOC and a thermocouple and solid state relays in the design. The OLED display would show the current temp and desired temp. Maybe it would also display cooking time and stats from other sensors. The data could be logged to the uSD card for later analysis (to get that perfect Q). The solid state relays would control the on/off of the hot plate. I figured a generic version of hardware could be made so that an electric smoker could be made or the same hardware setup could be used to make a reflow oven with some modifications to the firmware.

Please do share pics of your design!

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter

www.brilldea.com (http://www.brilldea.com)- uOLED-IOC, RGB LEDs, TLC5940 driver PCB
www.tdswieter.com (http://www.tdswieter.com)
------------------------------------------------------------
One little spark of imagination is all it takes for an idea to explode

Peter Verkaik
06-01-2008, 04:54 PM
Here is an article about a BBQ temperature controller using a javelin stamp.
It may give some ideas and provides links to used components.

regards peter

Chuck Rice
06-01-2008, 09:10 PM
Thanks Peter and Timothy.

I went ahead and ordered the solenoid. We will see what I get. I knew that it was an on/off switch. I am thinking about one of two paths at them moment.

First, I could use the on and off to heat fire bricks and a water pan. When the temperature is below a set point (say for example, 170 degrees F), it turns on, heating the brick. When it gets above a set point (about 180), it turns off and the bricks and water radiate the heat till the temp drops again. This would require a pilot light or electronic ignition to start.

The other way would be to use the solenoid to act as the safety-shutoff, then use a servo connected to a valve to control the flame size. That way in case of a failure the solenoid would close shutting off the gas. With a loss of power, the solenoid would snap shut. With a flame blowout, the thermocouple would detect no heat and the propeller would de-energize the solenoid and sound an alarm.

Peter, thanks for the link! Lots of info there!

Timothy D. Swieter
06-01-2008, 09:40 PM
If using your first method you will want to have a well controlled pilot light. You may want to implement a "peeper" or some way to verify the pilot light is on and burning before opening the larger gas valve, otherwise you may release a lot of gas without burning it.

Your second method is interesting and I like the safety aspects.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Timothy D. Swieter

www.brilldea.com (http://www.brilldea.com)- uOLED-IOC, RGB LEDs, TLC5940 driver PCB
www.tdswieter.com (http://www.tdswieter.com)
------------------------------------------------------------
One little spark of imagination is all it takes for an idea to explode