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Old 01-08-2014, 08:41 PM   #21
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Where is the thermopile mounted on your brinkmann? Is it directly in the flame?
Yes, it's in the flame, it's a little copper pencil shaped thingie (see picture)



In the case of the turkey fryer, it's there to energize a small coil that allows the gas safety valve to stay open. So, no flame the coil de-energizes, allowing the valve to close, that's why you have to hold the red button to light it for 30 seconds or so.
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Old 01-09-2014, 05:08 AM   #22
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I like this idea, I might go the hot surface ignitor if I was to do it again. The EMI mostly causes issues with low current signal lines. Like I said before, I have only seen issues on my LCD and 1-wire bus. The 1-wire bus is no longer an issue since I narrowed the spark gap, and stopped using the one badly grounded outlet in my garage. Additionally, I added some code to filter out any bad readings from the DS18B20. The DS18B20 will return a reading of 185 deg F if it is reset. I filter this out by looking at the previous value to determine if it has instantaneously jumped to 185 degrees. The LCD completely goes crazy when it gets hit with the EMI. However, a quick init command quickly fixes the problem. There are a few other places that you could potentially see issues even with a headless setup. All of the gpio are low current lines so they could potentially be affected. Keeping all of the wires associated with the gpio as short as possible should minimize any potential problems.


Where would you put the thermocouple? Do you think that they could withstand the prolonged exposure to the burner? I am not familiar with flame rectification. This might be an interesting option if it can withstand the high temps from the burner. Are these used in pilotless applications?


Not a bad idea, I might have to try the stake idea sometime. all of my equipment is grounded to the house ground right now but a more direct route to the earth might work a little better.


I like the simplicity of the pilot but I'd be worried about the wind blowing it out. I would absolutely not use a pilot unless a thermocouple was used with it. I think I've seen a few threads where people use some Honeywell pilot valves off the shelf. Some of these might even have electric ignition for the pilot.
I think any standard furnace thermocouple could be used to sense the flame. They are rated for continuous sensing of the pilot flame, so I think they could work for sensing flame from the burner as well. McMaster and other vendors sell K type thermocouples rated for very high temperature that could also be used, but the off-the-shelf furnace thermocouples would work and would be cheaper. You could source them from your local big box hardware store.

The hot surface ignitors are used in modern furnaces and gas dryers. They are a bit more expensive than sparkers, but would not have the EMI issues. They are designed to withstand the heat, and are often used in combination with a flame rectifier/flame sensor. I think this would be the best way forward.
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Old 01-09-2014, 05:29 AM   #23
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I think any standard furnace thermocouple could be used to sense the flame. They are rated for continuous sensing of the pilot flame, so I think they could work for sensing flame from the burner as well. McMaster and other vendors sell K type thermocouples rated for very high temperature that could also be used, but the off-the-shelf furnace thermocouples would work and would be cheaper. You could source them from your local big box hardware store.

The hot surface ignitors are used in modern furnaces and gas dryers. They are a bit more expensive than sparkers, but would not have the EMI issues. They are designed to withstand the heat, and are often used in combination with a flame rectifier/flame sensor. I think this would be the best way forward.
I think that the cheapest and easiest flame sensing idea would be the 1-wire + thermocouple idea. My only reservation is whether or not they can withstand the prolonged exposure to the burner. I've had to replace one on my hot water heater that was only on the pilot light. On the other hand, they are fairly cheap to replace if they go out. I think that it was only about $12 so the whole setup would be under $20 with the 1-wire thermocouple sensor. I might have to try this out sometime in the future. I think the 1-wire code would be easy to write and it has the added benifit that I don't have to rewire anything in my control panel
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Old 01-09-2014, 05:42 AM   #24
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In the case of the turkey fryer, it's there to energize a small coil that allows the gas safety valve to stay open. So, no flame the coil de-energizes, allowing the valve to close, that's why you have to hold the red button to light it for 30 seconds or so.
I looked up thermopiles and it looks like they consist of multiple thermocouples configured to produce a greater voltage than a single thermocouple. I think that they would be the best choice if we were going to design a circuit that would interface with the gpio. However, I think that the 1-wire thermocouple solution would be the easiest to implement. Thanks for the info!
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Old 01-09-2014, 03:23 PM   #25
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I think that the cheapest and easiest flame sensing idea would be the 1-wire + thermocouple idea. My only reservation is whether or not they can withstand the prolonged exposure to the burner. I've had to replace one on my hot water heater that was only on the pilot light. On the other hand, they are fairly cheap to replace if they go out. I think that it was only about $12 so the whole setup would be under $20 with the 1-wire thermocouple sensor. I might have to try this out sometime in the future. I think the 1-wire code would be easy to write and it has the added benifit that I don't have to rewire anything in my control panel
I agree that the thermocouple through the MAX31850 1-wire would be the easiest to implement, especially since you've already worked out the 1-wire bus for temperature probes.
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Old 01-20-2014, 05:50 AM   #26
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Hey guys, any thoughts on flame rods? Would the "flame diode" thing work for arduino/Rpi? if not, the thermocouple/1 wire method seems pretty srtaightforward.
http://www.ebay.com/itm/PFS401-Unive...-/380817076039

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Old 01-20-2014, 05:52 AM   #27
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Tob77, qq - how are you mounting the ds18b20? is that a specialty fitting or ...?

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Old 01-21-2014, 07:48 AM   #28
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Hey guys, any thoughts on flame rods? Would the "flame diode" thing work for arduino/Rpi? if not, the thermocouple/1 wire method seems pretty srtaightforward.
http://www.ebay.com/itm/PFS401-Unive...-/380817076039
I looked a little further into flame rectification, and it looks like it would be fairly difficult to implement. About 30VAC is placed on the flame sensor and then DC microamps are measured off of the burner (ground). I looked around a bit for an off the shelf flame rectification module but couldn't find anything useful.

I'm not sure that the MAX31850 will work with pilot thermocouples because they may not fall into the supported thermocouple types K, J, N, etc. There are some $6 K type thermocouples on amazon that have a max of 1250 deg C. I don't know if these will work or how long they would last though. I think that a propane burner can get fairly hot so idk.

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Tob77, qq - how are you mounting the ds18b20? is that a specialty fitting or ...?
I am using a stainless 1/2" Tee and 1/2" NPT to compression probe fitting from brewhardware.com: http://brewhardware.com/thermometers...becompression2
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Old 01-21-2014, 08:36 PM   #29
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So I've been looking around for a solution. I'm concerned about the low voltages of most thermocouples, though we're not really looking for max precision just "is fire"/"is not fire", so that may be okay. I've ordered a k type thermocouple to play with. I'd get one of those maxim one-wire pieces, but they seem to be out of stock everywhere.

I'm thinking that flame rectification has similar issues, plus the added challenge of a proper electrical ground.

I've found a possible third (fourth?fifteenth?) solution in robotics, where they are using an infrared sensor to find flames http://www.amazon.com/3-5-5V-Detecti..._bxgy_hi_img_y

Not sure it would work, but it's built for arduino and should be pretty easy to implement. May be worth trying for $4.

Thanks for the info on your thermowell.

Cheers!

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Old 01-22-2014, 07:24 AM   #30
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I'd get one of those maxim one-wire pieces, but they seem to be out of stock everywhere.
It looks like mouser.com has them in stock. They have the right part number but the description isn't quite right. Alternatively, you could try and get a sample directly from maximintegrated.com. It looks like they only make them in the TDFN (Thin Dual Flat No Leads) package that is kind of a pita for us.

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I've found a possible third (fourth?fifteenth?) solution in robotics, where they are using an infrared sensor to find flames http://www.amazon.com/3-5-5V-Detecti..._bxgy_hi_img_y
I ran across those when i was looking around as well. They sure would be easy to use with the rpi and Arduino, but I don't know how to mount one without it melting up from the heat. Maybe a glass heat shield? mirrors? will sunlight give a false positive?
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