United States Patent 9,784,449 Flame Sensing System Issued 10/10/2017 to Margolin
Jed Margolin
ABSTRACT OF THE DISCLOSURE
This invention relates to the field of sensing flames in equipment such as gas furnaces by using the electrical properties of flames. In a first group of embodiments flame rectification is used to cause distortion of a signal having a selected waveform. A harmonic of the distorted waveform is detected thereby providing flame proof. In a second group of embodiments flame rectification is used as a mixer to cause two signals having selected waveforms to produce sum and difference signals. The sum and/or difference signals are detected thereby providing flame proof.
July 2024 - When I did the R&D for this patent I did it all with MSI. I didn’t know if it could be done in the microcontroller family I was using (the Texas Instruments MSG430G2xxx family) and I didn’t want to spend the time to find out. I also didn’t want people to think this was a software patent. Because it was MSI I wire-wrapped the several boards it took to do it. But as a result I could look at every signal in the process in real time.
It wasn’t until after I got the patent that I decided to see if I could do it with the MSP430G2xxx. In the first version I used it only to produce the four signals I needed (874 Hz, 1262 Hz, 388 Hz, and 388 Hz in quadrature.). I continued to do the quadrature detection in hardware. Then I did the version where I used the MSP430G2xxx ADC and did the quadrature detection in software. It totally worked. (I did several iterations on the board,)
Since then I have done a version using the Raspberry Pi Pico. This is the original write-up for the MSP430G2xxx version. Notice that I mention the Raspberry Pi. This was the standard Raspberry Pi, not the Raspberry Pi Pico which only came out in January 2021. I had a Raspberry Pi but I considered it too slow to be useful for this.
Here is my original write-up for the MSP430G2xxx.
I have done a reference design using a MSP430G2352 which produces two signals (1262 Hz and 874 Hz) and sends it to a standard flame rod. The MSP430G2352 does quadrature detection of the difference signal (388 Hz) which can only be produced by the non-linearity of flame rectification. When a flame is detected it turns on an LED and also turns on a relay which sends a robust simulated flame signal to the furnace control board. The system operates at low voltage as opposed to the standard method used in residential gas furnaces which uses the un-isolated Mains (which is barbaric). Do it with SMT and it will be much smaller.
The MSP430G2352 also sends the detected quadrature values out through its SPI port. I made another board to receive it and display the values on a 16x2 LCD panel.
This demo is using a Meker burner. It works even better with a furnace.
This board produces a simulated flame signal used for testing.
Here’s an idea.
Send the SPI port to a Raspberry Pi with WiFi Direct so it can be used either with a Smart Phone (or Tablet) or through your home’s wireless router so you can read the detected quadrature values. It they start to go down it probably means your flame rod is getting dirty. Either clean it or replace it before it stops working and you wake up to a freezing cold house.
Even better, use an optocoupler to detect the Call For Heat produced by the thermostat. Now you know when the Call for Heat was issued and when you got a flame. If this time period starts to get longer then, again, your flame rod is getting dirty. Have the Raspberry Pi send you an email or text message.
Now the Raspberry Pi can log all of the furnace starts (and stops) by time and date so you will know the percentage of time your furnace is running. An oversized furnace will run a low percentage of the time. On the coldest night a properly sized furnace will run almost continuously. (BTW, houses are subject to wind-chill, too.) Is your furnace oversized? If it is, it means the blower isn’t running often enough. You could add a relay to control the Call For Fan and have the Raspberry Pi turn the blower on periodically (or on a schedule) so your house is properly ventilated. (Do any of the fancy schmancy thermostats do that?)
Suppose you have a family member or friend who still lives independently with some help. The failure of a furnace on a cold night could be life-threatening. If the furnace fails (or is about to fail) have the Raspberry Pi send you an email or text message so you can help your family member or friend.
You can instrument the furnace to provide more data. Measure the blower motor current. If it starts to get higher then either the filter needs to be replaced or the blower motor is wearing out. Measure the current to the gas valve so you know when the gas valve has been ordered to open. Measure the current to the inducer motor and read the signal from the pressure switch. If something goes wrong you will have a good idea what it is and what parts you or your furnace repair tech need. And detect a Call For Cooling and detect that the A/C is coming on. A failure of the A/C can also be life-threatening.
You can also make a thermostat with WiFi that talks to your RaspBerry Pi. It won’t need any control wires to the furnace, only power. And the power doesn’t have to come from the furnace. It doesn’t even need to be a thermostat, only a temperature sensor. The scheduling would be done in your RaspBerry Pi at the furnace. All you need for the remote WiFi temperature sensor is a $5 RaspBerry Pi Zero, a power supply, and a BME280 temperature sensor. If you use a sensor that measures temperature and humidity you can control the furnace according to the Comfort Index. (And why do Google/Nest and Honeywell charge so much for their WiFi thermostats?)
Since the remote WiFi sensor only needs power you can move it to different parts of the house according to the season. Or you can have more than one so that at different times of the day (and different seasons) you can use a different sensor to control the furnace (or A/C).
The patent covers only the Flame Sensing System. The rest is up to you.
Maybe you could start your own company and someday eat Google/Nest's and Honeywell's thermostat and furnace control businesses for lunch.
This patent is for sale or license to principals only.
Jed Margolin
Virginia City Highlands
Nevada
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