IR photodiode or phototransistor (Flame detection)

[xawtor]

Hello,
May I obtain your recommendations on a design suitable to detect a flame 10 meters away?

Our objective is to find an infrared photodiode or phototransistor for a fire-prevention product.
It needs to be able to detect a hot stove element ten meter away (with or without a fire on it),
while at the same time yielding the maximum dynamic range and accuracy for faraway heat sources.
(i.e. hopefully the microcontroller ADC can determine if a candle 10 meters away is lit / unlit with great precision)

Our research on fire has led me to the conclusion that carbon-based fires emit the most infrared rays at an average 4.3 um.
Is an IR detector at that range possible, while keeping a very tight budget (hopefully under 0.30$).

Any other information is appreciated as well, thanks!

 

[sky_123]

A thermopile or microbolometer will do it, but sadly they are not cheap.
Maybe open up a non-contact thermometer? Otherwise, Farnell sell ZTP-135S which
should work (I've not tried it).

 

[betwixt]

If the heat is coming from a stationary source, you might consider using two thermistors, one in a lens pointing at the source, the other close to it but not in the lens to take the ambient reading. The difference between them would indicate that heat was being produced and may be able to measure how much.

Brian.

 

[jiripolivka]

You can experimentally find the best IR element to use. As you need to detect IR radiation from a flame or a fire over ~10 meters distance, you need a suitable IR telescope (instead of a lens use a small parabolic mirror (the bottom of aluminum Coke can works well). To get the required sensitivity, I would add a mechanical modulator (a rotating wheel with holes or gaps) to interrupt the incoming radiation. To detect a fire alarm, you can use an audio amplifier and speaker which will sound if a fire or high heat is detected.

Many years ago I built such simple device, with two photodiodes (one as a reference), an audio opamp feeding a transistor switch that operated as a synchronous detector. With a small propeller (3 cm dia.) as the modulator I could hear and measure IR radiation from a bulb or a hot iron over >10 meters, and light from street lights over one kilometer.

 

[xawtor]

Wow, thanks for all your awnsers! Serves me right for not checking every 5 mins, you guys are amazing!

@Sky_123
The detector will be aimed at the oven, so yes, we are looking at a stationary source.
There are quite a number of possibilities, and I would love to try them all out. Thanks for the pointers!
What is inside a non-contact thermometer? Perhaps it would be a good idea to buy one a see for myself. I'll keep you posted. Sadly, we want to build a couple of these things, so price is an issue.

@betwixt
That's crazy and cheap! Can thermistors really be that directional with a lens? Are there companies that make lens adapted to thermistors, or would it be more of a DIY endeavor? How would we check the difference between a really hot stove and a fire on the elements? A mechanical filter at 4.3um, perhaps? Tell me what you think.
Is there something I should know while choosing one of said thermistors?

@jiripolivka
We will buy a couple of IR sensors, make a lot of tests, find out for ourselves what's good and what's bad. The parabolic mirror is to concentrate the rays, right? The fire alarm is meant to be inside, is it still needed? You'll have to explain the propeller/modulator concepts, I am baffled.

@ Everyone
For the design, we want it to be as low power and low cost as possible. For the photosensors, do you have any insight on photodiodes and phototransistors?
Should we use a photodiode and amplify the signal completely through an opamp, or should we use a phototransistor and use less power in the opamp?

I know it's a lot of questions, but what should we look out for when checking opamps?
Once again, thanks for all your help!

 

[jeffrey samuel]

my pal photo diode works on the intensity of light falling on it and not on IR rays falling on it

next the current of the photo diode is in the order of micro ampere so additional current amplifiers are required

photo transistors also produce current for diverse intensity of light but in the milli ampere line

if you are going to detect IR better go for thermo piles and stuff they are more help ful

 

[betwixt]

The parabolic reflector idea is a good one. I stress I have never tried this but I think a thermistor should be adequate. Photo diodes are fine when a fast response time is needed but they are more expensive and as mentioned they only produce a tiny output which needs amplification. A physically small thermistor will have a reaction time of only a few seconds and its output can be quite large if wired in a potential divider circuit. They are also immune to light of course.

I would experiment and see if further filtering is needed, you may find the difference between heating and igniting is big enough that they can be reliably distinguished.

Brian.

 

[Jestin_cubetech]

**broken link removed**

[url]http://www.hobbycomponents.com/index.php?route=product/product&product_id=144

[/url]

 

[jiripolivka]

Wow, thanks for all your awnsers! Serves me right for not checking every 5 mins, you guys are amazing!

@Sky_123
The detector will be aimed at the oven, so yes, we are looking at a stationary source.
There are quite a number of possibilities, and I would love to try them all out. Thanks for the pointers!
What is inside a non-contact thermometer? Perhaps it would be a good idea to buy one a see for myself. I'll keep you posted. Sadly, we want to build a couple of these things, so price is an issue.

@betwixt
That's crazy and cheap! Can thermistors really be that directional with a lens? Are there companies that make lens adapted to thermistors, or would it be more of a DIY endeavor? How would we check the difference between a really hot stove and a fire on the elements? A mechanical filter at 4.3um, perhaps? Tell me what you think.
Is there something I should know while choosing one of said thermistors?

@jiripolivka
We will buy a couple of IR sensors, make a lot of tests, find out for ourselves what's good and what's bad. The parabolic mirror is to concentrate the rays, right? The fire alarm is meant to be inside, is it still needed? You'll have to explain the propeller/modulator concepts, I am baffled.

@ Everyone
For the design, we want it to be as low power and low cost as possible. For the photosensors, do you have any insight on photodiodes and phototransistors?
Should we use a photodiode and amplify the signal completely through an opamp, or should we use a phototransistor and use less power in the opamp?

I know it's a lot of questions, but what should we look out for when checking opamps?
Once again, thanks for all your help!

I like the UV TRON by Hamamatsu as it senses a flame without expensive filters.

You can test a pocket IR thermometer, but try to find one with an analog output. I tried EXTECH but only OMEGA IR thermometers also have the analog output to indicate a flame.

Those IR thermometers utilize a thermopile or a PIR sensor and their response is slow, ~ 1...5 seconds. Also thermistors are slow in response.

Photodiodes are fast in response, and allow the chopping as I described. THe chopper disk alternates the ambient and target temperature to hit the sensor by an audio frequency. So the output is an audio signal which is easy to use to trigger a fire alarm.

MOst other sensors are slow and too much affected by te ambient temperature, drafts, etc.

 

[jeffrey samuel]

I would experiment and see if further filtering is needed, you may find the difference between heating and igniting is big enough that they can be reliably distinguished.

Brian.

I have this same question in mind your design may suit well in the Arctics and in cooler places but in the equatorial areas especiaaly in the month of May your design will not be able to stand cos of high levels of IR radiation go for something more reliable experimenting it is the best possible solution