Infrared Flame Detector

Put a cover over it.

Outdoors?

IFR150XTOutdoor Passive IR Detector-Sicurit-Perimeter Protection--Fire Alarm

If you are going to use IR detection, an IR3 unit is indicated. An IR3 detector will compare three specific IR wavelength bands and their ratio to each other, reducing false triggers.

As with any IR detector, rainwater and dew are a problem, diffusing and effectively blinding the unit.

Early heat-seeking missiles suffered the same problem; one which was quickly solved by sensing both infrared and visible wavelengths. If the target was bright, a pretty safe bet it was the Sun and so don't chase it. If not bright, or not very, a pretty safe bet it is the intended target.

A related problem is that the Sun's intensity in the IR can saturate the detector when in full view, swamping any other IR signal which might be detected. One solution is to restrict the wavelengths reaching the detector to a narrow range of wavelengths typically emitted by a flame. Overall the Sun emits a great deal of IR, but spread over a wide range of wavelengths. Restricting the range limits the total energy falling on the detector from this source.

Another technique is to place the detector in a collimator, with or without a lens, effectively limiting the area the detector can see to that where a flame might be expected. The collimator can be as simple as a short tube where the detector is mounted at one end, facing inward, looking out through the other end of the tube. The length of the tube is a function of the angular diameter of the target area and the size of the detector's active area.

We make detectors which, among other things, are used to detect missiles launched at aircraft. These are photon detectors which are built with what is known as a 'solar blind' input that will not react to sunlight but will detect the UV component in a flame. These are further enhanced by using various optical filters on the input side. We test these by shining a 3kW full spectrum lamp on to them from 1m away then, from outside the test lab & separated by a window, flicking a cigarette lighter on. The detector will immediately see the flame.

Infrared Flame detectors are specifically designed to be "solar blind".

Any given manufacturer might not tell you how they do it, but it all comes down to built-in algorithms.

Additionally, these devices discriminate by looking for the characteristic IR wavelength spikes at the exact frequency which exists during a hydrocarbon fire.

Most devices today use either double or triple IR receptors, meaning they look for either 2 or 3 of these specific frequency spikes, as compared to ordinary background radiation (including that from the sun).

I don't know about other flame detectors but our detectors discriminate by having a photocathode response that is tuned to peak at the wavelength of interest, no algorithms involved. In fact, these can be used as passive devices with no electronics other than a power supply.

Focus.

Infrared from sun will be more or less stable, however from fire it will be intense and highly unstable. Fire alarm never directly looks at sun so what it gets is scattered and black body radiation from environmental temperature. From human body radiation peaks at about 10000ns at 37C. This peak will shift depending on the environmental temperature. From fire at above 700C you get lots of UV, visible and IR and mostly UV is sensed for high level fires and sometime IR for low level fires.

Try solar blind IR Sensor and Solar blind UV sensor to make your own fire detector, smoke detector or even a visibility detector.

I am working on low frequency wireless transmitters for detectors and just made this inductor for the wireless resonance tank circuit.