Heat sensing, with IR diode?

Only if it is going to reach 800K or more. You would be much better off cannibalising a PIR burglar alarm sensor and tweaking it a bit.

They are optimised for detecting movement or change so you might need to interpose a chopper or do radical surgery to the sensor assembly.

Or find a supplier of the sensors for non-contact thermometers.

Use a thermopile. Hamamatsu sells them, and they're super easy to use. Pyro electrics are okay if you chop them, provided you know where the signal is coming from when the chopper is closed--it'll be either the chopper tempera ture, the detector board temperature, or somewhere in between.

A thermopile comes with a built-in thermistor and it gives you a DC reading of the temperature difference between the sensor and the scene.

Cheers

Phil Hobbs

roelectrics are okay if you chop them, provided you know where the signal i s coming from when the chopper is closed--it'll be either the chopper tempe rature, the detector board temperature, or somewhere in between.

ng of the temperature difference between the sensor and the scene.

I assume you missed this part :

Let's say that there is no other option than a contactless method.

It is contactless! (optical).

Probably both. PIR motion sensors use a vertically split sensor connected d ifferentially, with a segmented Fresnel lens to cast about a dozen images, so that tall narrow warm (or very cold) objects create an AC output as the y move. The AC is detected and rectified to control the switch. (It's a pre tty slick scheme actually.)

It's simple to pull off the lens, but less simple to defeat the differentia l action without damage. A little bit of aluminum tape covering one half mi ght work.

Cheers

Phil Hobbs

A chopper close to the elements can block the PIR elements in sequence to create AC signal. If you know the phase, you can measure if the target is warmer or cooler than the detector, too.

Also check the element geometry; dual element or quad with 2 outputs are much easier than quad with single output. Duals are also cheaper.

But the thermopiles you mentioned are way easier.

What is 'fast'? The pyroelectric IR sensors I worked with in the distant past were kinda slow... milliseconds. (But they may make faster ones these days.)

George H.

Look for thermopile sensor like:

or "Non-contact Infrared Temperature IR Sensor": MLX90614 $4 at

etc...

Regards, Arie

Macroscopic objects aren't going to heat up any faster than that anyway.

Cheers

Phil Hobbs

These are the ones we use:

Cheers

Phil Hobbs

Yeah, you could do that if you can get the chopper close enough. It would work better as well, since the DC bias on the sensor output isn't well defined--it's basically V_GS of a cheap small JFET, which varies all over the place.

Cheers

Phil Hobbs

Here's another one:

Omega makes high-end stuff, $200 and up.

Handheld IR thermometers are cheap on ebay or Amazon.