Make some near Thermal Images with a normal Cam? - Page 1
Forum section: electronics / general

author: Lord of nothing
author_rank: Super Contributor
timestamp: April 22, 2020, 10:00:16 am
content: HiI found out when I did make a Picture with my USB Cam who have no IR Filter the cold Pan is Black and when the get hot the turn into Gray. So I guess the Cam dedect some hight Wavelength to?Can I improof that by Cooling the back of the PCB with an Peltier Element?Thanks

author: Fraser
author_rank: Super Contributor
timestamp: April 22, 2020, 11:24:53 am
content: You are seeing Infrared that falls within the capabilities of your sensor (likely CMOS) If you look at a Planck plot for the temperature of the pan you will see that energy extend into the photon detection capabilities of a silicon sensor. The limit of such a sensor is at around 1.1um.Quantum efficiency needs to be understood....https://www.photometrics.com/learn/imaging-topics/quantum-efficiencyA silicon detector as used in your camera cannot image above around 1.1um but if the targets Planck curve extends into the area below 1.1um it can be images. As a target gets hotter, it’s emissions extend into wavelengths closer to NIR and can be seen by the sensor. At very high temperatures the target is actually glowing cherry red or brighter and even the human eye can see the photon energyI attach a Planck curve plot that may help you.The sensor in your camera cannot change its wavelength coverage but cooling with a Peltier TEC lowers internal noise levels to provide greater signal to noise ratio. Even cooled it will only image targets that are very hot at over 400C (673K) or there abouts.Fraser

author: Vipitis
author_rank: Frequent Contributor
timestamp: April 22, 2020, 11:27:50 am
content: your webcam is likely silicon based cmos. Without a IR filter like you normally find in most consumer products, you get some response beyond the visible range. But it cuts off at around 1100nm. Very high energy sources do emit into the visible(glowing redhot to white hot) but before that they glow in the near infrared.Thermal cameras are generally in two categories, MWIR and LWIR the latter being 7.5-14μm wavelength, far beyond what a cmos can see.

author: Lord of nothing
author_rank: Super Contributor
timestamp: April 22, 2020, 12:02:31 pm
content: Why does a hot pan look gray and the cold black?I guessed the emit some wavelenght the Sensor show as light image?Sure when I finish it I make more picture to test that.I know its the wrong area here but is there an easy way to power an mini Peltier element via USB?Is there some self heat controlling one or does i also need to check temperature to stay above 0C?I mention in enough post I will make a 3d printed case for the cam so a Peltier element need to be planed to make a working product.Thanks

author: Fraser
author_rank: Super Contributor
timestamp: April 22, 2020, 12:26:29 pm
content: Black = no significant emissions within the cameras detectable range except visible light reflections so you see the black surface. Look at the Planck curve of temperatures against wavelength. Normal Ambient temperature in a house is around 21C which is 294K.Grey = some photon emissions from the hot pan are now falling within the photon detection range of the camera and in the absence of visible light, the photon emissions are being captured by the sensor. Again, look at the Planck curve for the 500K temperature.... it is nearing the wavelength where the photon emissions can be seen bu a silicon based sensor. The grey is ‘just’ light (photon) emissions from the pan.Peltier elements are power hungry and draw significant current. They can be run ‘open loop’ from a variable voltage and current power supply. Running such a cooler from a 500mA USB port is possible if you limit the current to the capabilities of the USB port. From memory some USB ports will not deliver the full 500mA current capability until after negotiating with the usb accessory. YMMV.Fraser