Optical infrared detector for 350~450 kelvin - Page 1
Forum section: electronics / projects

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 15, 2022, 03:57:24 pm
content: Does anyone know of any "light" sensor components that are sensitive to IR light from 350 to 450 kelvin.Basically, I just want to detect if anything is "glowing" in the 100 to 200 Celsius region, without need to have physical conduction.No need for imaging, just "single pixel", though talking about pixels already sounds like an overshoot.

author: Benta
author_rank: Super Contributor
timestamp: June 15, 2022, 04:57:55 pm
content: "Kelvin" doesn't really make sense here. You need to look at the wavelength of the sensor, and for heat/cold sensing, 10 um is about right.Not easy to find at reasonable prices.

author: Wolfram
author_rank: Frequent Contributor
timestamp: June 15, 2022, 05:40:49 pm
content: Blackbody radiation from a 400 K object should peak around 7.5 µm in wavelength, deep into the area where you need special materials to focus and detect the light. If you are looking for something on a budget, it might make sense to check out sensors made for IR thermometry or PIR motion detection. For the optics, ZnSe and CdTe lenses made for CO2 laser cutters are mass-produced and affordable, plastic fresnel lenses might also be worth looking at.Edit: for example the IRA-S200ST01A01 from Murata is specified as having good sensitivity in the 5 to 10 µm range, not bad for less than four bucks. Paired with a mechanical chopper and some optics, it could be a good starting point, depending on exactly what you are trying to detect. Also IR thermopiles like the ZTP-148SR could be worth checking out. It's hard to give more specific advice without knowing more about the application.

author: Benta
author_rank: Super Contributor
timestamp: June 15, 2022, 06:18:17 pm
content: @Wolfram, I stand corrected, 7.5 um is probably more on point. I mentioned 10 um to emphasize that standard IR receivers (870...970 nm) won't bring joy for this application.Interesting Murata part that you found, Thanks.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 17, 2022, 04:41:06 am
content: IR thermometers was indeed what I was thinking of.But it seems the bandwidth of the sensors is typically to wide, making it rather impossible to detect 150C without also responding to 100CYes, I am talking about Kelvin and Celcius rather then wavelength. I did that because black body is no single wavelength.I wonder how handheld thermometers manage to get such a precise number out of such a wide bandwidth black body.I always though I roughly understood how a IR thermometer works, based on popular explanation. Until one tries to build something similar itself, it seems.I'll study the PDF of those sensor numbers mentioned, maybe I'll be more equipped for the right questions afterward.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 17, 2022, 05:42:02 am
content: So I admit being very noob on this specific topic.But what I read up so far, Pyroelectric (or PIR) sensors like that mentioned IRA-S200ST01A01 (or anything from Murata) are completely not suitable, because they work by measuring energy deposited on their surface, without caring about the wavelength. So a small amount of 150C waves (yes I keep talking equivalence wavelength for convenience) has the same effect as a slightly higher intensity of 50C waves. The only way they can separate is with filterglass, which is how they filter out normal light. Also, they detect variations, so a permanent stable exposure to even 250C waves would not trigger it (except briefly at the start)Please correct me if I am wrong, of which I admit there is a reasonable chance.I did find however this sensor (and I am sure it has brethren):MLX90614Not so much a component as an intelligent sensor circuit, with digital interface, so I will need a uC to make a relay go click, but I think I will see if how ecpensive they are and if I can source some to play around with.

author: mjs
author_rank: Regular Contributor
timestamp: June 17, 2022, 09:21:10 am
content: Started almost like a XY-question!PIRs are inherently AC devices and almost all of them are 2 or 4 elements in antiseries mode to detect movement.Most thermopile sensors are sensitive to those wavelengths, but also other thermal radiation. Total amount is usually enough to determine object temperature. Then there are radiators that are not black bodies (metal surfaces being quite common), where you can use 2-wavelength measurement with filters to get better whiff of the target temperature.While sensor design is an interesting field by itself, I would just pick Melexis or some similar factory calibrated IR temperature sensor. Some of those even come with silicon lens for narrow field of view and most have quite impressive performance.

author: cybermaus
author_rank: Frequent Contributor
timestamp: June 17, 2022, 01:17:42 pm
content: Yep, got two Melexis MLX90614 incoming tomorrowReading the datasheet, you can even program it to use one of the I2C lines as a simple on/off relay driver.So it can be usedwithoutdigital uC, just directly link to a relay (well, with a fet inbetween)Making it to exactly what I wanted: A simple 3 wire component that responds to a specific non-contact temperature in it field of view.Edit: PS what do you mean with a "XY question"

author: boB
author_rank: Frequent Contributor
timestamp: August 23, 2022, 05:42:29 pm
content: Looks like the MLX90614 are like, $20 a piece or even higher.Do they need a lens like the Murata does (I assume) ?It looked like the MLX90614 had some directionality to it in the spec sheet but I could not find a wavelength sensitivity specification.boB