IR Temperature Detection with sensitivty of 1 degree - possible?

[MIMSAR]

Hi,

I'm trying to design a system which will be able to detect a hot object on a cold surface. The downside is the temperature difference is only 1 degree celcius and I'd like to use IR from a distance of about 10cm (further away preferred if possible).

Does anyone with any experience of this know a suitable sensor or system I could use please. I'm guessing some form of calibration will be needed to tell the system the temperature of the cold surface first.

Thanks,

 

[joelupchurch]

The handheld Fluke Thermal Imagers I've used could detect differences down to 1/2 a degree C. They weren't that great for detecting the absolute temperature, but on a false color display, the relative differences were easy to see.

You might need to shop around. My experience was from a couple of years ago, but the cameras are very expensive. We leased rather than purchased one. We wanted a camera that could export the numeric data so we could do more quantitative analysis of the temperature gradients.

 

[MIMSAR]

Thanks. I've actually used a thermal imager and found it to be quite effective. However, I'm now trying to build my own system tuned to the required temperature and the ability to interface with other components. Are there any suitable sensors/circuits, ideally giving an analogue output of the temperature at the focus?

I considered an IR laser thermometer but wondered would the beam of IR actually heat the object up in addition to reflecting to give a temperature reading?

 

[joelupchurch]

You can buy thermal imaging cameras with USB interfaces like this:

http://www.infraredcamerasinc.com/fix-mounted-thermal-imaging-equipment.html"

I've never priced anything like this, but I'd imagine it is pretty expensive.

IR laser thermometers are still passive sensors. The laser is just for aiming. The aren't very accurate, but plenty good enough for detecting hot spots on circuit boards or in the AC system is working.

If you need a fairly precise infrared temperature, check the Omega catalog:

http://www.omega.com/search/esearch...ed+Sensor&submit=Search&ori=Infrared+Sensor+"

 

[Mike_In_Plano]

I've done this using infrared thermocouples. You can purchase them at Omega.com. There are a couple of downsides to using these:

1. The signal level is tiny - on the order of 50uv/C
2. They have a high impedance - several k-ohm, the leakage current of many standard thermocouple meters will swamp the circuits output.
3. They're affected by their case temperature - ours was compensated by a constant temperature jacket.
4. They're affected by the emissivity of the surface. We used a rough surface to help compensate.
5. Ours had a Germanium lens. Touching the lens was enough to start it corroding.

The easiest, most sure way of taking this measurement is to point the sensor at one surface, take a reference reading, point it at the other, take another reading, and then subtract the difference. This will make up for a great many shortcomings in the system.

Good Luck,

Mike