IR thermometer vs thermal imager

[Drakkith]

I mean quarantine checkpoints worldwide use solely ir thermometers in screening. They never use oral or armpit thermometers except in hospitals only.

And those thermometers very likely work just fine.

 

[Dr_Nate]

Do you know that putting 20C and 32C in the Reflected Temperature can affect the temperature even if the emissivity is 0.95? Yes, it can change it by up to 0.6 Celsius. In forehead measuring, this is important. So I was right in my previous 2 messages. You thought only huge reflected temperature could affect areas with low emissivity. But even high emissivity like 0.95 can change the temperature by 0.6 Celsius even if the reflected temperature varies by 20C to 32C only. Do you object to this?

Using your values, I did the math and got answers close to yours. I didn't take the wavelength range into effect so they will be a little different.

The problem is that your emissivity is likely wrong. The emissivity of skin is likely above 0.98. This reduces the amount of "reflected temperature".

I think you should do the experiment I said in post #46. This will show you how sensitive it is to reflected temperature. Set the imager to one set of values and do not change the settings through the whole experiment. Measure your arm in the room 5 times. Find and record the average of these 5 temperatures. Measure the same spot 5 times with your arm in the freezer (You need to make sure your arm isn't cooling during the measurements, so do it quick and remove your arm between measurements). Find another average. Measure the same spot outside in direct sunlight 5 times. Find another average. Then you can see how different environments affect your imager.

 

[chirhone]

Using your values, I did the math and got answers close to yours. I didn't take the wavelength range into effect so they will be a little different.

The problem is that your emissivity is likely wrong. The emissivity of skin is likely above 0.98. This reduces the amount of "reflected temperature".

I think you should do the experiment I said in post #46. This will show you how sensitive it is to reflected temperature. Set the imager to one set of values and do not change the settings through the whole experiment. Measure your arm in the room 5 times. Find and record the average of these 5 temperatures. Measure the same spot 5 times with your arm in the freezer (You need to make sure your arm isn't cooling during the measurements, so do it quick and remove your arm between measurements). Find another average. Measure the same spot outside in direct sunlight 5 times. Find another average. Then you can see how different environments affect your imager.

It took me an hour to do the tests above. This is because the imager is very sensitive (it can for example image the left over heat from the floor of the feet, etc.). As soon as I put my hand in the sun, the temperature increases very fast from the heat of the sun (2 seconds later). So I have to take many shots, and since the reading varies by each spot of the hands, I have to fix it at one spot. I managed to take one good shot. The effect is either only 0.1 degree Celsius or similar.

This is in the parking with the sun in the heated part of the pavement:

This is taking it in the shade.

This is when I put my hand in the heated area of the parking.

Difference of only 0.1 degree Celsius. And 1 or 2 seconds later, the temperature begins to increase due to the heat of the sun.

The imager is set to 0.98 emissivity with reflected temperature of 20 degree Celsius.

I think putting the values in the imager firmware means it has to subtract 2% of the software "reflection temperature" of 20 degree Celsius from the raw image it's taking? I wonder what is the temperature of the sun's rays? How do you determine the temperature of the sun's rays? And if it is high or a given value. You compute it by taking say 36 Celsius (actual) minus 20 Celsius (software setting) = 16 Celsius and taking off 2% of 16 Celsius deducting from the raw image temperature? How do you compute it?

I also tried putting my hands or fingers in the refrigerator. But the temperature decreases so suddenly (in milliseconds) I couldn't distinguish the reflected temperature from absorbed temperature. The imager is too sensitive in the freezer test to produce any useful data.