You're looking at a Fresnel lens sysem that we use for our infrared temperature guns. Notice the ridges along the tapering cone that lead down the barrel to the lens.
I've been hammering this theme home for a while as regards photoionization detectors, but I promised to bring it around to our infrared temperature guns and today I will,
Even though we handle 100:1 distance to spot infrared temperature guns with Class III laser sights, the situations that hazmat responders have to deal with can involve lots of smoke, dust, chemical leaks and or extinguishants. If you're not using our Top Temp Gun, it means you'll have to be even closer. With somebody else's infrared temp gun, say a 50:1 distance to spot ratio, you'll have to be twice as close to get a decent reading.
What is distance to spot ratio? For a 100:1 infrared temperature gun, it means that at one hundred feet you will be measuring a circle with a 1 foot radius. That's a tight spec. It's a real instrument that can save lives.
But what if, during an emergency run, you use your temperature gun in a smokey environment, or while your using it, extinguisher fumes blow your way. Or chemical fumes from a factory?
The answer is that you have to clean it, just like in the case of the PID. Swab the ridges and the lens with isopropyl alcohol. Most people forget to clean the ridges that lead up to the main lens. That's a cricital mistake. A bad mistake. Those ridges aren't there for nothing. They're part of the instrument's operative principle. So clean them as often as you clean the lens.
Clean them after every emergency you take the infrared gun to. That way you'll be sure to get more accurate readings. How inaccurate can the readings be if the unit's lens package (including the ridges)isn't cleaned?
I'll fill you in on that next time.