Infared thermometers

[digger242j]

Since the subject of infared temp guns came up in Dynamike's "slip and fall" thread I decided it was time to get one. In another thread, on another site, John Parker had commented that they were only useful for those doing liquid applications, but regardless of that opinion, I thought at the very least it would be a good educational tool for myself--I'd like to study how pavement temps change in relation to air temperature, especially over prolonged periods of cold, and what influence sunshine etc. may have.

Based pretty much on HerkFE's high opinion, I bought a Fluke 61 at Grainger's this afternoon. Since then, I've been gleefully taking readings from anything that'll stand still, and a few things that won't. Now I'm puzzled...

Most of the readings I've gotten are lower than credible. Bare asphalt pavements have shown temps around 10 or 11 degrees, but in some cases lower than 0. The air temp this afternoon is in the high teens. Daytime highs and nightime lows have hovered in the neighborhood of 10 to 20 degrees for the past couple of days, and certainly haven't been down to 0. Thus, I find it difficult to believe that the pavement is that cold, especially in midafternoon.

The instructions do say something about the unit needing 30 minutes to adapt to ambient air temperature changes, which is why it's sitting outside on the windowsill right now--all the readings I took earlier were immediatly after getting out of a warm truck. I sure hope I don't have to let the thing ride around in the bed of the truck to get accurate readings from it.

I also wondered if there's some sort of anomaly due to the pavement's emissivity being something other than that which the unit is set for. From reading the instructions it wouldn't seem so, but I don't know.

The other thing I wondered is if there might be a greater error in the readings that are so close to the bottom end of the scale--it's only supposed to read down to 0 degrees F.

Anybody have any suggestions? Maybe I'm just pushing the button with the wrong finger? Or is the pavement *really* holding on to the cold that much?
:huh

[HerkFE]

I haven't seen any problems with my unit. What I did to check it was to verify its temp reading against a reading taken by a thermocouple type thermometer that was in direct contact with the items being checked. I tried it against pavement, concrete, and the plastic tank we carry our liquid in on the truck.

Everything I saw was within a degree or two of each other with no real trend of one always being higher etc. I didn't even read about the ambient temp thing you mentioned, I just shoot it and go.

If you want a simple test, fill a thin wall container with water and lots of ice cubes. Give it a few minutes to stabilize and check the temp of the container. You will see that it is normally around 33-34 degrees. I tried it with my direct read and my infrared and it checked good. Not the most absolute, but a good place to start.

Hope this helps....

Pete

[Alan]

I've got a Raytek and I've wondered about the accuracy myself. I've seen those same wacky readings. I got one that made absolutely no sense. Just fooling around with it I shot my truck seat, air temps were about 10° and the truck had been sitting outside all night. An object surrounded by air can't be colder than the air without some external factor being involved, but the seat was (supposedly) right a 0°.

[digger242j]

As mentioned in my first post, I left it sitting outside on the windowsill. When I first took it out there I shot the concrete porch, the first piece of concrete past the porch, the snow on that concrete, and the plastic recycling bin sitting there. I just shot all those things again, and even though it's several hours past sunset all the readings were 7-12 degrees higher. NWS says it's 13 out there now. The concrete reads in the twenties now, and the recycling bin reads 17. I think it read 6 this afternoon, which was colder than the air temp at the time. Those readings make a lot more sense.

It was kinda neat earlier when I was out driving. While I waited at a red light I scanned over the heater box under the dashboard. At one end it read around 99 degrees, and six inches to the left of there it read 134. I guess that must be where the heater core is.

Experimenting will continue...

[GeoffD]

To get accurate pavement temps it is important that the thermoter has time to adjust to the air temperature. This is why my salt trucks run the road watch system, road watch shows both air and ground temp inside the cab. This system cost 500 but it is mounted to the drivers side mirror and is very accurate. The only thing that effects road watch is when we key up our radios, only a few frequencies causes this with the system. We just happen to use one of the radios that causes this problem.

People will argue that hand held is the way to go and its a good starting point. People will also say that hand held will allow you to check walks, pavement temp at the lot will be pretty close to the walkway. The problem i see with is a hand held is you are taking it in and out of a truck, this doesn't allow the thermorneter to adjust to the air temp. The trucks temp is say 55 to 60, but the air temp is 40, it take about 20 mins for these thermorneters to adjust themselves. When we back a salt truck out of the garage even at -1 the air temp will still be 55 which is the shop temp for 10 mins or so, the ground temp will also be off.

My advice is your serious buy the roadwatch it is always on your truck and is very acurate.

Geoff

[digger242j]

Well, I'm serious enough to spend the $116 it cost for the handheld unit, but my intention there is to find out if the information I'm able to gather with it is actually useful given our particular situation. Like I said earlier, I hope it'll at least prove to be educational. I'm not quite serious enough yet to spend $500 per truck on the Roadwatch system though.

So, Geoff, I take from your reply that the answer to my question is "Yes, it needs to ride around in the bed of the truck if you're going to get accurate readings from it."

I figured it'd be useful to know what the air temps are at the same time I'm measuring the pavement temps, so I stopped at the hardware store and made another substantial investment--$2.63 for a plain old thermometer that I'm going to attach to the sideboard of the dumptruck.

Thanks, guys, for the replies. I'll let you know what I'm able to learn by using it...

[GeoffD]

Yes either ride around in the back of the truck or stand there for 20 to 30 mins while the thermometer adjsut to the air temp.