Thread: Hand held lazer thermometer

I have had 3 held lazer thermometer's and used others from other inspectors. Several times I have held two units side by side, (All with fresh batteries) and gotten temp differences as mucy as 6 degrees. Wonder if anyone else had any comments on the accuracy of these devices? or has anyone did an comparison between two units side by side?

Gene

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Originally Posted by Gene South

I have had 3 held lazer thermometer's and used others from other inspectors. Several times I have held two units side by side, (All with fresh batteries) and gotten temp differences as mucy as 6 degrees.

Gene,

Were the units identical units? If not, there could have been differences in the cone of influence, a higher ratio means a tighter cone of where the unit reads, a lower ratio means you may be reading the entire neighborhood (okay, not quite that bad, but you get the idea - it makes a big difference).

Also, holding two high ratio (small cone of influence) side by side and you are actually reading "different areas".

Additionally, it would depend on what you are measuring and the consistency and evenness of the temperature across the surface being measured, taking into consideration that surface area could be quite large.

Hi Jerry. The ones I used today were not identical. One was a pistol grip type and the other a small compact handheld unit. The similarity is they were both manufactured by the same company and both units were brand new, right out of the box. One said it as a 6:1 distance to spot ratio and the other had a 8:1 ratio. I measuered 4 objects at a distance of four feet and got the different temperatures. When I said side-by-side, I actually meant I measured the same spot in succession, so they were measuring the same spot, as close as I could tell.

Gene

Originally Posted by Gene South

One said it as a 6:1 distance to spot ratio and the other had a 8:1 ratio. I measuered 4 objects at a distance of four feet and got the different temperatures.

At four feet the 6:1 measured a spot about 7" in diameter, the 8:1 measured a spot 6" in diameter - those should be fairly close in temperature as on even wall (meaning all shade, not near a window or door, nothing to really affect the temperature from the back side of the wall or the front side of the wall facing you).

Also, being as those units are not calibrated, their accuracy for actually being accurate as suspect, i.e., suitable for general temperature reading and comparing surface temperature to surface temperature of different areas, but not in comparing surface temperatures between units.

A better check would be to mark out two areas on different walls and check each area with each unit and compare temperature differences, not actually temperature readings.

As stated in posts above, it depends on the emissivity they are set at.

Kind of like using my sound level meter, the Fire Marshall using his, and the fire alarm installer using his, all to read the dbA of the sounders. The Fire Marshall's and mine consistently read 2 increments apart, with the fire installers reading another 2 increments different but varied slightly (also was difficult to hold all three and precise aim at the same direction when a slight change in direction made a difference in the reading), so we averaged the readings for a 'consensus' reading and went with that.

• Standard Infrared Thermometers
• Intended for general purpose applications.

• Fixed emissivity: 0.95

Infrared Thermometer, Temp Range -25 To 999 F/-32 To 535 C, Accuracy +/- 1% Of Reading, Spectral Response 8 To 14 Micrometers, Distance To Spot Ratio 12 To 1, Repeatability 0.50%, Single Point Laser Sighting, Emissivity Fixed 0.95, Display LCD With Backlight, Response Time 500 ms, Hand Held, Features Maximum Temp Capture, Includes Hard Case, Wrist Strap, 9 V Battery, Manual

Sorry

That info is for a Fluke 63. There is a bit to take into consideration when picking an IR Thermometer. These go for about the mid 2s. Everyone I bought over time that was less expensive, and I have bought a lot of them over time for myself and others, where just not worth the savings in price.

Gene,

Are these laser thermometers or infrared thermometers with laser pointers?

Hi Bruce, they are infared with lazer pointers. Sorry, I should have clarified that.

Gene

What's that quote?

"A man with a watch knows what time it is. A man with two watches is never quite sure." -Lee Segall

Originally Posted by Gene South

Hi Bruce, they are infared with lazer pointers. Sorry, I should have clarified that.

Gene

GS: Actually, those are "laser" (Light Amplification by Stimulated Emission of Radiation) pointers and not "lazer".

As I think about it since one had a 8:1 ration and the other a 6:1, then the distance may have accounted for the temp differences. All these thermometers will read warmer the closer to the object. I had them both at four feet, but since the ratios were different maybe the 6:1 had to closer to achieve the same temp rating ? Anyway, thanks for input from all.

Gene,

There are a few factors that effect the accuracy of a single point IR thermometer - each being a trade-off based on costs.

Detector type and filter - this selection is based on the wave length band selected for operations which can vary from one thermometer to another.

Optics - will generally define "spot size" a.k.a. D:S ratio. Placing different types of I.R. Thermometers side-by-side may result in different spot sizes in the test measurement.

The laser has absolutely nothing to do with the accuracy of the measurement! It is like a marksman on the shooting range using a laser or optical sighting (cross hair telescopic lens) either way can hit the target depends on operator skills.

Almost 85-90% of temperature measurement in the industry is more a case of "repeatability" as apposed to accuracy because most measurement are relative and not absolute. Hence they can get away with a "fixed" emissivity type thermometer. Generally speaking, a variable emissivity device does not increase costs that much, so why not have it? I guess it is more a case of trying to simplify the use for the operator.

All the best - Richard

Originally Posted by Gene South

All these thermometers will read warmer the closer to the object.

I've never heard that before. What I suspect is actually happening is when you are getting the lower temperatures you are too far away from the warm body you are trying to measure. The warm body does not completely fill the circle being measured so the cooler surfaces surrounding the warm body are lowering the average temperature of the circle of measurement.

As you move the IR thermometer closer to the warm body the warm body fills more of the circle of measurement (and likewise the coolers surfaces surrounding the warm body fill less of the circle of measurement) so the average temperature measured in the circle of measurement goes up. The temperature will no longer increase as you move the IR thermometer closer once the warm body completely fills the circle of measurement (assuming the temperature is uniform across its surface).

The small dot of the laser pointer on an IR thermometer can give you the false impression you are measuring only the body you are interested in when in reality the circle of measurement is much larger than that body. A flashlight casts an increasingly larger circle of light the further away it is moved from an object. Similarly the circle being measured by an IR thermometer increases in size the further it is moved from an object. To ensure accurate temperature measurements the object being measured should completely fill the circle of measurement.

Originally Posted by Bruce Breedlove

To ensure accurate temperature measurements the object being measured should completely fill the circle of measurement.

Which means only buy infrared thermometers with high ratios, 6:1 is good for measuring the temperature of a cup of coffee from within 12 inches vertically above the cup of coffee ... not much good for anything else an HI would want to measure ... and when within 12 inches of the cup of coffee you can feel it is hot, no need to use the infrared thermometer on it.

Absolutely right, Jerry. If the spot (the circle of measurement) is larger than the object being measured the measured temperature will not be accurate.

Let's say you want to measure the temperature of a 5"X11" ceiling register in a 12' ceiling. Assume you hold the IR thermometer 7'-6" above the floor; that means the ceiling register is 4'-6" from the IR thermometer. If your IR thermometer has a D/S (distance to spot) ratio of 6:1 the diameter of the spot at the ceiling will be 9" (54"/6). Even with your laser pointer centered on the register the spot (the circle being measured) extends 2" on either side of the register meaning you are measuring the temperature of the register and part of the ceiling.

In this example if your IR thermometer had a D/S ratio of 12:1 the diameter of the spot at the ceiling would be 4.5" (54"/12) so if your laser pointer was centered on the register the register would completely fill the spot and you would get a more accurate temperature measurement of the registe.

Originally Posted by Bruce Breedlove

if your laser pointer was centered on the register the register would completely fill the spot and you would get a more accurate temperature measurement of the registe.

Most laser pointers are not centered within the spot (are any?) and are mounted to one side or above/below, which means you need to allow for the laser offset, otherwise your laser could be centered but your spot is not.

My infrared thermometer with laser pointer is, oh, about 15 years old, and is a 33:1 ratio (pretty much the highest available at the time). In the time since then technology has improved and 50:1 ratio is now common.

Originally Posted by Jerry Peck

Most laser pointers are not centered within the spot (are any?) and are mounted to one side or above/below, which means you need to allow for the laser offset, otherwise your laser could be centered but your spot is not.

My infrared thermometer with laser pointer is, oh, about 15 years old, and is a 33:1 ratio (pretty much the highest available at the time). In the time since then technology has improved and 50:1 ratio is now common.

Good quality 12:1 260.00

Good quality 50:1 660

12:1 is the winner for home inspection use. If you do a lot of commercial or industrial equipment inspection then that would be the only reason one would have to venture higher than 12:1. Even 30:1 is way beyond what any home inspector would need.

Originally Posted by Bruce Breedlove

. . .

In this example if your IR thermometer had a D/S ratio of 12:1 the diameter of the spot at the ceiling would be 4.5" (54"/12) so if your laser pointer was centered on the register the register would completely fill the spot and you would get a more accurate temperature measurement of the registe.

Originally Posted by Jerry Peck

Most laser pointers are not centered within the spot (are any?) and are mounted to one side or above/below, which means you need to allow for the laser offset, otherwise your laser could be centered but your spot is not.

Poor choice of words, wasn't it? What I should have said was ". . . if you use your laser pointer as a guide and then center the spot on the register . . . ".

Jerry,

Just as a point of interest, most (I speak for Raytek/Fluke types) IR Thermometers are divided into 4 types of applications i.e. Utilities (~50:1), Commercial/Industrial (~30:1), General maintenance [HI's] (~7:1) as targeted for the USA market - so, although not stated it represents feet. The final category being auto/electronic application where non-contact is the preference and measurements are close to the target.

The lasers are centered to the application requirement. I am not sure I have stated this in a clear manner! Example the 7:1 spot size will give you 12" diameter at 7 feet and the spot is centered and calibrated to the 7 foot mark.

The optics are generally focused to the specific points I mentioned (theoretically the highest resolution) 50' 30' 7' etc....

Bet regards - Richard

Originally Posted by Richard Soundy

Just as a point of interest, most (I speak for Raytek/Fluke types) IR Thermometers are divided into 4 types of applications i.e. Utilities (~50:1), Commercial/Industrial (~30:1), General maintenance [HI's] (~7:1) as targeted for the USA market - so, although not stated it represents feet.

I would tend to agree with that statement except for ". . . although not stated it represents feet". The D/S ratio is just that - a ratio. A ratio has no units (e.g., feet, inches, meters) because it represents the relationship of one distance to another distance (the relationship of the distance between the IR thermometer and the object to the spot diameter).

Originally Posted by Richard Soundy

The lasers are centered to the application requirement. I am not sure I have stated this in a clear manner!

I have no idea what that means. The laser is simply a pointing device (much like a laser sight on a gun).

Originally Posted by Richard Soundy

Example the 7:1 spot size will give you 12" diameter at 7 feet and the spot is centered and calibrated to the 7 foot mark.

I agree that an IR thermometer with a D/S ratio of 7:1 will have a spot size of 12" (1') at 7'. Where exactly the spot will be centered depends on where the IR thermometer is pointed. I don't agree that the IR thermometer is calibrated for use at a distace of 7'.

Originally Posted by Richard Soundy

The optics are generally focused to the specific points I mentioned (theoretically the highest resolution) 50' 30' 7' etc....

Can you quote a source for that statement?

Bruce,

Firstly this reply was addressing Jerry's comments regarding "off set" lasers comment. Most lasers are offset, therefore Jerry is correct in his initial statement, except the laser aim is adjusted to the focal point. At the focal point it is centered and not off-set.

I agree it is a ratio, but strictly speaking that ratio only applies to the focal length of the optics. D:S of 7:1 will not give you a 1 mile spot size at a 7 mile distance, nor a 1cm spot at 7 cm distance due to the optics used.

In the case of Raytek/Fluke units the focal length of the optics were selected on the basis of the application. The first ratio number also happens to co-inside with the typical application/distance number if you read it as feet. Source of information - myself as an ex-Raytek person.

A drawing would be much easier than using words....

All the best - Richard

Originally Posted by Richard Soundy

Bruce,

Firstly this reply was addressing Jerry's comments regarding "off set" lasers comment. Most lasers are offset, therefore Jerry is correct in his initial statement, except the laser aim is adjusted to the focal point. At the focal point it is centered and not off-set.

OK, now I understand. What you are saying is that at some distance the center of the spot and the laser intersect and that the point of intersection is at a distance equal to the D/S ratio in feet. I will agree that the laser intersects the center of the spot (assuming the laser and the spot are in the same plane) but I will have to take your word for it that that distance is equal to the D/S ratio in feet.

Originally Posted by Richard Soundy

I agree it is a ratio, but strictly speaking that ratio only applies to the focal length of the optics. D:S of 7:1 will not give you a 1 mile spot size at a 7 mile distance, nor a 1cm spot at 7 cm distance due to the optics used.

Hmmm. The D/S ratio to me is a ratio. A D/S ratio of 7:1 means a spot size of 1' at 7', 6" at 3.5' or 2' at 14'. It also means a spot size of 1 mile at 7 miles or 1 cm at 7 cm (although those distances may be outside the working distance of the IR thermometer).