Fluke VT04 and VT02 Infrared Thermometer Review

Infrared thermometer or thermal imager?

The Good:

Excellent Fluke Quality
Excellent GUI, easy to navigate
Simple to use
Better than an infrared thermometer or spot radiometer

The Bad:

Poor Resolution, insufficient spot size for most electrical applications
Not fully radiometric, is truly a single point thermometer
Similarly priced to fully radiometric entry level thermal imagers
Part infrared thermometer, part thermal imager, the Fluke VT04 and VT02 Visual IR Thermometer has everyone asking the question… what exactly is it? Let’s take a look…

The reason for the confusion around this device is that Fluke call the new VT04/VT02 an infrared thermometer, yet it clearly provides a thermal image, albeit a low resolution one. Traditionally, an infrared thermometer has always been a single element (ie 1 pixel) detector device. The VT04 we tested clearly has more than a single pixel array, as it is able to crudely make out the shape of components and equipment.

Unfortunately the manual and the specification sheet do not disclose the actual pixel count on the detector. It is clearly quite low and I can only assume they don’t want to get into a competitive comparison with opposition models where people fight over who has the most inferior pixel count… it’s just taken of the table as a point of argument. The only measurement performance characteristics we are provided with is the spot measurement size and the thermal sensitivity, both of which are very useful from an operators perspective.

The VT04 has a distance to spot ratio of 9:1 with the smallest measurement being 26mm at 230mm. The VT02 has a distance to spot ratio of 6:1, with it’s smallest measurement being 38mm @ 230mm.
To put that into perspective, most entry level thermal imagers with a 160×120 detector have a distance to spot ration of approx. 100:1, with spot measurement sizes of 2mm at 200mm. Please note measurement characteristics differ considerably amongst brands, and this is a generalisation. The distance to spot ratio (DTS) is also quite low when you compare them to regular spot radiometers (infrared thermometers). Most standard models below $100 have a DTS of 10:1, with the more expensive models (still less than $300 to $800) at 30:1, or 50:1.

Now to be quite honest, after seeing the resolution of the VT04 we did not bother with the VT02. The VT04 claims to be 4 times sharper than the VT02, and that wasn’t particularly sharp.

The other performance characteristic we are given is the thermal sensitivity at 250mk, which is certainly acceptable for this kind of device, but still only half as sensitive as many competitive models. With such low resolution, assessing the sensitivity is almost pointless as the image is not sharp enough to discern any level of detail that would benefit from improved sensitivity.

Based on performance, it is aptly described by the manufacturer as a “Thermometer”.

The VT04 provides only single point measurement, and despite showing a thermal pattern across the image, does not provide radiometric measurement for the other temperature zones or points displayed in the image.

The image can not be post processed with respect to level/span or brightness/contrast settings as you would with a traditional thermal image. You can however select different colour palette, control the blending of the thermal and visual, and rotate the image should you need to.

So what about the rest of the claims….

“Breakthrough Affordability”
Yes, it certainly is for a Fluke unit, but not when you compare it against competitive models which offer significantly higher resolution for around the same cost.

“Built in Visual Camera”
The built in visual camera is excellent, and provides a great tool for documenting a piece of equipment. One of the shortcomings with a traditional infrared thermometers is you don’t know exactly where a reading was taken from (other than the operator’s description) or where the hottest point is to sample from. By providing the visual image overlay you can clearly see where the measurement point was on your target and the area of highest radiant intensity. To compensate for parallax error (natural offset of visual and thermal image) fluke have a very simple “near” and “far” adjustment on the user interface to align the visual to an acceptable level of alignment.

“Exclusive Thermal heat map blending overlay”
Mmmmm… this type of image blending hasn’t been exclusive for some years now and is utilised by most manufacturers. I am not sure what Fluke think they are doing exclusively but image overlay and blending is nothing new.

“No Training Required”
That is partly true, but it all depends what you are trying to measure. The product manual describes one of the key features: adjustable emissivity and reflected background compensation improves measurement accuracy on semi reflective surfaces.

Those features require a user input, and you would be well pressed to find an entry level user who could not only understand but measure and compensate for those error sources.
We all (thermographers) know users of Infrared Thermometers that have long been making measurement errors due to emissivity, reflections, and spot sizes being insufficient for the measurement task. Without sufficient training, users will continue to make these errors. Many of the application examples cited in the brochure include electrical components which are both small in size and made of low emissivity materials.
There is however a good warning in the manual…

Surfaces with an emissivity <0.60 make reliable and consisten determination of actual temperatures problematic. The lower the emissivity, the more potential error is associated with the temperature measurement calculations of the product, even when emissivity and reflected background adjustments are attempted and performed properly.

To prevent personal injury, see emissivity information for actual temperatures. Reflective objects result in lower than actual temperature measurements. These objects pose a burn hazard.

“True Pocket Size Design”
Fluke claim it’s “forty percept smaller than entry level infrared cameras”. Perhaps it’s smaller than their entry level cameras, but it’s about the same size as many other entry level thermal imagers on the market. It certainly is a very nice compact unit, it fits nicely in the hand and is slim enough to slide into your pocket. The size is quite convenient.

What’s it actually like to use….

As you would expect from Fluke, it’s a polished piece of equipment that lives up to the marque’s reputation. The user interface is excellent, the screen is clear, bright and easy to read. The menu is well laid out and intuitive. There is a sufficient number of navigation keys so you can make your way easily through the menu without having to use a confusing multifunction key. The icons are also quite intuitive and the camera is full of functions and options for the user to customise. Without reading the manual I was able to work out almost every function…. Except the “near and far” which I later discover were not focus, but parallax offset feature for the visual camera.

The unit simply charges of USB cable and/or the provide charger which is a great feature. It also stores imagery to a micro SD card, in the magnitude of 10,000 images!

What’s is it good for?
Personally, I believe this is a good tool for most in-house plant maintenance mechanical applications (think bearings, motors, and driven equipment) that would traditionally be tackled with infrared thermometers. The spot size for these applications would be sufficient and the visual aspect would provide a much improved data collection function over traditional infrared thermometers. The ability to visually identify the source of heat, or to confirm where a measurement was being taken is a significant advantage.

Where I would be cautious is using it for electrical applications that require much higher resolution to accurately identify exceptions, or any critical application where plant safety or reliability depended on accurate diagnosis.

Electrical Example:

75% Thermal/Visual Blending

100% Thermal

100% Visual

Image Comparison to IPI-R Zero (160×120)


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