Angle of Measurement

Always try to hold the lens or opening of your infrared thermometer directly perpendicular to the surface being measured. This produces a tight circle of surface measurement and will convey the most accurate readings. Holding your infrared thermometer at an angle relative to the surface being measured will result in an elliptical reading area which is harder to control.

Spot Size

Two variables control the “spot size” of any given measurement:

  1. 1. The distance to target ratio of your particular infrared thermometer
  2. 2. The distance between your infrared thermometer and the target

The distance to target ratio (DTR) is generally listed on the thermometer itself. It defines the diameter (circle) size of the surface area that will be measured. For example, an infrared thermometer with a 12:1 ratio will measure the temperature of a 1” diameter circle of surface area from 12” away, a 2” diameter circle of surface area from 24” away, and so on.

NB: In the case of an infrared thermometer DTR 1:1 or less, it should be held as close to the target as possible

For each and every measurement, it is important to either physically measure or estimate your distance from the target and the proportionate spot size. Some infrared thermometers come with laser guides to assist in gauging the distance. If you are too far back from your target, background elements may be subsequently encompassed in your measured surface area and can affect your reading.

Large holes like a grate or a grill can also affect the accuracy of your reading because the infrared thermometer will factor in the surface temp of the holes’ visible surfaces. To measure this type of surface successfully, first place a solid surface (eg, iron plate / pan) on the grate or grill and allow time for it to come to temperature. Then measure the solid surface for an accurate temperature reading.

Using Infrared Thermometer Laser Guides

Laser guides on an Infrared Thermometer help to gauge the size, or location, of the area being measured. The location of the lasers and their relativity to the area being measured can vary by unit. With this in mind, to use the infrared thermometer effectively, further familiarisation of the unit’s specifications and hands on experience is recommended.

Infrared thermometers with laser guides can mostly be divided into two groups:

Single laser units assist with aim and control (more precisely, the location being measured) particularly when taking measurements from far away. The laser guide can indicate the top, centre, middle or sides of the circle of surface diameter. It is also possible that the position of the laser point, relative to the circle of measurement, will change depending on the distance from the target (known as Optical Range). For more information, please refer to your user guide.

Multiple laser units generally offer a better indication of the spot size. Infrared thermometers with a small spot size and low distance to ratio can also benefit with effective and accurate results. Indicators can frequently cross each other and be affected when specified distances from the IR gun are reached.

Emissivity and Infrared

The emissivity value varies depending on the material being tested. Emissivity is the term used to describe the measurement of a material’s ability to emit radiating/infrared energy. Measuring from 0.00 to 1.00, the higher the emissivity value, the more efficient the radiating energy of the material is. It is recommended to calibrate your instrument using a material with 1.00 (100%) emissivity value also known as a black body. This is because a black body absorbs all reflective/ambient infrared energy and only emits its own infrared radiation.

Organic materials such as plants and animals generally have an emissivity rating of 0.95 whereas highly polished metals tend to be very reflective and subsequently provide a low emissivity value. With low emissivity materials energy is reflected not absorbed, for example, a reading from a stainless steel pot filled with boiling water will more likely be closer to 38°C than 100°C because the pot is reflecting the room’s radiation more effectively than emitting its own energy.

- Fixed Emissivity -

Some infrared thermometers are equipped with a fixed emissivity value (usually 0.95 or 0.97) to facilitate a more user friendly instrument while maintaining adequate readings for most material surfaces, including almost all foods. Other infrared thermometers offer adjustable emissivity settings in order to accurately set values and achieve accurate readings on low emissivity materials, particularly non-organic surfaces.

Fixed Emissivity: Mini RayTemp, RayTemp 2

Calculating Emissivity Values

Adjustable emissivity settings on your infrared thermometer allow you to counter the emissivity value of the material being tested to achieve more accurate readings. Please see Ross Brown Sales’ Emissivity Table for a list of estimated emissivity ratings of the most common materials. Obtaining a precise accuracy of your particular material may need additional verification as the emissivity can be affected by colour, thickness and even its temperature.

Materials with low emissivity are counterbalanced by your infrared thermometer amplifying the infrared radiation levels they detect when performing calculations. This can lead to the magnification of slight errors, making your measurements seem erratic.

Methods to verify accuracy of readings:

  1. 1. Use a surface probe and meter to help pinpoint the proper emissivity setting for your infrared thermometer
  2. 2. Use a high-emissivity patch between the target surface and the infrared thermometer
Using a surface Probe and meter

Take a surface reading with your surface probe and meter and document the temperature reading. Then, using a chart value as a starting point, adjust the emissivity setting on your infrared thermometer up and down until the temperature reading on your infrared thermometer matches the temperature recorded by the surface probe and meter.

You can now be confident that other measurements taken with that same infrared thermometer on that same surface material in the same general temperature range will be accurate.

Two-in-one infrared thermometers such as the RayTemp 8 are particularly useful because they have a type K socket that enables a wide range of air, liquid and surface temperature probes to be attached. This allows you to verify the accuracy of your infrared readings without the need of an additional device.

Using a high-emissivity patch

Put a patch of high emissivity material over the low emissivity (eg, reflective) material and allow it to come to temperature. For example, cover a polished metal skillet with a layer of cooking oil (.95 emissivity) and allow the oil to become the equivalent temperature of the skillet before taking an accurate temperature reading of the oil.

Another way to create a patch is to spray a spot with flat black paint or by applying a few pieces of black electrical tape (.95 emissivity). As well as waiting for the patch to be the equivalent temperature, it is important to ensure that the field of view does not extend beyond the patch or your reading will become skewed by the surrounding reflective metal.

This method can also be beneficial when using a fixed emissivity infrared thermometer on non-organic surfaces.

Emissivity Table

MaterialEmissivity Value
Aluminium: anodised0.77
Aluminium: polished0.05
Asbestos: board0.96
Asbestos: fabric0.78
Asbestos: paper0.93
Asbestos: slate0.96
Brass: highly polished0.03
Brass: oxidized0.61
Brick: common.81-.86
Brick: common, red0.93
Brick: facing, red0.92
Brick: fireclay0.75
Brick: masonry0.94
Brick: red0.9
Carbon: candle soot0.95
Carbon: graphite, filed surface0.98
Carbon: purified0.8
Charcoal: powder0.96
Chipboard: untreated0.9
Chromium: polished0.1
Clay: fired0.91
Concrete: dry0.95
Concrete: rough.92-.97
Copper: polished0.05
Copper: oxidized0.65
Enamel: lacquer0.9
Fabric: Hessian, green0.88
Fabric: Hessian, uncoloured0.87
Fibre board: porous, untreated0.85
Fibre board: hard, untreated0.85
Filler: white0.88
Galvanized Pipe0.46
Glass: chemical ware (partly transparent)0.97
Glass: frosted0.96
Glass: frosted0.7
Glass: polished plate0.94
Granite: natural surface0.96
Graphite: powder0.97
Hardwood: across grain0.82
Hardwood: along grain.68-.73
Iron: heavily rusted.91-.96
Lacquer: bakelite0.93
Lacquer: dull black0.97
Limestone: natural surface0.96
Mortar: dry0.94
Paint: 3M, black velvet coating 9560 series optical black@1.00
Paint: aluminium0.45
Paint, oil: average of 16 colours0.94
Paint: oil, black, flat0.94
Paint: oil, black, gloss0.92
Paint: oil, grey, flat0.97
Paint: oil, grey, gloss0.94
Paint: oil, various colours0.94
Paint: plastic, black0.95
Paint: plastic, white0.84
Paper: black0.9
Paper: black, dull0.94
Paper: black, shiny0.9
Paper: cardboard box0.81
Paper: green0.85
Paper: red0.76
Paper: white0.68
Paper: white bond0.93
Paper: yellow0.72
Paper: tar0.92
Pipes: glazed0.83
Plaster: rough coat0.91
Plasterboard: untreated0.9
Plastic: acrylic, clear0.94
Plastic: black0.95
Plastic: white0.84
Plastic paper: red0.94
Plastic paper: white0.84
Plexiglass: Perpex0.86
Plywood: commercial, smooth finish, dry0.82
Plywood: untreated0.83
Porcelain: glazed0.92
Redwood: wrought, untreated0.83
Redwood: unwrought, untreated0.84
Rubber: stopper, black0.97
Skin, human0.98
Soil: dry0.92
Soil: frozen0.93
Soil: saturated with water0.95
Stainless Steel0.59
Stainless Plate0.34
Steel: galvanized0.28
Steel: rolled freshly0.24
Styrofoam: insulation0.6
Tape: electrical, insulating, black0.97
Tape: masking0.92
Tile: floor, asbestos0.94
Tile: glazed0.94
Tin: burnished0.05
Tin: commercial tin-plated sheet iron0.06
Varnish: flat0.93
Wallpaper: slight pattern, light grey0.85
Wallpaper: slight pattern, red0.9
Water: distilled0.95
Water: ice, smooth0.96
Water: frost crystals0.98
Water: snow0.85
Wood: planed0.9
Wood: panelling, light finish0.87
Wood: spruce, polished, dry0.86
* Please be advised the above figures are estimated emissivity ratings only. Emissivity can be affected by colour, thickness and even its temperature and additional testing may be needed to verify accuracy.

Infrared Thermometer’s Additional Features

These additional features are particularly useful in food service or industrial settings where fixed operating procedures or government regulations specify adherence to certain temperatures.

How to Calibrate an Infrared Thermometer with an Ice Bath

Constructing an Ice Bath:

  1. Step 1: Fill a large glass to the very top with ice (crushed ice is preferred but not required)
  2. Step 2: Slowly add very cold water until the water reaches about ½” / 1cm below the top of the ice Note: If the ice floats up off the very bottom of the glass at all, the ice bath will likely be warmer than 0.0°C
  3. Step 3: Gently stir the ice mixture and let it sit for a minute or two

Testing your Infrared Thermometer:

  1. Step 4: Make sure your infrared thermometer is set to an emissivity setting of 0.95 or 0.97
  2. Step 5: Hold your infrared thermometer so that the lens or opening is directly above and perpendicular to the surface of the ice bath
Note: If you hold your infrared thermometer too far from the surface of the ice bath or hold it at an angle, your measurement will include the sides of the glass or container or even the table it is resting on and give you an inaccurate reading
  1. Step 6: Taking extra care to ensure that the field of view (the size and shape of surface area being measured) is well inside the sides of the glass or container, press the button on your infrared thermometer to take a measurement

If you perform the test correctly, and your infrared thermometer is properly calibrated, it should read within your unit’s stated accuracy specification of 0.0°C.

Infrared thermometers cannot typically be calibrated at home, but they are known for their low drift. If the results of your ice bath test are within your unit’s manufacturer’s listed specification, you are good to go. If, however, you get a result that is outside the listed accuracy specification, you should contact the manufacturer.