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Most pyrometers that appear not to work are measuring the wrong thing. Infrared thermometers infer surface temperature from emitted radiation, so a shiny or low-emissivity surface, a target smaller than the spot, or steam and glass in the path will all produce a reading that is wrong but not faulty. Check three things before condemning the device: whether the surface is shiny, whether the spot size at your distance covers the target, and whether anything transparent sits between the gun and the object. A gun like the DEASOMIYE 50:1 infrared thermometer is useful for hot, distant targets precisely because its narrow spot reduces one of these errors, but no infrared gun measures the internal temperature of food or the temperature of a gas.
What an infrared pyrometer actually measures, and why that matters when it reads wrong
An infrared pyrometer does not touch the object. It collects the infrared radiation leaving a surface and converts that radiance into a temperature using a calibration curve. The conversion assumes the surface behaves like a blackbody, or it applies an emissivity setting to correct for a surface that does not. When the reading is wrong, the cause is almost always one of four things: the surface emissivity is not what the meter assumes, the spot is larger than the target, something in the air is absorbing or emitting radiation, or the instrument is being asked to measure something infrared cannot see.
Emissivity is the efficiency with which a surface radiates. A matte black surface might radiate at 0.95, close to a perfect emitter. Bare metal can be 0.1 or lower. Point an infrared gun at a shiny stainless steel pan and it will read far below the true temperature, because the pan is reflecting the cool room rather than emitting its own heat. The instrument is working; the surface is not cooperating.
Spot size is the second trap. Every infrared thermometer has a distance-to-spot ratio. A 12:1 gun produces a spot about one twelfth of the distance across. At 36 centimetres, the spot is roughly 3 centimetres. If you are measuring a thin wire or a small component, the gun averages the target with the background. The Etekcity 774 listing states a 12:1 ratio and suggests measuring from about 36 centimetres, which is honest guidance for a general-purpose gun but a limitation for small targets.
The third trap is anything transparent in the path. Glass blocks most long-wave infrared, so a gun pointed through an oven door reads the door, not the food. Steam and smoke scatter and absorb radiation. A gun used over a boiling pot reads the steam plume.
The emissivity setting most owners never touch
Many infrared guns ship with emissivity fixed at 0.95, which suits food, matte paint, cardboard, and most organic surfaces. Others allow adjustment. The TempPro TempScan with two lasers lists adjustable emissivity from 0.1 to 1.0, and that range is the difference between a gun that can be used on bare metal and one that cannot. If your pyrometer reads implausibly low on a shiny surface, check whether the emissivity can be lowered to match. A reading of 60 degrees on a pan that is clearly hot enough to sizzle water is a classic emissivity error, not a sensor failure.
The practical workaround when emissivity cannot be adjusted is to change the surface, not the meter. A piece of matte black tape, a dab of high-temperature paint, or a soot coating gives the gun a known high-emissivity target. Measure the tape, not the metal. This is standard practice in industrial thermography and it costs nothing.
Do not assume a low reading means the gun is broken. Compare it against a contact thermometer on the same surface, or against a known reference such as boiling water on a matte surface. If the gun reads 100 degrees Celsius on matte black tape over boiling water, the sensor is fine and the problem is technique.
Spot ratio arithmetic: why distance changes the reading
The distance-to-spot ratio is the most useful number on the box and the least understood. It tells you the diameter of the measurement spot at a given distance. A 50:1 gun produces a spot one fiftieth of the distance across: at 1 metre, the spot is 2 centimetres. A 12:1 gun at the same distance produces a spot about 8 centimetres across. If the target is smaller than the spot, the gun averages target and background, and the reading drifts toward the background temperature.
This is why a gun that works well on a large griddle can read nonsense on a thin pipe or a small electronic component. The fix is to move closer, which increases the risk of burns or contamination, or to use a narrower-ratio gun. The DEASOMIYE 50:1 infrared thermometer is built for the second case: its listing states a 50:1 ratio aimed at molten metal and forging, where standing back is a safety requirement. The same arithmetic applies to any gun, however.
| Distance to target | Spot at 12:1 | Spot at 16:1 | Spot at 50:1 |
|---|---|---|---|
| 20 cm | 1.7 cm | 1.3 cm | 0.4 cm |
| 50 cm | 4.2 cm | 3.1 cm | 1.0 cm |
| 1 m | 8.3 cm | 6.3 cm | 2.0 cm |
| 2 m | 16.7 cm | 12.5 cm | 4.0 cm |
The arithmetic is simple division: spot diameter equals distance divided by the ratio. If the target is smaller than the calculated spot, the reading is an average, not a measurement. No amount of cleaning the lens fixes that.
When the problem is the instrument, not the method
Some failures are real. A gun that reads room temperature on everything, including a hot surface, may have a dead sensor or a flat battery. The TempPro TempScan 12:1 model lists a low battery indicator on some variants, but the listing does not publish the exact battery type for every version, so check the manual. A gun that reads wildly different values on the same target within seconds is usually seeing a changing spot because the hand is moving, not because the sensor is unstable.
Lens contamination is the maintenance nobody mentions. Dust, grease, and fingerprints on the infrared lens attenuate the signal and bias the reading low. Clean with a soft lens cloth and a little isopropyl alcohol, never a abrasive cloth. A gun used in a kitchen will collect aerosolised fat; a gun used in a workshop will collect metal dust. Both change the calibration over time.
If the gun has a laser, remember the laser is a pointer, not a thermometer. The laser dot shows roughly where the spot is centred, but the spot is usually larger than the dot. A gun with two lasers, such as the TempPro two-laser model, brackets the spot to show its approximate diameter, which helps at distance. It does not make the spot smaller.
What no infrared pyrometer can measure
Infrared thermometers measure surface temperature, not internal temperature. A gun pointed at a roast reads the crust, not the centre. A gun pointed at a pot of water reads the surface, which is cooler than the bulk because of evaporation. For internal temperature you need a probe thermometer, and for gas temperature you need a thermocouple in the stream. No infrared gun measures air temperature reliably, because air is largely transparent to infrared.
They also cannot see through glass, water, or plastic. A gun used to check an oven interior through the door reads the door glass. A gun used to check a liquid in a clear container reads the container wall. This is physics, not a defect.
For thermal imaging of a whole scene, where you need to see temperature distribution rather than a single spot, an infrared gun is the wrong class of instrument. A thermal camera maps surface temperature across a field of view, and the choice between camera types is covered in how to choose a thermal camera for home inspection. For inspecting inside cavities or behind walls, a borescope shows structure but not temperature; the difference is explained in thermal camera versus borescope.
A practical sequence for diagnosing a bad reading
Work through these steps in order before assuming the gun is faulty.
- Check the surface. Is it shiny, wet, or covered in tape? Shiny surfaces need emissivity correction or a matte target.
- Check the spot size. Calculate distance divided by the ratio. If the spot is larger than the target, move closer or change the gun.
- Check the path. Is there glass, steam, smoke, or plastic between the gun and the target?
- Check the battery and lens. A low battery can cause erratic readings; a dirty lens biases low.
- Compare against a contact thermometer on the same surface, ideally with a matte target applied.
If all five checks pass and the gun still reads wrong on a known reference, the sensor or electronics have failed. That is the point to replace it, not before.
The reading is usually right about the wrong thing
An infrared pyrometer that seems not to work is usually reporting the temperature of a reflection, a spot average, or a steam plume. Before you replace it, change the surface, the distance, or the path. If the reading is still wrong on a matte reference at close range, then the instrument has failed and a replacement is justified. For applications where surface temperature is not the question, such as internal food temperature or gas temperature, the right answer is a different instrument, not a better infrared gun.
Frequently Asked Questions
My infrared gun reads 60 degrees on a pan that is clearly hot. Is it broken?
Probably not. A shiny metal pan has low emissivity and reflects the room rather than emitting its own heat. Put a piece of matte black tape on the pan and measure the tape. If the tape reads hot, the gun is fine and the surface was the problem.
Why does the reading change when I move the gun slightly?
The spot is moving. At a 12:1 ratio, a small hand movement shifts the measurement spot onto a different part of the target or onto the background. Hold the gun steady or mount it. The Etekcity 774 listing suggests a fixed distance of about 36 centimetres for best results, which reduces this effect.
Can I use an infrared pyrometer to check if meat is cooked?
No. Infrared measures surface temperature. The surface of a roast can be well above the safe internal temperature while the centre is still cold. Use a probe thermometer for internal temperature. An infrared gun is useful for surface checks such as griddle temperature, not for food safety.
My gun reads through the oven door but the number seems low. Why?
Glass blocks most long-wave infrared. The gun is reading the temperature of the door glass, not the food or the oven interior. Open the door or use a probe. No infrared gun measures through glass.
The listing says accuracy is plus or minus 1.5 percent. Is that good enough?
That figure is typical for a general-purpose infrared gun, but accuracy is only part of the error budget. Emissivity error and spot-size error usually dominate. A gun with 1.5 percent accuracy on a shiny surface can still be wrong by tens of degrees. Fix the technique before worrying about the accuracy figure.
When should I replace the pyrometer rather than adjust my method?
Replace it when it reads wrong on a known reference: matte black tape over boiling water, measured close enough that the spot is smaller than the tape. If it cannot read 100 degrees Celsius there, the sensor or electronics have failed. Also replace it if the display is failing or the battery contacts are corroded beyond cleaning.