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You cannot calibrate a thermal camera the way you calibrate a multimeter. There is no zero screw and no user-accessible gain adjustment. What you can do is set the parameters that the camera uses to convert radiance into temperature: emissivity, reflected apparent temperature, distance, and sometimes humidity. You can also verify the camera against a reference source. If the camera fails that check, or if it is due for its periodic recalibration, it goes to a laboratory with blackbody sources. The products in this category differ in which parameters they expose. The MiLESEEY TR20 publishes a fixed accuracy of plus or minus 2 percent but does not state an emissivity adjustment in its listing bullets. The AMPBANK M192 states adjustable emissivity, ambient temperature and distance settings inside its app. The Bosch GTC600C and Dctopt listings do not publish calibration parameters. None of these listings states a calibration interval or a certificate.
Why a thermal camera is not calibrated like a meter
A thermal camera does not measure temperature directly. It measures infrared radiance arriving at its detector, then converts that radiance into a temperature using a model. The model contains constants for the detector response, the lens transmission, and the atmospheric path. Those constants are set at manufacture and are not exposed to the user. That is why you will not find a calibration menu with a zero and a span adjustment on a handheld thermal camera.
What the user can change are the parameters of the scene model: how much of the received radiance the target actually emits (emissivity), how much is reflected from the surroundings (reflected apparent temperature), and how much is absorbed by the air between the camera and the target (distance and humidity). These are not calibration of the instrument. They are corrections to the calculation. Getting them wrong produces a reading that is wrong by tens of degrees even when the camera itself is perfectly within specification.
The distinction matters because buyers often ask how to calibrate a thermal camera when what they need is to set emissivity correctly. The camera’s own accuracy specification, such as the plus or minus 2 percent published for the MiLESEEY TR20, applies only after those scene parameters are set to match reality. A camera that is accurate to 2 percent with the wrong emissivity can read 20 percent low.
The four settings that do the work of calibration
Emissivity is the first. It describes how efficiently a surface radiates compared with a perfect blackbody. Bare shiny metal has a low emissivity and is nearly a mirror in the thermal band. You cannot read its temperature reliably without either changing its surface or setting a low emissivity and accepting a large uncertainty. Electrical tape, matte paint or a dab of black marker on the target gives you a surface with a known, high emissivity. The emissivity guide covers the values for common materials.
Reflected apparent temperature is the second. It is the temperature of the surroundings that the target reflects into the camera. Indoors, that is roughly the wall temperature behind the camera. Outdoors on a clear day, the reflected temperature can be the cold sky, which is far below air temperature. If you leave the reflected temperature at the default and the target is a shiny busbar reflecting a cold window, the camera will subtract the wrong background and report a temperature that is too low.
Distance and humidity are the third and fourth. Water vapour in the air absorbs some of the infrared energy between the target and the lens. Over a few metres the effect is small. Over tens of metres in humid air it becomes significant. The camera uses the distance and relative humidity you enter to estimate that absorption. The HVAC diagnostics guide explains why this matters more for outdoor duct runs than for indoor panel inspections.
Not every camera exposes all four. The AMPBANK M192 listing states adjustable emissivity, ambient temperature and distance settings within its app, but does not mention humidity. The MiLESEEY TR20 listing does not mention emissivity adjustment at all, only a fixed accuracy figure. The Bosch GTC600C and Dctopt listings publish neither emissivity nor reflected temperature controls. If a camera does not let you set emissivity, you are limited to qualitative work or to targets whose emissivity happens to match the camera’s fixed assumption.
How to verify a thermal camera against a reference
Verification is not calibration. It is a check that the camera reads close to truth on a surface whose temperature you know independently. You can do a crude version at home. Bring a pot of water to a stable temperature, stir it, and measure it with a contact thermometer you trust. Cover the water surface with a thin layer of matte black tape or a floating matte disc so the emissivity is high and known. Point the camera at the surface from a fixed distance, set the emissivity to 0.95, set the reflected temperature to the room air temperature, and compare the camera reading with the contact reading. If they agree within the camera’s published accuracy, the camera is behaving. If they differ by more than that, either your setup is wrong or the camera needs attention.
The setup is the usual source of error. A shiny surface, a short distance that fills the frame with the pot rim rather than the water, or a reflected temperature that is not the room air will all produce a false failure. Repeat the check with a second surface at a different temperature, such as a bowl of ice water, to see whether the error is a fixed offset or a scale error. A fixed offset at both temperatures suggests a parameter problem. A growing difference suggests a camera problem.
For anything that matters commercially, the reference should be a calibrated blackbody source, and the check should be done by a laboratory that can issue a certificate. That is the same laboratory that performs the periodic recalibration. The listing bullets for all four products here do not state a calibration interval or a certificate. The resolution comparison guide explains why a camera with more pixels can still fail a verification if its lens is dirty or its detector is drifting.
When the answer is a laboratory, not a menu
If the verification shows an error larger than the published accuracy, and your scene parameters are correct, the camera needs a laboratory. There is no user procedure to correct detector non-uniformity or to restore a drifted gain constant. Some cameras have a non-uniformity correction routine that closes a shutter in front of the detector and equalises the pixel offsets. That routine runs automatically on many models and is not a calibration. It removes fixed pattern noise, not temperature error.
The same applies to a camera that has been dropped, exposed to extreme heat, or had its lens replaced. The optical path changes and the factory constants no longer describe the instrument. A laboratory with blackbody sources at several temperatures can re-derive those constants and issue a new certificate. For a camera used to make safety or compliance decisions, such as verifying that a conductor is below its rated temperature, that certificate is the difference between a measurement and an opinion.
Where the whole category stops being the right answer is when you need a traceable temperature measurement at a specific point. A thermal camera is a screening tool. It finds the hot joint among a row of joints. A contact probe or a clamp meter with a temperature function measures the hot joint. If your task is to record a temperature for a report that will be audited, use the camera to find the spot and the contact instrument to measure it. The home inspection guide makes the same point about moisture and insulation work.
What the listings do and do not publish about calibration
The table below collects only what the supplied listing bullets state. Where a listing is silent, the cell says so. Silence is not evidence that a feature is absent; it means the manufacturer has not published it in the text we have.
| Product | Stated accuracy | Emissivity adjustment | Reflected temperature or ambient setting | Distance setting | Calibration interval or certificate |
|---|---|---|---|---|---|
| MiLESEEY TR20 | plus or minus 2 percent | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets |
| Bosch GTC600C | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets |
| AMPBANK M192 | maximum of plus or minus 2 degrees Celsius or 2 percent | Stated as adjustable | Stated as ambient temperature setting in the app | Stated as distance setting in the app | Not stated in the listing bullets |
| Dctopt | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets | Not stated in the listing bullets |
The practical reading of this table is that the AMPBANK M192 is the only one of the four whose listing explicitly states the scene parameters that a user would adjust during a verification. The MiLESEEY TR20 publishes an accuracy figure but not the controls that would let you meet it on a low-emissivity target. The Bosch and Dctopt listings are silent on the parameters. That does not make them bad instruments. It means you cannot tell from the listing alone whether they will let you correct for a shiny target, and you should ask the supplier before relying on them for quantitative work.
The realistic answer to how to calibrate a thermal camera
You set the scene parameters, you verify against a reference you trust, and you send the camera to a laboratory when the verification fails or the interval comes due. The parameters you can set are emissivity, reflected apparent temperature, distance and sometimes humidity. The parameter you cannot set is the detector response, and that is the one a laboratory calibrates. If a listing does not publish emissivity control, treat the camera as a screening tool and confirm any critical reading with a contact instrument. No laboratory testing was performed for this article, and no measurements of our own are published.
Frequently Asked Questions
Can I calibrate a thermal camera myself?
You can adjust the scene parameters that the camera uses to calculate temperature: emissivity, reflected apparent temperature, distance and humidity where the camera exposes them. You cannot adjust the detector response. If the camera reads outside its published accuracy after those parameters are correct, it needs a laboratory with blackbody sources.
How often does a thermal camera need recalibration?
The listings supplied here do not state a calibration interval. Manufacturers commonly recommend an interval, often one or two years for professional use, but you should follow the interval published for your specific model rather than a general figure. If the camera is used for safety or compliance decisions, the interval is usually set by your quality system, not by the camera.
Why does my thermal camera read the wrong temperature on metal?
Bare metal has low emissivity and reflects its surroundings. The camera receives a mix of emitted and reflected infrared, and unless you set a low emissivity and the correct reflected temperature, the calculated temperature will be wrong. The usual fix is to cover the metal with matte tape or paint of known high emissivity and measure that.
Does the MiLESEEY TR20 let me set emissivity?
The listing bullets do not state an emissivity adjustment. They state a fixed accuracy of plus or minus 2 percent. Without a published emissivity control, you should treat readings on low-emissivity surfaces as qualitative and confirm critical measurements with a contact probe.
What is the difference between verification and calibration?
Verification is a check that the camera reads close to a known reference. Calibration is the adjustment of the camera's internal constants so that it does read correctly, performed by a laboratory with traceable sources. Verification can be done by the user with a suitable reference; calibration cannot.
Can a smartphone thermal camera be calibrated?
The AMPBANK M192 listing states adjustable emissivity, ambient temperature and distance settings in its app. Those are scene parameters, not detector calibration. The listing does not state a calibration interval or certificate. As with any thermal camera, the detector response is set at manufacture and corrected only by a laboratory.