Thermal Scope

Thermal imager: Insight into the invisible world of heat

A thermal imager (TIC) is an electronic optical device that uses infrared radiation (heat) to generate visible images of targets. It does not rely on visible light, but detects infrared heat energy naturally emitted by objects and invisible to the human eye, and converts these tiny temperature differences into clear grayscale or color images. Its core value lies in providing all-weather (available day and night), penetrating smoke/fog/dust, non-contact temperature measurement, and the powerful ability to detect hidden targets.

Core working principle

1. Infrared radiation reception: All objects with a temperature above absolute zero (-273.15°C) will emit infrared radiation (heat). Thermal imagers collect infrared radiation emitted by the target through their special infrared lenses.

2. Focusing and scanning: Infrared radiation is focused on an infrared focal plane array consisting of thousands or even millions of tiny detection units. Mainstream detector types:

2.1 Vanadium oxide microbolometer: Most common in civilian/industrial fields, it detects heat by causing resistance changes due to temperature changes. No cooling is required.

2.2 Indium antimonide/mercury cadmium telluride photon detector: Used for high-end military/scientific research, with extremely high sensitivity, usually requires Stirling refrigerators or thermoelectric coolers to cool down to improve performance.

3. Thermoelectric conversion: After each picture element (pixel) on the detector absorbs infrared radiation, the temperature changes slightly, which in turn causes changes in its electrical properties (such as resistance), converting thermal signals into electrical signals.

4. Signal processing: The electrical signal is amplified, digitized and processed by highly complex image processing circuits:

4.1 Calculate the temperature value or relative temperature difference of each pixel.

4.2 Apply various algorithms to optimize the image (noise reduction, contrast enhancement, edge sharpening, etc.).

5. Image generation and display: The processed data is mapped into different colors or grayscale levels according to the preset color palette, and finally a "thermal image" representing the temperature distribution of the target surface is generated on the built-in display (LCD/OLED). The hotter areas are usually displayed as "brighter" (white hot mode) or "warmer" (such as iron red, rainbow mode) in the image.

Core advantages and features

1. True all-weather operation:

1.1 Completely dark environment: No light source (natural light or infrared fill light) is required, and imaging is based purely on the target's own heat.

1.2 Penetrate smoke, mist, dust, light rain and snow: The wavelength characteristics make it more penetrating than visible light and near-infrared light, which is crucial in firefighting, search and rescue, and industrial environments.

1.3 Available day and night: Performance is not affected by lighting conditions.

2. Detection of hidden and camouflaged targets:

2.1 Can detect people or animals hiding in grass, bushes, and shadows (due to the temperature difference between their body temperature and the ambient temperature).

2.2 Can identify targets with simple camouflage (such as branches and canvas) (temperature difference causes thermal signal leakage).

2.3 Can detect "heat residue" left by targets that have just left (such as residual heat on seats, footprints).

3. Non-contact temperature measurement:

3.1 Can measure the temperature of any point, area, or entire image in the image (needs to be corrected for emissivity).

3.2 Widely used in industrial inspection, electrical maintenance, building diagnosis, medical screening (such as initial temperature screening).

4. Reveal hidden problems:

Can intuitively display temperature anomalies that cannot be seen by the naked eye, such as:

4.1 Hot spots in electrical systems (loose connections, overloads, insulation aging).

4.2 Thermal bridges, hot spots, and moisture areas in buildings.

4.3 Overheating, abnormal friction, and insufficient lubrication of bearings in mechanical equipment.

4.4 Blockages and leaks in pipelines.

5. Safe distance observation: High temperature areas, potential fault points, or dangerous targets can be detected at a safe distance.

6. No fear of strong light interference: Not affected by strong visible light sources such as direct sunlight, car lights, and searchlights.

Key performance parameters

1. Detector resolution:

1.1 Core indicator! Refers to the number of pixels on the detector (such as 160x120, 320x240, 384x288, 640x480, 1024x768).

1.2 The higher the resolution, the clearer the image, the richer the details, and the longer the detection and recognition distance.

1.3 Mainstream level: entry-level 160x120, mainstream level 320x240/384x288, professional level 640x480 and above.

2. Thermal sensitivity / noise equivalent temperature difference:

2.1 Measures the ability of the detector to distinguish small temperature differences (unit: mK, millikelvin).

2.2 The smaller the value, the better (such as <50mK, <40mK, <30mK). High sensitivity can present more delicate thermal contrast, which is especially important when the ambient temperature is close or when observing low-contrast targets.

3. Field of view:

3.1 Refers to the angle range that the lens can cover (horizontal x vertical, unit: degree °).

3.2 Wide field of view: Large observation range, easy to find targets, suitable for close-range and large-scale searches (such as fire rescue).

3.3 Narrow field of view: High magnification, see farther and clearer, suitable for long-distance observation or detection of details (such as power line inspection, hunting). Usually combined with zoom function.

4. Spatial resolution / instantaneous field of view:

4.1 Refers to the minimum target size that a single pixel can distinguish at a specific distance (unit: mrad, milliradian).

4.2 The smaller the value, the better, which means that smaller targets or finer temperature difference details can be seen at the same distance.

4.3 Directly related to the detector resolution and lens focal length.

5. Focal length and optical zoom:

5.1 Focal length: Determines the basic magnification and field of view. Telephoto can see far but has a narrow field of view.

5.2 Optical zoom: Change the focal length by physically adjusting the lens group, and enlarge the image without losing pixel information (such as 2x, 3x, 4x, 5x). It is the key to improving the effect of long-distance observation.

5.3 Digital zoom: Cropping and enlarging on the basis of optical zoom will reduce clarity.

6. Temperature measurement range and accuracy:

6.1 Temperature measurement range: The lowest to highest temperature that the instrument can measure (such as -20°C ~ +150°C, -40°C ~ +550°C, and higher for industrial use).

6.2 Temperature measurement accuracy: Usually expressed as ±X°C or ±Y% (such as ±2°C or ±2%, whichever is larger). High-precision temperature measurement requires regular calibration.

6.3 Emissivity setting: The ability of an object surface to emit infrared radiation (0.01-1.0). Accurate temperature measurement requires the correct emissivity to be set according to the target material (common materials have reference values).

7. Color palette:

A scheme that maps temperature differences to different colors or grayscales. Common ones are:

7.1 White heat: high temperature white, low temperature black. High contrast, most commonly used.

7.2 Black heat: high temperature black, low temperature white. A matter of habit.

7.3 Iron red/rainbow: Use multiple colors to distinguish temperature levels and intuitively display temperature distribution.

7.4 High contrast/Arctic, etc.: Optimized for specific scenes.

Can be switched to suit different scenes and personal preferences.

8. Detection and identification distance:

8.1 Detection distance: The maximum distance at which the target is detected (such as a human heat source).

8.2 Identification distance: The maximum distance at which the key features of the target can be clearly seen (such as a person, a deer, or a facial outline).

8.3 Affected greatly by detector resolution, lens focal length, atmospheric conditions, target size/temperature difference. Manufacturer data (such as the recognition distance for human-shaped targets) is an important reference, but the test conditions must be understood.

9. Refresh rate:

9.1 Refers to the number of times the screen updates the image per second (unit: Hz, such as 30Hz, 50Hz, 60Hz).

9.2 The higher the refresh rate (≥30Hz), the smoother the dynamic image, the more comfortable it is to observe moving targets, and the less dizziness. Low refresh rates (such as 9Hz) may cause the screen to freeze.

10. Environmental adaptability:

10.1 Protection level (IP): Waterproof and dustproof (such as IP54, IP67). Critical for outdoor, industrial, and firefighting applications.

10.2 Operating temperature range: Adaptable to severe cold or hot environments (such as -25°C ~ +50°C).

10.3 Shock/vibration resistance: Military or industrial grade requirements are high.

11. Funtional features:

11.1 Image/Video Recording: Stores thermal images and videos (with or without visible light fusion) for evidence or analysis.

11.2 Multispectral/Picture-in-Picture/Fusion: Combines with built-in or external visible light cameras to provide thermal and visible light overlay (fusion) or split-screen (Picture-in-Picture) views for easy positioning and identification.

11.3 Point/Line/Area Temperature Measurement: Measures the highest/lowest/average temperature at a specific point, along a line, or in an area.

11.4 High/Low Temperature Tracking: Automatically marks the highest and lowest temperature points in the image.

11.5 Alarm Function: Sounds/visual alarm when the temperature exceeds the set threshold.

11.6 Wireless Transmission (Wi-Fi): Real-time image transmission to mobile phones/tablets/computers for remote viewing, control, and sharing.

11.7 GPS & Electronic Compass: Records location and direction information.

11.8 Laser rangefinder integration: Accurately measure the target distance.

11.9 Laser pointer: Mark the target position.

12. Power supply and battery life:

12.1 Rechargeable lithium batteries (special or general-purpose such as 18650) are usually used.

12.2 Battery life: It is a key indicator (such as 2-8 hours), especially in high-performance mode. Backup batteries or external power supply are important.

Main types

1. Handheld thermal imager:

1.1 The most common type, portable and flexible.

1.2 Applications: fire rescue, power/industrial inspection, building diagnosis, security patrol, hunting observation, outdoor search and rescue, HVAC inspection, preventive maintenance.

2. Thermal imaging scope:

2.1 Designed for firearms, mounted on rails.

2.2 With aiming reticle, emphasizing shock resistance, fast target acquisition, and trajectory calculation (high-end models).

2.3 Applications: military, law enforcement, hunting (especially at night).

3. Thermal imaging telescope/monocular:

3.1 Similar to the telescope structure, used for handheld or tripod-fixed observation.

3.2 Applications: long-distance observation (wildlife monitoring, border patrol, sailing, bird watching), professional search and rescue.

4. Fixed/online thermal imager:

4.1 Fixed installation, used for continuous monitoring or automated detection.

4.2 Applications: industrial process monitoring, temperature alarm for key equipment, perimeter security, fire monitoring, substation monitoring.

5. Thermal imaging module:

5.1 Core imaging component that can be integrated into other systems (such as drones, robots, vehicle systems, security cameras, smartphones).

6. Smartphone external thermal imager:

6.1 Connect to the phone via USB or Lightning interface, and use the phone screen and computing power.

6.2 Applications: simple detection, DIY, entry-level applications.

Application scenarios

1. Firefighting and rescue: internal investigation of fire scene (penetrating thick smoke to locate fire source and trapped persons), search and rescue of missing persons (especially at night/complex terrain), and inspection of smoldering points of residual fire.

2. Power industry: detection of power transmission and distribution lines/equipment (joint overheating, insulator deterioration, transformer failure), substation inspection.

3. Industrial maintenance: predictive maintenance (detection of mechanical bearing overheating, motor overload, pipeline blockage/leakage, furnace insulation damage), process monitoring.

4. Building diagnosis: detection of thermal defects of building envelope structure (thermal bridge, heat leakage, insulation failure), detection of moisture leakage, evaluation of HVAC system efficiency, and inspection of floor heating.

5. Security and law enforcement: night patrol, perimeter alert, search for suspects (especially dark/hidden environment), action support, evidence collection (heat residue).

6. Hunting and outdoor: search for prey at night/dawn/dusk, observe animal activities, and ensure hunting safety (identify other people in the environment).

7. Automotive industry: Diagnosis of engine/exhaust system overheating, electrical faults, brake system testing, R&D testing.

8. Medical and veterinary: Temperature screening (non-contact, large area), inflammation localization, blood circulation assessment, animal health examination.

9. Scientific research and R&D: Material research, electronic circuit analysis, thermodynamic experiments, NDT (non-destructive testing).

10. HVAC: Check pipe insulation, duct leaks, radiator efficiency, and find cold bridges.

11. Agriculture: Monitoring crop health (water stress, early disease), livestock and poultry body temperature monitoring, and grain storage temperature monitoring.

12. Navigation and aviation: Night navigation, iceberg/floating object detection, search and rescue.

Limitations

1. Unable to "see through": Only the surface temperature of objects can be detected. It is impossible to see through solid walls or thick metal plates (but the temperature difference on the outer surface of these structures caused by internal heat sources can be detected).

2. Difficulty in glass imaging: Ordinary glass has high reflectivity and low transmittance for long-wave infrared radiation. The thermal imager mainly sees the ambient thermal image reflected by the glass itself and its surface temperature, making it difficult to see the object behind the glass.

3. Image interpretation: Thermal images show temperature distribution, not visible light details. Certain experience and training are required to accurately interpret the meaning of the image (such as distinguishing the nature of the heat source).

4. Temperature measurement accuracy depends on emissivity: Accurate temperature measurement requires the correct setting of the target's emissivity. Highly reflective or low-emissivity objects (such as bright metals) have large temperature measurement errors.

5. Cost: Compared with visible light cameras and digital night vision devices, high-performance thermal imagers are still expensive (especially high-resolution cooling types).

6. Environmental impact: Extreme environments (heavy rain, dense fog, sandstorms) can attenuate infrared radiation, reduce detection distance and image quality. Strong winds may cause a decrease in temperature differences.

Summary

Thermal imagers are revolutionary tools for perceiving the world. They give humans the ability of "thermal vision" and break through the limitations of visible light. Their core advantages of all-weather, penetrating, and non-contact temperature measurement make them indispensable professional equipment in a wide range of fields, including firefighting, industry, electricity, security, construction, medical treatment, scientific research, and even outdoor leisure.