The thermal imaging principle of industrial endoscopes is based on infrared thermal radiation detection. It captures the infrared energy (heat) emitted by the target object and converts it into a visual temperature distribution image to achieve non-contact temperature monitoring and defect detection. The following is a detailed analysis of its core principles and technical details:
Blackbody radiation law
All objects with temperatures above absolute zero (-273.15℃) will radiate energy in the form of electromagnetic waves, and the wavelength range covers the infrared band. According to Planck's radiation law, the peak wavelength (λ_max) of the object's radiation is inversely proportional to the temperature (T):
λmax=Tb
(where b≈2897.8μm⋅K is the Wien displacement constant)
For example: the human body (37℃) has a radiation peak of about 9.4μm, and the engine turbine (1000℃) is about 2.9μm.
The role of infrared detectors
The probe of a thermal imaging endoscope has a built-in infrared focal plane array (IRFPA), which is usually made of microbolometers or mercury cadmium telluride (HgCdTe) materials. The detector converts infrared radiation into an electrical signal, and the signal strength is proportional to the radiation energy (i.e., the target temperature).
Optical design
Infrared lens: Use infrared-transmitting materials such as germanium (Ge) or zinc sulfide (ZnS) to focus the target radiation to the detector.
Fiber optic transmission: Some systems transmit infrared signals from the probe to the processing unit through a fiber optic bundle to adapt to complex spaces (such as the inside of an engine).
Signal processing flow
Calibration: Eliminate detector deviations through built-in blackbody or ambient temperature reference points.
Noise reduction: Use digital filtering algorithms (such as non-uniformity correction NUC) to improve the signal-to-noise ratio.
Temperature mapping: Convert electrical signals into pseudo-color images, with red/yellow representing high temperature areas and blue/purple representing low temperatures.
Mechanical structure adaptation
Flexible probe: serpentine or articulated catheter allows entry into curved pipes or narrow cavities.
Protective design: ceramic or metal sheath protects the detector and withstands high temperatures (such as engine turbine area).
Technical advantages and application scenarios
Core value
Non-contact temperature measurement: avoid contact between the probe and the measured surface, suitable for high-temperature or rotating parts (such as turbine blades).
Fast scanning: generate thermal maps in real time to locate overheating, local damage or energy loss areas.
Compound detection: combined with visible light endoscope, observe physical damage and temperature anomalies at the same time.
Typical applications
Power equipment: detect hot spots in transformer windings and local overheating of cable joints.
Aerospace engines: identify carbon deposits in the combustion chamber and abnormal cooling of turbine blades.
Industrial furnaces: monitor erosion of refractory materials and combustion efficiency.
Technical challenges and solutions
Spatial resolution and temperature measurement accuracy
Challenges: small-size probes limit the number of detector pixels (such as 320×240 or 640×480), affecting detail recognition.
Solution: Use high-resolution detectors or AI algorithms (such as super-resolution reconstruction) to optimize images.
Environmental interference
Problem: Surrounding high-temperature components (such as engine housings) may reflect infrared radiation, causing misjudgment.
Countermeasures: Multispectral analysis or pulse phase method (such as phase-locked thermal imaging) to distinguish real signals.
Dynamic range limitation
Scenario: When detecting high-temperature areas (such as 1000°C) and low-temperature areas (such as 50°C) at the same time, details are lost.
Technology: Use high dynamic range (HDR) detectors or segmented exposure fusion algorithms.
Future development trends
Intelligent upgrade
AI defect recognition: Train deep learning models to automatically mark abnormal hot spots (such as cracks and blockages).
Predictive maintenance: Combine historical thermal data to predict the remaining life of equipment.
Multimodal fusion
Thermal imaging + ultrasound: Synchronously detect composite material delamination and internal temperature anomalies.
Thermal imaging + 3D scanning: Build a three-dimensional model with temperature information to assist virtual maintenance.
Extreme environment adaptation
Radiation-resistant design: Develop radiation-resistant detectors for nuclear industry or space equipment detection.
Ultra-high temperature probe: uses water cooling or active cooling technology to support environmental detection above 2000℃.
Summary
The thermal imaging technology of industrial endoscopes achieves efficient temperature monitoring by capturing infrared radiation. Its core lies in detector performance, optical design and algorithm optimization. Its non-contact and real-time characteristics make it irreplaceable in the fields of power equipment, aerospace, chemical industry, etc., and it will further develop in the direction of intelligence and multi-modal fusion in the future.
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