GB/T 43249-2023 “Passive Infrared Detection Systems for Automobiles” is China's first national technical standard specifically for vehicular passive infrared detection technology. This standard comprehensively regulates the technical requirements, test methods, and inspection rules of the system, aiming to improve the reliability and accuracy of vehicular infrared detection equipment in scenarios such as environmental perception, night vision assistance, and safety warning.

Related Terms
Passive Infrared Detection System
A device that converts infrared thermal radiation from object surfaces into resolvable image signals through an infrared optical system, an infrared focal plane array detector, and an electronic processing unit.
White Hot Mode
A display mode that maps higher infrared thermal radiation energy to high brightness and lower infrared thermal radiation energy to low brightness.
Black Hot Mode
A display mode that maps higher infrared thermal radiation energy to low brightness and lower infrared thermal radiation energy to high brightness.

Test Operating Modes
Operating Mode A (DUT not electrically connected)
Operating Mode A1: DUT is not powered on and is not connected to connectors or wiring harnesses.
Operating Mode A2: DUT is not powered on but is connected to connectors and wiring harnesses.

Operating Mode B (DUT electrically connected)
Operating Mode B: DUT is normally electrically connected, and all functions operate normally.

Image Performance Test Requirements and Methods
1. Resolution
Definition: The total number of pixels in the final image output by the system.
Requirement: Not less than 640×512 pixels.
Test Method: Test the output video signal using a video analysis device.

2. Sampling Frame Rate
Definition: The reciprocal of the time interval between two adjacent image frames, which determines video fluency.
Requirement: Not lower than 25 Hz.
Test Method: Test the output video signal using a video analysis device.

3. MTF Value (Modulation Transfer Function)
Definition: Essentially consistent with SFR (Spatial Frequency Response), used to evaluate the contrast transfer capability of the system.
Requirements:
Center Area: When the pixel pitch is 17μm, both horizontal and vertical MTF50P values shall be ≥320 LW/PH; when the pixel pitch is 12μm, both shall be ≥300 LW/PH.
70% Field of View Area: When the pixel pitch is 17μm, both shall be ≥300 LW/PH; when the pixel pitch is 12μm, both shall be ≥280 LW/PH.
Test Method:
Use a slanted-edge test target according to the slant requirements of ISO 12233. The DUT shall be tested according to the following steps:
a) Adjust the distance between the DUT and the test target to meet the minimum focus distance. The target shall cover the center field of view and at least two 70% fields of view, and the edge length of each square shall not be less than 10 pixels;
b) Adjust the DUT so that the angle between the edge of the test target square in the center field of view and its corresponding direction is approximately 5°;
c) Adjust the temperature difference between the high and low temperature areas of the target to 10℃±2℃;
d) Adjust the DUT so that its optical axis is orthogonal to the plane of the test target;
e) Flip the DUT so that the target square under test is located in the center field of view and the 70% field of view, and the edge length of the target square shall be no less than 10 pixels;
f) Use image processing software to analyze the MTF50P in the center area and the 70% field of view (the four corners: top-left, top-right, bottom-left, and bottom-right).
Refer to the following figure for the target layout:

4. Field of View
Definition: The maximum spatial angular range that can be observed by the passive infrared detection system.
Requirements: The horizontal field of view shall not be less than 24°; the vertical field of view shall not be less than 18°.
Test Method:
Test Equipment Layout:
Fix the DUT horizontally at the center of an indexing plate with an accuracy of no less than 0.5°, and select a four-bar target with an appropriate characteristic frequency. Adjust the distance between the DUT lens and the target to meet the minimum focus distance. Keep the center of the lens consistent with the center of the indexing plate, and ensure the center of the lens is perpendicular to the target plane and coincides with the center of the target. Set the temperature difference between the target and the blackbody background so that the DUT can form a clear image. Refer to the following figure for the equipment layout:
Horizontal Field of View Measurement:
a) Rotate the indexing plate so that the left edge of the target is exactly at the leftmost side of the monitor display interface, and record the rotation angle reading 'a' of the indexing plate at this time;
b) Rotate the indexing plate in the reverse direction so that the left edge of the target moves to the rightmost side of the monitor display interface, and record the rotation angle reading 'b' at this time;
c) The horizontal field of view is the absolute value of the difference between the two readings, i.e., |b−a|.
Vertical Field of View Measurement:
Rotate the DUT by 90°, fix it at the center of the indexing plate, and measure the vertical field of view in the same manner.

5. Noise Equivalent Temperature Difference (NETD)
Definition: When the system observes a circular or square target with a low spatial frequency, the temperature difference between the target and the background when the signal-to-noise ratio of its video signal is 1. It is used to evaluate the sensitivity and noise level of the detected target.
Requirement: When the ambient temperature is 23℃±5℃, the noise equivalent temperature difference of the system shall not be greater than 80mK.
Test Method:
The test equipment layout is as follows:
a) Connect the infrared test system to a computer, select an appropriate edge target, which is required to occupy more than 1/10 of the full field of view, set the blackbody to differential temperature mode, and set the temperature difference between the target and the blackbody background to $\Delta T=2\text{K}$;
b) Power on the DUT at room temperature, connect the video to an image acquisition card, and wait until the equipment reaches a thermally stable state;
c) Perform frame acquisition on the video output signal, acquire $n$ frames (an integer multiple of 10 frames is recommended), calculate the root mean square standard deviation according to the single-pixel grayscale values for the selected blackbody area to obtain the noise matrix, and then calculate the mean value to get $N$;
d) Perform frame acquisition on the video output signal, acquire $n$ frames (an integer multiple of 10 frames is recommended), select the blackbody area and the target area of the edge target to obtain the signal grayscale values, and calculate the mean value for each area. The difference between the mean values of the two areas is $S$;
e) Calculate NETD according to the following formula:
$$\text{NETD} = \frac{\Delta T}{S/N} $$ Where:
$\Delta T$ — Set temperature difference;
$S$ — Signal level;
$N$ — Root mean square noise level.

6. Minimum Resolvable Temperature Difference (MRTD)
Definition: At a specific spatial frequency, the temperature difference between the target and the background on a four-bar target that an observer can just resolve.
Requirement: When the ambient temperature is 23℃±5℃, the minimum resolvable temperature difference of the system shall not be greater than 500mK.
Test Method:
a) Connect the infrared test system to a computer. According to the optical parameters of the system under test, select a four-bar target with an appropriate characteristic frequency, set the blackbody to differential temperature mode, and set the temperature difference between the four-bar target and the blackbody background to 1K;
b) Power on the DUT at ambient temperature, wait until the equipment reaches a thermally stable state, and connect the video to a monitor;
c) Adjust the position of the DUT; if it is focusable, perform optical focusing so that it can clearly resolve the four-bar target pattern;
d) First set it to a positive temperature difference, and finely adjust the blackbody temperature until the four-bar pattern can just be resolved on the monitor (minimum step size 0.05℃), and record the temperature difference ΔT₁ at this time;
e) Then lower the temperature to make it a negative temperature difference, until the four-bar pattern can just be resolved again (at this time the pattern brightness is reversed), and record the temperature difference ΔT₂ at this time;
f) Calculate MRTD according to formula (2):
$$MRTD = \frac{|\Delta T_1| + |\Delta T_2|}{2}$$

7. Image Defective Pixels
Definition: In the output image, pixels whose brightness does not change with the target scene, or changes abnormally.
Requirement: No defective pixels shall appear in the field of view.
Test Method:
a) Aim at a 25℃ blackbody and make the blackbody fill the imaging frame. Take the 3×3 neighborhood of each pixel in a single image frame, and calculate the difference between the grayscale value of the current pixel and the mean value of the other 8 pixels in the neighborhood. If the grayscale value difference exceeds 50 (20% of 8-bit grayscale), it is considered a defective pixel;
b) Set the blackbody temperature to 85℃, repeat the above method, and calculate the defective pixels;
c) Set the blackbody temperature to 10℃, repeat the above method, and calculate the defective pixels;
d) Check the defective pixels in the field of view under the above three blackbody temperature conditions.

8. Startup Stabilization Time
Definition: The time interval from when the system is powered on to when a stable image is displayed.
Requirement: The startup stabilization time shall not be greater than 10s, of which the startup imaging time shall not be greater than 5s.
Test Method:
a) After adjusting the DUT's framing to normal, switch to Operating Mode A2;
b) Set the blackbody temperature to 40℃;
c) While switching the DUT's operating mode from A2 to B, use an analysis device to record the DUT's power supply voltage signal and the video output signal to the monitor until the video signal reaches a steady state;
d) Extract the imaging time on the analysis device; the time from the start of power supply to the appearance of the video signal (T₁) is the startup imaging time;
e) The time from the start of power supply to the output of a stable video signal (T₂) is the startup stabilization time.
Note: The monitor decoding and display time and the sensor response output time must be deducted here; for the analysis device, it is recommended to use a dual-channel oscilloscope with a bandwidth greater than 100MHz (sampling rate greater than 0.5GSamples/s).

9. Recognition Distance
Definition: The maximum distance at which the system can accurately recognize a target.
Requirement: The system shall be able to recognize an upright, laterally facing, stationary dummy target at a distance of not less than 110m, and the target shall occupy no less than 12 pixels in the imaging area.
Test Method:
Atmospheric visibility is not less than 10km, and the temperature difference between the target and the environmental background is not higher than 6K. Three observers recognize the dummy target, and the distance at which two or more observers can recognize it is the recognition distance. Use analysis software to calculate the imaging pixels.

10. Observation Range
Definition: The area range in which the system can normally observe targets within the specified ambient temperature range.
Requirement: Within the ambient temperature range of -40℃ to 80℃, the observation range of the system shall cover the shaded area in Figure 1.
Test Method:
Arrange the test equipment as shown in the figure below, and test the DUT in Operating Mode B. The test procedure is as follows: a) Place the DUT, the high-temperature blackbody, and the low-temperature blackbody in an environmental test chamber. Set the DUT to Operating Mode B at ambient temperature, wait until the equipment reaches a thermally stable state, connect the video to a monitor, and check that both blackbodies are in the field of view of the image;
b) After the check is completed, set the DUT to Operating Mode A2 and cool down the environmental test chamber;
c) Conduct tests at the specified temperature points according to the table below (Observation Range Test Temperature Points (℃)), maintain each temperature point for 30min, and observe the image areas of the low-temperature blackbody and the high-temperature blackbody respectively. In white hot mode, no abnormal phenomenon of white inversion shall appear in the image area of the low-temperature blackbody, and no abnormal phenomenon of black inversion shall appear in the image area of the high-temperature blackbody.

11. Thermal Response Time
Definition: The time interval from the start of the response to the complete end of the response for a target with fixed thermal radiation.
Requirement: The thermal response time of the system shall not be greater than 80ms.
Test Method:
Arrange the test equipment as shown in the figure below, and test the DUT in Operating Mode B. The test procedure is as follows:
a) Set the turntable speed to 30r/min~120r/min, and the temperature of the high-temperature target on the turntable to 40℃±2℃;
b) Start the turntable rotation, align the optical axis of the DUT lens with the center of the turntable, ensure the diameter of the turntable in the image is not less than 1/3 of the height of the DUT imaging frame, so that the high-temperature target in the turntable can be clearly imaged;
c) Record a video. In white hot mode, extract any 3 frames of images. The time corresponding to the rotated angle α is the thermal response time, and take the average value. The starting point of angle α is selected as the center of the high-temperature target dot, and the ending point is selected at the trailing edge where the brightness value = (starting point brightness - background brightness) × 10% + background brightness.
Note: The background brightness is the average pixel brightness of the non-high-temperature area of the turntable.

12. Single Freeze Time
Definition: The time during which the image output by the system does not change with the target scene.
Requirement: The single freeze time of the system shall be less than 350ms.
Test Method:
a) Set the turntable speed in the range of 30r/min~120r/min, and the temperature of the high-temperature target on the turntable to 40℃±2℃;
b) Start the turntable rotation, align the optical axis of the DUT lens with the center of the turntable, ensure the diameter of the turntable in the image is not less than 1/3 of the height of the DUT imaging frame, so that the high-temperature target on the turntable can be clearly imaged;
c) Record a video containing at least 3 freeze phenomena;
d) Analyze the number of frames for each freeze in the video, calculate the freeze time, and take the average value.

13. Freeze Time Interval
Definition: The time interval between two consecutive freezes of the system.
Requirement: After the image is stable, the freeze time interval of the system shall not be less than 3min.
Test Method:
a) Set the turntable speed in the range of 30r/min~120r/min, and the temperature of the high-temperature target on the turntable to 40℃±2℃;
b) Start the turntable rotation, align the optical axis of the DUT lens with the center of the turntable, ensure the diameter of the turntable in the image is not less than 1/3 of the height of the DUT imaging frame, so that the high-temperature target in the turntable can be clearly imaged;
c) Record videos, each segment containing at least 2 freeze phenomena, and record at least 10 segments;
d) Analyze the time interval between the 2 freezes in each segment, and take the minimum value.