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How does a DEF quality sensor work?

2026-06-02

‌DEF (diesel exhaust fluid) quality sensors work mainly through two core technologies: optical sensing and ultrasonic sensing‌ to detect urea concentration and judge fluid quality.

1. Optical sensing method

The core principle is to use the different optical characteristics of urea solutions with different concentrations to achieve measurement. The typical structure and working process are:

Equipped with a light source (usually LED, which can cover UV, visible light, near-infrared bands), an optical path/window that directly contacts the DEF, and a photodiode detector, plus a necessary temperature sensor.
After the light passes through the DEF, the light intensity signal received by the detector will change with the urea concentration. The actual concentration is calculated by comparing with the pre-calibrated signal-concentration relationship curve, and the quality is judged‌
This solution has high repeatability and sensitivity, and can identify small changes in urea concentration.

2. Ultrasonic sensing method

It judges the concentration by using the difference of sound propagation characteristics in different concentrations of urea solution, which is currently a common commercial solution. The core detection parameters are:

‌Sound velocity‌: The density and compressibility of the solution will change with the urea concentration, which will eventually lead to a corresponding change in the propagation velocity of ultrasonic waves in the fluid.
‌Attenuation amplitude‌: The attenuation speed of sound waves and the change of waveform will also be affected by impurities, bubbles and contamination in the fluid, which can assist in judging whether the DEF is contaminated.
The sensor calculates the urea concentration through the detection results, provides misfueling protection for the SCR system, and ensures that the urea concentration meets the standard.

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How does a DEF quality sensor work?

2026-06-02

‌DEF (diesel exhaust fluid) quality sensors work mainly through two core technologies: optical sensing and ultrasonic sensing‌ to detect urea concentration and judge fluid quality.

1. Optical sensing method

The core principle is to use the different optical characteristics of urea solutions with different concentrations to achieve measurement. The typical structure and working process are:

Equipped with a light source (usually LED, which can cover UV, visible light, near-infrared bands), an optical path/window that directly contacts the DEF, and a photodiode detector, plus a necessary temperature sensor.
After the light passes through the DEF, the light intensity signal received by the detector will change with the urea concentration. The actual concentration is calculated by comparing with the pre-calibrated signal-concentration relationship curve, and the quality is judged‌
This solution has high repeatability and sensitivity, and can identify small changes in urea concentration.

2. Ultrasonic sensing method

‌Sound velocity‌: The density and compressibility of the solution will change with the urea concentration, which will eventually lead to a corresponding change in the propagation velocity of ultrasonic waves in the fluid.
‌Attenuation amplitude‌: The attenuation speed of sound waves and the change of waveform will also be affected by impurities, bubbles and contamination in the fluid, which can assist in judging whether the DEF is contaminated.
The sensor calculates the urea concentration through the detection results, provides misfueling protection for the SCR system, and ensures that the urea concentration meets the standard.

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Engine NOx Sensor

Car NOx Sensor

Nitrogen Oxide NOx Sensor

Truck Blower Motor

Urea Doser Pump

DEF Sensor

PM Sensor

Truck ABS Sensor

Exhaust Temperature Sensor

Crankshaft Position Sensor

Truck Pressure Sensor

Power Window Switch

VGT turbo actuator

News Details

Company news about How does a DEF quality sensor work?

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Cases

How does a DEF quality sensor work?

1. Optical sensing method

2. Ultrasonic sensing method

Company news about-How does a DEF quality sensor work?

News

Cases

How does a DEF quality sensor work?

1. Optical sensing method

2. Ultrasonic sensing method