In the field of industrial automation level measurement, radar level transmitters have become core equipment in industries such as petrochemicals, water treatment, food and pharmaceuticals, thanks to their non-contact, high-precision, and strong adaptability advantages. Their working principle (radar level transmitter working principle) is the key to achieving accurate measurement.
A radar level transmitter is a level measurement device based on radar (electromagnetic wave) technology. It calculates the position of the liquid surface by transmitting and receiving electromagnetic waves, converts the liquid level height signal into industrial standard electrical signals (such as 4-20mA current signals, RS485 digital signals), and realizes long-distance transmission, real-time monitoring, and automatic control of liquid level data.
Compared with traditional level measurement equipment (such as float-type, ultrasonic-type), its core advantages lie in being unaffected by environmental factors such as medium density, viscosity, dust, and steam. It can be adapted to harsh industrial working conditions such as high temperature, high pressure, and strong corrosion, and its measurement accuracy remains stable for a long time.
The working logic of a radar level transmitter revolves around "electromagnetic wave transmission - reflection - reception - signal calculation". It infers the liquid level height through the interaction between electromagnetic waves and the liquid surface. The specific process is as follows:
The high-frequency oscillator inside the device generates electromagnetic waves of a specific frequency (commonly 6GHz, 26GHz). These electromagnetic waves are directionally transmitted to the liquid surface inside the container through a dedicated radar antenna (such as a horn antenna, rod antenna).
- Technical Key Point: The frequency of electromagnetic waves directly affects measurement performance. The higher the frequency, the narrower the beam angle (the beam angle of 26GHz is usually ≤3°), and the stronger the signal focusing, which is suitable for small-caliber containers or complex working conditions. Lower frequencies (such as 6GHz) result in a wider beam angle (about 15°), which is suitable for large-range measurement of large-caliber storage tanks and has stronger ability to penetrate dust and steam.
When the electromagnetic wave beam touches the liquid surface, due to the significant difference in dielectric constant between the liquid and air (the dielectric constant of the liquid is generally ≥1.8, much higher than that of air), most of the electromagnetic waves are reflected by the liquid surface to form an "effective echo signal". A small amount of electromagnetic waves will penetrate the liquid surface or be absorbed by the medium, which has a negligible impact on the measurement result.
- Adaptation Premise: As long as the dielectric constant of the liquid meets ≥1.8, a stable echo can be formed. If the dielectric constant of the medium is extremely low (such as some light oils, liquefied natural gas), a waveguide can be used to enhance the reflection effect and ensure the strength of the echo signal.
The reflected echo signal returns along the original path and is received by the radar antenna. The signal processing module (equipped with MCU and DSP chips) inside the device performs filtering, amplification, and noise reduction processing on the echo signal, eliminating interference signals such as container wall reflection, environmental dust, and equipment vibration, and only retaining the effective echo related to the liquid surface, providing a precise data basis for subsequent calculations.
By calculating the "time difference (Δt) between the transmission time of electromagnetic waves and the reception time of echoes", and combining with the propagation speed of electromagnetic waves in air (about 3×10⁸m/s under standard conditions, which can be calibrated in real time according to ambient temperature and pressure), the signal processing module infers the liquid level height through a formula:
Liquid Level Height (H) = Total Container Height (H_total) - Distance from Radar Antenna to Liquid Surface (d)
Among them, d = (Electromagnetic Wave Propagation Speed × Δt) / 2 (divided by 2 because the electromagnetic wave needs to travel back and forth between the antenna and the liquid surface).
- Special Technology: Some high-end devices adopt Frequency-Modulated Continuous Wave (FMCW) technology. By transmitting electromagnetic waves with linearly changing frequencies, they calculate the frequency difference between the transmitted wave and the echo, and indirectly infer the distance. This is suitable for high-precision (error ≤ ±0.05%) and long-distance (measurement range up to 70m) liquid level measurement scenarios.
After the calculation is completed, the device converts the liquid level height signal into industrial standard signals such as 4-20mA, RS485, or HART protocol, and transmits it to PLC, DCS control systems, or display instruments to realize real-time monitoring of the liquid level, over-limit alarm, or automatic liquid discharge/water supply control.
Based on the above working principle, the radar level transmitter has three core technical advantages, which can accurately meet the needs of industrial scenarios:
Since electromagnetic waves do not need to be in direct contact with the liquid, there is no physical friction between the device and the medium. The antenna is made of anti-corrosion materials (such as Hastelloy, PTFE coating) and is equipped with IP67/IP68-level sealing design. It can withstand a maximum pressure of 60MPa and a temperature range of -60℃ to 400℃, and is suitable for working conditions of strong corrosion, high temperature, and high pressure. The service life of the device is extended to 5-8 years (the service life of traditional contact devices is usually less than 3 years).
The propagation of electromagnetic waves is not affected by medium density, viscosity, or color, and can penetrate dust, steam, and mist. Even in complex containers with agitators and baffles, through narrow beam design or echo tracking algorithms, the liquid surface echo can still be accurately identified, and the measurement stability is not affected by environmental changes.
Through optimizations such as high-frequency signal design, temperature and pressure compensation modules, and FMCW technology, the measurement error of the device can be controlled within ±0.1%, and the measurement range covers 0.1m-70m. It can be adapted to the level/material level measurement of liquids and some solid particles (such as plastic particles, coal powder), meeting the needs of multiple industries such as petrochemicals, water treatment, food and pharmaceuticals, and energy storage.
Both are non-contact measurement methods, but their core technologies are different: Radar level transmitters are based on electromagnetic wave reflection, unaffected by dust, steam, and temperature, with a wide measurement range (0.1m-70m) and suitable for complex working conditions. Ultrasonic level meters are based on sound wave reflection; sound waves are easily attenuated by dust and temperature, with a narrow measurement range (0.2m-10m), and only suitable for liquid measurement scenarios that are clean and free of interference.
Optimizations need to be made from the perspective of working principle adaptation: select a frequency matching the working condition (26GHz for complex working conditions), calibrate the electromagnetic wave propagation speed (real-time compensation based on ambient temperature and pressure), ensure that the liquid surface dielectric constant meets the requirements (use a waveguide for low dielectric constant media), and regularly clean the antenna to avoid interference from material buildup, so as to maintain high-precision measurement.
Based on their working principle, they can be adapted to special working conditions such as high temperature (≤400℃), high pressure (≤60MPa), strong corrosion (acid-base media), high dust (such as cement silos, coal powder tanks), and easy fogging (such as beverage fermentation tanks). Moreover, they do not require frequent maintenance and are the preferred liquid level measurement equipment in harsh industrial environments.
The working principle of the radar level transmitter centers on "electromagnetic wave interaction". Through precise transmission, reflection, reception, and calculation, it realizes non-contact, high-precision, and highly adaptable liquid level measurement. Its technical advantages stem from in-depth adaptation to the needs of industrial scenarios. Whether it is the anti-interference ability in harsh working conditions or the wide-range measurement adaptability, both are driven by the optimization and iteration of the working principle. With the upgrading of industrial automation, radar level transmitters based on advanced working principles will continue to be the core equipment for liquid level measurement in various industries, promoting industrial measurement towards a "more precise, more stable, and lower maintenance" direction.
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