The 200kHz and 500kHz ultrasonic transducers used in ultrasonic gas meters have significant differences in physical characteristics, measurement performance,

and applications, which directly affect the measurement accuracy, anti-interference ability, and applicability of gas meters. The following is a systematic analysis of

the differences between the two from a technical perspective:

I. Differences in operating frequency band and physical characteristics

1. Frequency and wavelength

200kHz ultrasonic sensor: with a longer wavelength (about 1.65mm) and strong penetration, suitable for medium to high flow scenarios. Long wavelengths

have low sensitivity to larger particle impurities in gases, such as pipeline rust, but are susceptible to low-frequency noise interference.   

500kHz ultrasonic sensor: with a shorter wavelength (about 0.66mm), high resolution, and more sensitive to small changes in flow rate. Short wavelength can

more accurately capture the motion of gas molecules, but it is susceptible to high-frequency electromagnetic harmonic interference (such as mobile phone signals, WiFi).

2. Installation and sound path design

Two types of ultrasonic sensors usually use the same installation angle (45 °) and acoustic path distance to ensure consistency in flow velocity calculation

(flow velocity formula: U=(L/2cos θ) × (1/T1-1/T2), where L is the acoustic path and θ is the angle). However, 500kHz sensors are more sensitive to installation

position deviations due to their high frequency, requiring higher machining accuracy.

II. Comparison of Measurement Performance and Applications

1. Traffic adaptability

200kHz: default for routine flow measurement. When the flow rate is below the threshold (such as 0.5m ³/h), the system switches to a 500kHz sensor

to avoid small flow rate leakage.   

500kHz: Optimized for micro flow scenarios (such as gas stove standby mode), it can detect flow rates of 0.01m ³/h to prevent gas theft.

2. Comparison of anti-interference ability

200kHz: susceptible to low-frequency mechanical vibrations (such as pipeline resonance), requiring hardware filtering circuits to suppress noise.   

500kHz: Sensitive to high-frequency electromagnetic interference (such as nearby electrical appliances), requiring shielding cover or optocoupler isolation

III. Differences between technical implementation and system integration

1. Circuit design requirements

Signal processing: 500kHz signals require higher sampling rate ADCs (>1MHz) and impedance matching circuits to reduce waveform distortion.   

Redundant design: The dual channel gas meter switches between two sets of probes in a timed manner using a 4-to-1 analog switch (such as TMUX1209) to achieve fault backup.

2. Power consumption management

The 500kHz ultrasonic transducer is only activated during low flow periods due to high driving power consumption. Some systems adopt the "dual frequency wheel patrol" strategy:

200kHz continuous operation → flow below threshold → enable 500kHz → switch back after timeout.

IV. Industry Applications and Development Trends

1. Anti theft gas

500kHz transducer high-frequency detection (125~200ms/time) can crack electromagnetic valve gas theft (manual valve switching cycle>500ms), and trigger an alarm

by comparing the difference in dual frequency data (threshold>5%).   

200kHz transducer is used for basic metering, 500kHz is used for anti-theft verification, and dual frequency cooperation enhances security.

2. Direction of technological evolution

Intelligent switching algorithm: based on traffic adaptive dynamic frequency selection (such as AI predicting traffic change trends).   

Multi sensor fusion: Combining pressure/vibration sensors to predict anomalies and reduce high-frequency detection power consumption.

In summary, 200kHz and 500kHz ultrasonic transducers are essentially scene complementary technologies:

200kHz: high robustness, low power consumption, dominant in conventional flow metering;   

500kHz: High resolution, micro flow sensitive, specializing in precise small flow monitoring and anti cheating scenarios.   

Dual frequency collaborative design has become a standard configuration for high-end ultrasonic gas meters, surpassing traditional membrane gas meters in

accuracy (± 0.5 level) and reliability (± 1.5 level). The future trend will focus on adaptive frequency scheduling and interference co suppression, further optimizing energy

efficiency ratio.