## Common ground
All options refer to ultrasonic transducers—devices that generate or receive ultrasonic waves using piezoelectric or similar principles.
## Options at a glance
**8479.89 – Cleaning applications**
- **Defining trait:** Designed specifically for cleaning metal parts and other objects via ultrasonic cavitation.
- **Typical examples:** Transducers in ultrasonic cleaners for jewelry, tools, or medical instruments.
- **Best fit when:** The transducer is used in a cleaning system with liquid immersion.
**8543.70 – Depth sounding (sonar)**
- **Defining trait:** Used in electronic depth-sounding devices to measure water depth via echo timing.
- **Typical examples:** Transducers on boats or ships for sonar or fish finders.
- **Best fit when:** The device is mounted in water and measures distance to the seabed or underwater objects.
**8548.00 – Piezoelectric transceiver**
- **Defining trait:** A general-purpose transducer with a ceramic disc (piezoelectric element) for both transmitting and receiving ultrasound.
- **Typical examples:** Basic components in sensors, medical imaging probes, or industrial testers.
- **Best fit when:** The product is a standalone piezoelectric element used in diverse applications without fixed function.
**9026.90 – Flow measurement (gases)**
- **Defining trait:** Designed for measuring gas flow using ultrasonic time-of-flight principles.
- **Typical examples:** Transducers in gas meters or industrial flow sensors.
- **Best fit when:** The transducer is part of a system measuring gas velocity via sound wave transit time.
**9031.80 – General sound-wave measurement**
- **Defining trait:** Intended for any ultrasonic measurement using sound waves, including distance, level, or presence.
- **Typical examples:** Proximity sensors, level detectors, or non-destructive testing (NDT) devices.
- **Best fit when:** The transducer is used in a broad sensing application without specific focus on cleaning, depth, flow, or electronics.
## Key differences
| Option | Primary Use Case | Medium | Measurement Type | Integration Level |
|--------|------------------------|--------|----------------------|-------------------|
| 8479.89 | Cleaning (liquid) | Liquid | Cavitation-based | System-specific |
| 8543.70 | Depth sounding | Water | Time-of-flight (echo) | Embedded in sonar |
| 8548.00 | General transceiver | Any | Bidirectional signal | Component-level |
| 9026.90 | Gas flow measurement | Gas | Transit time difference| System-specific |
| 9031.80 | General ultrasonic sensing | Any | Distance, level, presence | Flexible application |
## How to choose
- Is it used in a liquid for cleaning? → 8479.89
- Does it measure water depth (e.g., on a boat)? → 8543.70
- Is it a basic piezoelectric disc for transmitting/receiving? → 8548.00
- Is it measuring gas flow via time-of-flight? → 9026.90
- Is it used in a general sensor (e.g., level, proximity)? → 9031.80
## Overlaps & pitfalls
- **Overlaps:** A transducer for gas flow (9026.90) may also be used in general sensing (9031.80), and a piezoelectric disc (8548.00) can serve multiple purposes.
- **Pitfall:** "General" labels like 9031.80 may be tempting for any ultrasonic device, but the main function should determine classification.
- **Priority rule:** If multiple options apply, choose based on the product’s **primary intended use**—not just technical capability