What are the differences in structure and measurement accuracy between single-path and multi-path ultrasonic water meters

In modern smart water management and industrial flow measurement and control, ultrasonic water meters have become a mainstream measurement tool due to their lack of mechanically moving parts, low pressure drop, and high accuracy. Ultrasonic water meters are primarily categorized into single-path and multi-path designs, depending on the number of acoustic wave paths. Understanding the core differences between these two structures in terms of principle, composition, and measurement accuracy is crucial for selecting the flow meter best suited for your application.

Structural Design and Acoustic Wave Path Layout

1. Single-Path Ultrasonic Water Meter

As the name suggests, a single-path ultrasonic water meter utilizes only one transducer pair (i.e., one acoustic wave measurement path) across the flow cross-section.

Structural Features: This design is the simplest and relatively low-cost. Two transducers are typically positioned obliquely along the pipe diameter or along a specific chord length, forming a single acoustic beam. Acoustic waves propagate along this fixed path, both upstream and downstream, and the flow velocity along this path is calculated using the transit-time method.

Applicable Scenarios: Typically used in small-diameter pipes or for residential meter reading applications with moderate measurement accuracy requirements. Because the acoustic wave path is single, it can be made more compact and offers greater installation flexibility.

2. Multi-Path Ultrasonic Water Meter

Multi-path ultrasonic water meters utilize two or more transducer pairs (e.g., two-channel, three-channel, or four-channel) installed across the pipe cross section, creating multiple acoustic wave paths.

Structural Features: The structure is relatively complex, requiring more transducers and more sophisticated signal processing circuitry. These acoustic wave paths are typically distributed along different chordal directions to maximize coverage or simulate the velocity distribution across the flow cross section.

Core Technology: Multi-path water meters utilize numerical integration or weighted averaging algorithms to comprehensively calculate the flow velocities along multiple paths and determine the average velocity across the entire cross section, thereby achieving higher-precision flow measurement.

Applicable Scenarios: Primarily used in large-diameter water supply networks, trade transfer, high-precision industrial metering, and applications requiring extremely high turndown ratios.

Measurement Accuracy and Flow Regime Adaptability

Structural differences directly determine the significant gap in measurement accuracy and flow regime adaptability between the two water meters.

1. Dependence on Velocity Distribution

Water in a pipe does not flow uniformly; instead, it exhibits a velocity profile, typically with high velocities at the center and low velocities near the pipe wall. This velocity profile can be affected by interference factors such as upstream valves, elbows, and pumps, resulting in distorted flow.

Limitations of Mono-channel Meters: Mono-channel meters only measure the flow velocity at a single point or along a line in a cross-section. They assume that the actual velocity distribution is consistent with an ideal velocity distribution (such as fully developed flow) and use a fixed correction factor to convert the path velocity to an average velocity. Once the actual flow pattern is distorted, the correction coefficient becomes ineffective, leading to a sharp drop in measurement accuracy. This is the biggest accuracy bottleneck of a single-channel system.

Advantages of multi-channel systems: By collecting multiple flow velocity samples at different locations, multi-channel systems can capture the true shape of the flow velocity distribution to a greater extent. Using sophisticated numerical integration algorithms, multi-channel systems can effectively compensate for and correct distorted flows, significantly reducing errors caused by flow pattern disturbances. Therefore, their measurement accuracy is significantly higher than that of a single-channel system. The stability advantage of multi-channel systems is particularly pronounced under less-than-ideal installation conditions (such as insufficient straight pipe length).

2. Turndown and Low-Flow Measurement Capability

The turndown ratio measures the ability of an ultrasonic water meter to maintain accuracy over a wide flow range.

Due to their ability to process weak signals and accurately capture flow velocity distribution, multi-channel systems often have a higher turndown ratio. This means they can maintain stable measurement at extremely low flows (such as at the Q1 flow point), making them more valuable for leak monitoring.

When the flow rate is low, the velocity difference signal on the sound wave path is weak, and the velocity distribution is more easily affected by temperature, bubbles, etc. The lower limit of measurement accuracy is high and the range ratio is relatively limited.