Ultrasonic Flow Meter Technology for accurate flow measurement
Ultrasonic Flow Meter Technologies employed in Starflow for accurate, reliable flow metering.
Starflow is an area velocity flow meter, which calculates flow by multiplying the average velocity of the stream by its cross-sectional area.
Measuring Velocity
When sound is reflected from a moving target, the frequency of the sound is varied by the velocity of the target. This variation, known as the Doppler shift, can be observed when a fast moving vehicle passes a stationary observer. Ultrasonic flow meters such as Starflow use this phenomenom to measure water velocity, transmitting a continuous ultrasonic signal at a fixed frequency, listening for reflected signals from moving particles (mainly air bubbles) in the water, and measuring any shift in the frequency between the transmitted and received signals.
Starflow will take up to 1,000 samples during each measuring cycle, but more typically is programmed to take 200-500. From these samples, the mean value of the velocity during the cycle can be calculated. A measuring cycle typically lasts for a few hundred milliseconds, depending on the number of targets in the sampling area. The Starflow beam is fired at an angle of 30º to the flow in order to reduce the impact of flow turbulence, and the profile used to adjust the velocity readings for any turbulence detected. The Starflow also measures water temperature as a proxy for water density (which will affect the speed of sound in the water), and automatically compensates for this effect.
Power Management
Ultrasonic signals are relatively power hungry, and to preserve battery life Starflow incorporates a Micrologger to shut down all non-essential functions (including the signal) until it is time to commence a measuring cycle. The interval between measuring cycles is known as the scan rate, and is user-defined during set-up. The scan rate can be set between 5 seconds and 5 minutes. The log interval, which is the period of time between readings being recorded to memory, can be set between 5 seconds and 7 days.
Measuring Cross-Sectional Area
The depth of the stream is gauged by a hydrostatic pressure sensor, which is corrected for changes in atmospheric pressure (measured through the vented power and signal cable). Cross-sectional area is calculated from channel dimension inputs which are user-defined.
The remaining stream dimensions or type of channel to be logged are user-defined during set-up using Starflow V.3 user-friendly software. This provides a complete hydrographic data logger scheme, including real-time velocity histograms and an extension for flow calculations which enables STARFLOW to be used in partly filled circular pipes, regular open channels and natural streams. Flow measurement in other closed shapes, like ovoid pipes, is accomplished by a user-defined Area Rating Table.
Features
- Velocity Trace
- Flow Measurement Extension
- Point and click commands
- Automatic STARFLOW configuration
- Scheme Editing
- View logged data in “real time”
- STARFLOW and Scheme Testing
- Report Creation
- Plot Generation
- Event-based Logging
