For a clamp-on ultrasonic flowmeter, installing the sensors at the correct position is an important part of achieving reliable flow measurement. The TF1100-EC transit time ultrasonic flowmeter uses two transducers mounted on the outside of a fully filled pipe. The transducers transmit and receive ultrasonic signals through the pipe wall, and the flowmeter determines liquid velocity from the difference in ultrasonic transit time between the two sensors.
For this reason, the distance between the two transducers cannot be selected randomly. The TF1100 series specifically states that transducer spacing and alignment are critical to system accuracy and performance.
1. What Is Transducer Spacing?
Transducer spacing refers to the distance between the two transducers installed on the pipe.
Depending on the pipe and liquid conditions, TF1100 transducers can be installed using different mounting methods:
- Z-Mode: The transducers are installed on opposite sides of the pipe, and the signal crosses the pipe once.
- V-Mode: The ultrasonic signal crosses the pipe twice.
- W-Mode: The ultrasonic signal crosses the pipe four times.
The selection of the mounting method depends on factors such as pipe material, pipe size, liquid composition, aeration, suspended solids, and piping conditions. The manual notes that selecting the appropriate mounting configuration can sometimes be an iterative process.
2. How Does TF1100 Determine the Correct Sensor Spacing?
One important feature of the TF1100 is that the flowmeter can calculate the appropriate sensor spacing automatically.
Before installation, the user needs to enter the relevant pipe and liquid parameters, including:
- Pipe outer diameter
- Pipe wall thickness
- Pipe material
- Pipe sound speed
- Pipe relative roughness
- Liner thickness
- Liner material
- Liner sound speed
- Fluid type
- Fluid sound speed
- Transducer type
- Transducer mounting method
The TF1100 uses this information to calculate the proper transducer spacing for the selected installation configuration.
Therefore, the sensor spacing displayed by the flowmeter is based on the actual pipeline configuration entered during setup. If incorrect pipe parameters are entered, the calculated spacing may not represent the actual installation conditions.
3. Why Should the Sensors Be Installed According to the Displayed Distance?
After the pipe parameters and mounting method have been configured, the TF1100 displays a value under the Sensor Distance menu.
The manual requires users to install the sensors according to this calculated spacing. It also specifies that the displayed spacing is the distance between the ends of the two transducers.
For normal Small and Standard-M transducers, the manual further explains that the actual spacing should be kept as close as possible to the displayed value, with the acceptable range stated as 97–103 relative to the displayed spacing value.
This means that the displayed sensor spacing should be treated as an important installation reference rather than simply placing the two sensors at an approximate position.
4. Is the Displayed Spacing Always the Final Position?
Not necessarily.
The calculated spacing provides the starting point for installation, but the actual pipe condition can affect the ultrasonic signal. After positioning the sensors at the calculated distance, the TF1100 manual recommends observing the Signal Strength (RSSI) while making small adjustments.
For V-Mode and W-Mode installation, the downstream transducer can be slowly moved toward and away from the upstream transducer while monitoring signal strength. The sensor should be secured at the position where the highest signal strength is observed. An RSSI value between 60 and 95 is considered acceptable according to the manual.
The same principle is described for Z-Mode installation: after placing the downstream transducer at the calculated spacing, the position can be adjusted while observing signal strength, and the transducer should be fixed where the highest signal strength is obtained.
5. What Should Be Checked If the Signal Is Too Weak?
If the sensors have been adjusted but the RSSI does not rise above 60, the manual recommends selecting an alternative transducer mounting method.
For example, if the original configuration uses W-Mode and the signal remains insufficient, the user can reconfigure the TF1100 for V-Mode, move the downstream transducer to the new calculated location, and repeat the signal-strength adjustment process.
The TF1100 also provides a Signal Quality (Q) value. Under normal working conditions, the manual specifies:
- RSSI ≥ 60.0
- Q value > 40
Higher signal strength and signal quality help support stable operation and measurement performance.
6. Proper Spacing Is Only One Part of Installation
Correct sensor spacing should be combined with proper installation location, orientation, and pipe preparation.
The TF1100 is designed for flow measurement in a fully filled pipe. The manual does not recommend installing the transducers where the pipe may become partially filled because this can result in erroneous and unpredictable operation.
For horizontal pipes, the two transducers should be positioned 180 radial degrees from each other and at least 45 degrees from the top and bottom dead centers of the pipe.
Before mounting, the pipe surface should also be prepared. Rust, scale, and moisture should be cleaned from the areas where the transducers will be installed. Rough surfaces, such as ductile iron, may need to be ground flat, while plastic pipes typically only require cleaning with soap and water.
7. Conclusion
For a clamp-on ultrasonic flowmeter, sensor spacing is not simply a mechanical installation dimension. It is part of the ultrasonic measurement setup.
For the TF1100-EC, the recommended procedure is to:
Enter the correct pipe and liquid parameters → Select the appropriate transducer type and mounting method → Check the calculated Sensor Distance → Install the sensors according to the displayed spacing → Fine-adjust the sensor position while monitoring RSSI → Secure the sensors at the position with the strongest acceptable signal.
Following this procedure helps ensure that the ultrasonic signal path is properly established and supports stable flow measurement. The TF1100 is specifically designed to calculate the appropriate transducer spacing from the configured pipeline and liquid parameters, making correct parameter entry an essential step before sensor installation.
Post time: Sep-03-2026