Selecting the right ultrasonic transducer for distance measurement requires more than choosing a frequency or maximum range. Sensing distance, beam angle, target characteristics, environment, mounting, and electronics all affect the performance of the finished ultrasonic system.
For OEM engineers and system designers, defining these requirements early helps narrow the transducer options and avoid performance problems later in development.
How Does an Ultrasonic Transducer Measure Distance?
An ultrasonic transducer converts an electrical pulse into high-frequency sound and directs it toward a target. The returning echo is converted back into an electrical signal.
The system measures the time of flight between transmission and reception and uses the speed of sound to calculate distance.
The transducer’s frequency, beam pattern, sensitivity, and ring-down characteristics influence how effectively this process works.
1. What Sensing Range Do You Need?
Start by defining:
- Minimum target distance
- Maximum target distance
The minimum distance is affected by transducer ring-down, the short period during which the transducer continues vibrating after transmitting.
Maximum sensing distance depends on more than the transducer itself. Drive electronics, receiver sensitivity, target characteristics, signal processing, and environmental conditions can all affect usable range.
Parsonics offers ultrasonic transducers designed for applications ranging from a few inches to more than 100 feet.
2. What Ultrasonic Frequency Should You Use?
Operating frequency directly affects sensing range and transducer performance.
In general:
- Lower frequencies are better suited for longer sensing distances.
- Higher frequencies are commonly used for shorter-range applications and smaller transducer designs.
For example, the Parsonics PAR2007TRS operates at 200 kHz with a specified sensing range of approximately 3 inches to 6 feet.
The PAR4012 Series operates at 40 kHz and extends to approximately 45 feet.
Frequency should therefore be selected around the application rather than treated as a standard value for every ultrasonic system.
3. How Does Beam Angle Affect Distance Measurement?
Ultrasonic transducers transmit sound through a three-dimensional acoustic beam, not a single point.
A narrow beam is useful when:
- Space around the target is limited
- Nearby structures could create unwanted echoes
- Target discrimination is important
A wider beam can help when:
- Target position varies
- Surfaces are rough or uneven
- Target angle changes during operation
Machine frames, tank walls, pipes, brackets, and other objects inside the beam can generate unwanted echoes. Reviewing the beam pattern before finalizing the mounting location can prevent many sensing problems.
4. What Type of Target Are You Measuring?
Target geometry has a major effect on the strength of the returning echo.
Hard, smooth surfaces positioned approximately perpendicular to the acoustic beam generally provide strong reflections. Angled targets can reflect sound away from the transducer, while rough surfaces scatter the acoustic energy.
Consider:
- Target size
- Shape
- Surface texture
- Orientation
- Movement
Target characteristics should be evaluated along with frequency and beam angle rather than after the transducer has already been selected.
5. What Environment Will the Transducer Operate In?
Temperature, chemical exposure, moisture, contamination, and vibration can influence both transducer performance and service life.
Housing material is particularly important in aggressive environments.
Parsonics transducers are available in materials including:
- PVC
- CPVC
- Teflon®
- Kynar®
- 316 stainless steel
The PAR4012 Series, for example, is available with multiple housing materials to accommodate different industrial environments.
Applications operating across wide temperature ranges may also require temperature compensation because the speed of sound changes with temperature.
6. How Should an Ultrasonic Transducer Be Mounted?
Mounting affects both alignment and acoustic performance.
The transducer should have a clear path to the target and remain positioned so the target stays within the useful sensing beam.
Mechanical vibration should also be considered because vibration transmitted through the mounting structure can interfere with the transducer.
Important mounting considerations include:
- Target alignment
- Acoustic isolation
- Available installation space
- Thread requirements
- Environmental sealing
- Cable routing
7. How Do the Electronics Affect Transducer Performance?
An ultrasonic transducer is one component of the complete measurement system.
Actual sensing performance also depends on:
- Drive voltage
- Pulse characteristics
- Receiver sensitivity
- Amplification
- Filtering
- Signal processing
Important transducer specifications can include frequency, impedance, capacitance, transmit and receive sensitivity, beam pattern, and maximum drive voltage.
Because of this relationship, a published maximum transducer range does not guarantee that every electronic design will achieve the same distance.
When Is a Custom Ultrasonic Transducer Needed?
A standard transducer may work for many applications, but OEM equipment sometimes requires a transducer designed around specific mechanical or acoustic requirements.
A custom ultrasonic transducer may be appropriate when you need:
- A specific operating frequency
- Different beam characteristics
- A unique housing or mounting configuration
- Chemical-resistant materials
- Temperature sensing
- Custom cable lengths or connections
- Integration into an existing OEM assembly
Parsonics works with OEMs and system designers on both standard and custom ultrasonic transducers for distance measurement, level measurement, proximity detection, obstacle avoidance, and industrial automation.
What Information Is Needed to Select an Ultrasonic Transducer?
Before selecting a transducer, define these seven factors:
Sensing range → Frequency → Beam angle → Target → Environment → Mounting → Electronics
Providing this information allows Parsonics to evaluate whether an existing transducer or a custom design is the better fit.
Developing an ultrasonic sensing system? Contact Parsonics to discuss your distance range, target, environment, mounting requirements, and electronics.