Electrostatic ultrasonic sensing measures both reflective liquids and soft, absorptive solids with a single transducer — resolving the full range of tank conditions that force conventional level sensors to lose their reading or require separate hardware.
KEY ANSWERS AT A GLANCE
Can one sensor measure both liquids and solids? Yes — a single electrostatic ultrasonic transducer can be configured to cover 1 inch to over 40 feet with appropriate drive and receive electronics, reading reflective liquids and soft, absorptive solids alike.
Why do piezoelectric ultrasonic sensors read “empty” on a full bin? Grain and powder settle into a cone, and the return off the peak is small and soft, so a piezoelectric ultrasonic sensor’s lower receive sensitivity loses that faint echo.
Does ring-out create a blind zone near the sensor? For piezoelectric ultrasonic transducers, yes — they ring after transmit, masking echoes inside roughly 13 to 14 inches or more; electrostatic ultrasonic transducers settle quickly and keep reading to within 1 inch of the face.
Do these transducers work in corrosive tank environments? Yes — Environmental Grade transducers add a parylene coating and a 304 stainless-steel housing, with minimal dampening of acoustic sensitivity
Do these sensors work in corrosive tank environments? Yes — Environmental Grade transducers add a parylene coating and a 304 stainless-steel housing, with minimal dampening of acoustic sensitivity.
Why does level sensing behave differently on reflective vs. soft targets?
Level sensing sounds straightforward until you look at what’s inside the tank. A flat water surface and a cone of granular powder don’t behave the same way acoustically, and engineers designing level measurement systems often need to account for both ends of that spectrum — and everything in between — within a single installation.
Ultrasonic level sensors work by emitting a pulse and timing the return echo that bounces back from the target surface, and the quality of that echo depends almost entirely on what the surface does with the incoming sound energy. Reflective targets — calm liquids, flat metal, smooth plastics — behave predictably: the pulse hits a hard, flat interface and returns a strong, clean echo, which most ultrasonic sensors, including piezo units, handle reasonably well under controlled conditions. Soft and absorptive targets are a different problem. Materials like grain, powder, foam, and loose fill absorb acoustic energy instead of reflecting it, so what does come back is faint, scattered, and often buried in noise. Piezoelectric ultrasonic sensors, with their lower sensitivity and narrow bandwidth, frequently lose the return signal entirely — the system reads “empty” when the bin is full, or the measurement jumps erratically. The challenge compounds when reflective and absorptive targets exist in the same system, such as a liquid with a foam layer on top, or a tank that holds water one week and slurry the next.
Why aren’t reflective surfaces always easy either?
Even cooperative targets can cause problems. Turbulent liquids scatter the return signal, and narrow tanks create multipath reflections where the pulse bounces off the sidewalls before returning to the sensor, producing false distance readings. Highly reflective surfaces at close range can saturate a sensor that’s still ringing out from its transmit pulse, creating a dead zone where measurement isn’t possible.
Piezoelectric ultrasonic transducers are particularly susceptible to this last issue. Because they’re resonant devices, they ring for a relatively long time after transmitting, and that ring-out window becomes a blind spot. In shallow-tank applications, or systems where the sensor is mounted close to the maximum fill level, that blind spot lands exactly where the most important data is needed.
How do ultrasonic sensors handle both soft and reflective targets?
Electrostatic ultrasonic transducers handle both target types with one device because they have approximately 40 dB greater receive sensitivity than piezoelectric ultrasonic transducers, and because their low-resonance membrane settles quickly after each transmit pulse. The sensitivity margin resolves the faint, scattered echoes that soft and absorptive materials return. The fast settling shortens the near-field dead zone that otherwise limits measurement on close, highly reflective surfaces.
Sensitivity on Soft Targets: Electrostatic ultrasonic transducers have approximately 40 dB greater receive sensitivity than piezoelectric ultrasonic transducers. Faint, scattered echoes from powder, grain, foam, and other absorptive surfaces that fall below a piezoelectric ultrasonic sensor’s detection threshold are well within range for an electrostatic ultrasonic transducer.
Minimal Dead Zone on Reflective Targets: Ring-out is minimal, which shrinks the near-field dead zone and allows accurate measurement much closer to the transducer face. A single transducer can be configured to cover 1 inch to over 40 feet with appropriate drive and receive electronics — handling both shallow-tank and deep-tank applications without swapping hardware.
Thermal Stability Across Operating Conditions: Frequency and gain remain stable from -40°C to +85°C. There’s no resonant frequency drift to compensate for, which means the system doesn’t need recalibration as ambient conditions change throughout the day or across seasons — a meaningful advantage for outdoor tanks, silos, and bins that see wide thermal swings.
Broadband Operation for Better Surface Discrimination: The broadband nature of the electrostatic pulse captures a richer acoustic picture of the target surface, helping the system distinguish between a valid echo from the actual material surface and noise from multipath reflections, foam layers, or tank wall interference.
What Should I Consider When Specifying a Sensor for Mixed Tank Conditions?
- Mounting position: Center-mount the transducer above the tank to minimize sidewall reflections. In bins with conical fill patterns, aim at the cone peak area.
- Environmental protection: For tanks containing corrosive chemicals or high-humidity environments, SensComp’s Environmental Grade electrostatic ultrasonic transducers add a parylene conformal coating and a 304 stainless-steel housing for long-term durability, with minimal dampening of acoustic sensitivity
- Temperature compensation: While the transducer itself is thermally stable, the speed of sound in air changes with temperature. A co-located temperature sensor allows the system to compensate and maintain measurement accuracy across conditions.
- Beam angle selection: The Series 600 transducer’s 15-degree beam works well for most tank geometries. For smaller tanks or applications requiring a wider coverage area, the Series 7000 transducer’s 17-degree beam in a more compact form factor may be a better fit.
How do electrostatic and piezoelectric ultrasonic sensors compare for level sensing?
|
Factor |
Electrostatic Ultrasonic (SensComp) |
Piezoelectric Ultrasonic |
|---|---|---|
|
Sensitivity on soft/absorptive targets |
Approximately 40 dB greater receive sensitivity; detects faint echoes off grain, powder, and foam |
Frequently loses the return signal on absorptive solids |
|
Near-field blind zone |
Low-resonance membrane settles quickly; with appropriate drive and receive electronics, measurement to within 1 inch of the transducer face |
Longer ring-out from the resonant ceramic element creates a larger dead zone |
|
Temperature stability |
Frequency and gain hold from -40°C to +85°C |
Resonant frequency and gain drift with temperature unless compensated |
|
Typical range |
1 inch to over 40 feet with a single transducer, with appropriate drive and receive electronics |
Narrower window; often requires different hardware for shallow vs. deep tanks |
|
Surface discrimination |
noiseBroadband — roughly 20 kHz to 100 kHz — helps distinguish a valid echo from multipath and noise |
Narrowband pulse offers less discrimination between echo sources |
Frequently Asked Questions
Yes. A SensComp electrostatic ultrasonic transducer can be configured to cover 1 inch to over 40 feet with appropriate drive and receive electronics, and it has approximately 40 dB greater receive sensitivity than a piezoelectric ultrasonic transducer. That lets the same transducer read a calm, reflective liquid surface and a soft, absorptive solid like grain or powder without swapping hardware.
This is typically a receive sensitivity problem. Grain and powder settle into a cone, and the return off the cone peak is small and soft, so a piezoelectric ultrasonic sensor may miss it and the bin reads empty. Electrostatic ultrasonic transducers have approximately 40 dB greater receive sensitivity than piezoelectric ultrasonic transducers, which is enough to detect that faint echo and give a valid product-height reading.
It can, particularly for lower-sensitivity sensors, since a foam layer absorbs acoustic energy rather than reflecting it cleanly. Electrostatic ultrasonic transducers have approximately 40 dB greater receive sensitivity than piezoelectric ultrasonic transducers, which improves the ability to resolve a valid echo even when a foam layer sits above the liquid surface.
Narrow tanks can create multipath reflections, where the transmitted pulse bounces off the sidewalls before returning to the sensor, producing a distance reading that doesn’t match the actual fill level. Center-mounting the transducer and selecting an appropriate beam angle reduces this effect — the Series 600 electrostatic ultrasonic transducer’s 15-degree beam is tight enough to limit sidewall returns in most tank geometries.
SensComp offers Environmental Grade electrostatic ultrasonic transducers with a parylene conformal coating and a 304 stainless-steel housing, which protect against moisture, chemical exposure, and corrosion with minimal dampening of acoustic sensitivity.
Specifying a Level Sensing System?
Explore SensComp’s electrostatic transducers, environmental grade housings, and integration options for level measurement across liquids, grains, and bulk solids. Try our Sensor Selector tool.