Frequently Asked Questions About Ultrasonic Sensors

1. What do Senix® ultrasonic sensors do?

Ultrasonic sensors measure the distance to or presence of a target object or material through air without touching it. The measured distance is provided as an output in a variety of standard electrical interfaces compatible with displays, machinery, PLC’s, computers and most electronic or electrical machinery.

Non-contact ultrasonic sensors have distinct advantages in challenging environments where corrosive, scaling, coating, or dirty materials are likely to negatively impact the performance and maintenance costs of contact sensors.  Non-contact ultrasonic sensors are also desirable where the material being measured cannot be corrupted by contact with any measuring device.

2. What DON’T Senix® ultrasonic sensors do?

They DO NOT measure through tank walls – they only measure through air.

They DO NOT measure material thickness by contacting the material. Search non-destructive testing (NDT) sensors for that purpose.

They DO NOT work in a vacuum. Sound does not travel in a vacuum.

They DO NOT work at very high temperatures or pressures.

They DO NOT locate objects moving about in a 3-dimentional space.

They DO NOT measure farther than about 70 feet (21 meters).

They DO NOT measure at very high repetition rates. Due to speed of sound limitations the fastest rate is 200 Hz at a max distance of about 24 inches.

They DO NOT work as accurately in vapor environments that change the speed of sound from that of air.

3. Where are Senix® ultrasonic sensors used?

Ultrasonic sensors are used wherever non-contact distance measurement is desirable.  Senix sensors are operating reliably on thousands of machines in all industries and many operating environments worldwide. Applications range from simple liquid level measurement to diameter measurements in converting machinery to robot positioning in automated warehouses.  Senix can also configure, adapt or design sensors for special needs. Applications fall into three general categories:

LIQUID LEVEL MEASUREMENT − measuring the height of liquids

Industries monitor liquid levels in tanks, vats, drums, bins, lift stations, flumes, weirs and stilling tubes. Environmental monitoring applications measure the ocean surface for Tsunami warnings, river & stream levels for flood warnings and irrigation channels and ponds for water delivery.  Where there is liquid there is usually a need for inventory or level control.  Read more about Liquid Level sensor applications …

OBJECT DETECTION detecting the presence of objects or people

Objects can be detected for security, counting, inventory or robotic obstacle avoidance. Ultrasonic sensors are not affected by the object’s color or optical characteristics such as reflectivity, transparency or opacity. People can be detected at kiosks, or determined to be approaching or leaving. Targets can be monitored over the full sensor range or restricted within user-defined distance ranges. Learn more about Object detection applications…


Senix sensors can discriminate objects by height or size, such as when selecting and routing boxes on a conveyor or rejecting out-of-dimension objects. Converting machines measure changing roll diameter to control web tension. Other applications measure the location of a target object for display or control feedback. Examples include dancer roll and web loops in printing and converting machinery, camera focusing, mirror positioning in flight simulators, robotic positioning and much more. Learn more about Distance Measurement applications …

4. How do ultrasonic sensors work?

Ultrasonic sensors (sometimes called ultrasonic transducers), measure the distance to or the presence of a target object by sending a sound pulse, above the range of human hearing (ultrasonic), toward the target and then measuring the time it takes the sound echo to return. Knowing the speed of sound, the sensor determines the distance of the target and sets its outputs accordingly. Learn more about our technology …

ultrasonic sensor bouncing sound wave off object

Sensor outputs are set based on the measured distance, or under override conditions, a lack of target detection or user-selected response algorithms. Outputs can be:
• an analog voltage or current signal proportional to the measured distance
• Switches or relay contact closures that open or close at specific distances
• distance data transmitted digitally as serial data communications.

5. What kind of targets can Senix® sensors detect?

Sensors will detect both large and small targets, including liquids, solids and granular materials. The size, shape and orientation of the target will affect the maximum distance at which it can be detected. The sensor is not affected by optical characteristics such as color, reflectivity, transparency or opaqueness.

6. How far can Senix® ultrasonic sensors measure?

The maximum range of our products is presently 20 meters (about 70 feet) and varies by model. The distance at which an object is detected depends on its size, shape and orientation. In general the target must be larger to be detected at longer distances – the object must reflect a sufficiently strong ultrasonic echo back to the sensor to be detected. Large, flat targets such as a liquid surface in a tank are detected at the maximum range. Curved objects or sound absorbing materials such as fabrics or non-wovens reflect less energy directly back to the sensor. Granular materials may absorb sound or deflect sound energy away from the sensor due to surface variation and/or angle of repose. Sensor maximum range should be de-rated for these targets.

ultrasonic sensor minimum and maximum range

Other factors affect how close an ultrasonic sensor can be to a target and still measure distance correctly. When too close the sensor will not detect the first echo, but may detect a second or third echo, yielding a longer than actual value. This deadband distance varies by model and is larger for longer range models, varying from 44 to 305 mm (1.75 to 14 inches). The minimum range and maximum range define the limits of the material window, which is the useful operating range of the sensor. The material window is user-adjustable with SenixVIEW software to ignore unwanted targets or optimize system performance. When used outdoors we recommend limiting the range to the sensor’s “Optimum Range” specification rather than the “Maximum Range” to allow for environmental extremes.

7. How do I select the right sensor range for my application?

Selecting the right sensor range for your application will depend on many variables including target characteristics and the measurement environment. In liquid level applications, we recommend that you select a sensor range at least 25% greater than the maximum distance you are likely to measure. When measuring dry materials or difficult targets, we recommend selecting a sensor range at least 50% greater than your maximum measurement distance. Senix Customer Service can help you select the right sensor for your needs. Learn more about our sensors.

8. How accurate are Senix® Ultrasonic sensors?

Most Senix® models have a measurement resolution of 0.086 mm (0.003384 inches). Other measurement, environmental and target factors affect the overall result. Typical repeatability is better than 0.5%, and accuracy is better than 1% of the measured target distance.

9. Can ultrasonic sensors be used to protect the life or safety of people?

NO – DO NOT USE any ultrasonic sensor as a primary safety device to detect and protect people! Although ultrasonic sensors generally detect people reliably, an ultrasonic echo may not be detected if a person is at the wrong angle or is wearing ultrasonically absorbent clothing. Ultrasonic sensors can be used as secondary devices for additional safety, but they should never be used in an application where life or health are at stake!

10. How wide is the ultrasonic beam?

The ultrasonic beam angle in Senix® sensors is typically 10-15 degrees and conically shaped. The real-world response to an off-angle target has a lot to do with the target size and orientation, and the sensitivity setting of the sensor. Computer configurable sensors can be adjusted to optimize detection of the desired target and ignore undesired targets.

11. What happens if the ultrasonic beam hits other objects?

A common misunderstanding is that if the ultrasonic beam is larger than the target there is a problem. This is not true in general. It does not matter that the beam is larger or reaches other objects as long as those objects do not reflect sound back to the sensor or are farther away than the target of interest. For example, this means that a sensor can be mounted next to a wall or can measure inside a tube and the measurement will not be affected as long as the wall or tube surface is smooth because no sound energy is reflected back to the sensor from the surface. In computer configurable sensors, the detection of undesired or off-axis objects can be affected by beam width, sensitivity adjustment, range adjustment, processing filters and object masking.

12. How well do Senix® sensors work in industrial environments?

Sensors operate reliably in all but the most extreme industrial environments. They are used with electrically noisy machinery including motor drives and other electrical and electromechanical controls.

Specific considerations are discussed below.

Ingress Ratings

Our ToughSonic line is IP68 / NEMA-4X / NEMA-6P rated and will operate after complete submersion. 

Outdoor Environments

The ToughSonic models are designed to withstand the harshest outdoor environment with full epoxy potting, UV shielded cables and stainless steel or polymer housings.   The sensor face must be protected from buildup of ice, snow, mud and other debris or the transmission of sound energy will be reduced or blocked.


The temperature of the air between the sensor and the target can affect measurement accuracy since the speed of sound varies with temperature. If this is an issue, temperature compensation is available in all computer configurable models. At room temperature the speed of sound changes approximately 0.175%/°C, or 1% for every 5.7 °C. As the temperature increases the target will measure closer, and vice versa.

Air temperature variations or gradients between the sensor face and the target will affect accuracy because the sensor assumes a constant temperature when it calculates distance. This can be an issue in vertical measurements such as a tank level if internal heating occurs when the tank is exposed to the sun, creating a temperature gradient inside the tank.

Some customers have had success with hot applications. Very hot environments above the sensor’s operating range are not recommended. In general, the readings become less reliable in a non-homogeneous environment. Severe temperature gradients, however, such as measuring red-hot metal cause the echo to reflect off the gradient rather than the intended target, making the measurement invalid.


Humidity change is generally not a significant factor (0.036% / 10% RH change).


Normal atmospheric pressure changes or small pressure changes in vessels will not affect ultrasonic sensor operation. Ultrasonic sensors are not designed for high pressure applications. Sound does not travel in a vacuum.

Audible Noise

Loud audible noises produced by machinery do not affect the sensor.

Ultrasonic Noise

Locally generated ultrasonic noise at the sensor operating frequency can interfere with measurements. Some potential sources are high pressure air releases near the sensor caused by air nozzles, pneumatic valves or solenoids, and ultrasonic welders. In computer programmable sensors, processing options can be selected to ignore the effects of noise bursts. Higher frequency sensors are less susceptible since there is less high frequency noise due to sound absorption in the air. Air paths are usually rearranged, blocked or eliminated to prevent this. Senix sensors are designed to allow several ultrasonic sensors in the same vicinity without mutual interference.

Hazardous environments

Senix products are not presently rated either explosion proof or intrinsically safe for hazardous areas.

13. How do I know what the measured distance is?

Senix sensors provide the measured distance in several analog and digital forms. Sensors can have one or more simultaneous outputs in various combinations for connection to displays, Programmable Logic Controllers (PLC’s), computers, motor drives − almost any type of electronic equipment. View product page….
The following output types are available:

Analog Output

Analog outputs are voltage or current signals that vary proportionally with the measured distance. Some sensor models provide two or three simultaneous analog outputs. The analog distance endpoints are easily set anywhere within the sensor’s measurement range. Either endpoint can be the analog high limit or analog low limit, allowing either a positive or negative slope. Standard analog output value selections include 0-10 VDC, 0-5 VDC and 4-20 ma. current loop. Computer configurable models permit user-entered analog high limit and analog low limit values.

The figure above shows typical analog 4-20 ma. current loop output scaling. A target is shown detected at about the midpoint of the current loop analog range, which yields a sensor output value of 12 ma.

Ultrasonic sensor analog output set points and output pattern

Switch/Relay Output

Switch outputs turn ON or OFF at a distance setpoint and are used to start and stop external actions or indicators at those distances. Senix sensors have one or two simultaneous switches depending on the model. Each is independently adjustable. Computer configurable models allow the switches to turn ON and OFF at different distances (hysteresis) or to be ON or OFF only when a target is within a specified switch window. The hysteresis feature allows a single sensor to perform a complete control function, such as turning a pump on at a low level and off at a high level to maintain a liquid level within limits. The switch window feature allows proximity sensing only within specific distance ranges.

Serial Data

Both RS-232 and RS-485 interfaces are available on most Senix sensors. All SenixVIEW computer configuration is done through RS-232 or RS-485 communications. Usually, other simultaneous outputs are also connected to the user’s equipment. The serial data interfaces also provide the measured distance as an output to any compatible external device. The RS-485 interface is used to connect several sensors in a network that is monitored by a single communication interface.

14. Mounting ultrasonic sensors

The following general sensor mounting guidelines should be adhered to. For more complex mounting guidance, please contact Senix Customer Service.

• Ultrasonic sensors should be mounted in plastic threaded adaptors to avoid acoustic energy absorption through the sensor body.

• Sensors should be hand tightened only.  Never apply a wrench to the sensor body.

• When tank mounting to a domed or round tank, adjust the sensor mount until the transducer face is square with the target surface.

• Mount the sensor directly to the tank ceiling at a flanged opening. If a riser is added, it must be of sufficient diameter to cause no inner wall reflections. Round off the lower edge of the riser.

• Provide a sun shade for outside installations to prevent the sensor body from over heating and causing erroneous measurements. The sensor body should stay equal to the ambient air temperature so the sensor’s built-in temperature compensation can work correctly.

15. How easy are Senix® sensors to install?

In 1990 Senix Corporation introduced two innovations that make our sensors the easiest to install:

Pushbutton “TEACH”

Many Senix sensors include pushbutton TEACH capability. This allows “point-and-shoot” calibration using actual targets for quick and easy setup. There are no touchy potentiometers to adjust, and pushbutton security features are provided to prevent accidental misadjustment. The TEACH features also provide many pushbutton-selected features that give our sensors increased flexibility.

SenixView Sensor and Analysis Software

Most of our sensors are configurable with our SenixView™ software. This is the ultimate tool for faster setup and superior visibility in any application. SenixView™ provides a wide range of sensor configuration options and several displays of sensor measurements, allowing users to better optimize performance. Complete sensor installations can be saved for quick repair or duplication!
Learn more about our SenixVIEW Software

16. How do I maintain my Senix® ultrasonic sensors?

Senix sensors are housed in rugged materials and fully potted in epoxy resin.  If you select the correct Senix sensor for your application, very little maintenance is required.  It is important to keep the ultrasonic transducer face clear of ice, snow, dirt and other physical barriers to prevent disruption of the ultrasonic signals.  Ideally, sensors will be mounted with transducer faces pointed downward to minimize material collection on the face.  If transducer faces do require cleaning, pressurized air can be used.  In liquid level applications, occasional submersion or spraying of the material being measured is often sufficient to maintain a clean transducer face.  Sensors with exposed transducer faces can also be cleaned with alcohol or window cleaner, if necessary. DO NOT use solvents such as MEK or acetone on ToughSonic sensors with exposed transducers.

17. Do I need a computer to use these sensors?

Absolutely not! The pushbutton TEACH features provide all the functionality many users require. The computer configurable sensor models, however, offer greater ease of use, feature flexibility and application visibility that many users find essential. The features provided by our SenixView™ software would not be possible without a computer. Once an installation setup is determined, it can be stored and duplicated easily and quickly using the computer, or Senix can provide sensors pre-configured to your exact needs.

18. What if I need something special?

At Senix, ultrasonic sensors are our only business! We routinely configure, modify and design ultrasonic products that meet special customer requirements. We have the expertise to develop and manufacture products for original equipment manufacturers (OEMs).

Senix has been designing, manufacturing and selling ultrasonic sensors since 1990 and has introduced technical innovations like pushbutton TEACH and computer configurable sensors. Let us know how we can put our knowledge into your products!

19. What is the difference between a level “Sensor” and a level “transmitter”?

The terms “level transmitter” and “level sensor” are often used interchangeably despite the fact that a transmitter, strictly speaking, is a device that generates and transmits electromagnetic messages or signals. A transmitter is not a sensor, although sensors generally include some type of transmitter to communicate what they sense. At Senix we use the term “level sensor” because that is what we make; devices that provide continuous and/or point-level sensing and transmit that information through a variety of output protocols.

Senix Glossary of Terms

An output type that can vary proportional to measured distance. Analog output types can be either current loop outputs or voltage outputs.

Analog High Limit
The maximum (highest) value of an analog output. For example, the Analog High Limit value for a 4-20 ma. current loop analog output is 20 ma. Computer configurable models allow this value to be user-entered.

Analog Low Limit
The minimum (lowest) value of an analog output. For example, the Analog Low Limit value for a 0-10 VDC analog output is 0 volts. Computer configurable models allow this value to be user-entered.

Analog Window
The range of distances between the two analog endpoints, within which the analog output will vary between the analog low limit and analog high limit in proportion to the measured distance.

Current Loop Output
An analog output type that drives an electrical current proportional to measured distance. Senix sensors can provide industry standard 4-20 ma. current loop outputs. Computer configurable models allow user-entered analog limits.

A distance band, starting at zero distance, within which the sensor cannot measure distance. The deadband varies with each sensor model. Targets within the deadband may still be detected but their distance cannot be determined.

One end of the analog window. Two endpoints define the analog window.

The difference between the distance that a switch turns ON and the distance that same switch turns OFF. This distance can be entered on some computer configurable models to implement simple control systems.

Ingress Rating
An enclosure rating that identifies how susceptible a product is to the entry (ingress) of external objects or liquids.

An output type that is either ON or OFF. Most switches are solid state outputs. Some are relay outputs.

Switch Window
A range of distances within which a switch output will be set to a defined state when a target is within the window and the opposite state when it is not. This feature is only available on some computer configurable models.

Measure Rate
The repetitive rate at which the sensor performs distance measurements.

Material Window
The range of distances between the minimum range and maximum range values.

Maximum Range
The maximum distance at which the sensor will detect a target and report distance. Computer configurable models allow this value to be user-entered.

Minimum Range
The minimum distance at which the sensor will begin to detect a target and report distance. Computer configurable models allow this value to be user-entered.

An electrical interface standard used to transfer information using serial data communications. This is a single ended interface with a specified maximum range of 15 meters (50 feet) that typically supports one device.

An electrical interface standard used to transfer information using serial data communications. This is a differential interface with a specified maximum range of 600 meters (2000 feet) that is capable of supporting multiple addressable devices.

Serial Data
A method of transferring information using a sequential (serial) on/off pattern to encode the data. Two common industry standards are RS-232 and RS-485. SenixView™ software uses serial data communications to configure sensors and to convey sensor measurements.

The measured distance at which a switch output turns ON.

A Senix® software product used to adjust all computer configurable sensor models.

Any object or material that reflects ultrasonic energy back to the sensor thus allowing the sensor to measure its distance.

A Senix product feature that uses the sensor’s pushbutton to tell the sensor to store a current target distance measurement into memory and automatically calibrate the output(s).

A sound wave of a frequency greater than 20,000 Hz, typically above the range of human hearing.

A transducer converts one form of energy to another.  Senix ultrasonic sensors use combination ultrasonic transducers.  These transducers produce and also detect ultrasonic signals.

Voltage Output
An analog output type that drives an electrical voltage proportional to measured distance. Senix sensors can provide industry standard 0-10 and 0-5 VDC outputs. Computer configurable models allow user-entered analog limits.

Zero Distance
The distance at the front surface of the sensor. Sensors cannot measure to zero distance but only as close as the deadband.