Ultrasonic Sensors: What Are They and How Do They Work?

A signal is considered to be ultrasonic where the frequency is higher than the upper range of the human hearing range – that is, greater than 20 kHz. There are a number of categories of ultrasonic transducers, which operate on the principle of converting a signal from one form of energy to another.

For example, industrial ultrasonic sensors measure through air and will generally transmit at somewhere between 30 kHz and 500 kHz range. As the ultrasonic frequency increases, so does the rate of attenuation being observed.

As a result, low frequency sensors operating in the 30–80 kHz range are found to be more effective for long range applications. By comparison, high frequency sensors operating at 80–500 kHz are more effective for short range applications while lessening the ringing-decay, meaning there can be a shorter minimum detection range.

Ultrasonic Sensors: What Are They and How Do They Work?

Image Credit: Senix Corporation

When employed in testing, for example, in non-destructive testing (NDT), ultrasonic sensors can transmit at higher frequencies, generally between 1 MHz and 10 MHz.

Ultrasonic sensors for medical ultrasound applications are also higher. These usually transmit at less than 2 MHz for therapeutic purposes and in the 1–20 MHz range for imaging purposes.

In instances where non-contact distance measurement is preferred, industrial ultrasonic sensors that transmit through air in the 30-300 kHz range can be employed.

This category of ultrasonic sensors, also called ultrasonic transducers, works by sending a sound pulse above the range of human hearing toward the target and measuring the time it takes the sound echo to return.

As the speed of sound will be a known figure, the sensor can ascertain the distance to its target and set its outputs accordingly.

Ultrasonic sensors can automatically apply an offset scaling for temperature compensation in instances where temperature changes or fluctuations are present.

Ultrasonic applications fall into three broad measurement categories. These are outlined below, with a number of examples.

Liquid Level

  • The level liquids and solids in closed or open tanks
  • Management and monitoring water level in channels, streams, ponds and canals
  • Measuring levels of streams and bodies of water to warn relevant parties of floods and tsunamis
  • Managing water use for conservation, safety and efficiency applications
  • Monitoring fuel inventory, its usage and potential theft
  • Measuring the height of liquids in weirs, channels and flumes to calculate the volumetric flow of eluents and water

Ultrasonic Sensors: What Are They and How Do They Work?

Image Credit: Senix Corporation

Distance Ranging and Dimensional

  • Measuring the height and size of objects such as containers and boxes
  • Calculating the roll diameter of paper, film or foil to detect variables such as web tension, or the amount left on a roll
  • Measuring the free loop of material while it is moving from one machine to another in order to prevent breakage
  • Measuring the position of an object in a closed loop system to maintain or control its position

Object Detection or Proximity Detection

  • Objects can be detected for counting, security, inventory, or to aid obstacle avoidance in automated moving agents such as robots
  • Detection of individuals at kiosks and whether they are approaching or leaving
  • Targets can be monitored over the full sensor range or restricted within a user-defined distance range
  • Longer range applications may involve detecting the presence or absence of objects and/or materials, as well as for obstacle avoidance.

An industrial ultrasonic sensor is capable of detecting both large and small targets. This can include solids, liquids and granular materials.

An ultrasonic sensor is not affected by optical characteristics such as color, transparency, reflectivity, or opaqueness. Certain variables, including the shape, size and orientation of a target, will affect the maximum distance at which it can be detected by an ultrasonic sensor.

How Are Ultrasonic Sensors Used?

Examples of practical applications for ultrasonic sensors include measuring water levels under a bridge, the level of diesel fuel in a tank, ensuring the correct quantity of water is fed to crops, that a pump is turned on to refill a tank, or that a motor is started when or an alarm is triggered or when a level gets to a predetermined point.

Ultrasonic sensors will detect large and small targets such as liquids, solids and granular materials. They can be employed in the presence of electrically noisy machinery, motor drives, electrical and electromechanical controls.

Caustic, coating, scaling, or dirty materials may impact the performance and maintenance costs of contact sensors.

In environments where a material being measured cannot be corrupted by contact with a measurement application, non-contact ultrasonic sensors will have distinct advantages over contact ultrasonic sensors. 

Normal atmospheric pressure changes and small pressure changes in vessels may affect ultrasonic sensor operation. Temperature can be compensated for by using the most appropriate sensor. However, in general, humidity is not a significant factor -  0.036% / 10% RH change.

High-Quality Ultrasonic Sensors from Senix

By using ultrasonic signals, non-contact and autonomous tools offer users the capability to register nearby surfaces and obstacles. Senix manufactures an array of ultrasonic sensors for use across different industries and applications, including level and distance sensors.

This information has been sourced, reviewed and adapted from materials provided by Senix Corporation.

For more information on this source, please visit Senix Corporation.

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