Choosing the Right Distance Sensor for Your Application
Several methods of detection are available for determining the proximity of an object or objects in real-time, each of which is differentiated by a diverse range of underlying hardware. As a result, distance sensors incorporate an extremely broad field of technologies: infrared (IR) triangulation, laser, light-emitting diode Time-of-Flight (LED-TOF), ultrasonic, etc. With so many options to choose from, how do you decide which distance sensor is right for your application?
The sheer variety offered by these four leading distance sensing technologies leads to a diverse range of key performance properties, including range, resolution, field-of-view (FOV), frequency, and transmission-reception times, alongside installation and ongoing operation costs.
In this post, the aim is to offer an overview of the various distance sensor types available to help you decide on a technology that best suits your requirements.
Ultrasonic Distance Sensors
An ultrasonic distance sensor measures proximity by emitting high-frequency soundwaves and recording the time elapsed before an echo reflects to the transducer. The time taken for the specific frequency to return to the signal transducer is known as the round trip time; the total distance traveled from the ultrasonic emitter to the object and back. To determine proximity to an object, the ultrasonic distance sensor multiplies the roundtrip time by the speed of sound – approximately 1129 feet per second (f/s) in ambient conditions – and halves the calculation.
Benefits of Ultrasonic Distance Sensors:
Ultrasonic distance sensors utilize short wavelength, high-frequency signals that are unaffected by dust, light, the color of detected objects, etc.
Drawbacks of Ultrasonic Distance Sensors:
Susceptible to interference by acoustic noise and crosstalk from other sensors with the same frequencies, ultrasonic distance sensors offer comparatively poor resolution and range compared to other technologies on this list. They also offer a wider FOV and longer transmission-reception times, with a short-range. This means they are not suited for detecting fast-moving objects.
Distance sensors equipped with IR light-emitting diodes (LEDs) often operate on the principle of triangulation: calculation of distance according to the angle of a reflected IR beam off a surface. When the LED focuses a beam of light on a surface, that light is reflected in all directions. A distance sensor adjacent to the LED source acquires a reflected signal and an integrated charge-coupled device (CCD) chip defines the angle of reflection to calculate distance.
Benefits of IR Triangulation Distance Sensors:
IR triangulation has a small form factor and a lightweight construction. They also tend to be competitively priced.
Drawbacks of IR Triangulation Distance Sensors:
IR distance sensors are generally short-range solutions that are used individually, as they cannot reliably be compounded with additional sensors.
Laser Distance Sensors
Proximity sensing with monochromatic laser light typically utilizes a laser source with integrated optics to measure the time taken for a narrow beam of pulsed light to reach an object and reflect to the sensor. The basic principle of this is known as Time-of-Flight, though laser distance sensors can adopt a choice of different measuring principles (phase comparison, etc.).
Benefits of Laser Distance Sensors:
Laser distance sensors deliver precise and stable results in a variety of operating environments with a long range. They also boast a fully-tunable FOV to provide the most stable results possible and remain one of the most competitive distance sensor technologies for outdoor applications.
Drawbacks of Laser Distance Sensors:
Lasers pose a risk to the eye safety of operating personnel and are generally integrated into robust arrays with large form factors and heavyweight profiles. Alongside that, they cannot be reliably integrated with additional sensors for broader measuring capabilities. These sensors also tend to be pricier than others.
A novel solution to the limitations of laser rangefinders, IR Time-of-Flight distance sensors measure proximity using an IR-LED according to the time-of-flight principle. This has numerous benefits with very few drawbacks, namely faster transmission-reception times, long-range (<60 meters), rapid refresh rates, fixed FOV, lower power consumption, and plug-and-play support for multi-sensor integration. While there is no one distance sensor for every application, IR time-of-flight provides the broadest range of KPIs for proximity sensing in indoor environments and specific outdoor environments.
Benefits of LED Time-of-Flight Distance Sensors:
LED time-of-flight sensors are compact, lightweight, and easy to use. They come with a simple plug-and-play multi-axis sensing technology which facilitates multi-sensor integration. This outstanding hardware is supported by a long-range and rapid refresh rates for extremely precise distance measurements.
Drawbacks of LED Time-of-Flight Distance Sensors:
Outdoor performance may be affected by direct sunlight, and reflective surfaces can inhibit the sensor range. The technology is also limited to centimeter (cm) level accuracy and distance readings are calculated using averaged readings.
Terabee offers a choice of TeraRanger Time-of-Flight distance sensors, which boast a range of practical enhancements over other products on the market. They have proven suitable for high-precision proximity measuring in applications as varied as drone flight, robotics, people counting, traffic monitoring, and more.