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Q&A: Ask an expert – Radar sensor FAQs

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Radar sensors are commonly used for a wide variety of vehicle detection and collision avoidance applications, and they are a particularly excellent choice for outdoor deployments. Turck Banner has offered some key answers to the questions they get asked most often. If you still have questions after reading this, contact Brandon Topham, brandon.topham@turckbanner.co.za

Brandon Topham

What are radar sensors?

Radar is an object detection system using radio waves. One benefit of radar includes reliable outdoor use. Radar sensors are unaffected by wind, falling rain and snow, fog, and sunlight. They are less affected by temperature fluctuations and operate in a wider range of temperatures than competing technologies. Additionally, they have a long sensing range for flexible mounting and are more durable and offer less downtime than other technologies.

Popular radar sensors utilise frequency modulated continuous waves (FMCW). FMCW radiates continuous transmission power and changes its operating frequency during the measurement. FMCW measures the frequency shift between emitted and received signals. FWMC radar can detect both moving and stationary targets (the alternative, Doppler, cannot see stationary targets).

Where should I use a radar sensor?

Radar sensors are an ideal solution for applications where you need to detect a vehicle or avoid a collision when moving equipment. For example, radar can be used for vehicle detection in traffic and parking applications, toll booths, loading docks, drive-thrus, shipping canals, and railroads. It can also be used for collision avoidance in ports and manufacturing, for on-board mobile equipment, and in low-visibility factory environments.

What objects can radar sensors detect?

Good targets for radar sensors include objects containing metal, large amounts of water, or similar high-dialectric materials. Poor targets for radar sensors include many plastics, cloth, wood, fiberglass, and organic materials.

Radar sensors can detect people, but the radar cross section of a person is very weak, so it is not intended to be used in personnel detection. Depending on sensor sensitivity settings, a person could interfere with sensing the intended target if a person is near the sensor and within the sensor’s direct field of view.

What is the difference between adjustable field and retro-reflective radar sensors?

An adjustable field radar sensor can detect vehicles and other objects by sensing the reflection of the radio waves bouncing off the object. Optimal targets include: large metallic objects that reflect a lot of radio waves, a property referred to as a large “radar cross section”; and objects that have surfaces that are perpendicular to the radar beam pattern to reflect the radio signal directly back to the sensor.

Adjustable field radar sensors have configurable “set-point distances” where the sensor will use the time between emitted pulse and reflected signal detection to calculate how far away a sensed object is from the sensor and only turn the output on when the object is within the set-point distance.

A retro-reflective radar sensor uses a taught reference condition like a wall, floor, or special retro-reflective target. The sensor detects objects between it and the reference target by looking for disruptions in the signal coming back from the reference target. This type of sensing can sense objects even if they do not have a good radar cross section, but they must block the signal reflection from the reference target. This makes retro-reflective radar sensors the most robust radar sensing option.

What is the dead zone for radar sensors?

Radar sensors often have a typical “dead zone” of 40 cm for moving targets and 1 m for stationary targets.  What this means is different depending on whether the sensor is adjustable field or retro-reflective. For adjustable field sensors, the sensor cannot reliably sense objects within the dead zone. With retro-reflective sensors, the retro-reflective target cannot be placed within the dead zone, but an object within the dead zone can still be sensed because it interrupts the signal from the reflector target.

When would I use a radar sensor with two zones?

It is common to use two zones in collision avoidance applications. For example, one long-range zone can be used as a “slow down” signal, and the other short-range zone can be used as a “stop” signal. Two zones can also be used to determine if the object is getting closer to or farther away from the sensor.

How wide is a radar sensor’s beam?

The effective beam pattern chart for each sensor is provided in its datasheet. If the sensor’s beam pattern is too wide, consider using a narrow-beam sensor. The effective beam width varies with the sensor, the distance to the target, the radar cross section of the target, and the sensor’s sensitivity (signal strength threshold) setting. Changing the sensitivity selection for a radar sensor can be used to ignore unwanted weak targets within the field of view of the sensor (focusing the beam on the main target you want to see vs. smaller objects in the beam path).

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