- People are traditionally a challenging target for ultrasonic sensor
- MaxBotix® Inc., offers ultrasonic proximity sensors that reliably detect people
- Proximity information is minimally affected by sensor cross-talk
Many ultrasonic sensor applications require the user to detect people in an environment. MaxBotix® Inc., provides ultrasonic sensor that reliably detect people, and our ultrasonic sensors have been installed in a large number of people detection applications. While every ultrasonic sensor carried by MaxBotix® Inc., has the ability to detect people, simply purchasing a sensor with 10 meter ranging capabilities does not mean the sensor will detect a person all the way out to 10 meters. Your application has the best chances of success when you put careful consideration into the ultrasonic sensor selection process.
Although two objects may be of similar size and shape, they may not be equally detected by an ultrasonic sensor. Large, flat, or solid objects reflect more sound back to the sensor than small, rounded, or hollow objects. Consider a cinderblock wall as a good example of large, flat, and solid. Compared to that wall, a person is not all that large, flat, or solid. A person reflects much less sound than a wall which makes it harder to detect people out to the same range as a cinderblock wall.
While our ultrasonic sensors can range to wall-like targets all the way out to their specified maximum range, people have a more limited maximum range. In general, people are detected in very much the same area as a one inch diameter dowel would be detected.
Understand that the clothing, body build, and environments surrounding the ultrasonic sensors affects the stability and ranging capabilities. With this in mind, the area in which a person is detected by our ultrasonic sensors usually falls between beam patterns A and B that we provide for each of our sensors.
Benefits of an Ultrasonic Proximity Sensor
Range information is not always the best choice for every application. When detecting people, proximity information, is someone in front of the ultrasonic sensor or not, may better suit the task. The main benefit to the proximity data is that it is more resistant to sensor cross-talk or sensor-to-sensor interference than range information. This allows the installation and deployment of a larger number of ultrasonic sensors before worrying about cross-talk.
When more than one sensor is ranging in an environment, the additional ultrasonic noise can make the range information from our ultrasonic sensors less stable. Proximity information can often be a good fit for such applications because it gives a more stable response. Do note that this proximity information indicates that something has been detected within a given range but does not provide the range to the object.
All of our standard sensors have a range output available, but a number of our sensor lines, for example our ProxSonar® lines, feature an additional proximity information output. This proximity information provides users with a digital high (1) low (0) logic level that corresponds to when person is detected (1) or not (0).
Our proximity sensors offer various preset trigger ranges, target acquire time requirements, and target release time requirements to meet the needs of most applications. Custom trigger distance, target acquire, and target release times can be set for a nominal NRE charge.
Consider the following example of a kiosk sensor in a mall. The kiosk owner may not want the kiosk to light up every time somebody walks in passed it but instead only want the kiosk to activate when somebody walks directly up to it. Applications where a target is intended to stand in front of the ultrasonic sensor to activate or trigger an event are great candidates for using the proximity data.
Choosing the Right Ultrasonic Sensor
The primary factor that limits the range to which you can detect a person is the sensitivity of the ultrasonic sensor itself. Higher sensitivity corresponds to longer range detection of people, but at the same time higher sensitivity also means greater sensitivity to noise. Thus, the goal is to find the ultrasonic sensor that is just sensitive enough for your application to avoid any potential issue where your sensor is picking up interference from an outside noise source.
If you are using one of our ultrasonic sensors for protected environments, the level of sensitivity can be determined by the EZ or AE designation at the end of the product name with EZ0/AE0 being the most sensitive and the EZ4/AE4 being the least sensitive.
On the other hand, if you are using one of our sensors for non-protected environments from one of our WR sensor lines, many of the ultrasonic sensors offer very similar detection zones. However, a number of sensors do have heightened sensitivity. Review the product datasheets to find a full listing of the WR sensors with heightened sensitivity.