Pepperl+Fuchs Blog

Ultrasonic Sensors - Which Mode is Best for My Application?

Posted by Zach Steck on Tue, Sep 10, 2013

Many of our ultrasonic sensor models can function in various operation modes. The modes available are determined by the model and output type of the sensor. Let’s take a look at some applications and determine which mode is best suited for that process:

Ultrasonic sensors for pumps

Q. I have an AGV (Automated Guided Vehicle) that keeps crashing into objects scattered throughout the warehouse. I need a sensor for collision detection capable of engaging two separate sets of brakes. Can I do this with one ultrasonic sensor?

A. Ultrasonic sensors are an excellent choice for AGV collision detection applications due to the large area covered by the sound cone. A sensor with dual outputs used in switch-point mode would be a good option for this case. Switch-point mode allows you to set a specific point within the sensing area where the output will trigger. A dual output sensor allows you to set two points and we can apply this to the collision application above. Switch-point two can be used to engage the first set of brakes, slowing the AGV and switch-point one can engage the second set of brakes, stopping the AGV before any damaging collisions.

Q. I work in a manufacturing plant. I need a sensor to monitor the height of our product in order to sort out any imperfections. The sensor must allow slight variances in height but detect if it is too tall or too short. What are my options?

A. This application would be best solved with an ultrasonic sensor in window mode. Window mode allows you to set the beginning and ending points of an active sensing window. This is accomplished by teaching the sensor a near point and far point in which the output will be triggered between these two points. Any objects within this range will be accepted, but any that fall below the near point or stretch beyond the far point will be sorted out.

Q. I need a sensor to control a pump. When the liquid reaches the high level, the pump would be switched off. Once the liquid level goes below the minimum, the pump would be switched on. Can I do this with an ultrasonic sensor?

A. An ultrasonic sensor in hysteresis mode is commonly used for pump control applications. In hysteresis mode, the evaluation window is limited by two switching points. These two switch points are programmed for the high and low level of the liquid. The pump turns on at the low level, and off at the high level. This allows the pump to be on until the high level is reached and then turned off at the low level. The two switch points create an adjustable hysteresis window.

Q. We have a conveyer belt where we need to detect the presence of objects varying in size for a counting application. Space is limited so the sensor needs to be mounted above the conveyer looking down at the belt. This rules out a retroreflective photoelectric sensor because we have no way to mount the reflector. Are there any products that function similarly and don’t require a plastic reflector?

A. Some ultrasonic sensors are available with a retroreflective mode. In this mode, a reference reflector such as the conveyer belt is taught into the sensor. There are three cases that will cause the sensor output to change state:

  1. The sensor receives an echo from a small object in the sound cone and from the reference reflector.
  2. The sensor detects a large object and no longer receives the echo from the reference reflector.
  3. The sensor does not receive an echo, for example, when an object is positioned at an angle that reflects the sound away.

This makes a retroreflective ultrasonic sensor a good choice when detecting objects of various sizes.

Q. I have a distance measurement application and need a sensor capable of detecting different shades and textures at the same distance. I have tried photoelectric distance sensors but the measurements lose accuracy when the textures or colors change.

A. An ultrasonic sensor with an analog output would be a good choice for this application. The sensor determines the distance to an object by measuring the time interval between sending an ultrasonic signal and receiving the reflected echo back into the transducer. These sensors operate in diffuse mode and many models will provide an analog output in either 4 mA...20 mA or 0 V...10 V. Ultrasonic sensors are not affected by color or texture of the target object.

Q. In a current application, we have a handful of ultrasonic sensors used in close proximity to each other. There have been some problems with the accuracy of the readings we are getting. I have heard that ultrasonic sensors can be susceptible to interference. Is this true, and what can I do to correct the problem?  Mounting space is very limited so it would be difficult to spread them out.

A. Ultrasonic sensors can be affected by mutual interference which creates a situation where reliable detection is no longer possible. Many of the ultrasonic sensors produced by Pepperl+Fuchs have a couple of mode options to reduce the space required between the sensors and eliminate cross-talk.

  • Multiplex mode provides a way to stagger the ultrasonic bursts in order to decrease the possibility of two or more sensors sending or receiving signals at the same time. In some cases, a barrier between sensors is also used to ensure no cross-talk. The sensors activate on a cycle over a period of time that increases with the number of sensors connected. The more sensors, the more time it will take to cycle through them.
  • In synchronized mode, the synchronization inputs for all of the sensors are linked and controlled by an external clock-pulse source. Unlike multiplex mode, this does not increase the cycle time, giving you a quicker response.

As you can see, the vast array of operation modes available for ultrasonic sensors makes them usable in a variety of applications. Ultrasonic sensors continue to be a popular choice for many industrial applications due to the flexibility and durability found with this sensor type.


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Topics: Applications, Ultrasonic Sensors

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