 Ultrasonic Sensors The ultrasonic sensor is a device that uses high-frequency sound waves to detect objects. An oscillator circuit inside the sensor's housing produces a frequency that causes a crystal disk to vibrate and emit sound pulses. Each pulse is emitted away from the housing. If an object, called a target, is within the sensing range, a sound wave will be reflected back to a receiver in the sensor to indicate its presence. The frequency of ultrasonic waves is above the range that can be heard by humans. The two categories of ultrasonic sensors are proximity switches and analog sensors. The difference between the two categories of sensors is the type of output signal that they produce. Let's look at these ultrasonic sensors. Proximity switches The proximity switching ultrasonic sensor detects the absence or presence of a target. The sensor will switch on when an object is detected within its sensing range. As soon as the object is no longer detected, the sensor will switch off. Analog sensors The analog sensor produces a variable output signal. A variable circuitry inside the sensor begins counting from when a sound wave is launched and stops when the reflected wave returns. The farther the target is from the sensor, the higher the count because the counting occurs over a longer time duration. The count is converted into a proportional analog output signal. Therefore, the magnitude of the output is proportional to the distance between the sensor and the target. The output produced by an analog ultrasonic sensor is a variable voltage or a variable current. The most common type of voltage output ranges from 0 volts to positive 10 volts. You can see the ranges below. The most common type of current output ranges from 4 milliamps to 20 milliamps. Calibration procedure Most analog sensors have the capability of varying the range at which they can detect a target. This function is performed by a procedure called calibration. The desired minimal distance at which the target is placed from the sensor is called the zero calibration setting. At this distance, the voltage sensor will produce a minimum output value of 0 volts and the current sensor will produce a minimum output value of 4 milliamps. The desired maximum distance at which the target is placed from the sensor is called the span calibration setting. At this distance, the voltage sensor will produce a maximum output value of 10 volts and the current sensor will produce a maximum output value of 20 milliamps. Zero setting Let's suppose that the desired minimum range of a target is one foot away from a current sensor. Adjust the zero screw until 4 milliamps is measured at the sensor's output. This is the zero setting adjustment. Let's suppose that the desired maximum distance of the target from the sensor is 33 feet. Let's adjust the span screw until the ammeter measures 20 milliamps at the sensor's output. This is the span setting adjustment. After the zero and span settings are made, the sensor produces a linear output that is proportional to the distance that the target is located from the sensor. For example, an analog signal of 12 milliamps will be produced if the target is 17 feet away from the target. Let's move the target through the sensing range and observe the results on the graph. Ultrasonic sensors are used in such applications as measuring the diameter of a roll being wound in a paper factory or detecting the presence of a box on a conveyor belt. In process control, ultrasonic sensors are commonly used to measure the level of a solid or liquid in a tank. However, they should not be used if a layer of foam exists at the top of a liquid. Inaccurate readings will also be made if a mist is present in the vapor space above the liquid because sound travels through a mist at a different speed than it travels through dry air. The controller to which the sensor is connected can be programmed to convert 20 milliamps to indicate that the tank is empty and 4 milliamps when the tank is at full capacity with 75 inches of material. Ultrasonic sensors are ideal for non-contact position and distance measurement and object detection. You have completed this activity, Ultrasonic Sensors. If you liked this video, please subscribe to our channel and we'll let you know if we have something new for you to learn.