1. What is Ultrasonic Sensor?
Ultrasound is a form of sound with a frequency much higher than the sound frequency heard by the human ear. As the picture above, we see the frequency range of each type of sound such as: lower sound (below 20Hz), audible human sound (20Hz – 20kHz), ultrasound (above 20kHz).
The ultrasonic waves can spread in many different environments such as air, liquid, solid … In the same propagating medium, the higher the frequency, the shorter the wavelength of the sound. . Because of that short wavelength, the resolution of the ultrasound makes contact with the object sufficient to achieve a precision of several millimeters.
Therefore, ultrasound is widely used in medicine or measuring the distance of liquids, ultrasonic cleaning, ultrasonic welding, inserting materials with ultrasonic waves, etc.
For short distances, the ultrasonic sensor is used to detect liquids or small objects to issue control signals while monitoring liquid or solid levels.
2. The principle of ultrasonic sensor operation
The ultrasonic sensor operates with the extremely simple principle. The principle of operation is based on the transmission and reception of ultrasound. When powered, the sensor will broadcast ultrasound with a certain period to space. When obstacles are encountered, the ultrasonic waves will bounce back toward the sensor. The sensor captures the reflected wave and calculates how long it takes to transmit and receive. From there calculate the distance to the barrier is how many millimeters.
Because the distance to an object is determined by measuring the time it takes to receive and receive the sound, not the sound intensity, the ultrasonic sensor is excellent at suppressing interference.
Almost all sound-reflecting materials can be detected, regardless of their color. Even transparent materials or foils are no problem for ultrasonic sensors.
The ultrasonic sensor can see through dusty and foggy air. The level of filling in wells and test tubes can be measured, as well as small bottles in the packaging industry can be detected easily. Even thin wires are detected correctly.
+ Clean water or Black coffee?
Ultrasonic sensors detect all types of liquids
+ Red, lemon yellow, pink, blue, light blue?
What is your favorite color? Ultrasonic sensors like all colors
+ Black objects in black and white background in white background?
So easy with the ultrasonic sensor
+ Cereals, chips or fine sand?
No problem, the ultrasonic sensor eats them all ^^
>>> As shown above, we can visualize the principle of ultrasonic sensor operation in the most accurate way. In fact, based on this operating principle, it is applied to measure liquids, solids, obstructions …
3. A “blind area” of the sensor
Determine the minimum allowable detection range of it. Note, do not place objects or reflectors that cause interference in the blind area as this may lead to inaccurate measurements.
4. Anatomy of ultrasonic sensor
The ultrasonic sensor consists of a unit that can emit ultrasound by a small power probe capable of generating signals. Ultrasound transducers come in a variety of forms, divided into straight transducers (longitudinal waves) and transducers (transverse waves), surface probes, dual probes (1 signal generator – 1 receiver) … Depending on the purpose of use, they choose the most suitable super-sensor probe. All have the same ultrasonic sensor structure as follows:
- Generator: Vibration by vibrator (usually made from ceramic material with a diameter of about 15 mm) to create ultrasonic waves and propagate into the air.
- Receiver: When the vibrator receives ultrasonic waves, it generates mechanical vibrations corresponding to the ultrasonic waves and converts into electrical energy at the output of the receiver.
- Control: Control the transmitter’s ultrasonic transmission using an integrated circuit and evaluate whether the receiver receives the signal (ultrasonic wave) and the size of the received signal.
- Power supply: Ultrasonic sensors are usually supplied by external DC power with a voltage of PCB ?10% or 24 V ?10% and are supplied to the sensor via an internal voltage stabilizer circuit.
Transducer indicators of an ultrasonic sensor include:
- Frequency: The operating frequency of the ultrasonic sensor is the resonant frequency of the sensor probe. The sensitivity of the sensor depends very much on the emitted frequency of the sensor, of course, the larger the frequency, the faster the response speed.
- Temperature: The temperature of the ultrasonic sensor probe will increase as the diagnostic process is performed. Because of its small capacity, the ultrasonic sensors measure the water level at a relatively low temperature and can operate for long periods without being affected. For medical ultrasound probes, the reverse requires a separate cooling device to ensure correct functioning.
- Sensitivity: The sensitivity of the sensor depends very much on the frequency of the sensor. The higher the frequency, the higher the sensitivity and vice versa.
- Display: The ultrasonic sensor has a built-in display to know how much the measurement distance is right on the sensor. In addition, some cheap water level ultrasonic sensors often remove the display but only send the Analog 4-20mA signal to the control center to save costs.
5. Application of ultrasonic sensors in industry
With the diversity in the industry with a multitude of monitoring, measurement and control requirements, ultrasonic wave leveling technology is required. There are two major applications for ultrasonic sensors.
+ Ultrasonic sensor for warning: Alerting a system or a line at risk or having an incident makes an important contribution to minimizing damage to factories. The exact or not warning depends on the technology and people.
+ Ultrasonic sensor for continuous monitoring: Ultrasonic sensors continuously measure the signal of 4-20mA or 0-10V to be sent to the PLC to shut down the pump or drive the inverter to stabilize the water level in the tanks. The accuracy of the ultrasonic sensor depends very much on the installer and installation because the greater the distance, the bigger the error.
6. Instructions to choose the most accurate ultrasonic sensor
To choose a device, especially the sensor, we need to understand the operating principle, how to use the sensor. For ultrasonic sensors is no exception. In this section, I will introduce to you how to choose for yourself the most accurate sensor. When choosing an ultrasonic sensor you must pay attention to the following:
- Need to measure liquid or solid
- Want to measure continuously 4-20mA / 0-10V output or measure ON / OFF
- What is the material to measure?
- How many meters is the distance to be measured?
- Does the sensor need a display kit on site?
- Need threaded connection or flange? If it’s lace, how much is lace?
- What is the allowable tolerance?
- What is the power supply for the sensor?
- Temperature, pressure of the working environment of the sensor
With what we share on plc247.com we hope to provide you with the most complete information about ultrasonic waves, ultrasonic sensors and their applications.