Working Principle and Structural Composition of an Ultrasonic Level Sensor

Operating Principle

Ultrasonic sensors are developed by utilizing the characteristics of ultrasonic waves. Ultrasonic waves are mechanical waves with a vibration frequency higher than that of sound waves, produced by the vibration of a transducer crystal under the excitation of voltage. They have high frequency, short wavelength, minimal diffraction, and especially good directionality, allowing them to propagate as beams in a specific direction. Ultrasonic waves have great penetration capabilities in liquids and solids, especially in opaque solids to sunlight, where they can penetrate depths of up to several dozen meters. When ultrasonic waves encounter impurities or interfaces, they produce significant reflections and form echoes. They can also generate Doppler effects when they encounter moving objects. Therefore, ultrasonic detection is widely used in various industries, and to use ultrasonic waves as a detection method, both the generation and reception of ultrasonic waves are necessary. The device that completes this function is the ultrasonic sensor, commonly referred to as an ultrasonic transducer or ultrasonic probe.

Structure composition

Ultrasonic sensors are primarily composed of piezoelectric crystals, which can both emit and receive ultrasonic waves. Low-power ultrasonic probes are mostly used for detection purposes. They come in various structures, including straight probes (longitudinal waves), angle probes (transverse waves), surface wave probes (surface waves), Lamb wave probes (Lamb waves), and dual probes (one probe reflects and one probe receives). The core of the ultrasonic sensor is a piezoelectric crystal within either a plastic or metal housing. The materials that make up the crystal can be numerous, and the size of the crystal, such as diameter and thickness, varies, thus each sensor's performance is different, and we must pre-understand its performance before use.

Primary Performance Indicators of Ultrasonic Sensors

(1) Operating Frequency. The operating frequency refers to the resonant frequency of the piezoelectric crystal. When the frequency of the alternating voltage applied across its terminals matches the resonant frequency of the crystal, the output energy and sensitivity are optimized.

(2) Operating Temperature. Due to the high Curie point of piezoelectric materials, especially for diagnostic ultrasound probes that use less power, the operating temperature is relatively low, allowing for long-term operation without failure. Medical-grade ultrasonic sensors have a higher operating temperature and require separate refrigeration equipment.

(3) Sensitivity. Primarily depends on the chip itself. A higher mechanical-electrical coupling coefficient results in higher sensitivity; conversely, lower sensitivity.

An ultrasonic sensor features a composite vibrator that is flexibly mounted on the base. This composite vibrator is a combination of a resonator and a vibration element consisting of a bimorph piezoelectric crystal, which is composed of a metal sheet and a piezoceramic sheet. The resonator is horn-shaped, designed to effectively radiate ultrasonic waves generated by the vibration and concentrate the ultrasonic waves centrally within the vibrator.

Outdoor ultrasonic sensors must have excellent sealing to prevent moisture, rain, and dust intrusion. Piezoelectric ceramics are fixed on the inner side of the top of the metal housing. The base is mounted on the open end of the housing and covered with resin. For ultrasonic sensors applied in industrial robots, the precision should reach 1mm and they must have strong ultrasonic radiation.

Operation Principle of Liquid Level Sensor

Using the principle of static pressure measurement: When the level transmitter is immersed at a certain depth in the measured liquid, the pressure formula faced by the sensor against the liquid surface is: Ρ = ρ.g.H + Po

Pressure at the level sensor

ρ: Density of the Liquid Being Tested

g: Local gravitational acceleration

PO: Atmospheric Pressure at the Surface of the Liquid

H: Transmitter immersion depth in liquid

Simultaneously, the pressure of the liquid is introduced into the positive pressure chamber of the sensor via conduit stainless steel, and then the atmospheric pressure Po above the liquid surface is connected to the negative pressure chamber of the sensor.

To nullify the Po at the back of the sensor, the pressure measured by the sensor is: ρ.g.H. It is apparent that by measuring the pressure P, the liquid level depth can be obtained.

Level Sensor Categories:

Contact type, including single flange static pressure/dual flange differential pressure level sensors, buoy type level sensors, magnetic level sensors.

Category two includes non-contact types, such as ultrasonic level sensors, radar level sensors, etc.

Working Principle and Structural Composition of an Ultrasonic Liquid Level Sensor

The basic principle of ultrasonic level measurement is: The ultrasonic pulse signal emitted by the ultrasonic probe propagates in the gas, is reflected after encountering the interface between air and liquid, and the time of flight of the ultrasonic wave is calculated upon receiving the echo signal, which can then be converted to distance or liquid level height. The ultrasonic measurement method has many advantages that cannot be compared with other methods: (1) It has no mechanical transmission components and does not come into contact with the measured liquid, making it a non-contact measurement that is not susceptible to electromagnetic interference or strong corrosive liquids like acids and alkalis, thus ensuring stable performance, high reliability, and long lifespan; (2) Its short response time allows for real-time measurements without delay.

The ultrasonic sensor used by the system operates at approximately 40 kHz. Ultrasonic pulses are emitted by the transmitting sensor, transmitted to the liquid surface, reflected back, and received by the receiving sensor. By measuring the time required for the ultrasonic pulse to travel from the transmitter to the receiver, the distance between the sensor and the liquid surface can be determined based on the sound velocity in the medium, thereby locating the liquid surface. Considering the impact of environmental temperature on the speed of ultrasonic propagation, the transmission speed is corrected using temperature compensation methods to enhance measurement accuracy. The calculation formula is:

　　v=331.5+0.607t

　　（1）

In the formula: v is the speed of ultrasound propagation in air; t is the ambient temperature.

　　s=v

　　×t/2=v×（t1－t0）/2

　　（2）

In the formula: s is the measured distance; t is the time difference between the emission of the ultrasonic pulse and the reception of its echo; t1 is the time of reception of the ultrasonic echo; t0 is the time of emission of the ultrasonic pulse. The mcu's capture function allows for convenient measurement of the t0 and t1 times. By using the above formula and software programming, the measured distance s can be obtained. Since the mcu in this system features a mixed-signal processor with soc capabilities, which internally integrates a temperature sensor, it is possible to easily implement temperature compensation for the sensor using software.

What is the working principle of an ultrasonic level gauge?

Ultrasonic Level Gauges are digital level instruments controlled by microprocessors. During measurement, ultrasonic pulses are emitted by the sensor (transducer), reflected by the liquid surface, and then received by the same sensor or an ultrasonic receiver. The sound waves are converted into electrical signals by piezoelectric crystals or magnetostrictive devices, and the distance from the sensor to the liquid surface is calculated based on the time between the emission and reception of the sound waves. Due to the non-contact measurement, the medium being measured is almost unrestricted and can be widely used for measuring the height of various liquids and solid materials. Ultrasonic level gauges can use two-wire, three-wire, or four-wire technology: two-wire system: power supply and signal output are shared; three-wire system: power supply and signal output circuits are independent; when using a DC 24V power supply, a single 3-core cable can be used with the power supply negative terminal and signal output negative terminal sharing a wire; four-wire system: when using AC 220V power supply or when using DC 24V power supply with complete isolation of power supply and signal output circuits, a 4-core cable should be used. Both DC and AC power supplies have a 4-20mA DC output with high and low level switch quantities. The measurement range is 0-50 meters, with multiple options available, suitable for various corrosive and chemical environments, high precision, remote signal output, and PLC system monitoring. Working Principle:

The working principle of the ultrasonic level gauge is as shown in the figure. Generally, ultrasonic level gauges use a ceramic ultrasonic transducer with integrated transmitter and receiver. The emission and reception of sound waves are both completed by the same probe. The probe emits an ultrasonic signal towards the liquid surface, which then propagates through the medium to the liquid surface, where it reflects. The reflected wave travels back along the original path to the probe, where it is received.

What is the working principle of an ultrasonic sensor?

The principle is as follows: The main materials of ultrasonic sensors include piezoelectric crystals (piezoelectric) and nickel-iron-aluminum alloys (magnetoelectric).

Electrostrictive materials include lead zirconate titanate (PZT) and the like.

A piezoelectric crystal ultrasonic sensor is a reversible sensor that can convert electrical energy into mechanical oscillations to generate ultrasonic waves. Additionally, it can convert mechanical oscillations back into electrical energy when it receives ultrasonic waves, so it can function as either a transmitter or a receiver.

Here is the introduction to ultrasonic sensors: 1. Components: Common ultrasonic sensors are composed of piezoelectric crystals, which can both emit and receive ultrasonic waves.

Low-power ultrasonic transducers are mostly used for detection purposes.

It comes in various configurations, including straight-beam probes (longitudinal waves), oblique-beam probes (transverse waves), surface wave probes (surface waves), Lamb wave probes (Lamb waves), and dual-probe systems (one probe for transmission and one for reception).

2. Performance Specifications: The core of an ultrasonic probe is a piezoelectric crystal housed within either a plastic or metal sheath.

The materials that make up the chip can be of many types.

The chip's diameter and thickness vary, resulting in different performance for each probe. It is essential to pre-understand its performance before use.

What is the working principle of an ultrasonic sensor?

The main materials of ultrasonic sensors are piezoelectric crystals and nickel-iron aluminum alloys. Ultrasonic sensors composed of piezoelectric crystals are reversible sensors that can convert electrical energy into mechanical oscillations to generate ultrasonic waves, and can also convert them back into electrical energy when receiving ultrasonic waves.

Ultrasonic sensors convert ultrasonic signals into other forms of energy signals, typically electrical signals. Ultrasonic waves are mechanical waves with vibration frequencies above 20kHz. They possess high frequency, short wavelengths, minimal diffraction, and excellent directionality, allowing them to propagate like beams. These waves have strong penetration capabilities through liquids and solids, especially opaque materials to sunlight. When they strike impurities or interfaces, they produce significant reflections, forming echo waves. Upon impact with moving objects, the Doppler effect occurs. Ultrasonic sensors utilize acoustic media to detect objects non-contactly and without wear. They can detect transparent or colored objects, metals or non-metals, solids, liquids, and powdered materials. Their detection performance is virtually unaffected by environmental conditions, including dusty environments and rainy days.

How does an ultrasonic sensor work??

The working principle of the ultrasonic sensor:

The ultrasonic sensor consists of a transmitter sensor (also known as a wave transmitter), a receiver sensor (also known as a wave receiver), a control section, and a power section. The transmitter sensor is composed of a transmitter and a ceramic transducer with a diameter of approximately 15mm, which converts the electrical vibration energy of the ceramic vibrator into ultrasonic energy and radiates it into the air; the receiver sensor is made up of a ceramic transducer and an amplification circuit, which receives the waves to produce mechanical vibrations, converting them into electrical energy as the output of the sensor receiver, thereby detecting the transmitted waves. In actual use, the ceramic vibrators used as transmitter sensors can also serve as receiver sensor vibrators. The control section primarily controls the frequency, duty cycle, sparse modulation, counting, and detection distance of the pulses emitted by the transmitter.

Introduction:

Ultrasonic sensors are developed by utilizing the characteristics of ultrasonic waves. Ultrasonic waves are mechanical waves with a vibration frequency higher than that of sound waves, generated by the vibration of a transducer crystal under the excitation of voltage. They possess high frequency, short wavelength, minimal diffraction, and especially good directionality, allowing them to propagate as beams in a specific direction. Ultrasonic sensors can detect the condition of containers and are applicable in food processing plants for implementing a closed-loop control system for plastic packaging inspection. These sensors can detect transparent or colored objects, metallic or non-metallic materials, as well as solids, liquids, and powdered substances.

Main Applications:

Ultrasonic waves possess significant penetration capabilities through liquids and solids, especially in opaque solids, where they can penetrate depths of up to several dozen meters.

Ultrasound produces significant reflections upon encountering impurities or interfaces, forming echo waves. It can also generate Doppler effects when encountering moving objects. Therefore, ultrasonic testing is widely used in industries such as manufacturing.

Ultrasonic distance sensors are widely applicable in level (liquid level) monitoring, collision avoidance for robots, various ultrasonic proximity switches, and anti-theft alarm systems. They are reliable, easy to install, waterproof, have a small emission angle, high sensitivity, and are convenient for connection with industrial display instruments. Larger emission angle probes are also available.