Industrial Ultrasonic Sensor

Ultrasonic Sensors:

The Complete Guide by Method and Principle

001 What is an ultrasonic sensor?

An ultrasonic sensor is a sensor that converts an ultrasonic signal into another energy signal (usually an electrical signal).

According to the use of methods, Ultrasonic sensor can be divided into broad categories: transmitters, receivers, and transceivers.

Ultrasonic sensors can be divided as an open ultrasonic sensor, waterproof ultrasonic sensor, and high-frequency sensors.

Ultrasonic waves are mechanical waves with vibration frequencies above 20 kHz. It has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directionality, and can be directional and propagated.

Ultrasonic penetration of liquids and solids is great, especially in sunlight-opaque solids.

When an ultrasonic wave hits an impurity or an interface, it produces a significant reflection to form a reflected echo, which can produce a Doppler effect when it hits a moving object.

Ultrasonic sensors are widely used in industrial, defense, biomedical and other fields.

Component

A commonly used ultrasonic sensor consists of a piezoelectric wafer that can emit both ultrasonic waves and ultrasonic waves.

This type of piezoelectric ultrasonic sensor small power ultrasound probes is used for detection.

Ultrasonic sensors has many different configurations, which can be divided into straight probe (longitudinal wave), oblique probe (transverse wave), surface wave probe (surface wave), Lamb wave probe (Lamp wave), dual probe (one probe emission, one probe reception) and so on.

performance index

The core of the ultrasound probe is a piezoelectric wafer in its plastic jacket or metal jacket. There are many kinds of materials constituting the wafer.

The size of the chip, such as diameter and thickness, also varies, so the performance of each probe is different and we must understand its performance before using it.

The main performance indexes of ultrasonic sensors include:

operating frequency

The operating frequency is the resonance frequency of the piezoelectric wafer.

When the frequency of the ac voltage applied to both ends is equal to the resonant frequency of the chip, the output energy, and the sensitivity are the highest.

The operating frequency is the resonant frequency of the piezoelectric wafer.

When the frequency of the alternating voltage applied to both ends thereof is equal to the resonant frequency of the wafer, the output energy is the largest and the sensitivity is also the highest.

operating temperature

Because the Curie point of piezoelectric material is generally high, especially the ultrasonic probe used for diagnosis USES less power, so the working temperature of the piezoelectric ultrasonic sensor is relatively low.

Ultrasonic sensors can work for a long time without failure.

Medical ultrasound probes have a high temperature and require separate refrigeration equipment.

sensitivity

It mainly depends on the wafer itself. The electromechanical coupling coefficient is large and the sensitivity is high; on the contrary, the sensitivity is low

DIrectivity

002 Advantages of ultrasonic sensors

Ultrasound has a great ability to penetrate liquid and solid, especially in the opaque solid, it can penetrate a depth of dozens of meters.

When an ultrasonic wave hits an impurity or an interface, it will produce a significant reflection to form a reflection into an echo, which can produce a Doppler effect when it hits a moving object.

Therefore, ultrasonic testing is widely used in industrial, national defense, biomedical, etc.

Ultrasonic distance sensor can be widely used in the measurement of the level (liquid level), the robot collision avoidance, various kinds of the ultrasonic proximity switch, as well as the anti-theft alarm, etc.,

It is features of no contact detection, reliable operation, easy installation, waterproof, small emission Angle, high sensitivity.

It is convenient to connect with industrial display instrument, and also provide launch Angle larger probe.

003 What are typical applications of ultrasonic sensors?

Loop control

Roll diameter, tension control, winding and unwind sensing

Liquid level control

Thru-beam detection for high-speed counting

Thread or wire break detection

Robotic sensing

Stacking height control

45° Deflection; inkwell level detection; hard to get at places

People detection for counting

Contouring or profiling using ultrasonic systems

Vehicle detection for car wash and automotive assembly

Irregular parts detection for hoppers and feeder bowls

Presence detection(Double Ultrasonic Sensors in Medical

Application

Ultrasonic sensing technology is applied in different aspects of industrial practices: vehicle detection for the car wash and automotive assembly, robotic sensing, Irregular parts detection, Distance detection, ultrasonic sensors applied to AGV, presence detection, ultrasonic sensor for pedestrian detection, liquid level measurement, material level detection, thread or wire break detection. Etc.

Medical application is one of the most important applications.

The application of ultrasonic sensing technology is illustrated with medical examples below.

The application of ultrasound in medicine is mainly to diagnose diseases.

It has become an indispensable diagnostic method in clinical medicine.

The advantages of ultrasonic diagnosis are no pain, no damage, simple method, clear imaging, high diagnostic accuracy.

As a result, it is easy to promote and is welcomed by medical workers and patients.

Ultrasound diagnosis can be based on different medical principles, let’s take A look at one of the representative so-called A type method. This method USES ultrasonic reflection.

When the ultrasonic wave propagates in the human body tissue, it encounters two media interfaces with different acoustic impedance, at which the echo will be reflected.

Each time a reflector is encountered, the echo is displayed on the oscilloscope screen, and the impedance difference between the two interfaces determines the amplitude of the echo.

Industrial Ultrasonic Sensor

In industry, the typical application of ultrasonic is the nondestructive inspection of metal and ultrasonic thickness measurement.

In the past, many technologies were hampered by the inability to detect the inner tissue of an object.

Of course, more ultrasonic sensors are fixed in different devices, “quietly” to detect the signal people need.

In the future application, ultrasonic will be combined with information technology and new material technology, and more intelligent and highly sensitive ultrasonic sensors will appear.

Industrial ultrasonic sensors are mostly high-frequency sensors.

004 What can ultrasonic sensors detect?

1. Tank level detection: Ultrasonic sensors can detect the status of containers. When the ultrasonic sensor is mounted on the top of the plastic melt tank or plastic granule chamber, the sound waves are emitted into the interior of the container, the status of the container, such as full, empty or half full, can be analyzed accordingly.

Ultrasonic sensors can be used to detect transparent objects, liquids, any table rough, smooth, the light of the dense material and irregular objects. It is not suitable for outdoor, hot or pressure tanks and foam objects

Ultrasonic sensors can be used in food processing plants to achieve a closed-loop control system for plastic packaging inspection. With new technology, it can be detected in humid environments such as bottle washers, noisy environments, and extremely temperature-changing environments.

An ultrasonic sensor can be used to detect liquid levels, detect transparent objects and materials, control tension and measure distance.

The ultrasonic sensors are mainly for packaging, bottle making, material handling, an inspection of coal equipment, plastics processing, and automotive industries. Ultrasonic sensors can be used for process monitoring to improve product quality, detect defects, determine the presence and other aspects.

005 What is the working principle of an ultrasonic sensor?

People can hear the sound produced by the vibration of the object. Its frequency is in the range of 20hz-20khz. If the frequency exceeds 20KHZ, it is called ultrasonic wave;

if the frequency is lower than 20HZ, it is called infrasound wave. The commonly used ultrasonic frequency is from tens of kHz to tens of MHZ.

An ultrasonic sensor sends short and high-frequency sound pulses from the sensor head at certain intervals.

If an ultrasonic wave hits an object, it will be reflected back to the sensor as an echo signal.

The ultrasonic sensor calculates the distance to the target based on the time span between the transmitted signal and the received echo signal.

The ultrasonic wave is a kind of mechanical oscillation in the elastic medium, which has two forms: transverse oscillation (transverse wave) and longitudinal oscillation (longitudinal wave).

Longitudinal oscillation is mainly used in industrial applications.

Ultrasonic waves can travel in gases, liquids, and solids at different speeds. In addition, it also has a refraction and reflection phenomenon, and there is attenuation in the propagation process.

The ultrasonic wave propagates in the air with a low frequency, usually dozens of kHz, while in solid and liquid, the frequency can be used higher. Attenuation is faster in the air, while in liquid and solid, attenuation is smaller and farther.

Ultrasonic characteristics can be used to make a variety of ultrasonic sensors, with different circuits, made of a variety of ultrasonic measuring instruments and devices, and in communications, medical appliances and other aspects have been widely used.

The main materials of ultrasonic sensors are piezoelectric crystal (electrostrictive) and nife-al alloy (magnetostrictive).

Electrostrictive materials include lead zirconate titanate (PZT), etc.

An ultrasonic transducer made up of piezoelectric crystals is a reversible transducer that converts electrical energy into mechanical oscillations to produce an ultrasonic wave. Some ultrasonic sensors can transmit as well as receive.

Only small ultrasonic sensors are introduced here. The transmission and reception are slightly different.

It is suitable for transmission in the air.

The working frequency is generally 23-25khz and 40-45khz. This kind of sensor is suitable for ranging, remote control, anti-theft, and other purposes. There are T/ r-40-16, T/ r-40-12, etc. (where T stands for send, R stands for receive, 40 stands for the frequency of 40KHZ, 16 and 12 stands for its outside diameter size in mm).

Another sealed ultrasonic sensor (MA40EI type). Its characteristic is to have waterproof action (but cannot put in water), can make makings level and approach switch are used, its function is better.

There are three basic types of ultrasonic application, transmission type for remote control, burglar alarm, automatic door, proximity switch; Separated reflection type for ranging, liquid level or material level; Reflective type is used for flaw detection and thickness measurement of materials.

It is composed of sending sensor (or wave sender), receiving sensor (or wave receiver), control part and power supply part.

The transmitter sensor is composed of a transmitter and a ceramic vibrator transducer with a diameter of about 15mm.

The role of the transducer is to convert the electric vibration energy of the ceramic vibrator into super energy and radiate it into the air.

And receiving sensor by the ceramic vibrator transducer and amplifying circuit, the transducer receives waves produce mechanical vibrations, its transformation into electric energy, as the sensor, the output of the receiver to detect the ultrasonic signal sent out.

And in practical use, as the sending sensor ceramic oscillator can also be used as a receiver sensor club ceramic vibrator.

The control part mainly controls the pulse chain frequency, duty cycle, sparse modulation, count and detection distance of the transmitter.

006 How does an ultrasonic Sensor work?

Work-program mode

If to send within the sensor resonance frequency of piezoelectric element is 40 kHz (double crystal oscillator) 40 kHz high-frequency voltage applied, the piezoelectric ceramic piece is based on the high-frequency voltage polarity elongation and shorten, so send 40 kHz frequency ultrasound, the ultrasonic wave propagation in the form of density (density modulation degree can be controlled by the circuit), and to the wave receiver.

The receiver USES the piezoelectric effect principle adopted by the pressure sensor, that is, applying pressure on the piezoelectric element and making the piezoelectric element strain will produce a sinusoidal voltage of 40KHz with one side as “+” pole and the other side as “-” pole. Because the high-frequency voltage amplitude is small, it must be amplified.

Ultrasonic sensors allow drivers to safely back up their vehicles by detecting any obstacles that may be in their path or nearby and warning them in time.

The designed detection system can provide aural and visual warnings with both sound and light.

The warning means that the distance and direction of obstacles in the blind area are detected.

In this way, whether parking or driving in a narrow place, with the help of the reversing obstacle alarm and detection system, the psychological pressure of the driver will be reduced, and the driver will be able to take necessary actions with ease.

Ultrasonic sensor uses an acoustic wave medium to detect the object without contact and wear.

Ultrasonic sensors can detect transparent or colored objects, metallic or non-metallic objects, solid, liquid, powdery substances.

Its detection performance is almost not affected by any environmental conditions, including smoke and dust environment and rainy days.

Detection Mode

Ultrasonic sensors mainly adopt the direct reflection detection mode.

The detected object in front of the sensor detects the detected object by partially transmitting the emitted sound wave back to the receiver of the sensor.

Some of the ultrasonic sensors adopt the mode of contrast detection. An oncoming ultrasonic sensor consists of a transmitter and a receiver that are continuously “listening” in between.

The detector, located between the receiver and the transmitter, blocks the sound waves emitted by the receiver, and the sensor generates a switching signal.

detection range

Adjust

Almost all ultrasonic sensors can adjust the near and far points of the switch output or the measuring range. Objects outside the set range can be detected but do not trigger a change in the output state. Some sensors have different adjustment parameters, such as sensor response time, echo loss performance, as well as the setting and adjustment of working direction when the sensor is connected with the pump equipment.

repeated accuracy

Wavelength and other factors will affect the accuracy of ultrasonic sensors, among which the most important factor is the acoustic velocity changing with temperature, so many ultrasonic sensors have the characteristics of temperature compensation.

This characteristic enables analog output type ultrasonic sensors to obtain repeatable accuracy up to 0.6mm over a wide temperature range.

Output function

All series of ultrasonic sensors have on-off output products. Some products also have two – way on-off output (such as minimum and maximum level control). Most product lines offer analog current or analog voltage outputs

noise suppression

The noise such as metal knock and rumble will not affect the parameter assignment of the ultrasonic sensor, which is mainly due to the optimization of the frequency range and the patented noise suppression circuit.

synchronizing function

Ultrasonic sensor synchronization function can prevent interference. They do this by simply connecting their own synchronization wires. They emit acoustic pulses simultaneously, work like a single sensor, and have extended detection angles.

alternation

Ultra long scan with the ultrasonic sensor

Ultrasonic sensors working in an alternate mode are independent of each other and will not affect each other.

The more sensors that work alternately, the lower the switching frequency of the response

detecting condition

Ultrasonic sensors are particularly suited to work in the medium of “air”.

This sensor can also work in other gaseous media but requires sensitivity adjustment.

dead zone

The direct reflection ultrasonic sensor cannot reliably detect part of the object located in the front part of the ultrasonic transducer.

Therefore, the area between the ultrasonic transducer and the starting point of the detection range is called the blind area. The sensor must remain unobstructed in this area.

Temperature and humidity

Air temperature and humidity affect the travel time of sound waves. Every 20 or rise in air temperature; C, detection distance increased by up to 3.5%. In relatively dry air, an increase in humidity causes the speed of sound to increase by up to 2%.

Air pressure

Under normal circumstances, the atmospheric change of 5% (a fixed reference point is selected) will lead to the detection range change of 0.6%. In most cases, the sensor is used without problems at 5Bar pressure.

airflow

Changes in the flow will affect sound speed. However, the impact of the air flow velocity of the highest to 10m/s is negligible. In the case of hot metal, such as the hot metal, it is recommended that the ultrasonic sensor should not be detected, because the echo of the distorted sound waves is difficult to

Standard sensing object

The square shape sound reflection plate is used to calibrate the rated switching distance sn

The thickness of 1 mm

Perpendicularity: perpendicular to the beam axis.

Is an ultrasonic sensor waterproof?

The housing is particle – and water-resistant

IP65: completely dustproof; Water column invasion.

IP67: completely dustproof; It can be effectively protected by immersing at a constant temperature at a depth of 1m underwater for 30 minutes.

pump function

Dual position control, such as pumping in and out of a liquid level control system, is available.

When an object far away from the sensor reaches the far point in the detection range, the output action.

When the measured object is close to the sensor and reaches the near point set in the detection range, it outputs the opposite action.

007 How far can ultrasonic sensors detect?

The detection range of ultrasonic sensors depends on the wavelength and frequency used

The longer the wavelength is, the smaller the frequency is, and the larger the detection distance is.

For example, the detection range of a compact sensor with millimeter wavelength is 300~500mm, and that of a sensor with a wavelength greater than 5mm can reach the detection range of 8m.

Some sensors have a narrower 6º The acoustic emission Angle is, therefore, more suitable for accurate detection of relatively small objects. Other acoustic emission angles are at 12º To 15 & ordm;

The sensor can detect objects with a large inclination Angle. In addition, we have an external probe-type ultrasonic sensor, the corresponding electronic circuit is located in the conventional sensor housing.

This structure is more suitable for detection of limited installation space occasions.

Can an ultrasonic sensor detect water?

Liquid level test

Yes, it can detect the water/liquid level.

The basic principle of ultrasonic liquid level measurement is: the ultrasonic pulse signal sent by the ultrasonic probe is transmitted in the gas, which is reflected after encountering the interface between the air and the liquid.

After receiving the echo signal, the ultrasonic transmission time is calculated, and the distance or liquid level height can be converted.

The ultrasonic measurement method has many advantages over other methods:

without any mechanical transmission parts, nor contact with the liquid under test, it belongs to non-contact measurement, not afraid of electromagnetic interference, not afraid of acid and alkali and other strong corrosive liquid, so stable performance, high reliability, long life;

Its short response time can easily realize the real-time measurement without lag

The working frequency of the ultrasonic sensor used in the system is about 40kHz.

The ultrasonic pulse is sent by the transmitting sensor to the liquid surface, which is reflected and then returned to the receiving sensor.

The time required for the ultrasonic pulse from the transmission to reception is measured. According to the sound velocity in the medium, the distance from the sensor to the liquid surface can be obtained, so as to determine the liquid surface.

Considering the influence of ambient temperature on the propagation velocity of the ultrasonic wave, the propagation velocity is corrected by means of temperature compensation to improve the measurement accuracy.

The formula is :

V=331.5+0.607T （1）

(V is the velocity of ultrasonic wave propagation in the air; T is the ambient temperature)

S=V ×t/2=V×（t1－t0）/2 （2）

S is the measured distance; T is the time difference between transmitting ultrasonic pulse and receiving its echo; T1 is the receiving time of ultrasonic echo; T0 is the time of ultrasonic pulse transmission.

The capture function of MCU can be used to easily measure the time of t0 and t1. According to the above formula, the measured distance S can be obtained by software programming.

Because the MCU of this system selects the mixed signal processor with SOC characteristics and the temperature sensor is integrated internally, the temperature compensation of the sensor can be easily realized by using the software.

008 What is an ultrasonic sensor system constitution?

system constitution

The ultrasonic sensor is mainly composed of the following four parts:

Transmitter: the ultrasonic wave is generated and radiated into the air through the vibration of the oscillator (generally ceramic, with a diameter of about 15 mm).

Receiver: when the oscillator receives the ultrasonic wave, it will produce corresponding mechanical vibration according to the ultrasonic wave and convert it into electrical energy as the output of the receiver

The control part: the ultrasonic transmission of the transmitter is controlled by an integrated circuit, and whether the receiver receives the signal (ultrasonic) and the size of the received signal is determined.

Power supply: the ultrasonic sensor is usually supplied by DC12V 10% or 24V 10% external dc power supply, which is supplied to the sensor by internal voltage stabilizing circuit.

009 Choose ultrasonic sensor detection method

According to the volume, material, movable and other characteristics of the detected object, the ultrasonic sensor adopts different detection methods. The common detection methods are as follows:

Penetrative: the transmitter and receiver are located on both sides. When the detected object passes between them, it is detected according to the attenuation (or occlusion) of the ultrasonic wave.

Limited distance type: the transmitter and receiver are on the same side. When the detected object passes within the limited distance, it will be detected according to the reflected ultrasonic wave.

Limited-range type: the transmitter and receiver are located at the center of the limited range, and the reflector is located at the edge of the limited-range, and the attenuation value of the reflected wave when there is no occlusion of the detected object is taken as the reference value.

When the detected object passes within the limited range, it is detected according to the attenuation of the reflected wave (comparing the attenuation value with the reference value).

Regression reflection type: the transmitter and receiver are located on the same side, and the detected object (plane object) is taken as the reflection surface to detect according to the attenuation of the reflected wave.

010 How to test an ultrasonic sensor

The ultrasonic sensor is not reflected by direct testing with a multimeter. To test the ultrasonic sensor is good or bad can build an audio oscillation circuit, when C1 is 390O F, in the inverter’s attending foot can produce an audio signal of about 1.9kHz.

The ultrasonic sensor (transmission and reception) to be tested is connected between the sets and attending feet; If the sensor can produce audio sound, it can be basically determined that the ultrasonic sensor is good.

Note: C1=3900 F, about 1.9kHZ; C1=0.O1 F, approximately 0.76kHZ.

011 Disadvantages of ultrasonic sensors and solutions

Ultrasonic sensors are simple, convenient and cost-effective. But current ultrasonic sensors all have some disadvantages, such as reflection problem, noise problem, and crossover problem.

Reflection problem

If the object is always at the right Angle, the ultrasonic sensor will get the right Angle. Unfortunately, in practice, very few objects are detected correctly.

Several errors may occur:

triangular error

When the measured object is at a certain Angle to the sensor, there is a triangulation error between the detected distance and the actual distance

specular reflection

The problem is the same as in high school physics. At certain angles, the sound waves emitted are reflected off the smooth surface of the object, so there is no echo and therefore no range reading. The ultrasonic sensor ignores the object.

multiple reflections

This phenomenon is more common when detecting objects in corners or similar structures. The sound wave is picked up by the sensor after many bounces, so the actual detection value is not the real distance value.

These problems can be solved by using multiple ultrasonic coils arranged at certain angles. The correct reading is screened by detecting the return value of multiple ultrasounds.

noise

Although most ultrasonic sensors operate at a frequency of 40-45 kHz, far higher than what humans can hear. But the surrounding environment also produces noise of a similar frequency.

For example, high frequency generated by motor rotation, high-frequency noise caused by wheel friction on hard ground, the vibration of the robot itself, and even sound waves emitted by ultrasonic sensors of other robots, even when there are multiple robots will cause the sensors to receive wrong signals.

This problem can be solved by encoding the transmitted ultrasonic wave, such as transmitting a group of short and long sound waves. Only when the probe detects the same combination of sound waves can the distance be calculated. This can effectively avoid misunderstanding caused by environmental noise.

Crossover Problem

The crossover problem is caused when multiple ultrasonic sensors are mounted at an Angle to the robot.

The sound wave emitted by ultrasonic X is reflected by the mirror and obtained by the sensor Z and Y. At this time, Z and Y will calculate the distance value according to this signal, thus unable to obtain the correct measurement.

The solution is to encode the signals sent by each sensor. Let each ultrasonic sensor hear only its own voice.

Others

differentiate

What is the difference between the ultrasonic sensor and sonar sensor?

Sonar sensor and ultrasonic sensor are often heard of the two detection device, many people think that the two are one kind of sensor, what is the difference between the two kinds of sensors?

Sonar sensors directly detect and identify objects in the water and the contours of the bottom.

The sonar sensor sends out a sound signal that will be reflected back when it encounters an object and calculates its distance and position based on the reflection time and wave pattern.

High-frequency ultrasonic sensor

The ultrasonic wave is a kind of mechanical wave whose vibration frequency is higher than that of the sound wave.

It is generated by the vibration of the energy-exchanging chip under the excitation of voltage. Sonar sensors are mainly used to detect living things, such as what kind of creatures are underwater and how big they are. The device you often hear about for detecting water monsters is the sonar sensor.

Ultrasound has a great ability to penetrate liquid and solid, especially in the opaque solid, it can penetrate a depth of dozens of meters.

When ultrasonic waves touch impurities or interfaces, they will produce significant reflections and echo, and when they touch moving objects, they will produce a Doppler effect.

Therefore, ultrasonic testing is widely used in industry, national defense, biomedicine, and other aspects. The ultrasonic sensor is a kind of ultrasonic sensor. In industry, the typical application of ultrasonic is the nondestructive inspection of metal and ultrasonic thickness measurement.

The application of ultrasonic sensors in medicine is mainly to diagnose diseases.

It has become an indispensable diagnostic method in clinical medicine.

precautions

To ensure reliability and long service life, do not use the sensor outdoors or above the rated temperature

As the ultrasonic sensor USES air as the transmission medium, the local temperature is not the same, the reflection and refraction at the boundary may lead to misoperation, and the detection distance will also change when the wind blows. Therefore, sensors should not be used near equipment such as forced ventilation fans.

A jet nozzle emits air at a variety of frequencies, which affects the sensor and should not be used near the sensor

Water droplets on the sensor surface shorten the detection distance

Materials such as fine powders and cotton yarns cannot be detected when absorbing sound (reflective sensors)

Do not use the sensor in the vacuum or explosion proof area

Do does not use the sensor in areas with steam; The atmosphere in this area is uneven. A temperature gradient will be generated, which will result in a measurement error.

012 Recommended ultrasonic sensor manufacturers

PD China

A promising pioneer of piezoelectric actuator manufacturer, who offers industrial ultrasonic sensors, piezo actuators and PZT technology, located in China.

Murata Japan

Murata Manufacturing is primarily involved in the manufacturing of ceramic passive electronic components, primarily capacitors, and it has an overwhelming share worldwide in ceramic filters, high-frequency parts, and sensors.

Pepperl+Fuchs

a leader and innovator of industrial sensors for factory automation and an expert for explosion protection in process automation.