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Advantages and disadvantages of using strain sensors for force measurement

Browse times:   Release time:2018-06-07 16:28:04

This article first introduces the working principle, composition, and advantages of strain sensors, secondly introduces the advantages and disadvantages of using strain sensors for force measurement, and finally introduces four commonly used strain sensors. Follow the sensor network editor to find out.
How strain sensors work
A strain sensor is a sensor that uses a resistance strain gauge to convert strain into a change in resistance. The sensor consists of a resistance strain sensitive element (converts strain into a change in resistance) attached to an elastic element (sensing strain). When the measured physical quantity acts on the elastic element, the deformation of the elastic element causes the resistance value of the sensitive element to change, and it is converted into a power output through a conversion circuit. The magnitude of the power change reflects the measured physical quantity. Strain sensors can measure physical quantities such as strain stress, bending moment, torque, acceleration, and displacement.
Strain is the phenomenon that an object deforms under the action of external pressure or tension. When the external force is removed, the strain that the object can completely recover to its original size and shape is called elastic strain, and objects with elastic strain characteristics are called elastic elements. The working principle of the resistance strain gauge is based on the strain effect, that is, when the conductor is mechanically deformed, its resistance value changes accordingly.
Strain sensor composition
(1) Sensitive grid The sensitive grid is the core part of the strain gauge, it senses the strain, and transforms the strain into a change in resistance. There are three types of sensitive grids: wire, foil and film.
(2) Substrate The substrate is an intermediate medium that transmits the strain on the surface of the sensor elastomer to the resistance wire grid, and plays the role of insulation and protection between the resistance wire and the elastomer. The insulation of the substrate should be good, otherwise, small changes in the strain gauge will be missed. The substrate is generally composed of thin paper, a gelatin film, and the like.
(3) Adhesive The adhesive is used for the adhesion between the sensitive grid and the substrate, the substrate and the test piece, and the substrate and the cover layer.
(4) Covering layer The covering layer has the function of protecting the strain gauges, and at the same time is resistant to moisture, corrosion and dust.
(5) Lead wire The lead wire is used to connect the resistance wire and the measurement circuit, and output the electrical parameters.
Advantages and disadvantages of using strain sensors for force measurement
Advantages of strain sensors
1. High resolution, can measure very slight strain, such as 1-2 micro strain;
2. The error is small, generally less than 1%;
3. Small size and light weight.
4. Large measurement range, from elastic deformation to plastic deformation (1-2%), up to 20%;
5. It can measure both static and rapid alternating stress;
6. It has all the advantages of electrical measurement, such as the measurement results are easy to transmit, record and process;
7, can work in a variety of harsh environments. Such as from cosmic vacuum to thousands of atmospheric pressure; from near absolute zero low temperature to nearly 1000 ℃ high temperature; centrifugal acceleration can reach hundreds of thousands of "g"; under the conditions of vibration, magnetic field, radioactivity, chemical corrosion, etc., as long as appropriate measures are taken, Also works reliably;
8, low price, variety, easy to choose and use.
Advantages and disadvantages of using strain sensors for force measurement
1. Compared with force sensors, the price of strain sensors is much lower, especially compared with force sensors.
2. The strain sensor will not affect the stiffness of the system. Therefore, the dynamic characteristics of the machine are not affected.
3. The force sensor requires a certain space for installation. This means that the overall structure of the measurement system will change.
1. Compared with force sensors, the accuracy of strain sensors is much lower.
2. The strain sensor needs to be calibrated after installation. A force sensor, such as C6A, is required during the calibration process. A signal comparison is then performed to convert the strain into a force value. Of course, calibration can also be performed with an object of known weight. Obviously, the accuracy of the strain sensor cannot exceed the accuracy of the calibration process.
Advantages and disadvantages of using strain sensors for force measurement
Commonly used strain sensors
1, diaphragm type
Its elastic sensitive element is a round metal flat diaphragm fixed around. When the diaphragm is deformed under pressure, both the radial strain and the tangential strain at the center reach a positive maximum, while the radial strain at the edge reaches a negative maximum, and the tangential strain is zero. Therefore, two strain gauges are often attached to the positive and negative maximum strains respectively, and connected to a half-bridge circuit of adjacent bridge arms to obtain greater sensitivity and temperature compensation. The use of circular foil strain gages (see resistance strain gages) maximizes the strain effect of the diaphragm. The non-linearity of this sensor is significant. The latest product of the diaphragm pressure sensor is the integration of the role of the elastic sensor and the strain gauge in the single-crystal silicon diaphragm, that is, the integrated circuit process is used to diffuse the single-crystal silicon diaphragm to make the resistance bar, and the peripheral fixed structure is used. Into a solid-state pressure sensor (see Piezoresistive sensors).
2.Strain tube type
Also known as strain tube type. Its elastic sensor is a thin-walled cylinder with one end closed, and the other end with a flange connected to the system under test. Two or four strain gauges are affixed to the cylinder wall, half of which is stuck to the solid part as a temperature compensation gauge, and the other half is used as a measurement strain gauge. When there is no pressure, the four strain gauges form a balanced full-bridge circuit. When pressure is applied to the internal cavity, the cylinder becomes a "waist-drum", causing the bridge to lose balance and output a voltage that has a certain relationship with the pressure. This sensor can also use a piston to convert the measured pressure into a force to be transmitted to a strain cylinder or through a vertical chain-shaped diaphragm to transmit the measured pressure. The strain tube pressure sensor has a simple structure, convenient manufacturing and strong applicability, and is widely used in the dynamic pressure measurement of rockets, artillery shells and artillery.
3.Strain beam type
When measuring small pressures, a fixed beam or an equal-strength beam can be used. One method is to use a diaphragm to convert pressure into force and then transmit it to the strain beam through a force transmission rod. The maximum strain of the fixed beam at both ends is at the two ends and the midpoint of the beam, and the strain gauges are attached to these places. There are other forms of this structure, such as suspension beams and diaphragms or bellows.
In the combined strain pressure sensor, the elastic sensitive element can be divided into a sensing element and an elastic strain element. The sensing element converts pressure into force and transmits it to the most sensitive part of the elastic strain element, and the strain gauge is attached to the maximum strain of the elastic strain element. In fact, the more complicated strain tube type and strain beam type belong to this type. Sensing elements include diaphragms, capsules, bellows, bourdon tubes, and so on. Elastic strain elements include cantilever beams, fixed beams, Π beams, ring beams, and thin-walled tubes. They can be combined into multiple types according to different needs. Strain pressure sensors are mainly used to measure the dynamic or static pressure of flowing media, such as the pressure of gas or liquid at the inlet and outlet of power pipeline equipment, and the pressure of internal combustion engine pipelines.