What are the types of strain gauges and what are the classifications of resistance strain gauges

Spot welded strain gauge (smart) Usage:

Strain gauges are mainly installed by spot welding, or they can be bonded to the surface of the object to be measured (steel or concrete) with epoxy or other high-strength adhesives.

The spot-welded strain gauge is measured using the vibrating wire principle: a steel string is tensioned between two mounting blocks, and the mounting blocks are welded on the surface of the steel parts to be measured.

When the measured object is deformed, it will drive the spot welding strain gauge to deform, and the deformation will be transmitted to the vibrating wire through the front and rear end seats, and the change of vibrating wire stress will be transformed, thereby changing the vibration frequency of the vibrating wire. The electromagnetic coil excites the vibrating string and measures its vibration frequency, and the frequency signal is transmitted to the reading device through the cable to measure the strain of the measured structure.

Vibrating wire surface strain gauge (parameter identification) Usage:

VWS-10F vibrating wire surface strain gauge is suitable for long-term laying on the surface of hydraulic structures or other structures, measuring the strain on the surface of the structure, and can simultaneously measure the temperature of the laying point.

The vibrating wire surface strain gauge has a small elastic modulus, good follow-up with the measured structure, will not interfere with the original stress field during the measurement, and contains the design, all stainless steel structure, simple installation and reliable use, and can be reused. Vibrating wire surface strain gauges have an intelligent identification function.

Vibrating wire embedded strain gauge (parameter identification) Purpose:

VWS vibrating wire strain gauge is suitable for long-term burial in hydraulic structures or other concrete structures, measuring the internal strain of the structure, and can simultaneously measure the temperature of the buried point.

According to the speed of the measured strain change with time, it is divided into two categories: static resistance strain gauge and dynamic resistance strain gauge. There is also a category of hyperdynamic resistance strain gauge in the dynamic resistance strain gauge. Static resistance strain gauges generally measure strains that do not change over time or change slowly over time.

Earlier, the static strain gauge relied on manual conversion of measuring points, manual adjustment of balance and reading, and later developed into a digital display static strain gauge, automatic adjustment of balance, automatic conversion of measurement points, automatic display monitoring, printing and storage. And from the strain measurement to the measurement of voltage, temperature and other parameters, it is called a data acquisition instrument or strain digital measurement system. Dynamic resistance strain gauge has developed from multi-channel analog signal output to digital dynamic strain gauge and digital dynamic data acquisition system.

At present, it has developed and developed a variety of static and dynamic strain measurement instruments and data acquisition systems in China.

The electrical strain gauge is the most widely used, and the circuit it uses can be DC bridge, AC bridge or potentiometer, and the most widely used is AC bridge circuit with carrier amplifier. The strain gauge with AC bridge circuit consists of a bridge, an amplifier, a phase-sensitive detector, a filter, an oscillator, and a power supply part.

Bridge: Converts the change in resistance of a strain gauge into a voltage or current signal so that the amplifier can amplify it. Usually the bridge is powered by a sinusoidal oscillator with a frequency of 500 Hz 50 kHz, and the measured strain signal of the lower frequency modulates the amplitude of the bridge voltage of the higher frequency to output a narrow frequency amplitude modulated wave signal.

Amplifier: Amplifies the weak signal output from the bridge without distortion and pushes the indicator and recorder with enough power. In order to improve the stability of the amplifier, the AC carrier amplifier is generally used, and the DC amplifier is only used for the ultra-dynamic strain gauge.

Phase-sensitive detector: The amplitude modulated wave is restored to the measured strain signal waveform, and the direction of the measured strain signal is reflected at the same time, usually using a ring phase-sensitive detector.

Filter: Filter out the higher harmonic components in the output signal of the phase-sensitive detector to obtain the ideal output waveform.

The strain gauge used in it is small in size, and the miniature foil strain gauge can measure the strain in a small area that is regarded as a "point" in engineering.

Strain range: 30000

Resolution: 1

Accuracy: full scale.

Equilibrium range: full scale.

Bridge voltage: DC2V

Zero drift: 1 hour.

Test points: 64

Measurement method: automatic, manual.

Strain gauge resistance: 50 10000

Strain gauge sensitivity factor:

Operating temperature: -10 +50.

Operating humidity: 85%RH (non-condensing).

Power supply: AC220V 10% 50Hz

Strain gauge is also commonly referred to as an electrical strain gauge. Wired strain gauges, foil strain gauges, semiconductor strain gauges, etc. The strain gauge whose resistance value changes with deformation is attached to the surface of the specimen in the specified direction, and the resistance value of the strain gauge changes due to the strain on the surface of the specimen.

A high-sensitivity galvanometer is used to measure changes in resistance values. And use this to derive the magnitude change of the strain value. Strain gauges are widely used in the testing of mechanical properties of materials, such as the determination of the tensile modulus of materials, which is calculated by calculating the applied load and the strain value measured by the strain gauge attached to the surface of the specimen.

An instrument for measuring the strain of a mechanical part, component, or specimen. Strain gauges are used to measure the static and dynamic tensile and compressive strains of materials and structures, as well as at any point in materials and structures, in experimental stress analysis and in the study of static and dynamic strength. In the mechanical industry, it can be used, for example, to measure the stress of turbine blades, boiler structures or cylinders of internal combustion engines.

If the strain gauge is equipped with a corresponding sensor, it can also measure physical quantities such as force, mass, pressure, displacement, torque, vibration, velocity and acceleration and their dynamic change processes, and can also be used as a non-destructive strain measurement and inspection.

The working mechanism of metal strain gages is the so-called geometric effect: when the strain gage is elongated, its cross-sectional area decreases, resulting in an increase in resistance. Metal strain gauges are mainly made of Cu-Ni alloys such as constantan, often with a curved strip structure.

This strain gauge has greater sensitivity and greater resistance at a lower power dissipation.

In addition to the geometric effect, the working mechanism of semiconductor strain gauges is also more important than the piezoresistive effect: when the strain gage is elongated or shortened, the carrier mobility of the semiconductor changes, resulting in a change in resistance. Semiconductor strain gauges are mainly made of SI and often use diffusion or ion implantation structure, which is compatible with IC processes.

This strain gauge offers good temperature stability, better linearity, a larger strain range and flexibility (e.g. easy adhesion to curved surfaces). In order to improve sensitivity and linearity, p-type semiconductors are often used (n-type semiconductors are not used); In addition, in order to improve temperature stability, highly doped semiconductors (1020cm-3) are often used, but sensitivity should be considered as a compromise.

Under the action of stress, the length l, area a and resistivity of the strain gauge will change, which causes the resistance r to change, and its resistance change rate is .

r/r = (δl/l)-(a/a)+(/ρ) = e(1+2n+p)

where e=δl l is the strain, n is the poisson ratio, and p is the parameter that characterizes the magnitude performance of the piezoresistive effect (called the gauge factor, p = (δ) (δl l)).

According to the piezoresistive effect of semiconductors, for the piezoresistive strain gauge of the [110] crystal orientation of p-type Si has δ l y el, then the following is obtained

p = (δr/r)/(δl/l) ≈/ρ)/e ≈ y σl

where l is the piezoresistive coefficient longitudinally (along the [110] crystal direction) and y is the Young's modulus of elasticity.

Under a certain strain, the greater the change in resistance, the higher the sensitivity of the strain gage, so the dr r at the unit strain can be defined as the strain sensitivity g, that is, there is:

g = (δr/r)/e = 1+2n+p

The larger the gauge factor p, the higher the sensitivity of the piezoresistive strain gauge. For P-type Si[110] piezoresistive strain gauges, because L 72 10-11Pa-1, Y 170 GPA, P 122 is obtainedIn the case of piezoresistive strain gauges for metal, the gauge factor is very small, only p. Therefore, it can be seen that the sensitivity of semiconductor piezoresistive strain gauges is much higher than that of metal strain gauges.