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How to choose a strain gauge
Nov 24, 2017

How to choose a strain gauge

The strain gauge selection method is to consider the test or application conditions (that is, application accuracy, environmental conditions, including temperature, humidity, harsh environmental conditions, various types of interference, common-mode problems, size of the specimen, paste area, radius of curvature, installation conditions, etc., as well as specimen or elastomer material status (material line expansion coefficient, elastic modulus, structure, In the case of force or stress distribution, the above-mentioned content is used to select a resistance strain gage matching the best price/performance ratio.


In practical application, the test or application condition should be followed (that is, the application precision, environmental conditions including temperature, humidity, harsh environment, various types of interference, common-mode problems, the size of the specimen material, paste area, radius of curvature, installation conditions, etc. as the first, specimen or elastomer material condition (material line expansion coefficient, elastic modulus, structure, Perhaps the principle of stress status or distribution of stresses, and so on, use the above content to select the best price/performance ratio of the strain gauge. The following table lists the elements that should be considered for the selection of strain gauges, which are only applicable to conventional conditions, excluding radiation, strong magnetic field, high centrifugal force and other special occasions.

 

A the procedure for selecting a strain gage

(1) First, according to the application of precision, environmental conditions to select the Strain gauge series.

(2) The sensitive gate length is selected according to the size of specimen material, paste area, radius of curvature, installation condition and strain gradient.

(3) Select sensitive grid structure according to strain gradient, stress type, heat dissipation condition, installation space and strain gage resistance.

(4) Choose nominal resistance according to usage condition, power consumption size and maximum allowable voltage.

(5) According to the specimen material type, the working temperature range, the application precision chooses the temperature self compensation coefficient or the elastic modulus self compensation coefficient.

(6) The Creep compensation code is selected according to the intrinsic creep property of the elastomer, the precision of the actual test, the process method, the type of protective adhesive and the sealing form.

(7) Select the lead connection mode of the strain gauge according to the actual need.

(B) method of selecting strain gauges


(1) The choice of the length of the strain Gage sensitive gate:

The output strain of the strain gage under loading state is the average strain of the sensitive gate region. In order to obtain the real measurement value, the grating length of the strain gauge should not be larger than the 1/5~1/10 of the measuring area radius. The long grating strain Gage has the advantages of easy pasting and wiring, good heat dissipation, and can improve the performance of strain Gage, but should be selected according to actual measurement needs, for the change of strain field and general sensor use, we recommend that the user chooses the 3~6mm strain Gage. If the strain measurement of non-uniform material (such as concrete, cast iron, cast steel, etc.) is carried out, the strain gage of the grating length not less than the non-uniform particle size of the material should be chosen so as to reflect the average strain in the structure more realistically. For strain measurement with large strain gradient, the strain gage with smaller length of sensitive gate should be selected as far as possible.


(2) The choice of the strain gage sensitive grid material and the base material:

The strain measurement of 60℃, long time and maximum strain under 1000μm/m a strain gage (be, ZF, BA and the daily-use weighing strain gage series) is generally selected for the base of the sensitive grid, modified phenolic or polyimide alloy foil. 150 ℃ within the strain measurement, generally selected to Kang copper, A strain Gage (BA series) with a sensitive grid and polyimide as the base of the polyurethane alloy foil; 60 ℃ in high precision sensors commonly used in Kang-CU alloy or MA alloy foil as sensitive grid, modified phenolic resin as the base of the strain gauge (BF, ZF series).

 

(3) The choice of the structure type of the strain gauge sensitive gate:

To measure the strain of the unknown principal stress direction specimen or to measure the shear strain, the Multiaxial strain Gage is selected, the former can be 45°, or 60°, or 120°, with a three-axis strain gauge, which uses a two-axis strain gauge with an angle of 9 0°; When measuring the strain of a known principal stress direction specimen, a single axle strain gage can be selected ; A strain gage for a pressure sensor can be used to select a multi-axis strain gage for a circular sensitive grating; When the stress distribution is measured, a multi-axis strain gage with a $number sensitive gate arranged in a series or rows can be selected.


(4) Selection of gate spacing

My company produces two-axle strain gauge of the grid spacing is generally l6= 6.0, l68=6.8, l7=7.0, l8=8.0,l0=10.5,l2=12.0,l4=14.0, etc., users can freely choose the different gate spacing strain gauge.


(5) Selection of strain Gage resistors:

The selection of strain gage resistance should be based on the heat dissipation area of strain gauge, the influence of conductor resistance, signal-to-noise ratio and power consumption. For sensors generally recommended the use of 350ω, 1000ω resistance strain gage. For stress distribution test, stress test, static strain measurement and so on, we should choose the resistance which matches with the instrument, generally recommend the 120ω and 350ω strain gauges.


(6) The choice of limit working temperature

This temperature indicates the limit operating temperature of the strain gage, which is usually omitted in our product naming when the limit operating temperature is not higher than ℃.


(7) Selection of self-compensating coefficient of temperature and elastic modulus

The selection of the strain gauge temperature and the self compensation coefficient of the elastic modulus can be selected according to the temperature self compensation function and the self compensation function of the elastic modulus.


(8) Selection of Creep label

The selection method of the creep self-compensating function can be referenced by the user in selecting the Strain gauge creep label.


(9) Choice of wiring mode

The Resistance strain Gage has several wiring modes, for example:

① standard lead mode, BQ, BA, BB, ZF, ZCF, ZFF series and structure of the form of Ka, BA, CA, BC, CB, CC, FD, Aa-w, ha-w, the strain gauge wiring mode for cylindrical lead; be, BF, BCF, BFF, RNF, The wiring mode of the RBF series Strain Gage is a strip lead. Lead length In addition to the HA series of ribbon leads for 25±2mm, the rest are 30±3mm.

② Ribbon lead way, HA series of lead length of 25mm and the remaining strain gauge lead length of 30mm, model does not have to reflect the lead, in addition, must indicate the lead length.

③ other lead way, such as enameled wire, high-temperature wire and so on.

(C) What to consider when selecting the usual strain gauge parameters:

The strain gage must be selected according to the actual situation when carrying out strain measurement or manufacturing sensor. As the following table lists the selection of strain gage parameters should be considered, only applicable to the general situation, not including radiation, strong magnetic field, high centrifugal force and other special occasions.