Strain Gauge Selection Method
In actual applications, the test or application conditions should be followed (application accuracy, environmental conditions including temperature, humidity, harsh environmental conditions, various interferences, common-mode common ground problems, sample material size, paste area, radius of curvature, installation Conditions, etc.) firstly, the condition of the test piece or elastomer material (material linear expansion coefficient, elastic modulus, structure, approximate force condition or stress distribution condition, etc.) is the second principle. Use the above content to select the most cost-effective strain gauge. The following table lists the content that should be considered when selecting strain gauges. It is only suitable for general conditions and does not include special occasions such as nuclear radiation, strong magnetic fields, and high centrifugal force and so on.
（A）Steps for selecting strain gauges
- First select the series of strain gauges according to the application accuracy and environmental conditions.
- Select the length of the sensitive grid depending on the size of the specimen material, the paste area, the radius of curvature, the installation conditions, and the strain gradient.
- Select the sensitive grid structure on the basis of strain gradient, stress type, heat dissipation conditions, installation space, strain gauge resistance, etc.
- Select nominal resistance according to usage conditions, power consumption, maximum allowable voltage,etc.
- Select temperature self-compensation coefficient or elastic modulus self-compensation coefficient based on the type of test piece material, working temperature range, and application accuracy.
- Select the creep compensation code according to the inherent creep characteristics of the elastomer, the accuracy of the actual test, the process method, the type of protective rubber, and the sealing form.
- Select the lead connection method of the strain gauge according to actual demands.
（B）Method of selecting strain gauge
1. Selection of the length of the strain gauge's sensitive grid:
The output strain of the strain gauge in the loaded state is the average strain of the sensitive grid area. In order to obtain the true measurement value, the grid length of the strain gauge should be no more than 1/5 to 1/10 of the radius of the measurement area. Strain gauges with a longer grid length have the advantages of easy sticking and wiring, good heat dissipation, etc. They can improve the performance of the strain gauge to a certain extent, but should be selected according to the actual measurement needs. For the strain field and general sensor applications, we recommended that users choose strain gauges with a grid length of 3 to 6 mm. If strain measurement is performed on non-uniform materials (such as concrete, cast iron, cast steel, etc.), a strain gauge with a grid length not less than the uneven particle size of the material should be selected,so as to more truly reflect the average strain in the structure. For strain measurement with large strain gradients, strain gauges with a smaller sensitive grid length should be better used.
2. Selection of strain gauge sensitive grid material and base material:
For strain measurement within 60℃, in a long time, and with a maximum strain below 1000μm/m, generally used the strain gauges with the base of constantan alloy or kama alloy foil as sensitive grid and modified phenolic or polyimide (BE, ZF, BA and daily-use weighing instrument strain gauge series); strain gauges within 150 ℃ are generally selected with constantan and Karma alloy foil as the sensitive grid and polyimide as the base strain gauge (BA series); 60 ℃ The high-precision sensors within are commonly used strain gauges (BF, ZF series) with constantan alloy or Karma alloy foil as the sensitive grid and modified phenolic aldehyde as the base.
3. Selection of strain gauge sensitive grid structure:
Multiaxial strain gauges are used when measuring the strain of the specimen with unknown principal stress direction or measuring shear strain. The former can be used with a strain gauge with an angle of 45°, 60°, or 120° between the three axes, and the latter can be used with an angle of 90° two-axis strain gauge; when measuring the strain of the specimen with known principal stress direction, a uniaxial strain gauge can be used; the strain gauge used for the pressure sensor can be a multi-axis strain gauge with a circular sensitive grid; when measuring the stress distribution, a multi-axis strain gauge with 5 to 10 sensitive grids arranged in strings or rows can be used. Strain gauge resistance multi-axis strain gauge; when measuring the stress distribution, a multi-axis strain gauge with 5 to 10 sensitive grids arranged in strings or rows can be used.
4. Selection of grid spacing
The grid spacing of the biaxial strain gauges produced by our company 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 different grids according to their needs of different spacing strain gauges.
5. Selection of strain gauge resistance
The selection of strain gauge resistance should be based on the heat dissipation area of the strain gauge, the influence of wire resistance, signal-to-noise ratio, and power consumption. For the sensor, it is generally recommended to use strain gauges with 350Ω and 1000Ω resistance. For stress distribution test, stress test, static strain measurement, etc., the resistance value that matches the instrument should be selected as far as possible. Generally, strain gauges of 120Ω and 350Ω is recommended to be used.
6. Selection of extreme working temperature
This temperature represents the limit working temperature of the strain gauge. When the limit working temperature is lower than ℃, this item will generally be omitted in our product naming.
7. Selection of temperature and elastic modulus self-compensation coefficient
The selection of strain gauge temperature and elastic modulus self-compensation coefficient can be selected by referring to the temperature self-compensation function and elastic modulus self-compensation function.
8. Selection of creep label
N※ and T※ in the strain gauge model are creep marks. Different marks have different creep values. The regulation is: the actual creep value difference between adjacent marks is 0.01～0.015%FS/30min. The user can refer to the selection method described in the creep self-compensation function when selecting the strain gauge creep label.
9. Selection of wiring method
The resistance strain gauges produced by our company have a variety of wiring methods, which are divided into:
- Standard lead type, BQ, BA, BB, ZF, ZCF, ZFF series and structural form of KA, BA, CA, BC, CB, CC, FD, AA-W, HA-W strain gauge wiring method is cylindrical Lead: The wiring method of BE, BF, BCF, BFF, RNF, RBF series strain gauges is ribbon lead. The lead length is 30±3mm except for the HA series ribbon lead which is 25±2mm.
- Ribbon lead mode, when the lead length of HA series is 25mm and the other strain gauge lead length is 30mm, the lead does not need to be included in the model. Otherwise, the lead length must be indicated.
- Other lead methods, such as enameled wire, high temperature wire, etc.
（C）The content usually considered when selecting the parameters of commonly used strain gauges
When performing strain measurement or manufacturing sensors, strain gauges must be selected according to actual conditions. The following table lists the content that should be considered when selecting strain gauge parameters. It is only suitable for general conditions and does not include special occasions such as nuclear radiation, strong magnetic fields, and high centrifugal force,etc.
|
Selection steps |
Select parameters |
Consider content |
|
1 |
Grid length |
1. Strain gradient; 2. Maximum strain area; 3. Required accuracy; 4. Static strain stability; 5. Maximum strain value; 6. Alternate installation cycles; 7. Heat dissipation; 8. Easy to install |
|
2 |
The structural shape of the sensitive grid |
1. Strain gradient; 2. Stress dimension; 3. Heat dissipation conditions; 4. Installation space 5. Is there a suitable strain gauge resistance; 6. Creep |
|
3 |
Strain gauge series |
1. Strain measurement type (static, dynamic, field, etc.); 2. Working temperature; 3. Test period; 4. Number of strain cycles; 5. Required accuracy; 6. Easy to install |
|
4 |
Strain gauge resistance |
1. Heat dissipation; 2. Influence of wire resistance; 3. Signal-to-noise ratio(SNR) |
|
5 |
Temperature self-compensation coefficient or |
|
|
Elastic modulus self-compensation coefficient |
||
|
6 |
Creep compensation code |
1. Inherent creep of elastomer; 2. Protective glue; 3. Sealing form; 4. Process method; 5. Required precision |