Selection Method of Resistance Strain Gauges

Resistance strain gauges (referred to as strain gauges) are core sensitive components that convert mechanical strain of structural members into resistance changes, widely used in load cells, force sensors, structural health monitoring, aerospace testing and other fields. Their selection directly determines the accuracy, stability and service life of the measurement system. The core logic is "two-way matching of strain characteristics and service environment"—avoiding cost waste caused by parameter redundancy and preventing measurement failure due to insufficient performance. Below is a full-process selection method, combining technical parameters, environmental adaptation and practical key points to assist in precise selection.

Step 1: Clarify Core Measurement Requirements and Application Scenarios (Prerequisite for Selection)

Before selection, it is necessary to define "what strain to measure, under what environment to measure, and how to install," which is the basis for subsequent parameter selection and avoids blind pursuit of high-performance parameters.

1. Definition of Core Measurement Requirements

• Strain type and range: Clarify the strain nature of the measured component (static strain such as structural dead weight deformation, dynamic strain such as mechanical vibration strain) and the maximum strain value, and reserve a 1.2~1.5 times safety range. Example: If the actual maximum strain is 1000με, a strain gauge with a range of 1200~1500με should be selected; for dynamic strain (such as impact load), it is recommended to reserve a 1.5~2 times safety factor to avoid damage to the sensitive grid caused by instantaneous overload.
• Accuracy requirement: Is it qualitative monitoring (such as structural crack early warning), quantitative analysis (such as sensor calibration) or precision measurement (such as laboratory stress testing)? Example: Strain gauges for load cells need to meet a sensitivity error of ±0.1%, structural health monitoring can have an error of ≤±0.5%, and laboratory precision measurement requires ≤±0.05%.
• Force direction: Is the component subjected to unidirectional force (such as cantilever beam bending), bidirectional force (such as mechanical parts in plane stress state) or multi-directional force (such as complex structural nodes)? Select uniaxial strain gauges for unidirectional force, and biaxial (right-angle, strain rosette) or multi-axial strain gauges for bidirectional/multi-directional force.
• Measurement frequency: For dynamic measurement, the frequency range of the strain signal must be clarified. The response frequency of the strain gauge must be ≥3 times the measured signal frequency (to avoid signal distortion). Example: To measure vibration strain of 50Hz, a strain gauge with a response frequency of ≥150Hz should be selected.

2. Installation and Structural Conditions

• Component surface characteristics: Is the component surface flat, curved (what is the radius of curvature) or special-shaped? Flexible strain gauges (such as foil type) are suitable for curved components, and short grid length strain gauges are required for small radius of curvature (≤10mm); types with strong substrate adhesion are suitable for rough surfaces.
• Installation space: Miniaturized strain gauges (grid length ≤2mm) are required for narrow areas of components (such as chamfers of precision parts), and medium and long grid length strain gauges can be selected for large-size components according to strain uniformity.
• Installation method: Is it room temperature bonding installation, high-temperature welding installation or temporary pasting? Weldable strain gauges are required for high-temperature scenarios, and magnetic suction type strain gauges can be used for temporary monitoring.

3. Environmental Working Conditions

• Temperature range: Clarify the normal temperature (-20℃~60℃), medium temperature (60℃~200℃), high temperature (200℃~1000℃) or low temperature (＜-20℃) range of the working environment. The temperature compensation range of the strain gauge must fully cover the actual temperature to avoid accuracy impact caused by temperature drift.
• Medium environment: Is there humidity (such as underwater, humid workshops), corrosion (such as acid-base gases, oil pollution in chemical workshops), dust or strong radiation? Waterproof strain gauges are required for humid environments, corrosion-resistant materials (such as nickel-chromium alloy grids, polyimide substrates) are required for corrosive environments, combined with sealing treatment.
• Interference factors: Is there strong electromagnetic interference (such as near motors, high-voltage equipment) or vibration impact? Strain gauges with shielding layers are required for strong interference scenarios, and types with good toughness of substrates and adhesives are required for vibration impact scenarios.

Step 2: Selection of Core Technical Parameters (Precisely Match Requirements)

After clarifying the requirements, focus on the core technical parameters of the strain gauge, which is the core link of selection and directly determines the measurement performance.

1. Core Parameters of Sensitive Grid (Determine Basic Measurement Performance)

• Resistance value: The conventional resistance value of strain gauges is 120Ω (compatible with most strain gauges, with the strongest versatility), and there are also specifications such as 350Ω and 1000Ω. High-resistance strain gauges are suitable for low-power consumption systems, and 120Ω strain gauges have the highest cost-effectiveness in industrial scenarios. During selection, ensure that the strain gauge resistance value matches the input resistance of the strain gauge (deviation ≤±5%) to avoid signal attenuation.
• Gauge factor: Indicates the proportional relationship between strain and resistance change (conventional value 2.0±0.02), which is a key parameter for calculating strain value. During selection, priority should be given to strain gauges with good gauge factor consistency (batch deviation ≤±1%), especially when multiple gauges are used in a bridge (such as a full-bridge circuit of a load cell), poor consistency will lead to increased measurement errors.
• Grid length and grid width: Grid length determines the "average measurement range" of the strain gauge. Small grid length (0.2~2mm) is suitable for measuring local strain (such as crack tips), medium grid length (3~10mm) is suitable for conventional components, and large grid length (10~100mm) is suitable for large-size components with small strain gradients. Grid width must match the force direction of the component: narrow grid width for unidirectional force, and wide grid width or strain rosette structure for bidirectional force.
• Sensitive grid material:
  • Copper-nickel alloy (Constantan): Preferred for normal temperature scenarios (-20℃~150℃), with small temperature coefficient and good stability, suitable for load cells and structural monitoring;
  • Nickel-chromium alloy (Karma): For medium and high temperature scenarios (-50℃~400℃), with high sensitivity, suitable for engine and high-temperature pipeline monitoring;
  • Platinum-iridium alloy: For high temperature scenarios (400℃~1000℃), with strong corrosion resistance, suitable for aerospace and metallurgical equipment;
  • Semiconductor materials: Extremely high sensitivity (50~100 times that of metals), but poor temperature stability, suitable for laboratory precision measurement.

2. Parameters of Substrate and Adhesive (Determine Environmental Adaptability)

• Substrate material:
  • Paper substrate: Low cost, easy to paste, suitable for normal temperature and dry environments (≤60℃), such as temporary monitoring of civil equipment;
  • Phenolic resin substrate: Temperature resistance of 120℃, good oil resistance, suitable for conventional industrial machinery scenarios;
  • Polyimide substrate: Temperature resistance of 250℃, corrosion and water resistance, suitable for chemical, humid and medium-high temperature scenarios;
  • Ceramic substrate: Temperature resistance above 1000℃, suitable for extreme environments such as high-temperature kilns and aero-engines.
• Adhesive type: Must match the substrate material and working temperature. Cyanoacrylate-based (fast-drying) adhesives are selected for normal temperature scenarios, epoxy resin-based (temperature resistance of 150℃) for medium temperature scenarios, and inorganic adhesives (temperature resistance above 500℃) for high temperature scenarios. The shear strength of the adhesive must be ≥2MPa to avoid strain gauge detachment.

3. Temperature Compensation Parameters (Determine Measurement Stability)

• Temperature compensation method:
  • Self-compensating strain gauges: By selecting sensitive grid materials, the resistance change caused by temperature is offset by the thermal expansion of the component, suitable for single-material components (such as steel, aluminum), easy to install, and preferred for industrial scenarios;
  • Compensating gauge compensation: Additional strain gauges of the same model as the working gauges are pasted on unstressed identical components, and temperature errors are offset through circuits, suitable for complex temperature fields or multi-material components.
• Temperature compensation range: Must cover the actual working temperature range. Example: In a workshop environment of -10℃~80℃, a strain gauge with a compensation range of -20℃~100℃ should be selected to reserve temperature redundancy.

4. Structure and Lead Parameters (Determine Installation and Signal Transmission)

• Strain gauge structure:
  • Uniaxial strain gauges: For unidirectional force scenarios (such as cantilever beams, tie rods), simple structure and low cost;
  • Biaxial strain gauges (right-angle strain gauges): For bidirectional force scenarios (such as plane stress components), can measure strains in two vertical directions simultaneously;
  • Strain rosettes (45°, 60°): For multi-directional force scenarios (such as structural nodes, complex parts), can calculate principal strain and principal stress direction, suitable for stress analysis.
• Lead specifications: Lead materials are usually silver-plated copper wires. PVC insulated wires are selected for normal temperature scenarios, and PTFE insulated wires for high temperature scenarios. The lead length must match the measurement distance. For long-distance transmission (10m), leads with shielding layers are required to avoid electromagnetic interference.

Step 3: Scenario Adaptation and Avoidance of Selection Mistakes

Select strain gauges according to the characteristics of different application scenarios, and avoid common selection errors to ensure the stability and reliability of the measurement system.

1. Typical Scenario Selection Examples

2. Common Selection Mistakes and Avoidance Methods

• Mistake 1: Only focusing on gauge factor and ignoring consistency—when multiple gauges are used in a bridge, even if the gauge factor of a single gauge meets the standard, large batch deviations (±1%) will cause bridge imbalance and sharply increase measurement errors. Avoidance: Require suppliers to provide gauge factor test reports for strain gauges of the same batch, and control the deviation within ±0.5%.
• Mistake 2: Mismatch between grid length and strain gradient—selecting large grid length strain gauges in local strain concentration areas such as crack tips will lead to "averaging" of measured values and failure to reflect real strain. Avoidance: Select grid length ≤2mm for areas with large strain gradients, and 5~10mm for areas with uniform strain.
• Mistake 3: Ignoring the matching between temperature compensation and component material—using steel-compensated strain gauges for aluminum components will cause serious temperature errors due to differences in thermal expansion coefficients. Avoidance: Select self-compensating strain gauges of corresponding compensation types according to the component material (steel, aluminum, copper, etc.).
• Mistake 4: "Making do" with environmental adaptability parameters—selecting ordinary paper substrate strain gauges in humid environments without sealing treatment will cause substrate failure due to moisture in a short period of time. Avoidance: Select corresponding substrate materials according to environmental grades (humid/corrosive/high-temperature), and add waterproof sealing coatings if necessary.

Step 4: Additional Notes for Practical Selection

• Bridge compatibility: When multiple gauges form a full-bridge/half-bridge circuit, ensure that the resistance value, gauge factor and temperature characteristics of the strain gauges are consistent. It is recommended to select from the same batch to reduce bridge errors.
• Calibration requirements: For strain gauges used in trade settlement (such as load cells) or precision measurement, select traceable brands to ensure that the products have passed metrological certification, facilitating subsequent system calibration.
• Matching of installation process: For curved components, confirm the bending performance of the strain gauge in advance (bendable radius of curvature ≤ component radius of curvature). For weldable strain gauges, match the corresponding welding equipment and process.
• Supplier support: Prioritize suppliers that provide technical support. Inform them of the component material, force condition and environmental parameters to obtain more accurate selection recommendations and avoid the blindness of independent selection.

Summary: Core Logic of Resistance Strain Gauge Selection

The essence of resistance strain gauge selection is a closed loop of "requirement decomposition → parameter matching → scenario verification": first decompose the four core requirements of "strain range, accuracy, environment and installation", then targetedly match key parameters such as sensitive grid, substrate and temperature compensation, and finally verify the rationality of selection through scenario examples and mistake avoidance.

If you are still unsure about the selection, you can provide the following information to the supplier: ① Component material and force type (uniaxial/bidirectional); ② Maximum strain value and accuracy requirement; ③ Working temperature and medium environment; ④ Installation space and method. The supplier can quickly lock in the suitable model.