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Factors affecting the stability of force transducer May 09, 2022

There are many factors affecting the stability of force sensor, which can be summarized as follows:

1. Structure of force sensor

The design of the elastic element, shell, diaphragm and upper pressure head and lower pressure pad of the force sensor must ensure that the performance fluctuation does not occur in the structure after loading, or the performance fluctuation is very small. Therefore, when designing the force sensor, the stress in the strain area should be single and uniform as far as possible. The patch site is best flat; In the structure to ensure a certain degree of anti-eccentric load and lateral load capacity; The mounting force is far away from the strain zone, and the displacement of the load bearing point should be avoided during measurement. Although force sensors are manufactured by assembly, they are designed as a whole structure to ensure the best technical performance and long-term stability.

2. Metal materials for elastic components

The metal material of elastic element plays a key role in the comprehensive performance and long-term stability of force transducer. Materials with high strength limit and elastic limit, good time and temperature stability of elastic modulus, small elastic hysteresis, and low residual stress caused by mechanical processing and heat treatment should be selected. Data show that: as long as the plasticity of the material after quenching is good, its residual stress after mechanical processing and heat treatment is small. Special attention should be paid to the stability of elastic modulus with time, and the elastic mold of the material should not change during the service life of the force sensor.

3. Mechanical processing and heat treatment process

In the machining process of elastic components, due to the uneven surface deformation, the larger the cutting amount, the larger the residual stress, grinding residual stress is the largest. Reasonable processing technology and appropriate cutting dosage should be formulated. In the process of heat treatment, the residual stress in the core and the surface is different because of the uneven cooling temperature and the phase transformation of metal materials. The tensile stress is in the core and the compressive stress is in the surface. A tempering process must be used to produce stress in the opposite direction, which is offset with the residual stress to reduce the influence of the residual stress.

4. Resistance strain gauge and strain binder

The resistance strain gauge should have the best performance, requiring good sensitivity coefficient stability, small thermal output, mechanical hysteresis and creep, fatigue life up to 108 when strain variable is 1000×10 -- 6, small deviation of resistance value, good uniformity of batch quality, etc. Strain binder should have high bond strength and shear strength. The elastic modulus is large and stable; Good electrical insulation performance; Having the same or similar coefficient of thermal expansion as the elastic element; Small creep and hysteresis; When curing, the volume of adhesive layer shrinks. Adhesive resistance strain timing must strictly control the thickness of the adhesive layer, because the adhesive strength decreases with the increase of the thickness of the adhesive layer. This is because the thin adhesive layer needs greater stress to deform, it is not easy to produce flow and creep, the internal stress on the interface is very small, the probability of bubbles and defects is relatively small, the strain transfer performance is good, as long as the protection and sealing is reasonable can achieve a higher level of stability.

5. Manufacturing process

The working principle and overall structure of strain type force sensor determine that some processes must be manually operated in the production process, and human factors have a great impact on the quality of force sensor. Therefore, it is necessary to formulate a scientific and reasonable and repeatable manufacturing process, and to increase the automatic or semi-automatic process controlled by computer, so as to reduce the influence of human factors on product quality as much as possible.

6. Circuit compensation and adjustment

Strain type force transducer assembly manufacturing, SMT team was formed after bridge products, due to internal inevitably produce some defects and the influence of the external environment condition, some performance index of the strain sensors can not meet the design requirements, therefore must undertake various circuit compensation and adjustment, improve the stability of the force transducer itself and the stability of the external environment condition. Perfect and fine circuit compensation process is an important link to improve the stability of load cell.

7. Protection and sealing

Protection and sealing are the key process in the process of force sensor manufacturing, and the fundamental guarantee for force sensor to bear the influence of objective environment and induction environment and work stably and reliably. If the protective seal is not good, the resistance strain gauge pasted on the elastic element and the strain adhesive adhesive layer will absorb moisture in the air and produce plasticizing, resulting in the decline of bond strength and stiffness, causing zero drift and irregular changes in output, until the force sensor fails. Therefore, the effective protective seal is the fundamental guarantee of the long-term stable work of the force sensor, otherwise it will make all the technological achievements wasted.

8. Stability treatment (artificial aging test)

The most important way to improve the stability of force sensor is to take various technical measures and technological means to simulate the conditions of use and carry out effective manual sophisticated test, so as to release the residual stress as much as possible to minimize the fluctuation of its performance.

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