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Strain gauge bonding technology and protection technology

Data: 2016-7-7 View: 2202

Zero drift
 
We know that the easiest and most difficult to control zero strain drift in strain gage applications. Zero drift is affected by various factors. We will analyze in detail below.
 
(1) the impact of insulation resistance
Insulation resistance is an important indicator of the electrical properties of the strain gauge, the size of its performance is the most direct strain gauge zero drift. The so-called insulation resistance is the resistance between the strain gage sensitive grid and the measured member or elastomer. If the insulation strength is lower or lower, there will be leakage current between the sensitive grid and the components or between the elastic members, which will affect the strain Zero stability of the meter, that is drift. So what are the factors that cause this problem? How to solve it is something we are more concerned about.
a. Strain gauge is not cleaned after cleaning or cleaning is not clean, causing the dielectric strength decreased. The main is the presence of flux welding, and flux is generally good activity, good wetting material conducive to the solder and the solder joint, but it is often an ionic object, if not cleaned or not, the cation will Migration, causing the dielectric strength can not meet the requirements.
b. strain gauge soldering due to iron leakage or temperature is too high, the time is too long, causing strain to say base breakdown, resulting in decreased dielectric strength. In response to this problem, the use of iron must be tested to ensure that the welding end of the dielectric strength, in order to avoid breakdown or cause harm to life; welding temperature to ensure that the temperature can not exceed 250 ° C, short welding several times, Avoid base alienation breakdown.
c. The strain gauge damp dielectric strength decreased. This phenomenon is mainly due to the use of strain gauges when the protection is not good or the use of environmental humidity is too large, this drift is more similar to a, so in the process of application, the environment must be controlled within 60% humidity; in the application Strain gauges must be protected against moisture ingress, affecting the stability of the strain gauge.
d. strain gauge pierced, resulting in decreased dielectric strength. This problem is mainly in the patch or group bridge formed in the process, if there are hard objects to hold strain gages or components, surface burr, scratches and other scratches Strain gauge or soldering tip too sharp piercing strain gauge .
 
(2) patch defects caused by the impact
This problem is mainly formed in the patch process.
a. After the patch there is a void phenomenon, resulting strain gauge zero drift. This phenomenon is mainly manifested in the light inspection, you will find the back of the strain gauge with a sense of foreign body, hair, while using soft objects on the strain gauge to exert force, the strain gauge resistance will change, and removed, The resistance will recover soon. And due to the void, resulting in strain gages when the local heat increases heat drift caused.
b. Patch when the adhesive layer is too thick or glued glue after the patch, drum kits, resulting in strain gauge zero drift. This phenomenon is mainly manifested in the back of the strain gauge has a sense of hierarchy, gum residue around more, leaving glue after curing prism, Peng package. The main reason for this phenomenon is the component surface cleaning is not clean with particles or glue uneven brushing or glue too much.
 
(3) strain gauge floating gate or sealing layer off, resulting in strain gauge zero drift
 a. Strain gauge floating gate. Mainly for the side light observation strain gauge, and found that the surface of the strain gauge needle-like bright spots or sensitive microscope with a microscope distortion phenomenon. Caused by this problem may be excessive humidity or cleaning solvent water content is too large, resulting in strain gauge due to moisture.
b. Sealing layer off. The main performance of the sealing layer has some or all off, causing the main reason for this problem is the sealing layer and the sensitivity of the grid caused by insufficient adhesion, causing the uneven sensitivity of heat dissipation caused.
 
2. Patch abnormal resistance
 
Under normal circumstances, the strain gauge after its resistance will change slightly or unchanged, but often have users reflect the strain gauge resistance has undergone great changes in the factors that cause this problem are the following:
 
(1) pressure curing pressure is too large, resulting in resistance after the patch abnormalities, appropriate to reduce the pressure, the user is recommended to add pressure range 0.1Mpa - 0.3Mpa.
 
(2) Pressurized pressure is not uniform, causing strain gauge sensitive grid deformation caused by abnormal resistance, the problem is not standardized pressurized fixture, the strain gauge caused by uneven force.
 
(3) tooling design radius of curvature does not match with the components, resulting in strain gauge deformation or bulging and abnormal resistance.
 
(4) The use of a period of time, the abnormal resistance. The main problem is the existence of a bubble inside the strain gauge or individual empty or welding there are unreliable factors exist.
 
3. Patch surface defects
 
It can be seen from the foregoing that the main defects of the patch are empty, drum kits, uneven rubber layer, glue layer is too thick, glue edge, pressure pit, deformation, etc., Can be used. In response to these defects, we must conduct a visual inspection after the patch, pick out defective, to ensure the quality of the patch. At the same time to deal with resistance, insulation resistance checks, so as not to waste after the procedure.

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