How to choose and use the load cell sensors?
The load cell is actually a device that converts the quality signal into a measurable electrical signal output. When using a sensor, we must first consider the actual working environment in which the sensor is located. This is very important for the correct selection of the sensor. It is related to whether the sensor can work normally, its safety and service life, and even the reliability and safety of the entire weighing instrument.
The environmental impact on the sensor mainly has the following aspects:
(1) The high temperature environment causes problems such as the melting of the coating material, the opening of the solder joint, and the structural change of the stress in the elastomer. For sensors that work in high temperature environments, high temperature resistant sensors are often used; in addition, heat insulation, water cooling or air cooling must be added.
(2) The influence of dust and humidity on the sensor caused by short circuit. In this environmental condition, a sensor with high airtightness should be selected. Different sensors have different sealing methods, and their airtightness is very different.
Common seals include sealant filling or coating; rubber gasket mechanical fastening seal; welding (argon arc welding, plasma beam welding) and vacuum nitrogen filling seal.
From the perspective of sealing effect, welding and sealing is the best, and filling and coating sealant is poor in quantity. For sensors that work in a clean and dry indoor environment, you can choose a glue-sealed sensor. For some sensors that work in a humid and dusty environment, you should choose a diaphragm heat seal or a diaphragm welding seal, and Vacuum nitrogen filled sensor.
(3) In a highly corrosive environment, such as damp or acid causing damage to the elastic body or short circuit of the sensor, the outer surface should be sprayed or stainless steel cover, with good corrosion resistance and good airtightness sensor.
(4) The influence of electromagnetic field on sensor output disturbance signal. In this case, the shielding of the sensor should be strictly checked to see if it has good electromagnetic resistance.
(5) Flammable and explosive not only cause thorough damage to the sensor, but also pose a great threat to other equipment and personal safety. Therefore, sensors that work in flammable and explosive environments have higher requirements for explosion-proof performance: explosion-proof sensors must be selected in flammable and explosive environments. The sealed housing of such sensors must not only consider its airtightness, but also Consider the explosion-proof strength, as well as the waterproof, moisture-proof, and explosion-proof properties of the cable leads.
Secondly, the selection of the number and range of sensors.
The selection of the number of sensors is based on the purpose of the electronic weighing instrument and the number of points that the scale needs to support (the number of support points should be determined according to the principle that the geometric center of gravity of the scale body coincides with the actual center of gravity). Generally speaking, if the scale has several supporting points, several sensors are used. However, for some special scales such as electronic hook scales, only one sensor can be used. For some electromechanical scales, the sensor should be selected according to the actual situation. Number.
The selection of the sensor range can be determined based on the comprehensive evaluation of factors such as the maximum weighing value of the scale, the number of selected sensors, the weight of the scale body, the maximum possible partial load and the dynamic load. Generally speaking, the closer the range of the sensor is to the load assigned to each sensor, the higher the accuracy of its weighing. However, in actual use, in addition to the object being weighed, the load on the sensor also contains the weight, tare, eccentric load, and vibration shock. Therefore, when selecting the sensor range, many factors must be considered to ensure The safety and longevity of the sensor.
The calculation formula of the sensor range is determined after a large number of experiments after fully considering the various factors affecting the scale body.
The formula is as follows:
C=K0K1K2K3 (Wmax+W)/N
C—the rated range of a single sensor;
W—the self-weight of the scale;
Wmax—the maximum value of the net weight of the object to be weighed;
N—the number of support points used by the scale;
K-0—the insurance factor, which is generally between 1.2 and 1.3 Between people;
K-1—impact coefficient;
K-2—gravity deviation coefficient of the scale body;
K-3—wind pressure coefficient.
According to experience, the sensor should generally work within 30% to 70% of its range. However, for some weighing instruments that have a large impact during use, such as dynamic railroad scales, dynamic truck scales, steel scales, etc., when selecting sensors, Generally, it is necessary to expand its range to make the sensor work within 20% to 30% of its range and increase the weighing reserve of the sensor to ensure the safety and life of the sensor.
Again, we must consider the scope of application of various types of sensors.
The choice of sensor type mainly depends on the weighing type and installation space, to ensure proper installation, safe and reliable weighing; on the other hand, the manufacturer's recommendations must be considered. Manufacturers generally stipulate the scope of application of the sensor according to the force condition, performance index, installation form, structural type, and material of the elastic body. For example, aluminum cantilever beam sensors are suitable for price calculation scales, platform scales, and case scales; steel Cantilever beam sensor is suitable for hopper scales, electronic belt scales, sorting scales, etc.; steel bridge sensors are suitable for rail scales, truck scales, crane scales, etc.; column sensors are suitable for truck scales, dynamic rail scales, and large-tonnage hopper scales Wait.
Finally, the sensor accuracy level must be selected.
The accuracy level of the sensor includes the sensor's non-linear, creep, creep recovery, hysteresis, repeatability, sensitivity and other technical indicators. When selecting sensors, don't simply pursue high-level sensors, but consider meeting the accuracy requirements of electronic scales and the cost.
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