What are the types of load cells? What is the basis for selection?

Weight sensors - sometimes referred to as "force", "scale", or "net weight" sensors, can convert effective loads into measurable output signals. The size of the output signal is proportional to the applied force or load. What types of weight sensors are there? What is the basis for selection? This article has collected and organized some materials, hoping to have great reference value for readers.

Type of weight sensor

There are mainly six types of weight sensors: photoelectric, oil pressure, capacitance, magnetic field force, magnetic field deformation, and plate ring.

1. The photoelectric weight sensor is divided into grating type and encoder type.

(1) Grating sensor

Utilizing the Moire fringes formed by gratings to convert angular velocity into photoelectric signals. The grating has two parts, one is a fixed grating, and the other is a moving grating installed on the dial shaft. According to the transmission lever system, add the object to be tested to the load table, rotate the dial shaft, push the moving grating to rotate, and move the Moir é fringes. Use Phototube, conversion circuit and digital display instrument to calculate the number of moving Moire fringes, measure the size of grating rotation angle, and then determine and read the quality of the object to be measured.

(2) Encoder type sensor

A code plate (marker board) is a transparent glass installed on the dial shaft, which contains black and white codes for a certain coding method. When the dial shaft rotates according to the force lever, the code dial will rotate from a certain angle. The photocell will receive optical signals through a code disk and convert them into electrical signals, and carry out data solutions through a circuit, ultimately displaying numbers representing the measurement quality. Photoelectric sensors are mainly used for electromechanical integrated scales.

2. Oil pressure type When the gravity P of the measured object acts, the pressure of Gear oil increases, and the degree of increase is positively related to P. Measuring the increase in pressure can determine the mass of the object to be tested. The structure of the oil pressure sensor is simple and firm, with a large detection range, but the accuracy generally does not exceed 1/100.

3. The capacitive weight sensor operates in a positive proportion relationship between the oscillation frequency f of the capacitor resonant circuit and the distance d between the electrodes. There are two polar plates, one fixed and the other movable. When the loading platform loads the object to be tested, the leaf spring bends, the distance between the two plates changes, and the oscillation frequency of the power supply also changes. The change in measurement frequency can be used to calculate the mass of the item to be tested on the load-bearing platform. Capacitive sensors have low power consumption, low cost, and an accuracy of 1/200-1/500.

4. Magnetic field force equation

The magnetic field force weight sensor adopts the principle of balancing the load and magnetic field force on the load platform. When the tested object is placed on the loading platform, one end of the lever tilts upwards; The photoelectric component detects the slope signal, amplifies it, flows into the coil and generates magnetic force, causing the lever to regain balance. Digitally convert the current that generates electromagnetic balance to determine the mass of the substance to be tested. The magnetic force sensor has high accuracy, ranging from 1/2000 to 1/60000, but the weighing range is only between tens of milligrams and 10 kilograms.

5. Magnetic field variation

When a ferromagnetic element undergoes mechanical deformation under the gravity of the measuring object, internal stress is generated, resulting in a change in permeability, thereby changing the induced voltage of the secondary coils on both sides of the ferromagnetic element (magnetic field). Measuring the change in voltage can calculate the force added to the magnetic field to determine the mass of the object being tested. The accuracy of magnetic field deformation sensors is not high, usually 1/100, suitable for large tonnage weighing work, with a weighing range of tens to tens of thousands of kilograms.

6. The plate ring type plate ring weight sensor has the characteristics of clear stress streamline distribution, high export sensitivity, overall elasticity, compact structure, stable stress, and convenient processing. At present, it still accounts for a large proportion in sensor production, and the design formula for this type of structural sensor is not yet perfect. The strain calculation of this type of elastic body is relatively complex and is generally considered as a circular elastic body for estimation in design. Especially for plate ring sensors below 1 ton, the design error is relatively large, and the nonlinear error is relatively large.

Selection basis for weight sensors

It mainly includes four aspects: sensor sensitivity, sensor accuracy, sensor stability, number of sensors, and range.

1. The higher the sensitivity, the better. Only when the sensitivity is high can more accurate data be obtained when detecting the weight of an object.

However, the greater the external impact on the weight sensor, the more external noise will interfere with the sensor's judgment. Therefore, there are certain requirements for the anti noise performance of sensors, and the impact of noise on sensors should be minimized as much as possible.

2. Precision weight sensors require high precision, which is a crucial link in weighing equipment. The higher the accuracy of weight sensors, the higher the price.

However, for the regulation of accuracy, it is only necessary to reach a high level that meets the export regulations of the weighing equipment's instruments, and there is no need to choose too high to avoid unnecessary costs.

3. Stability refers to the ability of a sensor to continue to operate normally after long-term use. Sensors with high stability have a longer service life. In addition to the quality of the weight sensor, there is also the working atmosphere of the weight sensor. A good weight sensor environment has little impact on it.

Therefore, when purchasing a weight sensor, pay attention to its applicable environment, choose a weight sensor based on the actual environment, and choose a suitable weight sensor to reduce the impact of the environment on the weight sensor, which is beneficial for improving the service life of the weight sensor. For example, in flammable and explosive environments, it is necessary to use weight sensors with explosion-proof functions.

4. Number and range of sensors

The number and range of sensors for different purposes vary. The actual quantity and range shall be determined according to the weight and type of specific test objects. Generally speaking, the specific weight of the weighed object should be less than 70%, and the consumption of the symmetrical weight sensor will be smaller, which is beneficial for extending its service life.

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