Weighing sensors - sometimes referred to as "force", "weighing" or "weight" sensors, can convert the load acting on them into measurable output signals. The size of the output signal is proportional to the applied force or load. What are the types of weighing sensors? What is the selection basis? This article has collected and organized some information, hoping to have a significant reference for readers.
There are six main types of weighing sensors, namely photoelectric, hydraulic, capacitive, electromagnetic force, magnetic pole change, and plate ring.
1. Photoelectric type
There are two types of photoelectric weighing sensors: grating type and encoder type.
(1) Grating sensor
Using the Moir é fringes formed by gratings to convert angular displacement into photoelectric signals. There are two gratings, one is a fixed grating and the other is a moving grating installed on the dial shaft. The measured object added to the load-bearing platform rotates the dial shaft through a force transmission lever system, driving the moving grating to rotate and causing the Moir é fringes to move accordingly. By using photoelectric tubes, conversion circuits, and display instruments, the number of shifted Moir é fringes can be calculated, and the rotation angle of the grating can be measured to determine and read out the mass of the measured object.
(2) Encoder type sensor
A code plate (symbol board) is a transparent glass mounted on the dial shaft, with black and white codes programmed according to a certain coding method. When the measured object added to the load-bearing platform rotates the dial shaft through a force transmission lever, the dial rotates at a certain angle. The photovoltaic cell will receive light signals through the encoder and convert them into electrical signals, which will be digitally processed by the circuit. Finally, the number representing the measured quality will be displayed on the display. Optoelectronic sensors were mainly used in electromechanical integrated scales.
2. Hydraulic type
When subjected to the gravity of the measured object P, the pressure of the hydraulic oil increases, and the degree of increase is proportional to P. By measuring the increase in pressure, the mass of the measured object can be determined. Hydraulic sensors have a simple and sturdy structure, a large measurement range, but their accuracy generally does not exceed 1/100.
3. Capacitive type
The capacitive weighing sensor works by utilizing the proportional relationship between the oscillation frequency f of the capacitor oscillation circuit and the distance d between the electrode plates. There are two plates, one fixed and the other movable. When loading the tested object on the load-bearing platform, the plate spring flexes, the distance between the two plates changes, and the oscillation frequency of the circuit also changes accordingly. By measuring the change in frequency, the mass of the object being measured on the load-bearing platform can be determined. Capacitive sensors have low power consumption, low cost, and accuracy ranging from 1/200 to 1/500.
4. Electromagnetic force type
The electromagnetic force type weighing sensor works by balancing the load on the load-bearing platform with the electromagnetic force. When there is a measured object placed on the load-bearing platform, one end of the lever tilts upwards; The photoelectric device detects a tilt signal, which is amplified and flows into the coil to generate electromagnetic force, restoring the lever to a balanced state. The mass of the measured object can be determined by digital conversion of the current that generates electromagnetic balance force. Electromagnetic force sensors have high accuracy, ranging from 1/2000 to 1/60000, but their weighing range is only between a few tens of milligrams to 10 kilograms.
5. Magnetic pole variation
When a ferromagnetic element undergoes mechanical deformation under the influence of the measured object's gravity, internal stress is generated and causes a change in permeability, resulting in a change in the induced voltage of the secondary coils on both sides of the ferromagnetic element (magnetic pole). By measuring the change in voltage, the force applied to the magnetic pole can be calculated, thereby determining the mass of the object being measured. The accuracy of magnetic pole shaped sensors is not high, usually 1/100, suitable for weighing large tonnage work, with a weighing range of tens to tens of thousands of kilograms.
6. Plate ring type
The structure of the plate ring weighing sensor has the advantages of clear stress streamline distribution, high output sensitivity, elastic body as a whole, simple structure, stable stress state, and easy 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 very complete. The strain calculation of this type of elastic body is relatively complex, and it is generally considered as a ring shaped elastic body for estimation during design. Especially for plate ring sensors with a range of 1T and below, the design calculation error is greater, and there may be significant nonlinear errors.
Selection criteria for weighing sensors
It mainly includes four aspects, namely sensor sensitivity, sensor accuracy, sensor stability, as well as the number and range of sensors.
1. Sensitivity
The higher the sensitivity, the better. Only with higher sensitivity can more accurate data be obtained when measuring the weight of an object.
However, the higher the sensitivity, the greater the impact of external symmetrical weight sensors, and external noise can interfere with the sensor's judgment. So, 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. Accuracy
The precision requirement for weighing sensors is very high, which is a very important part of the weighing system. The higher the accuracy of weighing sensors, the higher their price.
However, for accuracy requirements, as long as the instrument output level that meets the weighing system requirements is slightly higher, there is no need to choose too high to avoid unnecessary expenses.
3. Stability
Stability refers to the ability of a sensor to continue working normally after prolonged use, and a sensor with high stability has a longer lifespan. The factors that affect the stability of sensors include not only the quality of the weighing sensor, but also the working environment of the weighing sensor. A good weighing sensor environment has a relatively small impact on it.
So, when choosing a weighing sensor, pay attention to its suitable environment and choose the weighing sensor according to the specific environment. Choosing the correct weighing sensor can reduce the impact of environmental symmetry on the weighing sensor and help extend its service life. For example, in flammable and explosive environments, it is necessary to choose weighing sensors with explosion-proof functions.
4. Number and range of sensors
The number and range of sensors for different purposes vary, and the specific number and range selection should be determined based on the weight and type of object being measured. The actual weight of the object being weighed should generally be below 70%, and the loss of the symmetrical weight sensor will be smaller, which is beneficial for extending its service life.
