What Is a Load Cell?

A load cell is actually a device that converts a mass signal into a measurable electrical signal output. When using sensors, we must first consider the actual working environment where the sensors are located. This is important for the correct selection of load cells. It is related to the normal operation of the sensor and its safety and service life, as well as the reliability and safety of the entire weighing instrument. Sex. In terms of the basic concepts and evaluation methods of the main technical indicators of the load cell, there is a qualitative difference between the old and the new national standards. There are several types of S type, cantilever type, spoke type, plate ring type, capsule type, bridge type, column type and so on.

The old national standard considers two types of sensors: "weighing" and "force measurement", which have completely different application and use environment conditions. It does not distinguish between test and evaluation methods. The old national standard has a total of 21 indicators, all of which are tested at room temperature; and the largest error among the six indicators of non-linearity, hysteresis error, repeatability error, creep, zero temperature additional error, and rated output temperature additional error is used to determine the weighing sensor

According to the conversion method, the load cell is divided into 8 types: photoelectric type, hydraulic type, electromagnetic force type, capacitive type, magnetic pole change type, vibration type, gyro ceremony, resistance strain type, etc. The resistance strain type is the most widely used.

Resistance strain gauge load cell ^[3]

The performance of the load cell depends largely on the choice of manufacturing materials. Load cell materials include the following parts: strain gauge material, elastomer material ^[4]

In addition, the load cell's sensitivity, maximum number of divisions, minimum

Load cell ^[7]

1. Load cell ^[8]

During the measurement, the load on the elastic body of the load cell will cause plastic deformation.

Disadvantage 1: high output impedance and poor load capacity

The capacity of a capacitive load cell is not easy to be made very large due to the limitation of the electrode's geometric size, and it is generally tens to hundreds of microfarads, or even only a few microfarads. Therefore, the capacitive load cell has a high output impedance, so the load capacity is poor, and it is easy to be unstable due to the influence of external interference. Proper shielding measures must be taken to inconvenience the design and use. Large capacitive reactance also requires the resistance of the sensor's insulation part to be extremely high, otherwise the insulation part will act as a bypass resistance and affect the performance of the instrument. For this reason, special attention must be paid to the surrounding environment such as temperature and cleanliness. If high-frequency power supply is used, the output impedance of the capacitive load cell can be reduced, but the high-frequency amplification, the sensor is far more complicated than the low-frequency, and the parasitic capacitance has a large impact, and it is not easy to ensure the stability of the work.

Disadvantage 2: Non-linear output characteristics

The output characteristics of capacitive load cells are non-linear. Although the differential type is used to improve them, it is impossible to completely eliminate them. The output characteristics of other types of capacitive sensors are linear only when the edge effects of the electric field are ignored. Otherwise, the additional capacitance generated by the edge effect will be directly superimposed on the sensor capacitor, making the output characteristics non-linear.

Disadvantage 3: Large influence of parasitic capacitance

The initial capacity of a capacitive load cell is small, and the so-called parasitic capacitance, such as the lead capacitance connecting the sensor and the electronic circuit, the stray capacitance of the electronic circuit, and the capacitance formed by the inner plate of the sensor and the surrounding conductor, is large, which not only reduces the sensor Sensitivity, and these capacitors often change randomly, which will make the instrument work very unstable and affect the measurement accuracy. Therefore, there are strict requirements on the selection, installation and connection of cables. For example, high-frequency wires with good shielding properties and small distributed capacitance are used as leads. The leads are thick and short. The stray capacitance of the instrument must be small and stable. Otherwise, high measurement accuracy cannot be guaranteed.

It should be pointed out that with the rapid development of materials, processes, electronic technology, especially integrated technology, the advantages of capacitive load cells have been carried forward and the disadvantages have been continuously overcome. Capacitive sensors are gradually becoming a kind of high-sensitivity, high-precision sensors that have great development prospects in dynamic, low-voltage, and some special measurements.

1. Load cell ^[9]

Model: STC-100Kg (model specifications)

Cap: 100Kg (range)

Date: 2005/01/14 (production date)

S / N: X02274 (factory number)

FSO: 2.9981 mV / V (sensitivity)

Recommended Excitation: 10V AC / DC (recommended excitation voltage)

Maximum Excitation: 15V AC / DC

Output at Rated Load: 2.9981 mV / V (rated load output)

Non Linearity: <0.020%

Hysteresis: <0.020% (lag)

Creep (30 minutes): 0.029%

Non Repeatability: <0.01%

Zero Retum (30 minutes): 0.030% (30 minutes zero drift)

Temp. Effect / on Span: <0.0015% (The effect of temperature change of 1 on span)

Temp. Effect / on Zero: <0.0026% (The effect of temperature change of 1 on the zero point)

Compensated Temp.Range: -10 to 40 (temperature compensation range)

Operating Temp.Range: -20 to 60 (operating temperature range)

Zero Balance: ± 1% (zero balance)

Input Resistance: 380 ± 5 (input resistance)

Output Resistance: 350 ± 3

Insulation Resistance (50VDC):> 5000M (insulation resistance)

Deflecion at Rated Load: Nil (zero)

Safe Overload: 150% (allow overload)

Ultimate Overload: 300%

9. Specific judgment method of load cell lead function

Because the colors of sensor leads from different manufacturers are different, the function of the leads cannot be judged by specific colors.

With the advent of the new technological revolution, the world has begun to enter the information age. In the process of using information, the first thing to be solved is to obtain accurate and reliable information, and sensors are the main ways and means to obtain information in the fields of nature and production. In modern industrial production, especially in automated production processes, various Load cell ^[10]

In order to obtain information from the outside world, people must rely on sensory organs, but their own sensory organs alone are not enough to study natural phenomena and laws and their production activities. To adapt to this situation, sensors are needed Therefore, it can be said that the sensor is an extension of human features, also known as electric features.