The weighing platform and the force transmission mechanism accurately transfer the weight of the object to the weighing sensor; The weighing sensor located between the weighing platform and the foundation converts the weight of the object to millivolt electrical signals according to a specific functional relationship, and then outputs to the weighing instrument. After processing, the meter directly displays the weight data of the object being weighed. Through the combination of instrument and industrial computer, the measured data can be processed and various operations can be completed according to user requirements. The weighing system is composed of three parts: display instrument, sensor and scale body. Among them, the scale body is called the mechanical transfer system between the material and the instrument.

1) The number and range of sensors

The selection of its number is based on the use of electronic weighing instrument, the number of points needed to support the scale body. In general, the scale body has a few support points on the selection of several sensors % range selection can be based on the weighing value of the scale, choose the number of sensors, the weight of the scale body, can produce partial load and dynamic load factors comprehensive consideration decision. In general, the closer the range of the sensor is to the load assigned to each sensor, the more accurate the weighing will be. However, in the actual use, due to the load added to the sensor, in addition to the object, there are weight, tare weight, partial load and vibration and impact load, therefore, the selection of sensors, to consider many aspects of the factor. An empirical formula verified by extensive experiments is given below. Where: C is the rated range of a single sensor; W to balance Body weight; Wmax is the maximum value of the net weight of the object; N is the number of support points used by the scale body,K0 is the coefficient of insurance, generally taken between 1.2 and 1.3; K1 is the impact coefficient; K3 is the gravity shift coefficient of the scale body; K3 where is the wind pressure coefficient.

2 Sensor selection and field debugging

Selection and field debugging, mainly including the following content of scale design, sensor selection, calibration and Angle difference adjustment, fault detection and processing, weighing instrument selection.

1.1 Design of scale body

The design of the scale body needs to consider the handling capacity of the weighing system, the frame, the number of sensors used and the layout. The company's weighing system is mainly for automatic batting, the scale body for bucket suspension, sensors have /, a horizontal direction, equilateral triangle layout.

When the scale body is installed, the verticality of the weighing sensor should be ensured, and its deviation cannot exceed /0. The upper and lower connection bolts of the weighing sensor should adopt universal connection mechanism that can automatically adjust the force direction, so as to keep the vertical force when the position of the scale body changes, so as to avoid being damaged.

1.2 Selection of weighing sensor

The sensitivity, degree and test degree of the weighing sensor should be considered when selecting it.

1) Use environment

In fact, a weight sensor is an output device that converts a mass signal into a measurable electrical signal. When using a sensor, the actual working environment should be considered first. This is crucial for the correct selection of sensors. In general, the high temperature environment will make the coating material of the sensor melt, solder joint melting, structural changes in the stress of the elastomer, etc. Dust, humidity will make the sensor short-circuit; A strong corrosive environment may damage the sensor elastomer or cause a short circuit. The electromagnetic field may interfere with the sensor output.

3) The range of use of sensors

Type selection mainly depends on the type of weighing and installation space. For manufacturers, it generally stipulates the force of the sensor, performance indicators, installation form, structure form and elastomer material. Such as aluminum alloy cantilever beam sensor, suitable for electronic valuation scale, platform scale, case scale, etc.; Steel cantilever sensor is suitable for electronic belt scale, sorting scale, etc. Steel bridge sensor, suitable for rail scale, truck scale, etc.; Column type sensor is suitable for truck scale, dynamic rail scale and large tonnage hopper scale.

4) Grade selection of accuracy. The accuracy level includes nonlinearity, creep, repeatability, hysteresis, sensitivity and other indicators of the sensor. When selecting, we should not blindly pursue high grade sensors, but should consider the accuracy level and cost of electronic scale.

1.3 Calibration and Angle difference adjustment

Taking electronic crane scale as an example, Angle difference adjustment is a very important step. For the scale with multiple bearing points, a quad code should be used to observe the instrument display after each bearing point. If the display data is the same, the calibration operation can be carried out; If the results are different, adjust as needed. Empirically, it is usually to lower the display weight. The scale body adjustment described above can also be adjusted in the sensor junction box. There are two types of arch bridge signal regulation and output signal regulation. Theoretically speaking, the Angle difference is artificially generated, and the offset load is mainly caused by the following factors: the design defect of the scale body, the improper selection of the weighing sensor and the wrong installation of the scale body. For weighing calibration, there are two methods: repeated correction method and calculation method.

1) Repeated correction method steps.

Peel and zero. In the ingredients scale under the empty scale, with the scale put the channel zero adjustment potentiometer, so that the balance value display near zero, and write down the display value, as the zero value. Sensitivity coarse adjustment. Add the batching value on the batching scale, evenly put it in the scale body, adjust the sensitivity potentiometer, so that the scale display value is equal to the maximum value; Dispelling weight & AMP; Zero value. Remove the dispel code and repeat the previous two steps Fine adjustment of sensitivity. The empty scale is set to zero and the zero value is recorded. The addition code is evenly placed in the scale body to the value of the ingredients, adjust the sensitivity potentiometer, so that the display value is equal to; Remove the weight of ten zero points. Observe and record a number of intermediate values and zero values, calculate the error, if necessary, you can repeat the fine adjustment step.

2) Calculation method steps, using the following formula.

Type; X is the display value to be adjusted after removing the code; X1 is the total weight of the removed code; X2 is the actual display value after removing the code; X3 is the tare weight display value before removing the code. Under the condition of empty scale, adjust the zero potentiometer, so that the tare weight display value is greater than zero, write down the display value, X3. Add the code on the scale (evenly placed in the scale body) to the maximum value of the ingredients, and get X1. Observe the record display value, get X2. Calculate X by X1, X2 and X3 generation formula, adjust the sensitivity potentiometer to display X value, that is, complete sensitivity adjustment. Add and subtract remove code, observe and record a number of intermediate values, calculate intermediate accuracy. 2 Sensor fault detection and elimination For any kind of electronic scale, its fault handling should follow such steps; Observe the fault observation bucket analysis of the cause of the fault detection to provide a basis for fault judgment or to verify the judgment results to repair or replace. The following methods can be selected according to the actual situation; Visual method, alternative method, comparative method, plug and pull method and code diagnostic method.

1) Impedance discrimination method; Remove the two output wires and input wires of the sensor one by one, and use a multimeter to test the output and input impedance and the insulation resistance between each core wire of the signal cable and the shielding layer. If the test result does not reach the value on the certificate, it can be judged as the fault sensor 0

2) Signal output judgment; If the impedance method can not judge the quality of the sensor, this method can be used for further inspection. First, the instrument is energized, the output line of the sensor is removed, and the Mv output value is measured with a multimeter under the empty scale.

Assuming that the rated excitation voltage is U (v), the sensitivity of the sensor is M(Mv/V), and the rated load of the sensor is F(kg), the output of each sensor is U×. M× K÷ F of Mv. If the output value of a sensor exceeds the calculated value too much or is unstable, it can be judged that the sensor is faulty or damaged. 3. Selection of weighing instrument Weighing instrument, generally composed of analog circuit and digital circuit two parts.

The analog circuit includes power supply, preamplifier, filter, A/D; Conversion, etc.; Digital circuits include processors, memory, keyboards and monitors. The simple and effective method of instrument fault diagnosis is to use substitution method. After the damaged parts are confirmed by testing, the spare parts can be directly replaced, so that the system can be put into use faster.

When multiple weighing sensors are used to form a weighing system, it is necessary to consider what kind of working mode it adopts, and the technical parameters of the weighing sensors must match the parameters of the instrument. Taking the current weighing system in parallel operation as an example, it requires that the actual current of the system must be less than the arch bridge current of the weighing instrument.

This can be judged by calculating the input and output impedance of the sensor group and matching it with the technical data of the instrument.