Working principle of weighing instrument and fault identification method

2022-12-30 11:21:16

The weighing controller is one of the important components of the weighing system. It converts the weak signal (mV level) output by the load cell into a readable weight signal through amplification and conversion; it can also be converted and output according to requirements. Various defined industry standard signals are used by other equipment.

The weighing system sometimes has problems of one kind or another during use. Below we recommend some conventional fault identification methods, hoping to help everyone.

Working principle of weighing instrument:

The electronic weighing system is generally composed of a scale body, a load cell, a junction box, and a weighing display instrument. The working principle is shown in the figure below. After summarizing, it enters the instrument (if there is only one sensor in the weighing system, the junction box is not needed for signal summarization), the instrument will amplify, filter and A/D the weak weight signal (mV level), and then pass it through the digital processing, and display the weighing signal on the digital screen; in addition, for the system that needs to connect the signal to PLC, touch screen, computer, printer and other equipment, the weighing instrument will also output different signals through the interface circuit, and the weight data and control The signal is sent to other system equipment; in order to meet the versatility and convenience of the instrument, the weighing instrument will generally add a setting/calibration function, a zero-setting tare function, a zero-point tracking function, and a preset point output function.

The method of weighing instrument fault identification:

Due to the various failure phenomena of the weighing instrument, there are also many reasons for the failure. Therefore, to troubleshoot the weighing instrument, you must first be familiar with the working principle of the weighing instrument and the functions and judgment methods of each component. Check the source of the fault one by one through the relevant components of the fault phenomenon, so as to determine the location of the fault. The following introduces several common methods for you to use when troubleshooting. one

1. Observation method

“Observation method” is a method of direct inspection through human senses to find the cause of the fault. There are usually several methods of eye observation, ear hearing, hand touch, and nose smell:

Visual observation is to observe whether the wiring between the instrument and the sensor (junction box) is normal, whether the power supply and control lines are connected normally, and whether there are disconnections, bumps, short circuits, etc.? And observe whether there is burnt inside the meter, whether there is water ingress, whether the insurance is disconnected, etc.?

Listening, that is, listening carefully to see if there is any abnormal sound inside the instrument?

Touch by hand, that is, touch the temperature of transformers, wire packs, filter capacitors and other components?

Sniffing is to smell whether there is a burning smell in the machine.

Two, plug method

The “plug method” is to unplug a certain component and then plug in the analog component to see where the fault is and find the cause of the fault.

For example: the weighing instrument shows unstable, unplug the connection cable between the junction box (load cell) and the instrument, and connect the simulator, if the meter reading returns to stability, it indicates that the problem lies in the junction box or the sensor. Otherwise, find the problem from the instrument.

3. Alternative method

The “substitution method” is to use normal components, circuit boards, etc. to replace the parts with suspected faults, and whether they return to normal after replacement, so as to find out the cause of the fault.

4. Comparative method

The “comparison method” is to use multimeters, oscilloscopes and other instruments to measure the voltage, resistance, waveform and other data of components with suspected faults, and compare them with normal values to determine whether the components are faulty.

5. Static characteristic measurement method (measurement method)

“Measurement method” is a method to measure the level of each point in a certain state of the instrument with a multimeter, and then analyze and judge the cause of the fault according to the logic principle.

6. Code Diagnosis

“Code diagnosis method” is a judgment method to find out the problem through the error code obtained by the self-diagnosis of the instrument.


Don’t panic when encountering problems with the weighing system, first avoid blindness, and don’t look for reasons without reason. The cause of the failure should be judged from the weighing instrument and the whole principle of the weighing system, and the scope of the parts that may cause the problem should be narrowed down step by step, and checked one by one, and finally the fault can be quickly and accurately eliminated.


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