Prevent Cheating Measures for Weighbridge with Analog/Digital Load Cell

In recent years, weighing cheating occurs in the measurement of weighbridge in many areas. Driven by economic interests, some outlaws take various cheating ways in weighing the gross weight and tare of vehicles, which may lead to a measurement deviation of several hundred kilograms to several tons, thus benefiting from it. This paper mainly analyzes the cheating ways of weighbridge, puts forward the methods of on-site inspection and suggests how to prevent and avoid cheating.
I. Types of weighbridge
A weighbridge with an analog load cell transmits the output signal of the analog load cell to the weighing controller through an analog junction box. Or weighbridge converts the output signal of the analog load cell into a digital signal through a digital junction box, and then according to the predetermined protocol, it is transmitted to the digital weighing controller (or RS232/RS485 transmitter, the transmitter directly send the signal to computer and display the weight data on digital weighing software), and after the weighing controller processing, it displays the measured weight. In addition, the weighing controller transmits the data to auxiliary devices such as printer, large screen, and weighing software in the computer.

A weighbridge using a digital load cell transmits a digital signal of digital load cell to a digital weighing controller (or RS232/RS485 transmitter, the load cell transmitter directly send the signal to computer and display the weight data on digital weighing software), and after the weighing controller processing, it displays the measured weight. In addition, the weighing controller transmits the data to auxiliary devices such as printer, large screen, and weighing software in the computer.
II. Common cheating of weighbridge
From the perspective of cheating type, cheating of weighbridge can be divided into two types: non-circuit cheating and circuit cheating.
1. Non-circuit cheating

1. Adjusting the limit bolt of the loader to the point where the loader can't move freely, blocking the loader with stones or other objects around, supporting the loader or mounting position of load cell with other objects. these ways would lead to a low measurement value. Such a cheating is easier, but also rare.
2. The vehicle hasn't stopped on the scale completely, which leads to a smaller measurement value. Several vehicles are on the scale, leading to a larger measurement value. Large trucks or trailers generally have longer lengths, as there are many cars waiting for weighing and the narrow vision of weight house, it's difficult to judge the position of front wheels or rear wheels, so the truck may be not on the scale. In other case, two cars keep a short distance, the front wheels press on the scale, resulting in a fact that many cars are on the scale. This case occurs occasionally when there are many weighing, different kinds of vehicles or long load-bearing length.
3. Man-made cheating from the gager or weighing officer. In case of benefit-based relationship, the gager or weighing officer would try all the ways to change the weighing result. For example, pulling off the wire at the back of instrument, connecting a prepared simulator to adjust the result to setting value for printing or transmitting.
4. Cheating through instruments or software. Some instrument manufacturers would produce instruments with deduction rate, whose weighing value would be decreased or increased by pressing relevant combination key. Weighing software are also various, some software have set bugs in programming, and the weighing value can be changed through button. Such a cheating is generally colluded between the installer of weighbridge and the weigher or controller manufacturer. The ultimate victim is the shipper. The most obvious feature of this cheating means is that it is very concealed and no problem would be found when checking. It's really unconscious.
   

2. Circuit Cheating
Weighbridge generally adopts the form of ground balance without foundation pit, lower edge of the loader is above the ground and a certain amount of space is left on both sides, so as to facilitate debugging and maintenance of load cells and cables. The outlaws just use this drawback. Through the loader space, they add circuit device to load cell cable and wiring terminal, so as to change the weighing signal input to weighing controller by load cell.
2.1 Weighbridge with analog load cell
2.1.1 Typical cheating circuits

• Series resistance method. The cheating circuit is as follows:
  
  
• Parallel resistance method.
• Series signal method. It can achieve the goal of low weighing value when buying and high weighing value when selling.
• Parallel signal method.
  

2.1.2 Typical circuit cheating ways

• Switch cheating method.
  This is the simplest method, which realizes the access or exit of a cheating circuit with an electrical switch, instant cheating, instant return to normal state.
  
• Remote control cheating method.
  At present, remote control cheating is the most common cheating method. There are many kinds of remote controllers. The bridge voltage of load cell in weighbridge is about 10V, the cheating devices use this power supply, so its size reduces greatly. There is a remote controller that integrates the remote control receiver and cheating circuit in a matchbox-sized plastic box, there are 3 voltage regulator holes on the box, which can be used to adjust the cheating voltage before cheating. Such a cheating device usually has multiple voltage gears. Through controlling multiple function gears of the remote controller, it can change the voltage direction while choosing the appropriate cheating value.
  
  

The cheating remote controller is usually installed on load cell cables, junction boxes, bus cables or weighing instruments.
2.2 Weighbridge with digital load cell
It's more difficult for digital weighbridge to cheat in the circuit part. It is impossible to change the weighing value by changing impedance and voltage, if the voltage is too low, the load cell will not work. Outlaws acquire the communication protocol of digital load cell by means of monitoring and decryption, and then change the output value through remote control, the values can be increased or decreased according to linear or predetermined values. So AES encryption technology and seal shall be combined to improve the anti-cheating ability of scale.
III. Field investigation of weighbridge cheating
1. Observation method
Step the loader in the horizontal direction forcefully and observe whether the loader swings flexibly, ensure the accurate transmission of measurement value. Observe if there are plastic bags, paper and other wrappings on the lead-out wires and cables of the load cells under the loader, or if there are cheater pasted with tape or is adsorbed under the bearing table with a magnet, if there's a damage in the cable, whether there are any abnormalities in the stud screw and plug-in in the load cell junction box. Inspect the weighing controllers and computer peripheral circuits and plugs.
2. Test method
Testing with the multimeter resistance gear to see if there's short circuit or open circuit in the cable, check whether the impedance of the input and output terminals of the load cell group is within the parameter range. Focus on actual load cell data and pay more attention to inspect the load cells and cables with abnormal resistance value.
Check with the multimeter voltage gear whether the input voltage of the load cell is normal, and compare with the voltage provided by the instrument. Check whether the output signal voltage of each load cell is stable, and whether the deviation of the output signal voltage of each load cell is too large.
3. Substitution method
When you have found that the weighbridge is not working properly, but you can't judge accurately, you can use the substitution method to test the suspicious or cheating components. For example, replacing corresponding devices with load cells, load cell junction boxes and weighing controllers at the same type and specifications, then check whether the weighing results become normal. Generally, substitution method is used for inspection of weighing instruments. It's used to determine whether cheating circuit is installed inside weighing controllers.
4. Exclusion method
In case that it is impossible to determine the fault, to not affect the normal operation, relevant devices can only be checked one by one through exclusion method. For example, when it is impossible to judge whether the fault lies in the load cell or wiring box, and there are no relevant substitutes, it's possible to remove the load cell one by one or change the wiring position in the wiring box, so as to observe the weighing results, thus accurately finding out the cheating circuit or cheating components.
IV. Prevent cheating measures for weighbridge
According to the cheating types and cheating ways in weighbridge, we can easily know that investigation of cheating scene can't completely eliminate the occurrence of cheating. For example, controller or software cheating, personnel cheating in the non-circuit cheating, they are quite concealment and can't be detected. But we must pay attention to the following points if we want to minimize and reduce the cheating.

1. When designing the loader, good material must be used to the threading pipe. There should be no gap in the middle. Protective cover or lateral protection plate shall be installed at the wire outlet (position from wire outlet to threading pipe) of load cell, moreover, they shall be fastened with non-standard screws. In order to prevent cheaters from pulling out the cable to connect external cheating device, we should tighten the cable as far as possible in the threading pipe.
2. If the loader is too long or the weighing room has a narrow vision, add more cameras. Judge whether the car is fully weighed through video, or whether several vehicles are on the scale. Camera is an important monitoring device in unattended weighbridge application system. It's the key equipment to judge the accuracy of weighing results.
3. The load cell controllers and wiring boxes must be sealed with lead, they can't be opened randomly, and regular inspection shall be made. So as to avoid outlaws to add related circuits, as well as avoiding internal personnel to re-calibrate weighing controllers with the effect of illegal interests.
4. Conduct legal training for gager and weighing officers in metrology legal department, increase their legal sense, or conduct frequent work shift.
5. Apply the weighing controllers and software produced by formal enterprises with good reputation. Generally, enterprises with good reputation and large enterprises shoulder a certain mission, and they will not reserve the possibility of cheating on the instrument for the sake of small profits.
6. Use digital weighbridge as far as possible when conditions permit. Increase the cheating difficulty and cost for outlaws. Digital weighbridge uses related communication protocol to transmit data, and these communication protocols have a certain ability to prevent cheating, high cracking difficulty and cheating cost, so it can effectively curb the cheating. Meanwhile, simple simulator is not suitable for digital load cell controller, which can't print and transmit relevant data at will.
7. Try 24-hour surveillance to the loader periphery, stop suspicious persons in time, leave no space for outlaws to come nearby. Strict surveillance will make it impossible for criminals to cheat. Without man-made cheating, accuracy of weighing results can be guaranteed. At present, some people have threatened to interfere the weighing results without installing any remote control device on the weighbridge. But as far as we concerned, it may refer to interfere the crystal oscillator, it can't guarantee or control the weighing results. Nobody can do anything uncertain.
8. Carry out calibration and comparison frequently apart from the annual legal inspection. If there is no internal cheating of human factors, regular calibration and comparison can't only prevent cheating, but also judge whether the scale has relevant faults at any time.
   

V. Conclusion
Weighbridge cheating has greatly affected fair trade settlement, and has brought huge losses to relevant enterprises and individuals, so it would undoubtedly arise from the public attentions. We sincerely hope that our peers in load cell controller manufacturing industry will actively participate in preventing cheating and strictly abide by professional ethics, so as to make a contribution to fair trade.