Modern logistics is unthinkable without accurate cargo accounting, and weighing systems become a key element in this chain. The principle of how they work travel scales, is based on the conversion of mechanical pressure from the mass of the car into an electrical signal. It is a complex engineering process that ensures fair trading and safe roadways. Understanding the internal mechanics allows you to operate equipment correctly, avoiding costly weighing errors.
At the heart of any system is a platform that perceives the load, and strain gauges that record changes. When a heavy truck drives onto a platform, the metal elements of the structure experience deformation. It is this microscopic deformation that the electronics capture, translating physical efforts into understandable numbers on the scale display. Without this technology, congestion control would be impossible and the economics of transportation would be thrown into chaos.
Physical principle of operation of strain gauges
The heart of any modern weighing system is strain gauge. This device is a metal elastic element onto which a thin foil grid is glued. The principle of operation is based on the tensoelectric effect: when a conductor is stretched or compressed, its electrical resistance changes. When the car is placed on the scale, the sensor beam bends and the resistance of the foil changes in proportion to the applied force.
Changes in resistance are extremely small, so a Wheatstone bridge circuit is used to record them. It allows you to convert a change in resistance into a change in voltage. The signal from the sensor output goes to the summing block, where data from all platform supports is combined. Measurement accuracy directly depends on the quality of manufacture of strain gauges and the stability of their characteristics over time.
⚠️ Attention: Sudden temperature changes can cause temperature drift in readings, therefore high-quality sensors are always equipped with temperature compensators.
To protect against external influences, the sensitive elements are sealed. Depending on the protection class IP67 or IP68, the device can withstand complete immersion in water or exposure to aggressive chemicals. This is critical because travel scales operate in harsh conditions such as rain, snow and extreme temperatures.
How long do strain gauges last?
The average service life of high-quality strain gauges with proper operation is 10-15 years. However, their metrological characteristics may deteriorate faster due to dynamic shocks from trucks or contact corrosion.
The design of the weighing platform and its role
The platform is a massive metal structure that must withstand enormous loads without losing its geometry. It rests on several points, at each of which a strain gauge is installed. Even distribution of weight across all supports ensures correct final readings. If one of the supports is higher or lower than the others, a misalignment will occur, leading to weighing errors.
There are two main types of platforms: all-welded and modular. Solid structures are a single rigid box, which is easier to install, but more difficult to transport. Modular systems are assembled from several sections on site. Correct docking of the modules is critical for them so that the truck wheels do not get stuck in the seams and the load is transferred evenly.
The platform material also plays an important role. The most commonly used is structural steel, which has high strength and elasticity. The surface is treated with anti-corrosion compounds.
Converting an analog signal to digital code
Once the mechanical force is converted into a weak electrical signal, the weighing terminal or instrument comes into play. The first stage of processing is signal amplification, since the voltage from the strain gauges is measured in millivolts. The analog signal then passes through an analog-to-digital converter (ADC).
The ADC samples the continuous signal, assigning each voltage level a specific digital value. Sensor polling rates can reach hundreds of times per second, allowing you to track dynamic weight changes in real time. The resulting digital code is processed by a microprocessor according to the established algorithms.
There is a program running inside the device that filters noise and vibrations. For example, if there is a strong wind or a train passes nearby, the scale should ignore these disturbances. The algorithm averages the readings over a certain period of time, producing a stable mass value. Modern terminals also allow you to calibrate the system and enter containers.
| Parameter | Description | Impact on the result |
|---|---|---|
| ADC capacity | Number of bits in a digital code | Determines the discreteness of the count (weighing step) |
| Polling frequency | Number of measurements per second | Affects system response speed |
| Filtration | Software anti-aliasing | Removes jitter of numbers on the scoreboard |
To improve weighing accuracy in windy conditions, use windbreaks around the platform or turn on the high filtration mode in the terminal.
Types of road scales and their features
The market offers various weighing solutions, and the choice depends on the specific application. Stationary scales require a solid foundation and are intended for permanent work with high flow rates. They provide the highest accuracy and reliability. At the same time, mobile analogues can be quickly deployed anywhere and transported to a new facility.
A special feature is axle scales, which measure the load on each axle separately. They are compact and are often used to monitor compliance with traffic regulations on axle loads. The principle of their operation is similar, but the platform dimensions are smaller, and the design is adapted for the gradual entry of wheels.
There are also scales for weighing in motion. They do not require stopping the vehicle, which significantly increases the throughput of the control point. However, the accuracy of such systems is generally lower than that of static scales, and they require complex calibration for different moving speeds.
- 🚛 Stationary — high accuracy, require a foundation, permanent location.
- 🚐 Mobile - quick installation, ability to move, suitable for temporary posts.
- ⚖️ Axial - control of axle loads, compactness, use to detect overload.
Factors affecting measurement accuracy
Even perfectly calibrated scales can malfunction under the influence of external factors. One of the main enemies of accuracy is the condition of the access roads. If there are potholes or bumps in front of or after the scale, the vehicle will “bounce”, creating dynamic loads that distort the actual weight. The length of the access roads must be no less than the length of the road train.
The temperature regime also makes its own adjustments. The metal of the platform and sensors expands when heated and contracts when cold. Although the sensors have compensation, sudden changes can cause temporary zero drifts. In addition, the adhesion of dirt, snow or ice to structural elements adds extra mass, which the system perceives as part of the load.
⚠️ Attention: The presence of electromagnetic interference from high-voltage lines or welding work nearby may interfere with the operation of the electronics of the scale.
It is important to carry out regular maintenance. This includes cleaning the gaps between the platform and frame, checking contacts and making adjustments. If the gap between the platform and the stops is clogged with rocks or dirt, the platform may rest against the base and the scale will no longer display the correct weight or may malfunction.
☑️ Daily check of scales
Calibration and verification process
In order for the numbers on the display to have legal force, the scales must undergo regular verification. This process confirms that measurement error is within acceptable limits established by law. Calibration is the setting of the scales, which is carried out by service specialists. It is necessary after repairs, replacement of sensors or long-term downtime.
For calibration, standard weights or the technique of “rolling” a standard car with a known mass are used. In some cases, when a set of weights is not possible, the substitution method or angle calibration is used (when a known weight is moved to different points on the platform). This allows the sensitivity of all strain gauges to be equalized.
The verification results are recorded in a certificate, which is a mandatory document for the commercial use of scales. The absence of a valid certificate makes it impossible to use the scales for trading operations or issue fines. Owners must strictly monitor the validity period of the metrological certificate.
The accuracy of scales is not only the quality of the equipment, but also regular maintenance, correct installation and timely metrological verification.
Prospects for the development of weighing technology
Technologies do not stand still, and the weighing industry is actively digitalizing. Modern scales are increasingly equipped with interfaces for transferring data to cloud services. This allows dispatchers to see the weight of the cargo in real time without being on site. Integration with ERP and 1C systems automates document flow.
Automatic vehicle identification systems are being developed. The cameras read the license plate, and the scales transmit the weight, forming a single entry in the database. Artificial intelligence helps analyze overload statistics and identify anomalies in equipment operation. The future belongs to fully autonomous systems that minimize human participation.
The use of wireless technology simplifies installation and maintenance. Digital sensors with interface RS-485 or Ethernet allow you to diagnose the status of each system element remotely. This reduces downtime and increases the reliability of the entire complex as a whole.
What should I do if the scales show different weights when weighing me again?
You should check driveways for unevenness, ensure that the vehicle is completely on the platform, and check for any foreign objects touching the platform. Calibration may also be necessary.
Is it possible to weigh yourself on a travel scale in extreme cold?
Yes, most industrial scales are designed to operate at temperatures from -40 to +50 degrees Celsius. However, in extreme conditions, it is necessary to warm up the electronics for a longer time before starting work.
How often should load cells be replaced?
With proper operation and the absence of mechanical damage (shocks, overloads), strain gauges last for decades. Replacement is required only in case of failure or loss of metrological characteristics after a lightning strike or power surge.