Hello! That’s a very solid question, one that goes straight to the heart of what a truck scale is all about—accuracy. At Fujian Fangda, we’ve been manufacturing weighbridges for many years, and we often get asked similar questions: What level of error is considered normal for an 80-ton truck scale? And what should you do if it’s not accurate? Today, I’d like to give you a systematic overview from a manufacturer’s perspective.

I hope this helps you understand the issue. I wouldn’t call it overly complex, but it’s definitely packed with practical insights.

I. Accuracy Class and Error Standards for 80-Ton Truck Scales

Before rushing to ask “how to calibrate,” we must first clarify “what constitutes a qualified calibration.” Only by understanding the standards can we identify the calibration objectives.

1. Accuracy Class

According to the national standard “Fixed Electronic Weighing Instruments” (GB/T 7723-2017), standard weighing bridges commonly used for trade settlements generally fall under Class III, which is the “medium accuracy class.” The 80-ton weighbridge you mentioned almost all belong to this class.

2. Error Standards (Maximum Permissible Error)

Many people assume that the error margin of a truck scale is a fixed percentage, but this is not the case. It is calculated in segments based on the load weight and the “verification scale interval (e).”

For an 80-ton (80,000 kg) truck scale, the verification scale interval (e) and the display scale interval (d) are typically set to 20 kg. According to Class III scale standards, its maximum permissible error is as follows:

Initial verification (new scales or after major repairs):

- 0 – 10,000 kg: Error ±20 kg

- 10,020 kg – 40,000 kg: Error ±40 kg

- 40,020 kg – 80,000 kg: Error ±60 kg

In-service verification (scales in daily use):

- 0 – 10,000 kg: Error ±40 kg

- 10,020 kg – 40,000 kg: Error ±80 kg

- 40,020 kg – 80,000 kg: Error ±120 kg

To summarize: For a qualified 80-ton truck scale, an error within ±40 kg is considered normal when weighing 10 tons of cargo; ±80 kg when weighing 40 tons; and ±120 kg when weighing 80 tons. These are the practically acceptable ranges.

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II. How Exactly Do You Adjust the Accuracy of a Truck Scale?

In our industry, we generally don’t refer to this as “adjusting accuracy,” but rather as “calibration” or “standardization.” It’s important to note: Non-professionals should never attempt to tinker with the equipment on their own, as this can lead to further complications or even damage the sensors or the instrument panel,which would be counterproductive.

Calibration must be performed by a professional technician using standard weights. Below, I’ll outline the standard procedure:

1. Preparation

- First, clean the scale platform thoroughly; ensure there is no debris or foreign objects underneath.

- Check that the clearance of the limit bolts is normal and inspect the sensors and junction boxes for any visible damage.

- Turn on the indicator and let it warm up for at least 30 minutes to reach a stable state.

2. Zero Calibration

With the scale empty, enter the indicator’s calibration program, confirm, and save the zero point. If this step is not done correctly, all subsequent efforts will be in vain. Ensure that the display reads “0” when the empty scale is placed on the platform.

3. Range Calibration (also known as Linear Calibration)

This is the most critical step. The technician will use certified standard weights (such as 20 tons or more) and place them in batches at the center of the weighing platform—starting with 5 tons, then 10 tons, 15 tons, and 20 tons, and so on. Each time a weight is added, the corresponding weight value is entered into the instrument so it can learn the data. The indicator will automatically calculate a coefficient (SPAN value) and save it. This process is equivalent to telling the indicator: “A signal of this magnitude corresponds to a load of this weight.”

Experienced technicians will also perform multi-point calibration to ensure accuracy for both light and heavy loads.

4. Off-Center Load Error Adjustment (Also Known as Four-Corner Error)

This step ensures consistent readings regardless of where the vehicle is positioned on the scale.

The method involves using weights of a specific mass (typically about one-third of the maximum capacity) and placing them sequentially on the corners of the platform corresponding to each load cell. Record the reading for each corner. If there is a deviation, adjust the potentiometer in the junction box (one for each load cell) to slightly lower the reading of the corner that is too high, using the corner with the lowest reading as the reference. Repeat the testing and fine-tuning until the readings at all corners are consistent.

This step requires considerable skill; it cannot be accomplished by simply turning the knobs a couple of times.

Once the above steps are completed, the accuracy of the truck scale is essentially calibrated. Finally, you must have the local metrology supervision department perform a mandatory verification. Only after passing the verification and obtaining the certificate can the scale be officially used for trade settlements.

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To summarize

- An 80-ton truck scale is typically a Class III scale, and its error margin is segmented rather than a fixed percentage.

- Adjusting accuracy actually involves systematic calibration of three main components: zero point, range, and four corners. This must be performed by a professional technician using standard weights.

- If you notice inaccurate readings during daily use, don’t rush to adjust the indicator. First, check for debris around the scale frame, ensure the limit switches aren’t jammed, and verify that the load cells are functioning properly. In most cases, the issue stems from environmental or mechanical factors. If you can’t resolve it, contact professional after-sales support—never tamper with the junction box or indicator settings yourself.

At Fujian Fangda, having manufactured weighbridges for many years, our biggest concern is when customers attempt to adjust the equipment themselves. If they mess up the settings and then ask us to repair it, it only creates more trouble. We hope this response is helpful. If you’re using one of our weighbridges and encounter any issues, please get in touch with our after-sales service directly—our technicians will come to your site and resolve the problem in one visit.

Fujian Fangda Weighing Instruments provides a full range of electronic weighbridge from 30 tons to 200 tons