OIML R60 is one of the fundamental international recommendations used to evaluate the metrological performance of load cells. The terms C2, C3, C4, or C6 seen on a load cell are not solely “quality levels”; they gain meaning together with criteria such as verification interval, temperature effects, creep, and minimum dead load output return.
What does OIML R60 evaluate?
The purpose of the standard is to classify the measurement performance of a load cell under specified conditions. Features such as combined error, creep, the effect of temperature on zero and sensitivity, minimum dead load output return, and moisture behavior are tested. The certificate does not mean that the entire installed scale is automatically approved; the indicator, mechanical structure, and system configuration must also be appropriate.
What do C2, C3, C4, and C6 mean?
The letter represents the accuracy class, while the number usually indicates the maximum verification range in thousands. For example, in class C3, the nLC value is generally up to 3000. However, the manufacturer’s certificate may contain specific limits depending on capacity and usage conditions. A higher class does not automatically give better results in every application; indicator resolution, platform structure, and environmental conditions can be limiting factors.
What is nLC or nmax?
nLC is the maximum number of verification intervals allowed for the load cell. Whether the cell meets this limit is checked by evaluating the scale’s maximum capacity, the division value, and the tare together. In multi-cell systems, load distribution and total cell capacity are also taken into account.
What does vmin indicate?
vmin, expressed as the minimum load cell verification interval, helps to understand within which limit the cell can support small weight changes. Looking at the nLC value alone is insufficient; the targeted division along with the maximum capacity assigned to each cell and vmin should be calculated together.
How is the Y value interpreted?
The Y ratio is the ratio of the maximum capacity to the minimum verification interval. A high Y value can help achieve smaller divisions with proper system design. However, mechanical vibration, the indicator’s input sensitivity, and cable losses can limit the theoretical result.
Z value and return to zero
Z is a ratio related to the return of the minimum dead load output and is particularly important in multi-range weighing systems. Keeping the zero point within an acceptable limit after the load is removed is necessary not only for repeatability but also for the accuracy of the next weighing.
How is the accuracy class selected?
- The scale capacity and target division are determined.
- The tare of the platform and the maximum load that can fall on each load cell are calculated.
- If there is legal use, the relevant compliance requirements are checked.
- The capacity and temperature range in the cell’s OIML certificate are examined.
- The system is calculated together with the sensitivity of the indicator and the excitation voltage.
Why is a high class alone not sufficient?
A C6 load cell does not give the expected performance when connected to a flexible platform or a low-resolution indicator. Friction in load transmission, incorrect assembly, temperature gradient, and electrical interference affect the entire measurement chain. Therefore, certificate selection is only a part of system engineering.
Frequently Asked Questions
How many divisions does the C3 load cell have?
It is generally associated with a 3000 verification interval; however, the exact nLC value must be verified from the product certificate.
Is the OIML certificate a calibration document?
No. The type evaluation/conformity certificate and the calibration result of a specific device are different documents.
Can every C3 load cell be interchanged with each other?
No. Capacity, output sensitivity, input/output resistance, mounting, cable, and certificate scope must also match.
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