As an expert in process engineering, I can explain that the natural tolerance limits of a process refer to the inherent variability that occurs within a system due to uncontrollable factors. These limits are crucial in quality control and process improvement because they help determine the consistency and reliability of a process.

In statistical process control (SPC), natural tolerance limits are often estimated using control charts. A control chart will typically show the process's mean and the upper and lower control limits, which are calculated based on the process's inherent variability. The process is considered to be in a state of statistical control when its output remains within these control limits.

It's important to note that natural tolerance limits are not the same as specification limits, which are the acceptable limits for a product or process as defined by the customer or regulatory standards.

Now, let's translate that into Chinese:

作为过程工程领域的专家，我可以解释，过程的自然容差极限是指由于不可控因素在系统内发生的固有变异性。这些极限在质量控制和过程改进中至关重要，因为它们有助于确定过程的一致性和可靠性。

在统计过程控制（SPC）中，通常使用控制图来估计自然容差极限。控制图通常会显示过程的平均值和基于过程固有变异性计算出的上下控制极限。当过程输出保持在这些控制极限内时，认为过程处于统计控制状态。

需要注意的是，自然容差极限与规格极限不同，后者是由客户或法规标准定义的产品或过程的可接受极限。

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The next concept we must understand is the Natural Tolerance Limits (NTL) of the process. The NTL are also known as the process capability limits of the process and are established or influenced by the process itself assuming a normal distribution. All processes have an upper and a lower Natural Tolerance Limit.read more >>