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Identifying periods where parameter readings increase or decrease is crucial for process monitoring!

Why it matters? Changes often indicate potential issues or opportunities for optimization.

How to analyze? Calculating the derivative of a tag allows for a more precise assessment of how sensitive a process is to fluctuations in specific parameters.

 In TrendMiner : Different methods are available to determine the derivative based on the type of analysis needed.

 Preparation: Smoothing Signals

For noisy or highly fluctuating signals, it is recommended to perform an aggregation before calculating the derivative.

This helps achieve a more accurate approximation of the derivative of the selected function.

Recommended Aggregation:

• Tag: The tag for which the derivative should be calculated
• Operator: Average
• Direction: e.g., Backward
• Aggregation interval: e.g., 10 minutes

 Option A: Calculating the Derivative Using a Formula

The derivative can be determined by calculating the slope of a tag over a short period. This is done by subtracting a time-shifted version of the tag from itself. The shorter the time interval, the more accurate the approximation of the actual derivative.

Formula:

A - B

Variable Mapping:

• A = (Smoothed) tag for which the derivative should be calculated
• B = (Smoothed) tag for which the derivative should be calculated, shifted by e.g., 1 minute

Advantages of the Formula-Based Derivative:

•  High accuracy for short time intervals (delta_t < 2x index resolution)
•  Ideal for long-term trends, such as fouling detection, when delta_t > 24 hours
• Enables unit calculations within the formula
•  Simplifies nested formulas by counting as just one level when calculating slopes

 Option B: Calculating the Derivative Using Aggregation

An alternative approach is to use delta aggregation, which simplifies the derivative calculation over defined time intervals.

Recommended Aggregation:

• Tag: (Smoothed) tag for which the derivative should be calculated
• Operator: Delta
• Direction: e.g., Central
• Aggregation interval: e.g., 1 minute

Advantages of the Delta Aggregation Derivative:

• It is particularly useful for general trend analysis and process monitoring with stable signals

 Conclusion

Calculating the derivative of a tag in TrendMiner can help detect process changes early. The choice of method depends on the specific analysis requirements.

• Formula-based method is ideal for high-precision calculations
• Delta aggregation offers a quick and straightforward alternative.

Have you used derivative calculations in TrendMiner? Which method do you prefer and why? Let us know in the comments!