WinCC Unified - Clamping Tag Value

In my previous post, I shared the importance of setting tag limits to prevent bad data from causing issues in SCADA systems. Now, let’s talk about another essential safeguard — clamping values.

Clamping vs. Tag Limits

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While both clamping and tag limits help control data quality, they serve different purposes:

• Tag limits: Used to filter out and reject values that exceed a predefined range, preventing them from being processed at all.

• Clamping: Adjusts out-of-range values to stay within acceptable limits, ensuring the system continues to function without interruption.

Steps to implement Clamping in WinCC Unified

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1. Create Data, Lower and Upper Bound Tags

   • Open the Tag Table and create a data tag (e.g., Data_Integer_Value), a lower bound tag and an upper bound tag
   • Set the lower and upper bound tags with their respective Start value (e.g. upper bound = 100, lower bound = 0)

     

2. Link Data Tag to a Screen Element

   • Add a new Screen.
   • In the new screen, add an IO Field element.
   • Link the Process Value of the IO Field to the tag Data_Integer_Value.

     

3. Define Upper and Lower Clamping Function

   • Add a Input finished event with the code below.

export function IO_field_1_OnInputFinished(item, value) {

  let tag = Tags("Data_Integer_Value");
  let lower = Tags("lower_bound").Read();
  let upper = Tags("upper_bound").Read();
  let result;

  if(value < lower){
    result = lower;
  }
  else if (value > upper){
    result = upper;
  }
  else{
    result = value;
  }

  tag.Write(result);
  return result;
}

4. Run Simulation Mode to verify the range settings
   • Start Simulation Mode.
   • Try entering values beyond the defined limits to see how the system handles them.