There may be times when you need to identify whether a collected measurement value is nearing a defined upper or lower limit so you can take corrective action before measurements exceed limits and are recorded as failed measurements.

In the NPI Process Definition window, when you add a Numeric Data Collection Activity or a Numeric Data Range Collection Activity to a process definition, you can specify control limits on the Activity Details tab. Min Value and Max Value are standard settings for numeric data collection activities. In addition, when you enable validation for these activities, you can also define upper and lower control limit values.

• An Upper Control Limit value identifies a range of values (the Upper Guard Band) where the higher value is the existing maximum value and the lower value is greater than the minimum value.
  
  The upper control limit value you specify is less than the Max Value and greater than the Min Value (or the lower control limit value when defined).
  
  

• A Lower Control Limit value identifies a range of values (the Lower Guard Band) where the lower value is the existing minimum value and the higher value is less than the maximum value.
  
  The lower control limit value you specify is greater than the Min Value and less than the Max Value (or the upper control limit value when defined).
  
  
  

Assign a status comment for control limits

When you define one or both control limits for numeric collection activities, you can also use the Status Comment field (as a warning, for example) to assign/record a status comment  if the data collection value recorded falls within the range you specify.

• In Production, when a numeric data collection activity is executed and the collected value (one or both in the case of the Numeric Data Range Activity) falls within the defined range (guard band), the Status Comment is recorded as indicated in the activity definition.
• In Production, when a numeric data collection activity is executed and the collected value (one or both in the case of the Numeric Data Range Activity) doesn't fall within the defined range (guard band) or no control limit was defined, the Status Comment is not recorded.

When a Numeric Data Collection Activity or Numeric Data Range Collection Activity is executed and the collected data value is recorded, if a validation range is defined for the activity the Min Value, Max Value, Lower Limit and Upper Limit values are recorded against the measurement.

Control limits in the xTend API

To support control limits and the guard band concept, the NumericMeasurement and NumericRangeMeasurement classes in the xTend API include the following properties:

public double LowerControlLimit { get; set; }
public double UpperControlLimit { get; set; }

A measurement that falls within a guard band is a passed measurement. To quickly identify measurements that have a measured value that falls within a guard band, a new string field called StatusComment was added.

When you use xLink or the xTend API, FactoryLogix doesn't evaluate the measured value against any of the measurement properties (Min Value and Max Value, for example). The information presented is recorded "as-is". If a non-Aegis application records a measurement in FactoryLogix using the xTend API, the measurement is recorded as directed by the non-Aegis application. If a measured value falls within a guard band, the non-Aegis application must set the StatusComment property accordingly. The StatusComment property also allows measurements to be recorded with StatusComment values such as INFO and SKIPPED.

View recorded control limits and status comments

Upper and lower control limits are available to view in the Trace window in Production (Test Data and Parametric tabs) and in the Test and Measurement data source results (Quality and Test category) in DataMiner. (Use the Column Chooser to add or remove these columns as you would any other columns.)