Automated testing reduces costs, improves quality

April 21, 2003
One of the most significant advanced process control (APC) technology advances in recent years is automated process testing.

One of the most significant advanced process control (APC) technology advances in recent years is automated process testing. This technology provides automated development of process models typically required for an APC application.

Similar in application structure to an operating APC controller, an automated test system generates manipulated variable moves suitable for identifying a process model. Data generated by a closed-loop APC system contain little identification information due to the nature of the correlation between control variable and manipulated variable changes.

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Automated testing reduces the initial cost of implementing an APC project because it eliminates a significant portion of the man-power required from testing engineers. It also improves the final model quality by optimizing the test signal and allowing for longer periods of data collection (Fig. 2).

With a few commercial and some in-house multivariable technologies in use, automated testing has quickly spread to more than 100 known applications. Single variable versions such as pseudo-random binary sequence testing have been around for years.

The new more capable technologies include:

  • Optimal test pattern design, which produces manipulated variable adjustments that encompass fast and slow dynamics, and optimizes the signal-to-noise ratio of the resulting process measurements.
  • Testing within constraints, which modifies the test plan to deal with process upsets without operator intervention.
  • The ability to handle difficult variables such as "ramps," whose integrating behavior must be continuously accounted for in the test plan.

Automated testing is also a valuable tool for sustaining the performance of an APC application. Automated retesting of problematic variables improves the process models.