AAOM Handbook

MP.12 Determine the maximum rate of change for the process

Context

Measurements can contain ‘noise’, i.e. values that are not a true representation of the process performance. Noise may arise from various sources but is identifiable as changes that are too rapid for the process to actually deliver. Noise is not a relevant component of the measure and should be excluded. For example, each area of a process will have a maximum throughput rate limited by the physical design and capacities of the equipment. This limit will affect the rate of change that can occur in all of the quantities that we may need to measure, whether they be product level in a tank, chemical concentration in a solution, or temperature in a furnace. A simple approach to maximum rate of change is to understand the maximum period over which a process can change during normal operation. This obviously guides sampling intervals. • The maximum rate of level change in a tank will be determined by the tank volume and the maximum rate of the inflows and outflows. • The maximum rate of change of the concentration of a solution will be determined by the volume of the solution and the maximum rate at which a chemical can be added. • The maximum rate of change of temperature in a furnace is determined by the maximum difference between the heat injection and thermal losses. For example:

Purpose

To develop an appropriate filter to remove irrelevant data (noise).

Quantity One definition for the appropriate conditioning filter.

Quality

A conditioning filter must be specified, based on the above criteria, and applied to the measure so that rates of change that are irrelevant are removed.

Resources

This task is completed by the manager responsible for the process.