Analog Interfacing to Embedded Microprocessor Systems, 2nd Edition

within a certain percentage of the setpoint. This avoids building up a large

integral term while the output is ramping toward the setpoint.

The derivative term in a PID design is the amount of change in the error over a

specific unit of time. Because a microprocessor control system uses a regular

sampling rate, the unit of time is usually the sample interval (or some multiple

of the sample interval). The derivative is then calculated by subtracting two

samples. Subtracting the error at time n from the error at time n þ 1 gives the

amount of change in one time interval. To prevent noise problems, the software

may average two or more successive samples.

The integral is the sum of error over a period of time. In a practical micro-

processor system, the ...