Book Analog Interfacing to Embedded Microprocessors
typical way to handle an input change like this is to cut off the PWM output
and let the system “coast” until things stabilize. The key thing here is to be
sure the integral and/or derivative values don’t result in an erroneous output
when the control is reinitiated. You may have to reset or otherwise modify
these values when a sudden input change occurs.
Special Requirements
Many systems that require PID control must handle specific inputs. A
cruise-control system may need to go to a quiescent state, resetting the
122 Analog Interfacing to Embedded Microprocessors
integral and derivative values, when the driver hits the brake. The automo-
bile voltage regulator may need to operate differently, with different PID
parameters, at different motor speeds. A heater may have a differing ON-
time PWM power limitation for heating different materials. The software
must insure that all these special requirements are met, and that a change
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