Speed Error
Speed error is the difference between the speed reference and the measured speed, and it is the basic quantity that produces the controller's output. A positive error requires fuel to be increased, a negative error requires it to be decreased. An error that cannot be permanently brought to zero shows that the system is working with droop.
The control loop performs the same three steps in every cycle: measure, take the difference, update the output. The sign of the error determines the direction, its magnitude the strength of the correction. In a purely proportional controller the output is proportional to the error, so if the error were exactly zero the output would be zero as well; that is why a small permanent error always remains in steady state.
- On a sudden load application the error grows at once, the actuator moves quickly, then the error shrinks.
- If the error keeps changing sign the system is oscillating; the gain is too high.
- If the error is large and not decreasing, the actuator has hit its limit or there is a mechanical binding.
The same logic applies in position control as well. On the GS740-3P the quantities compared are the commanded position and the actual position read by the AS5600 encoder; the error is produced from that and the actuator is driven in the direction that closes it.
Context in which this term is used: Electronic speed and throttle control on a diesel engine