Speed Setpoint
The speed setpoint is the target speed the control system tries to hold the engine at, and it is expressed in rpm. It can be a potentiometer, an analogue voltage, or a value stored in memory. The difference between it and the measured speed forms the error signal that produces the control output.
How the setpoint is given determines the character of the system:
- By potentiometer: the operator selects the point they want, steplessly. On the GS740-3P each channel has its own potentiometer and the signal is read proportionally in the 0–3.3 V range.
- From memory: on the GS740, holding the metal button for 3 seconds stores the current working speed; a short press switches between idle and that value.
- By external trigger: the setpoint can be pulled down to idle with a dry contact signal.
There is a distinction here: on the standard kit, what the potentiometer determines is not speed directly but the position of the throttle lever. The same position gives a different speed when the load changes. To speak of a speed setpoint in the true sense, the system must be measuring speed; otherwise the setpoint is a throttle position setpoint.
Context in which this term is used: Electronic speed and throttle control on a diesel engine