Electric governors have become in favour due to their compact size, rapid response and high reliability allied to low maintenance costs.
The main part of the governor is the controller and signal amplifier. This receives a D.C. signal proportional to the engine speed and compares it to a speed set signal. The difference between the measured value (engine speed) and the set value is the offset, this offset value is passed to the output circuit which produces an appropriate output signal . In this case, a signal which raises or lowers the fuel rack by an amount dependent on the degree of offset. This system is inherently stable due to the feedback layout.
For this system the engine speed is measured using an alternator driven off the camshaft- this is a common arrangement. The speed set signal is typically supplied by the bridge control arrangement via the engine management system.
An arrangement for a generator set might replace the camshaft driven alternator with a tapping off the alternator output. The frequency of the alternator output is now the measured value. In addition a load sensing element can be introduced detecting changes in current flow. For increased current, that is an increased electrical load, the governor can act to supply increased fuel before the engine has began to slow.