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4.8.3 ELECTRONIC GOVERNOR - ESD5500E SERIES SPEED CONTROL UNIT
INTRODUCTION
The ESD5500E Series speed control unit is an all electronic device designed to control engine speed with
fast and precise response to transient load changes. This closed loop control, when connected to a
proportional electric actuator and supplied with a magnetic speed sensor signal, will control a wide variety
of engines in an isochronous or droop mode. It is designed for high reliability and built ruggedly to withstand
the engine environment.
Simplicity of installation and adjustment was foremost in the design. Non-interacting performance controls
allow near optimum response to be easily obtained.
The primary features of the ESD5500E Series speed control unit are the engine STARTING FUEL and
SPEED RAMPING adjustments. The use of these features will minimize engine exhaust smoke experienced
prior to attaining engine operating speed.
Other features include adjustable droop and idle operation, inputs for accessories used in multi-engine or
special applications, protection against reverse battery voltage, transient voltages, accidental short circuit
of the actuator and fail safe design in the event of loss of speed sensor signal or battery supply.
The ESD5500E Series speed control unit is compatible with all GAG proportional actuators except the
ACB2000 electric actuator. When the ESD5500E Series speed control unit is used with a ADC100 Series
electric actuator, the DROOP adjustment range will be less due to this actuator’s low current demand.
DESCRIPTION
Engine speed information for the speed control unit is usually received from a magnetic speed sensor. Any
other signal generating device may be used provided the generated frequency is proportional to engine
speed and meets the voltage input and frequency range specification. The speed sensor is typically
mounted in close proximity to an engine driven ferrous gear, usually the engine ring gear. As theteeth of the
gear pass the magnetic sensor, a signal is generated which is proportional to engine speed.
Signal strength must be within the range of the input amplifier. An amplitude of 0.5 to 120 volts RMS is
required to allow the unit to function within its design specifications. The speed signal is applied to Terminals
C and D of the speed control unit. Between these terminals there is an input impedance of over 33,000
ohms. Terminal D is internally connected to Terminal E, battery negative. Only one end of the shielded
cable should be connected.
When a speed sensor signal is received by the controller, the signal is amplified and shaped by an internal
circuit to provide an analog speed signal. If the speed sensor monitor does not detect a speed sensor
signal, the output circuit of the speed control unit will turn off all current to the actuator.
A summing circuit receives the speed sensor signal along with the speed adjust set point input. The speed
range has a ratio of 8:1 and is adjusted with a 25 turn potentiometer. The output from the summing circuit
is the input to the dynamic control section of the speed control unit. The dynamic control circuit, of which
the gain and stability adjustments are part, has a control function that will provide isochronous and stable
performance for most engine types and fuel systems.
The speed control unit circuit is influenced by the gain and stability performance adjustments. The governor
system sensitivity is increased with clockwise rotation of the gain adjustment. The gain adjustment has a
range of 33:1. The stability adjustment, when advanced clockwise, increases the time rate of response of
the governor system to match the various time constants of a wide variety of engines. The speed control
unit is a PID device, the “D”, derivative portion can be varied when required. (See Instability section.)
During the engine cranking cycle, STARTING FUEL can be adjusted from an almost closed, to a nearly full
fuel position. Once the engine has started, the speed control point is determined, first by the IDLE speed
set point and the SPEED RAMPING circuit. After engine speed ramping has been completed, the engine
will be at its governed operating speed. At the desired governed engine speed, the actuator will be energized
with sufficient current to maintain the desired engine speed, independent of load (isochronous operation).
The output circuit provides switching current at a frequency of about 500 Hz. to drive the actuator. Since
the switching frequency is well beyond the natural frequency of the actuator, there is no visible motion of
the actuator output shaft. Switching the output transistors reduces its internal power dissipation for efficient
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