0316980 JOHNSON NEEDLE VALVE, High speed

Control Dynamics
The control algorithms used in the 701 control are designed specifically for reciprocating engine applications. Control dynamics are varied automatically as functions of both speed and load to provide better performance over the operating range of the engine.The 701 control provides two mappings of control dynamics as a function of speed (see the following sections for more information on maps and tuning parameters). The control automatically maps gain proportional to engine speed. This provides higher gain at normal operating speeds and lower gain at low speeds. This provides a better match with engine control requirements than a constant gain control. A second optional dynamics mapping provides additional stability as speed is decreased. This feature is useful particularly on large, low-speed engines where dead time between cylinder firings becomes an important factor in performance.To provide better transient performance, the control can be operated automatically with two gain settings depending on engine speed error (speed error is the difference between the speed setting and the actual engine speed). During steady-state operation with a constant load, the control uses the base gain setting. This gain is adjusted by the user to a value to prevent the control from responding to minor fluctuations in engine speed, a common problem with gas-fueled, spark-ignited engines. This feature eliminates potentially damaging jiggle of the actuator and fuel system. The control automatically increases gain by an adjustable ratio when a speed error exceeding an adjustable window occurs. Operation with base gain is restored once the control senses the return to steady-state speed.The control can also compensate for nonlinear fuel systems and changes in engine dynamics with load. The control dynamics are mapped as a function of actuator current (actuator current is proportional to engine load). This provides optimal dynamics and smooth steady-state operation for all conditions from no load to full engine load.The control also provides two complete sets of dynamic adjustments which are externally selectable. The two sets of dynamics are provided for use where engine operating conditions change, such as in systems with clutched-in loads, dual fuel sources, and electrical power generation where the unit may be operated stand alone or paralleled with an infinite bus.Fuel Limiters
The 701 Digital Speed Control provides a Start Fuel Limiter to limit overfueling or flooding during start-up. The limiter is set to provide the desired maximum rack position during starts. The control will reduce the fuel when the speed set point is reached as required to control engine speed, but will not exceed the start limit.A Load Limit set point is provided to limit the maximum output current of the control during normal engine operating conditions.A two-slope torque limiter is provided for mechanical drive applications (or a six-slope torque limiter on the 9905-457). The torque limiter provides a maximum rack position determined by current engine speed to limit overfueling and subsequent smoke emission during engine acceleration. The torque limiter is low signal selected with the load limit.Speed Reference and Ramps
The 701 control provides local control of the speed reference with discrete inputs to issue raise and lower speed commands. For remote speed setting, the control provides a 4 to 20 mA/1 to 5 Vdc input which is used for the speed reference. This section describes the operation of each of the speed reference and ramp functions and their relation to each other. Read this section carefully to be sure your switchgear sequencing provides the proper operating modes.The control provides Idle, Lower Limit, Rated, and Raise Limit set points along with Accel and Decel Time and Raise and Lower Rates for local operation. Accel Time determines the time required for the engine to ramp from idle (low idle) to rated (fast idle) speed. Decel Time determines the time required for the engine to ramp from rated speed to idle speed. Raise and Lower Rates determine how fast speed is increased or decreased by the Raise and Lower command inputs.The Idle Speed set point is provided for engine start-up or cool down speed. Idle speed may be set equal to or less than the rated speed set point. Idle is independent of the Lower Limit set point and may be set to a lower speed. When Idle is selected (Idle/Rated switch in Idle position with contacts open), Remote, Raise, and Lower inputs are all disabled. Idle speed cannot be changed except through adjustment of the Idle Speed set point. In idle, the start fuel limit is in effect, and the max fuel limit and torque limiter are disabled. This means the maximum fuel available is determined only by the Start Fuel Limit set point, and the speed reference is determined only by the idle speed set point.When Rated Speed (high or fast idle) is selected by closing the Idle/Rated switch contact, the fuel limit is set to the Maximum Fuel Limit set point value or the Torque Limit, whichever is less for the current engine operating speed. The speed reference selected at this time is determined by the status of the Local/Remote switch. If Local is selected when the switch contacts are closed, the speed reference will ramp from low idle to fast idle (rated) speed, based on the Accel Time set point. Closing either the Raise or Lower contacts (or the Remote contacts) while ramping from idle to rated results in immediate cancellation of the idle to rated ramp.After acceleration to rated speed is completed, the Raise and Lower commands increase and decrease engine speed based on the Raise and Lower Rate set points. The Raise and Lower Limits determine the limits of these commands.If Remote is selected after the engine reaches rated speed, the control will ramp speed to the reference value set by the remote speed setting milliamp input based on the Raise or Lower Rate. The remote speed setting operates from 4 to 20 mA (1 to 5 Vdc). The values of the 4 mA and 20