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The EMIT Governor module is an electronic speed control system for stationary carbureted natural gas engines. The Governor system consists of two main components: the control board and an electronic throttle body. The control board is intended to be mounted in a panel or EIM enclosure. The throttle body comes in a variety of sizes for different engines, and mounts directly between the carburetor and intake manifold.
The Governor works by monitoring the speed of the engine by reading a magnetic pickup (MPU) over the flywheel teeth. If the engine is running too slow or fast for the current control RPM, the throttle position is adjusted according to a PID control algorithm. The control speed is determined by a variety of conditions. First, the user can select through a panel switch one of three operating modes. They are “Idle,” “Manual,” or “Auto” speed control mode. In Idle mode, the Governor will hold the engine to an idle speed. In Manual mode, the user can increase or decrease the engine RPM, starting from the engine’s current speed, by using the “Speed+ / Speed-” switch on the panel. In Auto mode, the Governor control behavior will be determined in setup control mode, which may be configured to hold a fixed run speed or control to a certain compressor pressure.
Pressure control under Auto mode, can either control to suction pressure or discharge pressure. In suction control mode, the speed decreases as suction pressure drops and increases as the pressure rises. This is intended for wells or situations where the intake pressure varies but the downstream system can handle the discharge pressure changes. In discharge control mode, by contrast, the engine will increase speed if discharge pressure is too low, and lower speed if discharge pressure is too high. This aims to keep the discharge pressure constant.
MODES OF OPERATION
The user can select through the panel’s mode switch either “Idle,” “Manual,” or “Auto” (Run) mode for the Governor. Additionally, Auto mode can be setup to function in various ways. A description of each control mode is provided below.
When the panel’s mode switch is in Idle, the Governor will hold the engine at the user-specified idle speed. This speed is specified during governor setup, described in a later section.
When the panel’s mode switch is in Manual, the Governor will hold at a fixed manual speed. Whenever the switch is switched to Manual, the manual speed will start at whatever speed the engine is currently operating at and from there, the user can use the panel’s speed switch to increase or decrease the speed. This mode is intended to be used only temporarily.
If the mode switch is in Manual when the engine is
started, the manual speed will start at the idle speed.
Note: If the mode switch is not at Manual, then the “Speed+ / Speed-” speed switch will have no effect.
The Auto setting is used for normal run operation of the engine. The behavior of the Governor in the Auto setting can currently be set to one of three ways, described below.
Note: When switching between operating modes (Idle, Manual, or Auto), the Governor will ramp more slowly than it would during normal operation.
AUTO – CONTROL TO FIXED SPEED
For a fixed speed setpoint, the Governor will hold the engine at a specified run speed. This run speed can be adjusted in governor setup.
AUTO – CONTROL TO SUCTION PRESSURE
For a suction pressure setpoint, the engine will increase speed when the suction pressure is too high and decrease speed when the suction pressure is too low. The user specifies some range that the Governor should not deviate from during the Auto operation. This mode is useful for cases where the incoming pressure varies, such as a low-producing well. Decreasing the RPM when the pressure drops gives the supply a chance to replenish. This can result considerable fuel savings and reduction of engine wear by eliminating wasted work by the engine.
AUTO – CONTROL TO DISCHARGE PRESSURE
For a discharge pressure setpoint, the engine will increase speed when the discharge pressure is too low and decrease speed when the discharge pressure is too high. Overall, this keeps the discharge at a constant rate. This mode can be used when the supply pressure is unconstrained, but the outgoing pressure is desired to be constant.