Speed Overview
Speed(Governor) Overview
Video available for this topic: https://www.youtube.com/watch?v=wzNx_1Ptvis
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.
IDLE
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.
MANUAL
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.
Note: 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.
AUTO
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.
Installation Guide
The governor installation guide can be downloaded here: https://drive.google.com/file/d/0BzOiNHLPWdg1WTkxTHcyQVYwM0k/view?usp=sharing&resourcekey=0-8Ovr-Q5y1b8QsLgYHVAYew
Additionally a quick start guide is available here: https://drive.google.com/file/d/0BzOiNHLPWdg1TWxhbG9VOWJJUTQ/view?usp=sharing&resourcekey=0-mRNb-S93kqJdCdpomt1lJQ
Home Screen
The Governor Home screen (Pg. 500) shows an overview of governor operation. The current status is shown at the top of this screen.
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Governor Home Page
The left section of the governor home screen shows the control state, with the inner box in the left section showing the state of the panel’s mode switch – Idle, Manual, or Auto. The current control settings are shown in the lower part of this section.
The middle section of the governor home screen shows the current speed. There are several additional markers on the speed gauge. The green marker or markers show the auto operating speed or speed range. A blue marker, if present, shows the temporary speed setpoint – either idle speed or manual speed. Red bars show the over- and underspeed alarm ranges. Under the gauge, the manifold pressure is shown if a sensor is present. The speed gauge can be selected to go to the speed graph screen, which shows a graph of the last two minutes of the speed setpoint and actual speed.
The right section on the home screen shows the current throttle position, which ranges from 0-100%, with 100% being fully open.
Setup
After initial install, or when settings changes are needed, the Governor setup screens are used. The setup screens are accessed by selecting “Setup” on the Governor Home screen, then the “Governor Setup” button. An access level of Setup or higher is needed to access these screens.
STEP 1: ENGINE SETTINGS
Step 1 of governor setup specifies the basic engine settings. These are the number of flywheel teeth, the idle speed for when the panel switch is in “Idle”, and the speed alarm values. After initial setup, these settings are not commonly changed.
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Setup Step 1
If an underspeed alarm is not needed, it can be set to “0”. The speed alarm will always shut down the engine regardless of the control mode or condition. If an RPM setpoint higher than the overspeed alarm is specified, the setting will be allowed, but once the engine hits the overspeed value it will be shut down.
STEP 2: CONTROL SELECTION
In step 2 of the governor setup, the setpoint type and value are specified. For the fixed speed control type, the setpoint is an engine RPM. For suction or discharge control, the setpoint is a PSI value.
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If fixed speed control is selected, the setup will skip to Governor Setup Review after this step.
For pressure control modes, the control type can be "Setpoint, Deadband" or "Linear Ramp". (Note: Linear Ramp mode requires software version 848 or newer).
Setpoint, Deadband: In this mode, a pressure setpoint and deadband is given. If the pressure is outside of the range [Setpoint +/- Deadband], the speed will change (with the direction depending on if it is suction or discharge control). Within the deadband, the speed will not change. The speed will increase or decrease only until the speed hits a range limit, given on the next setup page.
Linear Ramp: For linear ramp mode, a low and high pressure will be given. Between this high and low value, the speed target will be calculated linearly with respect to the low and high operating RPM. Example setup (suction control):
- Low pressure: 20 PSI
- High pressure: 30 PSI
- Low RPM: 1200
- High RPM: 1600
In the above example, if the current suction input pressure is 25 PSI, the RPM target will be 1400 RPM.
STEP 3: PRESSURE CONTROL SETTINGS
If using a pressure control mode (suction or discharge), step 3 will specify some additional settings.
The High and Low Auto RPM specify the operating range of the engine while controlling to the specified pressure. The Governor will not let the engine out of this range, even if the pressure is still too low or high. This is separate from the over- and underspeed alarms mentioned earlier, which specify the absolute min and max speed for the engine.
The response rate determines how fast the Governor will ramp up or down the RPM when in a pressure control mode. The default is 50 RPM/s. A lower value will result in less tight control, but more stable operation because the engine will ramp more slowly.
Note: Generally, for suction control the response rate can be lower, since a well (or upstream supply) changes pressure so slowly. For discharge control, the response rate is usually higher.
STEP 4: SENSOR SETUP (PRESSURE CONTROL ONLY)
If using pressure control mode, this step specifies the low and high specification of the sensor. The low value is the pressure that causes the sensor to output 4mA. The high value is the pressure that causes the sensor to output 20mA. These values should be printed on the sensor itself. For example, a suction sensor might say “4-20mA output for 0-100 PSI”. In this case enter “0” for the minimum PSI value and “100” for the maximum PSI value.
If only one sensor type is used, the other can be left unchanged.
Note that this step is skipped if an EMIT annunciator is present, because the sensor will be set up and wired to the annunciator instead.
SETUP SUMMARY
The setup summary page shows a summary of all the selected settings for the Governor. If the page looks correct, the “Submit” button can be pressed to send the settings to the Governor.
Alarms
The Governor Alarm Setup page (Pg. 522) specifies alarms for RPM and pressure sensors. An access level of Setup or higher is needed to see this screen.
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Governor Alarm Setup
The RPM alarm values duplicate the settings from setup step 1. These specify the low and high shutdown values for the engine. If an underspeed is not needed, it can be set to 0.
Each of the three pressure inputs can have an alarm set up for it. To enable an alarm, click the enable “X” on that row, which will allow the parameters for that sensor to be changed. A low alarm, high alarm, and duration can be specified. If the sensor is outside the operating range for longer than the duration, an alarm will be triggered. If the action selected under “Action” is “Warning,” then triggering the alarm only adds the event to the Alarms screen. If the action is “Shutdown,” then the engine will be shut down in addition to adding the event to the alarm screen.
Note: If a “Shutdown” alarm is needed, the alarm relay on the Governor circuit board should be connected to an annunciator panel. During a shutdown the relay is closed to kill the engine. Additionally, the Governor will close the throttle, but this does not guarantee an engine kill.
Sensor Setup
The Governor Sensor Setup page (Pg. 520) specifies the pressure sensor settings. This duplicates the functionality on setup step 4. An access level of Setup or higher is needed to see this screen.
For each sensor used, specify the low and high PSI value that corresponds to the input that causes an output of 4mA and 20mA respectively. This information can be found stamped on the sensor itself.
Engineering Setup
The Governor Advanced Setup page (Pg. 521) contains advanced settings for governor operation. An access level of Engineering is needed to use this page. A description of each setting is listed below.
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Governor Advanced Setup
Starting RPM: This is the value which the Governor uses to determine if the engine is done cranking. It would not likely need to be changed unless an engine cranks very quickly.
Starting Throttle: This is the throttle position that is held when the engine is cranking. If an engine is hard to start, this could be increased. If an engine starts but overshoots the idle rpm, this could be decreased. Note: When the engine is not turning, the throttle is kept closed. The Governor only opens the throttle when it detects flywheel movement.
RPM Ramp Rate: This value determines how fast the RPM will change when changing between modes (Auto/Idle/Manual). It does not affect how fast the throttle changes when a mode is not changing.
Gov rpm gain adjustment: This value, which can range from 1-100% with a default of 50%, scales the control gains for the throttle. A higher value will result in faster response but possibly more instability. A lower value will result in slower response but more stability.
PID Gains
The "PID Gains" button can be selected to go to the Governor PID Adjustment screen (Pg. 532). This page can be used to change each of the gains. These should only be adjusted by qualified personnel.
Throttle Calibration
The Governor Throttle Calibration page (Pg. 523) can be used to re-calibrate the throttle body. This moves the throttle through its full range of motion and saves the values for the endpoints and also what effort is required to move the throttle. To get to this page, from the Governor Home Screen select "Setup" followed by "Throttle Calibration".
The throttle will usually only need to be recalibrated if the throttle is changed. It could also help to recalibrate it if it seems the calibration is bad, such as if the throttle does not show “0%” with the engine is off.
To calibrate, make sure the engine is off and click the “Calibrate Now” button. Wait for about 20 seconds for the calibration to complete.
Auto Override
In some cases, it is useful to have the governor go to full speed during a pressure-control mode to anticipate an upcoming load change. The governor auto override allows for this.
In general, starting the override mode causes the governor to enter full speed for a given time period (e.g. 3 minutes). Once this time period expires, the governor returns to normal control mode.
The timer will start and count down regardless of control mode, but if the governor is not running in "Auto", the override timer will have no effect.
Methods of triggering
The override mode can be triggered one of these ways:
- Modbus command: A write to modbus register 45107 at the governor address will cause the governor to start the override timer with the written value, in seconds. For example, if '60' is written to modbus register 45107, the governor will go to high 'auto' RPM for 60 seconds.
- CAN command: A command might come to the governor from another module triggering the override. This is set up from the module used.
- 'Discharge' input: The discharge pressure input can be configured to be used as the trigger to control the override mode. This is discussed in more detail below.
More than one of the above can be used at a time. For example, if the 'discharge' input is used to trigger an override period, a modbus command will still be accepted and will become the new timer value.
Override Setup Page
The override setup page is accessed from the governor setup, then "Pressure-Control Override Setup". The page is shown below.
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The setting "Turn on 'Error Relay' output during override", if enabled, will cause the governor error relay to be on (closed to ground) whenever the override is active. This can be used to drive a lamp or to chain to another governor so that one master governor controls override on multiple units.
The next three options are related to the 'discharge' input trigger. This is discussed in the next section.
Discharge input setup
The discharge input can be used to trigger the governor override. This can work in one of two ways
- Signal at discharge starts timer: In this mode, "Use Discharge input to control override" is set to YES, and "Hold override while discharge input active" is set to NO. In this configuration, when the discharge input becomes active (more than 6 mA) the 'default discharge time' starts counting down for the override period. For example, if setup as shown in the above screenshot, when the discharge input goes from below 6mA to above 6mA the governor will go to override mode (full speed) for three minutes, then the timer expires and the speed returns to normal.
- Hold override while discharge active: In this mode, both "Use Discharge input to control override" and "Hold override while discharge input active" are set to YES. This causes the governor to constantly override (go full speed) while the discharge input is above 6mA. As soon as the input goes below 6mA, the override ends. This is the only use of override mode where there is no timer involved.
Note: If discharge input is used for triggering override, it will always show up as "0" in the datalog and on the sensors screen to prevent false recordings.
Wiring
One method for wiring the discharge input to be above 6mA is the following:
- Wire one end of a normally-open relay contact to the "+12V OUT" on the governor
- Wire the other end to a 1kOhm resistor
- Wire the other end of the resistor to the discharge input
- Wire the coil side of the relay to any control source
In this way, when the relay turns on, the discharge input becomes active. This example is shown below.
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