Basic Interfacing
The diagram below illustrates the basic interfacing of the SGCU to the operator and the other system components.
Operator Interface
The pilot has one switch and one button to control and two annunciation lights to monitor:
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The S/G on-off switch enables or disables both starting and generating.
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The START button initiates the starter to begin spinning the engine only if the S/G on-off switch is in the enabled position.
If depressed again, with the starter already engaged, it disengages the starter.
The START button can be implimented with a momentary toggle switch or a button.
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The GEN-OFF light indicates (turns on) when power generation is OFF-LINE.
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The STARTER light indicates (turns on) when the starter is engaged.
Starter-Generator / Line-Contactor / Electrical System Interface
The SGCU interfaces with the MG94 starter/generator to drive the shunt field, and measure S/G loading, speed and voltage.
The line-contactor links the main aircraft electrical bus to the starter/generator and is also controlled by the SGCU.
Operational Scenario
When you switch the aircraft MASTER switch ON you will notice both the GEN-OFF and the STARTER indicators turn on for about
2 seconds while the SGCU performs a system self-check. The lights go out to show all is good and ready.
To start your turbine engine, you switch S/G on-off switch ON, switch the ignition ON and depress the START button.
The STARTER light turns on as the engine starts to spin.
You apply fuel at the right time, the engine lights up and eventually
reaches idle speed at which time the STARTER light turns off, while the GEN-OFF light remains dark to indicate that the
starter/generator has successfully switched from being a starter to being a generator.
Should you decide to turn the generator off, you can simply move the S/G on-off switch to the OFF position. With the engine
turning the GEN-OFF light comes on to indicate the generator is now off-line. To bring the generator back on-line you simply
return the S/G on-off switch to the ON position. The GEN-OFF light will go dark as the generator again kicks in.
The SGCU has built-in protection against fault conditions as listed under features above. If one of the conditions is detected
by the SGCU, it will firstly take the generator off-line by opening the line-contactor to isolate the starter/generator from the main bus.
Secondly, the GEN-OFF light will turn on. The pilot can address the cause of the fault and decide to
re-engage (reset) the generator. This is done by switching the S/G on-off switch to OFF for about a second and then back to ON again.
The SGCU will attempt to bring the generator back on-line, and if successful the GEN-OFF light will turn off and stay dark.
Maintenance Operations
From time to time a Laptop PC and USB-to-Serial Converter may be connected to the SGCU-MG94 within the system,
as depicted below, in order to perform maintenance operations on an installed system.
Maintenance operations allow you to confirm (troubleshoot) your installation, make adjustments,
view operational information and record a certain operation. All these tasks are done through the
VR System Link software running on the laptop.
System Link enables making adjustments to set-points, calibration values and
other configuration settings, such as adjusting the relugation voltage set-point (26.0V to 30.0V).
More Information
Additional information is contained in our SGCU-MG94 manual, wiring diagrams, etc. listed in the colum
on the right side of the web page. You'll also find SGCU-MG94 firmware updates here that we provide free of charge to all customers.
This firmware will be updated from time to time to provide additional features and improvements.
Also, please feel free to contact us with any query you may have regarding any of our products.
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