Avionics Flashcards: Volume 2 - Pt.2
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What are the three basic requirements of facility power?
Be at proper voltage, at the required amperage, and at the necessary frequencies.
What is the input voltage requirement of a test station?
What are the input frequency requirements of a test station?
60 Hz and 400 Hz.
What two components are required to produce voltage outputs from an AC power supply?
Transformers and filters.
DC power supplies use what three types of rectifiers?
Half-wave, full-wave, and bridge.
What is the purpose of the 400 Hz power to a test station?
To provide all the necessary voltages for the TRUs and the LRUs involved in checkout procedures.
What is stimulus?
Anything generated for application to a TRU or UUT.
What items are considered stimulus?
Cooling air, AC & DC voltages, RF Signals, AF signals, and logic signals.
What are the possible output signals of a waveform generator?
Sine, square, or triangular waveform and DC voltage levels.
What is the frequency range of an AF generator?
20 to 20,000 Hz.
What is the purpose of a measurement device?
Measure, monitor, or evaluate responses from the UUT.
What type of signals do digital multimeters measure?
AC RMS voltage, DC voltage, and resistance.
What is frequency counter period measurement?
The time from one input pulse or signal to the next - measured in seconds.
What is used to measure the power level of RF signals?
What is considered the most versatile measurement instrument capable of visual display?
What primary function does switching provide?
A means of interconnecting test station resources with the UUT.
Test station switching has what two classifications?
Stimulus and measurement.
What are the three major considerations in designing proper switching in a test station?
- 1. Selection of stimulus signals.
- 2. Routing of signals throughout the test station and the UUT.
- 3. Routing of UUT response to a selected measurement device.
What controls the switching in a computerized test station?
Program execution of specific test statements.
What is considered to be the most important test station function?
What is a major factor in determining the type of control device a test station will have?
Speed of UUT operation.
What is a computer program?
A set of instructions that allow a digital computer to process data.
Instructions identified by a code number describe what type of computer program?
What is commonly used to represent the digits in computer language?
Voltages and currents.
How many devices may be connected to one bus?
Up to 15 devices.
List the four categories in which the IEEE-488 bus lines are grouped.
- 1. Data Lines
- 2. Handshake Lines
- 3. Bus management Lines
- 4. Ground Lines
List the three handshake lines.
Which of the handshake lines is asserted by a listener to indicate it is not yet ready for the next data or control byte?
List the five bus management lines.
- 1. ATN
- 2. EOI
- 3. IFC
- 4. REN
- 5. SRQ
Describe a service request line.
The SRQ line is like an interrupt; it may be asserted by any device, the SRQ is released when polled by the controller.
When can the NDAC handshake line go high?
When the slowest listener has accepted the data byte.
What is multiplexing?
The process of transmitting information from several sources through one system with different signals staggered in time to form a composite pulse train.
What is the biggest advantage of multiplexing?
The significant savings in size and weight of avionic units and the interconnecting wiring between them.
How many types of avionic terminals are there, and list them?
Three; bus controller, monitor, and remote terminal.
What is the purpose of the bus controller?
To coordinate the flow of information on the data bus.
What is the purpose of an RT on an avionic data bus?
Any terminal not acting as the bus controller or a bus monitor.
What are the four elements making up the MIL-STD-1553 data bus system?
- 1. Bus controller
- 2. Remote terminal
- 3. Bus monitor
- 4. The Data bus
What does the bus controller do when it detects an error?
It will typically re-transmit the command to the offending RT. If multiple attempts of transmitting to an RT continue to result in errors, the bus controller usually attempts to establish communications with the failing RT on the redundant, backup data bus.
An RT must be able to handle protocol errors. What's a protocol error?
An incoming command and data that's electrically correct, but the message is illegal by the protocol established within the MIL-STD-1553.
What element of the data bus is capable of assuming the task of bus controller in the event the bus controller fails?
A remote terminal.
What element of a data bus is not needed for normal operation and its not normally included in avionic data bus systems?
When are transformer-coupled stubs used in the 1553 bus?
With stub lengths over 20 feet.
Which type of stub coupling is better, transformer-coupled or direct-coupled?
The transformer-coupled stub is far superior.
What types of digital information or words are used on a data bus?
Command, status, and data.
Describe the common structure of command, data, and data words.
Each word type is 20 bits-period in length. Each word has a command sync character, which is 3 bits-period in length, followed by 16 information bits and, finally, 1 parity bit.
In the SAM field of a command word, to what does "sub-address" refer?
To a function or an area within the RT to which the command is being directed.
Which elements of the data bus transmit data words?
Either the bus controller or an RT.
During a controller-to-RT transfer, what does the RT do after receiving command and data words from the bus controller?
The receiving RT validates the incoming command and data words. If the message is valid, the RT responds with a status word, acknowledging receipt of the command and data.
In an RT-to-RT transfer, what does the receiving RT do upon completion of the transfer?
Once the receiving remote terminal has received and validated the data words, it responds with its own status word indicating the successful completion of the transfer.
In a mode command without a data word, what does the word count field contain?
Mode code for the command to be implemented.
For what does the abbreviation VXI stand?
VME extension for instrumentation.
What factors largely drove industry to develop the VXI standard?
Industry demand for reduction in physical size, tighter time and synchronization between multiple instruments, and faster transfer rates.
List four benefits that VXI brings to instrumentation users.
- 1. Open, multivendor standards
- 2. Increased system throughput
- 3. Smaller size and higher density
- 4. More precise timing and synchronization
- 5. Standardized VXI "plug&play" software
- 6. Modular, rugged design improves reliability
How can the logical address of a VXI device be set?
Can be manually set or automatically configured by the system start-up.
What are the two classifications of VXI devices with respect to register capability?
Register-based and message-based devices.
What are VXI message-based devices required to use in order to communicate in a standard way?
Word serial protocol.
What is defined by the VXI bus and used to construct a hierarchical system of VXI devices?
Commander - servant communication protocol.
How does a message-based device communicate with its commander?
By word serial protocol.
How does a register-based device communicate with its commander?
By device - specific register manipulation.
The VXI bus specifies how many modules?
What are the larger size modules (C and D) for?
Higher performance instrumentation.
Within the VXI mainframe, what provides the communication path between the other modules in the mainframe and the host computer?
Slot - 0 controller.
A VXI controller may contain an embedded computer and/or with what can it communicate?
What are the three methods used to control a VXI system?
- 1. VXI mainframe linked to an external controller via the GPIB
- 2. VXI - based embedded computer
- 3. A high-speed MXI bus link from an external computer.
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