chapter 2 Flashcards
What are the three types of hardware in a DAQ system?
- Terminal Block
- cable
- DAQ device
What does a DAQ system do?
- ADC
- Signal conditioning
- Samples ADC output in batches
- Store data temporarily
- Communicate the stored data to computer when needed
What does a terminal block do?
A terminal block provides a place to connect signals
It is a place where you can hold the wires coming from the sensor.
What are the types of terminals ?
- Screw type
- Spring type
- BNC type
What is the function of the BNC type and why is it used?
It shields noise and is used to transfer high frequency signals in a secure way
When is the spring type used?
When the load is small
When is the screw type used?
For Industries
List 5 advantages of a terminal block
- protects from electrical surge
- Protection from noise
- I/V and V/I conversion (compatible signal with DAQ)
- Clean and organized
- Easy maintenance
The type of terminal block you choose depends on which 2 factors?
- Device
- Number of signals you are measuring
What is the main advantage of shielded terminal blocks over non-shielded terminal blocks?
They offer better protection against noise
What additional features might some terminal blocks include, and why are they necessary?
Some terminal blocks contain cold-junction compensation that are necessary to measure a thermocouple properly.
What is the function of a cable in a DAQ system?
transports the signal from the terminal block to the DAQ device
Can cables also be shielded or non shielded?
Yes, cables can be shielded or non-shielded, just like terminal blocks.
Which DAQ device series is the BNC-2120 compatible with?
compatible with NI X Series, M Series, E Series, and S Series multifunction I/O DAQ devices, as well as analog output devices.
What components does the BNC-2120’s function generator include?
It includes a frequency range selection switch, a frequency knob, and an amplitude knob.
What types of waveforms can the BNC-2120 function generator produce?
It can produce sine and triangle waveforms, as well as TTL-compatible square waveforms.
What is the purpose of the mechanical quadrature encoder circuit in the BNC-2120?
The quadrature encoder circuit produces 96 pulses per encoder revolution and provides information about rotation direction.
What do the PULSES and UP/DN outputs from the quadrature encoder indicate?
PULSES: outputs a pulse train generated by rotating the encoder shaft, with four pulses per one mechanical click.
UP/DN: indicates the rotation direction, with a low signal for counterclockwise rotation and a high signal for clockwise rotation.
What are the four standard elements of typical NI multifunction I/O DAQ devices?
Analog input, analog output, digital I/O, and counters.
How can you transfer signals from a DAQ device to a computer?
variety of bus structures, such as PCI, PCMCIA, or USB.
What are the three interfaces for receiving and sending signals in a DAQ device? ie: What are the components of a I/O DAQ device?
- I/O connector
- computer I/O interface circuitry
- Real-Time System Integration (RTSI) Bus.
What is the function of the I/O connector in a DAQ device?
The I/O connector is where the signal enters or leaves the DAQ device.
one end of the cable connects to I/O connector and the other end connects to the terminal block
How does the computer I/O interface circuitry work in a DAQ system?
It transfers information between the DAQ device and the computer.
What is the purpose of the RTSI Bus in a DAQ system?
The RTSI Bus synchronizes signals between multiple DAQ devices in the same computer.
What happens to the analog input signal after entering the I/O connector in a DAQ system?
It passes through the analog input circuitry before reaching the analog-to-digital converter (ADC).
What are the two main components of the analog input circuitry in a DAQ device?
- MUX
- Instrumentation amplifier
What is the function of the multiplexer (mux) in the analog input circuitry?
It connects several input channels to the instrumentation amplifier at a time. It rotates through multiple channels, connecting them one by one to the amplifier.
What is the role of the instrumentation amplifier in the analog input circuitry?
The instrumentation amplifier amplifies or attenuates the incoming signal to make it fill the range of the ADC as much as possible.
What is the function of an Analog-to-Digital Converter (ADC) in a DAQ system?
The ADC converts an analog voltage into a digital number that can be sent to the computer for interpretation.
How does the ADC work with other components in the DAQ system?
The analog input circuitry works with the ADC to acquire an analog signal, enabling the system to measure the level, shape, or frequency of the signal.
What is the function of a Digital-to-Analog Converter (DAC) in a DAQ system?
A DAC converts a digital number from the computer into an analog signal that is output through the I/O connector.
How does a DAC differ from an ADC?
A DAC performs the opposite task of an ADC. While an ADC converts an analog signal to a digital number, a DAC converts a digital number into an analog signal.
How is the digital number sent to the DAC in a DAQ system?
The digital number is sent from the computer through the computer I/O interface circuitry to the DAC.
What functions can the digital I/O circuitry of a DAQ device perform?
The digital I/O circuitry can perform both input and output functions. (read digital i/p and write digital o/p)
What are some examples of applications for digital I/O functionality in a DAQ system?
Applications include monitoring a switch to detect state changes or controlling a relay.
How are digital signals managed in a typical DAQ device?
A DAQ device has multiple digital lines that can acquire or generate digital signals using software timing or hardware timing.
What is the difference between software timing and hardware timing in digital I/O?
Software timing relies on the computer’s operating system for timing, while hardware timing uses a dedicated clock to ensure more precise timing.
What is the primary function of counters in a DAQ system?
Counters acquire and generate digital signals.
What are timebases, and why are they important for counters?
Timebases are built-in timing signals that make counters ideal for measuring the rate of a digital signal.
In what types of applications can the counter functionality of a DAQ device be used?
It can be used for measuring the frequency of a motor shaft and for controlling stepper motors by generating a specific frequency pulse train.
What does the term ‘measuring the rate of a digital signal’ refer to in the context of counters?
It refers to determining how quickly the digital signal changes state, such as counting pulses or measuring frequency.
What factors should you consider when choosing DAQ hardware?
- BUS of DAQ device
- Signals to measure
- Accuracy of measurements
What are the 5 questions to consider when choosing the right bus for a data acquisition application?
- How much data will i be streaming across the bus?
2.what are my single point I/O requirements? - Do i need to synchronize multiple devices?
- How portable should this system be?
- How far will my measurements be from my computer ?
What is bus bandwidth, and why is it important?
Bus bandwidth is the limit on the amount of data that can be transferred over a bus in a certain period, typically specified in megabytes per second (MB/s). It is important for ensuring that enough data can be transmitted for dynamic waveform measurements.
How does the PCI bus’s bandwidth compare to that of PCI Express and PXI Express?
The PCI bus has a theoretical bandwidth of 132 MB/s shared among all PCI devices
PCI Express and PXI Express provide dedicated bandwidth for maximum data throughput per device.
What is the equation for calculating minimum bandwidth?
Min BW= (# of bytes per sample) x (sampling speed) x (# of channels)
Why is bus bandwidth important for data acquisition systems?
Bus bandwidth must support the speed at which data is acquired. If data is being streamed on multiple channels, bandwidth becomes a critical factor in choosing the data acquisition bus.
Why is single-point I/O important for some applications?
Single-point I/O is crucial for applications where I/O values must be updated immediately and consistently, such as in control systems.
What is bus latency?
Bus latency is the delay between when a software function is called and when the actual hardware I/O value is updated.
What is determinism in the context of I/O systems?
Determinism refers to the consistency of I/O execution time. A bus with consistent latency is more deterministic
Why is determinism important for control applications?
Determinism ensures the control loop executes at a constant rate.
Which types of buses should be avoided for closed-loop control applications and why?
Buses with high latency and poor determinism, such as USB or wireless
Which bus types are preferred for low-latency, single-point I/O applications, and why?
Internal buses such as PCI Express and PXI Express are preferred because they offer lower latency
Why might you need to synchronize multiple devices in a measurement system?
Complex measurement systems, such as those with hundreds of input channels or multiple types of instruments, may require synchronization to share clocks and triggers
What feature do almost all NI DAQ devices provide for synchronization?
NI DAQ devices provide Programmable Function Input (PFI) lines, which can be used to route clocks and triggers between devices for synchronization.
What advantage do PCI and PCI Express devices offer for device synchronization?
PCI and PCI Express devices support the Real-Time System Integration (RTSI) bus, which allows multiple DAQ boards in a desktop system to be directly cabled together
What is the best bus option for high-performance synchronization and triggering across multiple devices?
The PXI platform, including PXI and PXI Express, is the best option for high-performance synchronization
Why is portability an important consideration for a data acquisition system?
For applications that require compact and easily transportable hardware, such as in-vehicle data acquisition.
What are some bus options that are well-suited for portable data acquisition systems?
External buses like USB and Ethernet
What kind of applications particularly benefit from compact and portable DAQ hardware?
In-vehicle data acquisition applications benefit greatly from compact, portable hardware that can easily be transported
Why is it important to place data acquisition hardware close to the signal source?
Placing the hardware close to the signal source helps achieve better signal integrity and measurement accuracy.
What challenges can arise when measurements are taken far from the computer?
Running long cables for large distributed measurements, such as in structural or environmental monitoring, can be costly and may result in noisy signals.
How does the distance between the measurement source and the computer affect signal integrity?
Longer distances can degrade signal quality, potentially introducing noise and reducing measurement accuracy.
What is one solution to address the challenge of distance in data acquisition systems?
Using a portable computing platform can move the system closer to the signal source
How can wireless technology help in data acquisition when measurements are far from the computer?
Wireless technology removes the need for physical connections
Wireless technology removes the need for physical connections
Applications like structural health monitoring and environmental monitoring
What factors should you consider when choosing a DAQ device for your application?
number of channels, sampling rate, input range
What is ‘code width’ in the context of a DAQ device?
Code width is the smallest change in the signal that the DAQ device can detect
What is resolution, and how does it affect measurements in a DAQ system?
Resolution is the number of bits used to represent an analog signal, and it determines the precision of the measurement.
Why is higher resolution important in a DAQ device?
Higher resolution increases the number of divisions the ADC can break down, making it possible to detect smaller changes in the signal
What is the purpose of amplification or attenuation in a DAQ system?
Amplification or attenuation improves the representation of a signal by decreasing the input range of an ADC
How is code width calculated in a DAQ device?
code width= (device i/p range)/ (2^resolution in bits)
What factors influence the accuracy of a measurement in a DAQ system?
Accuracy is influenced by gain errors, offset errors from the amplifier and ADC, and noise in the system.
