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chapter 2 Flashcards

1
Q

What are the three types of hardware in a DAQ system?

A
  1. Terminal Block
  2. cable
  3. DAQ device
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2
Q

What does a DAQ system do?

A
  1. ADC
  2. Signal conditioning
  3. Samples ADC output in batches
  4. Store data temporarily
  5. Communicate the stored data to computer when needed
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3
Q

What does a terminal block do?

A

A terminal block provides a place to connect signals
It is a place where you can hold the wires coming from the sensor.

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4
Q

What are the types of terminals ?

A
  1. Screw type
  2. Spring type
  3. BNC type
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5
Q

What is the function of the BNC type and why is it used?

A

It shields noise and is used to transfer high frequency signals in a secure way

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6
Q

When is the spring type used?

A

When the load is small

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7
Q

When is the screw type used?

A

For Industries

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8
Q

List 5 advantages of a terminal block

A
  1. protects from electrical surge
  2. Protection from noise
  3. I/V and V/I conversion (compatible signal with DAQ)
  4. Clean and organized
  5. Easy maintenance
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9
Q

The type of terminal block you choose depends on which 2 factors?

A
  1. Device
  2. Number of signals you are measuring
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10
Q

What is the main advantage of shielded terminal blocks over non-shielded terminal blocks?

A

They offer better protection against noise

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11
Q

What additional features might some terminal blocks include, and why are they necessary?

A

Some terminal blocks contain cold-junction compensation that are necessary to measure a thermocouple properly.

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12
Q

What is the function of a cable in a DAQ system?

A

transports the signal from the terminal block to the DAQ device

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13
Q

Can cables also be shielded or non shielded?

A

Yes, cables can be shielded or non-shielded, just like terminal blocks.

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14
Q

Which DAQ device series is the BNC-2120 compatible with?

A

compatible with NI X Series, M Series, E Series, and S Series multifunction I/O DAQ devices, as well as analog output devices.

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15
Q

What components does the BNC-2120’s function generator include?

A

It includes a frequency range selection switch, a frequency knob, and an amplitude knob.

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16
Q

What types of waveforms can the BNC-2120 function generator produce?

A

It can produce sine and triangle waveforms, as well as TTL-compatible square waveforms.

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17
Q

What is the purpose of the mechanical quadrature encoder circuit in the BNC-2120?

A

The quadrature encoder circuit produces 96 pulses per encoder revolution and provides information about rotation direction.

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18
Q

What do the PULSES and UP/DN outputs from the quadrature encoder indicate?

A

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.

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19
Q

What are the four standard elements of typical NI multifunction I/O DAQ devices?

A

Analog input, analog output, digital I/O, and counters.

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20
Q

How can you transfer signals from a DAQ device to a computer?

A

variety of bus structures, such as PCI, PCMCIA, or USB.

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21
Q

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?

A
  1. I/O connector
  2. computer I/O interface circuitry
  3. Real-Time System Integration (RTSI) Bus.
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22
Q

What is the function of the I/O connector in a DAQ device?

A

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

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23
Q

How does the computer I/O interface circuitry work in a DAQ system?

A

It transfers information between the DAQ device and the computer.

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24
Q

What is the purpose of the RTSI Bus in a DAQ system?

A

The RTSI Bus synchronizes signals between multiple DAQ devices in the same computer.

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25
Q

What happens to the analog input signal after entering the I/O connector in a DAQ system?

A

It passes through the analog input circuitry before reaching the analog-to-digital converter (ADC).

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26
Q

What are the two main components of the analog input circuitry in a DAQ device?

A
  1. MUX
  2. Instrumentation amplifier
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27
Q

What is the function of the multiplexer (mux) in the analog input circuitry?

A

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.

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28
Q

What is the role of the instrumentation amplifier in the analog input circuitry?

A

The instrumentation amplifier amplifies or attenuates the incoming signal to make it fill the range of the ADC as much as possible.

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29
Q

What is the function of an Analog-to-Digital Converter (ADC) in a DAQ system?

A

The ADC converts an analog voltage into a digital number that can be sent to the computer for interpretation.

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30
Q

How does the ADC work with other components in the DAQ system?

A

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.

31
Q

What is the function of a Digital-to-Analog Converter (DAC) in a DAQ system?

A

A DAC converts a digital number from the computer into an analog signal that is output through the I/O connector.

32
Q

How does a DAC differ from an ADC?

A

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.

33
Q

How is the digital number sent to the DAC in a DAQ system?

A

The digital number is sent from the computer through the computer I/O interface circuitry to the DAC.

34
Q

What functions can the digital I/O circuitry of a DAQ device perform?

A

The digital I/O circuitry can perform both input and output functions. (read digital i/p and write digital o/p)

35
Q

What are some examples of applications for digital I/O functionality in a DAQ system?

A

Applications include monitoring a switch to detect state changes or controlling a relay.

36
Q

How are digital signals managed in a typical DAQ device?

A

A DAQ device has multiple digital lines that can acquire or generate digital signals using software timing or hardware timing.

37
Q

What is the difference between software timing and hardware timing in digital I/O?

A

Software timing relies on the computer’s operating system for timing, while hardware timing uses a dedicated clock to ensure more precise timing.

38
Q

What is the primary function of counters in a DAQ system?

A

Counters acquire and generate digital signals.

39
Q

What are timebases, and why are they important for counters?

A

Timebases are built-in timing signals that make counters ideal for measuring the rate of a digital signal.

40
Q

In what types of applications can the counter functionality of a DAQ device be used?

A

It can be used for measuring the frequency of a motor shaft and for controlling stepper motors by generating a specific frequency pulse train.

41
Q

What does the term ‘measuring the rate of a digital signal’ refer to in the context of counters?

A

It refers to determining how quickly the digital signal changes state, such as counting pulses or measuring frequency.

42
Q

What factors should you consider when choosing DAQ hardware?

A
  1. BUS of DAQ device
  2. Signals to measure
  3. Accuracy of measurements
43
Q

What are the 5 questions to consider when choosing the right bus for a data acquisition application?

A
  1. How much data will i be streaming across the bus?
    2.what are my single point I/O requirements?
  2. Do i need to synchronize multiple devices?
  3. How portable should this system be?
  4. How far will my measurements be from my computer ?
44
Q

What is bus bandwidth, and why is it important?

A

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.

45
Q

How does the PCI bus’s bandwidth compare to that of PCI Express and PXI Express?

A

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.

46
Q

What is the equation for calculating minimum bandwidth?

A

Min BW= (# of bytes per sample) x (sampling speed) x (# of channels)

47
Q

Why is bus bandwidth important for data acquisition systems?

A

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.

48
Q

Why is single-point I/O important for some applications?

A

Single-point I/O is crucial for applications where I/O values must be updated immediately and consistently, such as in control systems.

49
Q

What is bus latency?

A

Bus latency is the delay between when a software function is called and when the actual hardware I/O value is updated.

50
Q

What is determinism in the context of I/O systems?

A

Determinism refers to the consistency of I/O execution time. A bus with consistent latency is more deterministic

51
Q

Why is determinism important for control applications?

A

Determinism ensures the control loop executes at a constant rate.

52
Q

Which types of buses should be avoided for closed-loop control applications and why?

A

Buses with high latency and poor determinism, such as USB or wireless

53
Q

Which bus types are preferred for low-latency, single-point I/O applications, and why?

A

Internal buses such as PCI Express and PXI Express are preferred because they offer lower latency

54
Q

Why might you need to synchronize multiple devices in a measurement system?

A

Complex measurement systems, such as those with hundreds of input channels or multiple types of instruments, may require synchronization to share clocks and triggers

55
Q

What feature do almost all NI DAQ devices provide for synchronization?

A

NI DAQ devices provide Programmable Function Input (PFI) lines, which can be used to route clocks and triggers between devices for synchronization.

56
Q

What advantage do PCI and PCI Express devices offer for device synchronization?

A

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

57
Q

What is the best bus option for high-performance synchronization and triggering across multiple devices?

A

The PXI platform, including PXI and PXI Express, is the best option for high-performance synchronization

58
Q

Why is portability an important consideration for a data acquisition system?

A

For applications that require compact and easily transportable hardware, such as in-vehicle data acquisition.

59
Q

What are some bus options that are well-suited for portable data acquisition systems?

A

External buses like USB and Ethernet

60
Q

What kind of applications particularly benefit from compact and portable DAQ hardware?

A

In-vehicle data acquisition applications benefit greatly from compact, portable hardware that can easily be transported

61
Q

Why is it important to place data acquisition hardware close to the signal source?

A

Placing the hardware close to the signal source helps achieve better signal integrity and measurement accuracy.

62
Q

What challenges can arise when measurements are taken far from the computer?

A

Running long cables for large distributed measurements, such as in structural or environmental monitoring, can be costly and may result in noisy signals.

63
Q

How does the distance between the measurement source and the computer affect signal integrity?

A

Longer distances can degrade signal quality, potentially introducing noise and reducing measurement accuracy.

64
Q

What is one solution to address the challenge of distance in data acquisition systems?

A

Using a portable computing platform can move the system closer to the signal source

65
Q

How can wireless technology help in data acquisition when measurements are far from the computer?

A

Wireless technology removes the need for physical connections

66
Q

Wireless technology removes the need for physical connections

A

Applications like structural health monitoring and environmental monitoring

67
Q

What factors should you consider when choosing a DAQ device for your application?

A

number of channels, sampling rate, input range

68
Q

What is ‘code width’ in the context of a DAQ device?

A

Code width is the smallest change in the signal that the DAQ device can detect

69
Q

What is resolution, and how does it affect measurements in a DAQ system?

A

Resolution is the number of bits used to represent an analog signal, and it determines the precision of the measurement.

70
Q

Why is higher resolution important in a DAQ device?

A

Higher resolution increases the number of divisions the ADC can break down, making it possible to detect smaller changes in the signal

71
Q

What is the purpose of amplification or attenuation in a DAQ system?

A

Amplification or attenuation improves the representation of a signal by decreasing the input range of an ADC

72
Q

How is code width calculated in a DAQ device?

A

code width= (device i/p range)/ (2^resolution in bits)

73
Q

What factors influence the accuracy of a measurement in a DAQ system?

A

Accuracy is influenced by gain errors, offset errors from the amplifier and ADC, and noise in the system.

computer aided (4 decks)

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