1. www.ni.com CHAPTER 1 Transducers, Signals, and Signal Conditioning Topics Data Acquisition Overview Transducers Signals Signal Conditioning Lesson 8 Data Acquisition and Waveforms

2. System Overview

3. Transducer Overview Topics What is a Transducer? Types of Transducers

4. What is a Transducer? A transducer converts a physical phenomena into a measurable signal Signal Physical Phenomena

5. Signal Overview Topics Types of Signals Information in a Signal –State, Rate, Level, Shape, and Frequency

6. Signal Classification Your Signal AnalogDigital

7. Two possible levels: High/On (2 - 5 Volts) Low/Off (0 - 0.8 Volts) Two types of information: State Rate Digital Signals Digital Your Signal

8. Digital Signal Information Digital Your Signal

9. Analog Signals Your Signal Analog Continuous signal Can be at any value with respect to time Three types of information: Level Shape Frequency (Analysis required)

10. Analog Signal Information Your Signal Analog Analysis Required

11. Signal Conditioning Overview Topics Purpose of Signal Conditioning Types of Signal Conditioning

12. Why Use Signal Conditioning? Signal Conditioning takes a signal that is difficult for your DAQ device to measure and makes it easier to measure Signal Conditioning is not always required –Depends on the signal being measured Noisy, Low-Level Signal Filtered, Amplified Signal

13. Amplification Used on low-level signals (i.e. thermocouples) Maximizes use of Analog-to-Digital Converter (ADC) range and increases accuracy Increases Signal to Noise Ratio (SNR) Low-Level Signal External Amplifier DAQ Device Lead Wires Instrumentation Amplifier Noise ADC +_+_

14. DAQ Hardware Overview Topics Types of DAQ Hardware Components of a DAQ device Configuration Considerations

15. Data Acquisition Hardware DAQ Hardware turns your PC into a measurement and automation system Computer Your Signal DAQ Device Terminal Block Cable

16. Terminal Block and Cable Your Signal Terminal Block Cable Terminal Block and Cable route your signal to specific pins on your DAQ device Terminal Block and Cable can be a combination of 68 pin or 50 pin 50 pin connector

17. DAQ Device Computer DAQ Device Most DAQ devices have: –Analog Input –Analog Output –Digital I/O –Counters Specialty devices exist for specific applications –High speed digital I/O –High speed waveform generation –Dynamic Signal Acquisition (vibration, sonar) Connect to the bus of your computer Compatible with a variety of bus protocols –PCI, PXI/CompactPCI, ISA/AT, PCMCIA, USB, 1394/Firewire

18. Configuration Considerations Analog Input –Resolution –Range –Gain –Code Width –Mode (Differential, RSE, or NRSE) Analog Output –Internal vs. External Reference Voltage –Bipolar vs. Unipolar

19. Resolution Number of bits the ADC uses to represent a signal Resolution determines how many different voltage changes can be measured Example: 12-bit resolution Larger resolution = more precise representation of your signal # of levels = 2 resolution = 2 12 = 4,096 levels

20. 100200150500 Time (  s) 0 1.25 5.00 2.50 3.75 6.25 7.50 8.75 10.00 Amplitude (volts) 16-Bit Versus 3-Bit Resolution (5kHz Sine Wave) 16-bit resolution 3-bit resolution 000 001 010 011 100 101 110 111 | ||| | Resolution Example 3-bit resolution can represent 8 voltage levels 16-bit resolution can represent 65,536 voltage levels

21. Range Minimum and maximum voltages the ADC can digitize DAQ devices often have different available ranges –0 to +10 volts –-10 to +10 volts Pick a range that your signal fits in Smaller range = more precise representation of your signal –Allows you to use all of your available resolution

22. Range 100200150500 Time (  s) 0 1.25 5.00 2.50 3.75 6.25 7.50 8.75 10.00 Amplitude (volts) Range = 0 to +10 volts (5kHz Sine Wave) 3-bit resolution 000 001 010 011 100 101 110 111 | ||| | 10020015050 Time (  s) 0 -7.50 -10.00 -5.00 -2.50 2.50 5.00 7.50 10.00 Amplitude (volts) Range = -10 to +10 volts (5kHz Sine Wave) 3-bit resolution 000 001 010 011 100 101 110 111 | ||| | Proper Range Using all 8 levels to represent your signal Improper Range Only using 4 levels to represent your signal

23. Gain Gain setting amplifies the signal for best fit in ADC range Gain settings are 0.5, 1, 2, 5, 10, 20, 50, or 100 for most devices You don’t choose the gain directly –Choose the input limits of your signal in LabVIEW –Maximum gain possible is selected –Maximum gain possible depends on the limits of your signal and the chosen range of your ADC Proper gain = more precise representation of your signal –Allows you to use all of your available resolution

24. Gain Example 100200150500 Time (  s) 0 1.25 5.00 2.50 3.75 6.25 7.50 8.75 10.00 Amplitude (volts) Different Gains for 16-bit Resolution (5kHz Sine Wave) Gain = 2 | ||| | Your Signal Gain = 1 –Input limits of the signal = 0 to 5 Volts –Range Setting for the ADC = 0 to 10 Volts –Gain Setting applied by Instrumentation Amplifier = 2

25. Code Width is the smallest change in the signal your system can detect (determined by resolution, range, and gain) Smaller Code Width = more precise representation of your signal Example: 12-bit device, range = 0 to 10V, gain = 1 code width = range gain * 2 resolution 10 1 * 2 12 = 2.4 mV range gain * 2 resolution = 20 1 * 2 12 = 4.8 mV Increase range: 10 100 * 2 12 = 24  V Increase gain: Code Width

26. Grounding Issues To get correct measurements you must properly ground your system How the signal is grounded will affect how we ground the instrumentation amplifier on the DAQ device Steps to proper grounding of your system: –Determine how your signal is grounded –Choose a grounding mode for your Measurement System Measurement System Signal Source VSVS - + VMVM

27. Signal Source Categories Grounded + _ VsVs Floating + _ VsVs Signal Source

28. Grounded Signal Source Signal is referenced to a system ground –earth ground –building ground Examples: –Power supplies –Signal Generators –Anything that plugs into an outlet ground Grounded + _ VsVs Signal Source

29. Floating Signal Source Floating Signal is NOT referenced to a system ground –earth ground –building ground Examples: –Batteries –Thermocouples –Transformers –Isolation Amplifiers + _ VsVs Signal Source

30. Measurement System Three modes of grounding for your Measurement System –Differential –Referenced Single- Ended (RSE) –Non-Referenced Single- Ended (NRSE) Mode you choose will depend on how your signal is grounded Measurement System - +

31. VMVM ACH (n) ACH (n + 8) + _ Instrumentation Amplifier + _ VSVS + _ AISENSE AIGND Measurement System Differential Mode Two channels used for each signal –ACH 0 is paired with ACH 8, ACH 1 is paired with ACH 9, etc. Rejects common-mode voltage and common-mode noise

32. VMVM ACH (n) ACH (n + 8) + _ Instrumentation Amplifier + _ VSVS + AISENSE AIGND _ RSE Mode Referenced Single-Ended (RSE) Measurement made with respect to system ground One channel used for each signal Doesn’t reject common mode voltage Measurement System

33. VMVM ACH (n) ACH (n + 8) + _ Instrumentation Amplifier + _ VSVS + _ AISENSE AIGND NRSE Mode Non-Referenced Single-Ended (NRSE) Variation on RSE One channel used for each signal Measurement made with respect to AISENSE not system ground AISENSE is floating Doesn’t reject common mode voltage Measurement System

34. Choosing Your Measurement System Signal Source DifferentialRSENRSE Measurement System Grounded + _ VsVs Floating + _ VsVs DifferentialRSENRSE Measurement System

35. Options for Grounded Signal Sources RSE NRSE Differential BETTER + Rejects Common-Mode Voltage - Cuts Channel Count in Half NOT RECOMMENDED - Voltage difference (Vg) between the two grounds makes a ground loop that could damage the device GOOD + Allows use of entire channel count - Doesn’t reject Common-Mode Voltage

36. Options for Floating Signal Sources RSE NRSE Differential BEST + Rejects Common-Mode Voltage - Cuts Channel Count in Half - Need bias resistors BETTER + Allows use of entire channel count + Don’t need bias resistors - Doesn’t reject Common-Mode Voltage GOOD + Allows use of entire channel count - Need bias resistors - Doesn’t reject Common-Mode Voltage

37. DAQ Software Overview Topics Levels of DAQ Software NI-DAQ Overview Measurement & Automation Explorer (MAX) Overview

38. Levels of Software DAQ Device User

39. What is NI-DAQ? Driver level software –DLL that makes direct calls to your DAQ device Supports the following National Instruments software: –LabVIEW –Measurement Studio Also supports the following 3rd party languages: –Microsoft C/C++ –Visual Basic –Borland C++ –Borland Delphi

40. What is MAX? MAX stands for Measurement & Automation Explorer MAX provides access to all your National Instruments DAQ, GPIB, IMAQ, IVI, Motion, VISA, and VXI devices Used for configuring and testing devices Functionality broken into: –Data Neighborhood –Devices and Interfaces –Scales –Software Icon on your Desktop

41. Data Neighborhood Provides access to the DAQ Channel Wizard Shows configured Virtual Channels Includes utilities for testing and reconfiguring Virtual Channels

42. DAQ Channel Wizard Interface to create Virtual Channels for: –Analog Input –Analog Output –Digital I/O Each channel has: –Name and Description –Transducer type –Range (determines Gain) –Mode (Differential, RSE, NRSE) –Scaling

43. Devices and Interfaces Shows currently installed and detected National Instruments hardware Includes utilities for configuring and testing your DAQ devices –Properties –Test Panels

44. Properties Basic Resource Test –Base I/O Address –Interrupts (IRQ) –Direct Memory Access (DMA) Link to Test Panels Configuration for: –Device Number –Range and Mode (AI) –Polarity (AO) –Accessories –OPC

45. Test Panels Utility for testing –Analog Input –Analog Output –Digital I/O –Counters Great tool for troubleshooting

46. Scales Provides access to DAQ Custom Scales Wizard Shows configured scales Includes utility for viewing and reconfiguring your custom scales

47. DAQ Custom Scales Wizard Interface to create custom scales that can be used with Virtual Channels Each scale has its own: –Name and Description –Choice of Scale Type (Linear, Polynomial, or Table)

48. Sampling Considerations Analog signal is continuous Sampled signal is series of discrete samples acquired at a specified sampling rate Faster we sample the more our sampled signal will look like our actual signal If not sampled fast enough a problem known as aliasing will occur Actual Signal Sampled Signal

49. Aliasing Adequately Sampled Signal Aliased Signal

50. Nyquist Theorem You must sample at greater than 2 times the maximum frequency component of your signal to accurately represent the FREQUENCY of your signal NOTE: You must sample between 5 - 10 times greater than the maximum frequency component of your signal to accurately represent the SHAPE of your signal

51. Nyquist Example Aliased Signal Adequately Sampled for Frequency Only (Same # of cycles) Adequately Sampled for Frequency and Shape 100Hz Sine Wave Sampled at 100Hz Sampled at 200Hz Sampled at 1kHz 100Hz Sine Wave

52. Data Acquisition Palette Analog Input Analog Output Calibration and Configuration Signal Conditioning Digital I/O Counter DAQ Channel Name Constant

53. DAQ Channel Name Data Type Allows you to use numeric channels (0, 1, etc.) or virtual channels Automatically detects all currently configured virtual channels ControlTerminal Constant

54. Analog Input Palette Intermediate VIs –Built out of Advanced VIs + Highly recommended + Very flexible Easy VIs –Built out of Utility VIs + Easy to use - Less flexible Utility VIs –Convenient groupings of Intermediate VIs Advanced VIs –Building blocks for other levels Easy VIs Intermediate VIs Advanced VIs Utility VIs

55. Single-Point AI VIs Perform a software-timed, non-buffered acquisition + Good for battery testing, control systems - Not good for rapidly changing signals due to software timing AI Sample Channel –Acquires one point on one channel AI Sample Channels –Acquires one point on multiple channels

56. Multiple-Point (Buffered) AI VIs Perform a hardware-timed, buffered acquisition Highly recommended for most applications Allows triggering, continuous acquisition, different input limits for different channels, streaming to disk, and error handling AI Config –Configures your device, channels, buffer AI Start –Starts your acquisition, configure triggers AI Read –Returns data from the buffer AI Clear –Clears resources assigned to the acquisition

57. AI Config Interchannel Delay –Determines the time (in seconds) between samples in a scan Input Limits –Max and Min values for your signal –Used by NI-DAQ to set gain Device –Number of the device (from MAX) you are addressing Channels –Chooses what channel(s) you are addressing Buffer Size –Number of scans the buffer can hold –A scan acquires one sample for every channel you specify –1000 scans x 2 channels = 2000 total samples Task ID –Passes configuration information to other VIs Error In/Out –Receives/Passes any errors from/to other VIs

58. Different Gains for Different Channels AI Config allows different gains for different channels The first element of the input limits array corresponds to the first element of the channel array Gain = 2 Gain = 20 Range = 0 to +10V

59. AI Start Task ID In/Out –Receives/Passes configuration information to/from other VIs Number of Scans to Acquire –Total number of scans acquired before the acquisition completes –Default value (-1) sets # of Scans to Acquire = Buffer Size (AI Config) –A value of 0 acquires continuously Scan Rate –Chooses the number of scans per second Error In/Out –Receives/Passes any errors from/to other VIs

60. AI Read & AI Clear Number of Scans to Read –Specifies how many scans to retrieve from the buffer –Default value (-1) sets # of Scans to Read = # of Scans to Acquire (AI Start) –If # of Scans to Acquire (AI Start) = 0, default for # of Scans to Read is 100 Scan Backlog –Number of unread scans in the buffer Waveform Data –Returns t0, dt (inverse of scan rate), and Y array for your data Clears resources assigned to the device

61. Error Cluster Cluster containing: –Boolean - tells if an error occurred –Numeric - tells the error code –String - tells the source of the error Right-click on edge of cluster and select Explain Error for dialog box (see below) with more information Terminal Indicator

62. Clear Resources Return Data from the Buffer Display Errors Configure the Device Start the Acquisition Buffered Acquisition Flowchart

63. Buffered Acquisition AI Start begins the acquisition Acquisition stops when the buffer is full AI Read will wait until the buffer is full to return data If error input is true then Config, Start, and Read pass the error on but don’t execute; Clear passes AND executes

64. Start the Acquisition Return Data from the Buffer Display Errors Clear Resources Configure the Device Continuous Acquisition Flowchart Done? NO YES

65. Continuous Buffered Acquisition Differences from a buffered acquisition # of scans to acquire = 0 While loop around AI Read Number of Scans to read does not = buffer size Scan backlog tells how well you are keeping up

66. Analog Output Architecture DAC Channel 0 Channel 1 DAC Channel 0 Channel 1 Most E-Series DAQ devices have a Digital- to-Analog Converter (DAC) for each analog output channel DACs are updated at the same time Similar to Simultaneous Sampling for Analog Input

67. Analog Output Palette Intermediate VIs –Built out of Advanced VIs + Highly recommended + Very flexible Easy VIs –Built out of Utility VIs + Easy to use - Less flexible Utility VIs –Convenient groupings of Intermediate VIs Advanced VIs –Building blocks for other levels Easy VIs Intermediate VIs Advanced VIs Utility VIs

68. Single-Point AO VIs Perform a software-timed, non-buffered generation + Good for generating DC voltages, or control systems - Not good for waveform generation because software timing is slow AO Update Channel –Generates one point on one channel AO Update Channels –Generates one point on multiple channels

69. AO Update Channels Device –Number of the device (from MAX) you are addressing –Ignored if using virtual channel Channels –Chooses what channel(s) you are addressing –Can either be a number or a virtual channel name –Uses the DAQ Channel Name control Values –1-D array of data –The first element of the array corresponds to the first channel in your channels input

70. Multiple-Point (Buffered) AO VIs Perform a hardware-timed, buffered generation Highly recommended for most applications Allows continuous generation, triggering, and error handling AO Config –Configures your device, channels, buffer AO Write –Writes data to the buffer AO Start –Starts your generation AO Wait –Waits until the generation is complete AO Clear –Clears resources assigned to the generation

71. Clear Resources Display Errors Buffered Generation Flowchart Wait Until Generation Completes Configure the Device Start the Generation Write Data to the Buffer

72. Buffered Generation AO Write fills the buffer with waveform data AO Start begins the generation Without AO Wait the generation would start (AO Start) and then end immediately after (AO Clear) If error input is true then Config, Write, Start, and Wait pass the error on but don’t execute; Clear passes AND executes

73. AO Write One Update Your analog output channel will continue to output the last value written to it until either: –The device is reset (power off, reset VI) –A new value is written Use AO Write One Update at the end of your generation to set the channel back to 0

74. Clear Resources Start the Generation Configure the Device Write Data to the Buffer Display Errors Continuous Generation Flowchart Done? NO YES

75. Continuous Generation Differences from a buffered generation number of buffer iterations = 0 No AO Wait –AO Wait would hang because the generation never completes While loop with AO Write –The second AO Write is used for error checking ONLY