daqmx(multi-channels). 2 data acquisition and waveforms topics plug-in daq devices data acquisition...
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DAQmx 下多點 (Multi-channels)訊號量測
許智超
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Data Acquisition and Waveforms
TOPICSPlug-in DAQ devicesData Acquisition in LabVIEWAnalog InputData LoggingAnalog OutputCountersDigital I/O
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大綱
NI-DAQ7.3Task 與 Global ChannelTask 與 Physical ChannelMAX 的設定量測程式結論
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NI-DAQ7.3
NI-DAQ7.3
TraditionalNI-DAQ
NI-DAQmx NI-Switch
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Overview and ConfigurationFundamental task of a DAQ system is to measure or generate real-world physical signals
DAQ system consists of:•Transducers•Signal Conditioning•Plug-in DAQ device•Driver•Software
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Measurement
Software Framework
NI-DAQ contains:•Traditional NI-DAQ•NI-DAQmx
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DAQ Hardware Configuration
Measurement & Automation Explorer (MAX)
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Channels and Tasks
Signalsai 0
ai 1
ai 2
Sine Wave 1
Sine Wave 2
Sine Wave 3
Channel names
TasksTiming and Triggering
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NI-DAQmx versus Traditional NI-DAQ Feature NI-DAQmx Traditional NI-
DAQ
Test Panels
DAQ Assistant with code generation
no
On-line diagnostics
Scaling to voltage and physical units
50 kS/s with single point I/O ž
Measurement multithreading ž
Instant calibration
Automatic selection of optimal gains
Guaranteed lossless data
650 Alliance members
Integration with LabVIEW
Developer Exchange discussion forum
Compatible with Legacy ISA Boards
no
Accuracy
Performance
Productivity
Quality Best
Good FairCompatibility
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Data Acquisition in LabVIEW
Traditional NI-DAQSpecific VIs for performing:• Analog Input• Analog Output• Digital I/O• Counter operations
NI-DAQmxNext generation driver: • VIs for performing a
task• One set of VIs for all
measurement types
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NI-DAQmx Data Acquisition
Single set of VIs used to perform analog I/O, digital I/O, and counter operations
DAQ Assistant Express VI• Quickly and easily program the DAQ device• Creates a local task• Most applications can use the DAQ
Assistant Express VI
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NI-DAQmx Data Acquisition Task Types
Measurement type can be:•Analog Input•Analog Output•Counter Input•Counter Output•Digital I/O
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Analog Input
Analog Input task is specific to the measurement
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Analog Input Task Timing and Triggering
Configures the number of samples and sample rate for the task
Configures the start and reference triggers for the task
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Data Logging It is often necessary to permanently store data that
is acquired from the DAQ device LabVIEW includes the ability to read and write a
LabVIEW Measurement File LabVIEW Measurement File is an ASCII text file
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Analog Output
Analog Output task is specific to the generation type
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Analog Output Task Timing and Triggering
Configures the number of samples and sample rate for the task
Configures the start and reference triggers for the task
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CountersA counter is a digital timing deviceTypical uses of a counter:• Event counting• Frequency measurement• Period measurement• Position measurement• Pulse generation
Gate
Source
Output
Count Register
Count register – Stores the current count of the counterSource – Input that causes the counter to increment each time it togglesGate – Input that is used to enable or disable the function of the counterOutput – Signal that generates pulses or a series of pulses
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Digital Input and OutputDigital I/O can
read from or write to a line or an entire digital port
A digital port is a collection of digital lines
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SummaryMAX is the primary configuration and testing utility
that is available for the DAQ device.The DAQ Assistant is used to configure the DAQ
device and perform data acquisition.Most application can use the DAQ Assistant. For
applications that require advanced timing and synchronization use the VIs that come with NI-DAQmx.
The DAQ Assistant can perform Analog Input, Analog Output, Digital I/O, and Counter operations.
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NI-DAQmx 的優點
DAQ Assistant.Increased performance-faster single point I/
O and multithreading( 多緒 ).Simple and intuitive API.DAQ property nodes and waveform support.Similar API for all programming languages.
Trad. DAQ DAQmx
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Task 與 Global Channel
一個 task 包含多個 global channel 。當 global channel 的參數改變, task
也會改變。用 task 或多個 global channels 來達成
multi-channel 。
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Task 與 Physical Channel
Task 要在 MAX 中設定。Physical Channel 的參數在 LabVIEW 中
設定。
PS : Global Channel 也要在 MAX 中設定。
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MAX 中關於 Global Channel 的設定
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MAX 中關於 Task 的設定
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量測程式
Using the task.Using multiple global channels.Using multi-thready with physical channel.Using the “Write LVM” VI.
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Front PanelBlock Diagram
Single-channel Measurement Program-Using Task
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Front PanelBlock Diagram
Multi-channel Measurement Program-Using Task
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Front PanelBlock Diagram
Single-channel Measurement Program-Using global channel
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Front PanelBlock Diagram
Multi-channel Measurement Program-Using global channel
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Single-channel Measurement Program-Using Physical Channel
Front PanelBlock Diagram
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Multi-channel Measurement Program-Using Physical Channel ?!
用多緒執行來達成,但是會增加負擔,不建議使用。
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結論
Task 是相當方便的架構,但是有彈性不夠的缺點。
使用 Global Channel 是一個較佳的方式,在量測時間的處理上比較活用。
多緒執行不適合用執行這樣的訊號量測程式。
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結論 -1較理想的加速度規量測程式 for Multi-channels
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附錄