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Data Acquisition Sampling Terminology for NI-DAQmx and Traditional NI-DAQ



Hardware: Multifunction DAQ (MIO)

Problem:
I am confused about some of the vocabulary used to describe the data acquisition process, particularly the vocabulary used by NI-DAQmx and Traditional NI-DAQ. Some terms seem to be proprietary, and some terminology is different between NI-DAQmx and Traditional NI-DAQ.

Solution:
Earlier releases of NI-DAQ software included a translational table in order to assist users who were migrating from Traditional NI-DAQ to NI-DAQmx. This translational table also provided definitions for much of the terminology used by the DAQ software. As NI-DAQmx is now the standard, later releases of the help documentation omit this section.

The following information is that which used to be found in the NI-DAQmx Help.

The following table translates terms from Traditional NI-DAQ to NI-DAQmx for both the C API and LabVIEW API.

Analog Input Clock and Trigger Names in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ C API Traditional NI-DAQ LabVIEW NI-DAQmx Explanation
Sample Interval Counter (and Channel Clock) Channel Clock or Interchannel Delay AI Convert Clock The E Series clock that directly causes analog-to-digital conversions
Points per Second (as Sample Rate) Channels per Second Conversions per Second Units for specifying AI convert clock rate
Sample Timebase (and Channel Clock Timebase) Timebase AI Convert Clock Timebase The clock that is divided down to produce the AI convert clock
Sample Interval Timebase Divisor AI Convert Clock Timebase Divisor The number of AI convert timebase ticks used to divide down the AI convert timebase
Scan Interval Counter (and Scan Clock) Scan Clock Sample Clock The clock that controls the time interval between samples. Each time the sample clock ticks (produces a pulse) one sample per channel is acquired.
Scans per Second (as scanRate) Scans per Second Samples per Channel per Second Units for specifying sample acquisition rate (the sample rate)
Scan Timebase Timebase Sample Clock Timebase The clock that is divided down to produce the sample clock
Scan Interval Timebase Divisor Sample Clock Timebase Divisor The number of sample clock timebase ticks used to divide down the sample clock timebase
Start Trigger Start Trigger Start Trigger The trigger that begins an acquisition
Stop Trigger Stop Trigger Reference Trigger The trigger that creates the reference point between the pretrigger samples and the post-trigger samples
No Equivalent Scan Clock Gating Pause Trigger The signal that pauses and resumes an acquisition
No Equivalent ATCOUT Analog Comparison Event The signal from the analog comparator circuit, used most often for analog triggering
SCANCLK SCANCLK AI Hold Complete Event A digital signal emitted by an E Series device when the analog signal about to be converted by the ADC has been held

Analog Input Read Terminology in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ C API Traditional NI-DAQ LabVIEW NI-DAQmx Explanation
Reading, Voltage, Sample Sample Sample A single measurement from a single channel
Scan Scan No Equivalent A set of samples, one from each channel in the task
Sample Count Scans per buffer Buffer Size (in Samples Per Channel) Method for specifying the buffer size
No Equivalent — the Sequential parameter in DAQ_Monitor is the closest Read/Search Mode Position Where to place the read position prior to adding the offset
No Equivalent Read/Search Offset Offset After placing the read position, this offset is added to determine where the read takes place; all subsequent reads use this offset until the offset is changed
No Equivalent Read Mark Scan Current Sample Number The current read position
No Equivalent Scan Backlog Available Samples Per Channel The amount of unread data in the buffer
Retrieved End of Data Scan Total Samples Per Channel Acquired The total number of samples acquired into the buffer
Count Total Scans to Acquire Samples per Channel The total number of samples to acquire
numPts Number to Read Number of Samples per channel The number of samples to read

Analog Input Physical Channel Names in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ NI-DAQmx Explanation
0,1, and so on Dev1/ai0, Dev1/ai1, and so on In Traditional NI-DAQ, physical channel names were numbers. In NI-DAQmx, physical channels are string names that combine the device name, the I/O type, and the physical channel number

Analog Output Clock and Trigger Names in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ C API Traditional NI-DAQ LabVIEW NI-DAQmx Explanation
Update Clock Update Clock Sample Clock The clock that causes D/A conversions
Updates per Second Updates per Second Samples per Channel per Second Units for Specifying digital-to-analog conversion (DAC) rate
Timebase Timebase Sample Clock Timebase The clock that is divided down to product the sample clock
Interval Timebase Divisor Sample Clock Timebase Divisor The number of sample clock timebase ticks used to divide down the sample clock timebase
Start Trigger Start Trigger Start Trigger The trigger that begins a generation
No Equivalent Gate Pause Trigger The signal that pauses and resumes a generation

Analog Output Write Terminology in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ C API Traditional NI-DAQ LabVIEW NI-DAQmx Explanation
Voltage, Sample Update Sample A single measurement generated at a single channel
No Equivalent Update No Equivalent A set of samples, one for each channel in the task
No Equivalent Write Mode Position Where to place the write position prior to adding the offset
No Equivalent Write Offset Offset After placing the write position, this offset is added to determine where the write will take place. All subsequent writes will use this offset until the offset is changed
No Equivalent Write Mark Current Sample Number The place in the buffer where the next write begins if the Position property/attribute is Relative to Current Write Position and the Offset property/attribute is 0
No Equivalent No Equivalent Space Available in Buffer The number of samples that can be written without overwriting a sample that has not been output
pointsDone, itersDone Output Mark, Buffer Iterations Total Samples Per Channel Generated The total number of samples that have been written to the device; although the samples have been written to the device, they may not have been generated yet
oldDataStop Regeneration Mode Regeneration The property/attribute that controls whether old data is regenerated
partialTransfer Regeneration Mode No Equivalent To stop a waveform generation after a specific number of samples are generated, set the NI-DAQmx property/attribute samples per channel to the desired number of samples
Iterations Iterations Samples per Channel To generate a finite number of iterations of a buffer, set the samples per channel property/attribute to I × N, where I is the desired number of iterations, and N is the number of samples per channel in the buffer.

Analog Output Physical Channel Names in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ NI-DAQmx Explanation
0,1, and so on Dev1/ao0, Dev1/ao1, and so on In Traditional NI-DAQ, physical channel names were numbers. In NI-DAQmx, physical channels are string names that combine the device name, the I/O type, and the physical channel number

Counter Clock and Trigger Names in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ C API Traditional NI-DAQ LabVIEW NI-DAQmx Explanation
Start Trigger Start Trigger Start Trigger The signal that begins a counter operation
Gate Gate Pause Trigger The signal that pauses and resumes a counter operation

Counter Application Names
Traditional NI-DAQ C API Traditional NI-DAQ LabVIEW NI-DAQmx Explanation
Event Counting Event Counting Edge Counting A counter tallies the total number of rising or falling edges
No Equivalent Frequency Shift Keying NI-DAQmx does not support Frequency Shift Keying  

Counter Physical Channel Names in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ NI-DAQmx Explanation
0, 1, and so on Dev1/ctr0, Dev1/ctr1, and so on In Traditional NI-DAQ, physical channel names were numbers. In NI-DAQmx, physical channels are string names that combine the device name, the I/O type, and the physical channel number

Digital Physical Channel Names in Traditional NI-DAQ and NI-DAQmx
Traditional NI-DAQ NI-DAQmx Explanation
0, 1, as port Dev1/port0, Dev1/port1, and so on In Traditional NI-DAQ, physical channel names were numbers. In NI-DAQmx, physical channels are string names that combine the device name, the I/O type, and the physical channel number. If the line number is omitted from the NI-DAQmx name, all lines in the port are included.
0, 1 as line Dev1/port0/line0, Dev1/port0/line1 When the line number is present in the NI-DAQmx name, only that line is meant
No Equivalent Dev1/port1_16 Concatenated ports, porta_b, where a is the port number of the beginning port and b is the width in lines

 


Notes:
  • Some non-plug and play (legacy) DAQ boards do not have a sample (scan) clock—they only have a convert (channel) clock. These boards use round-robin sampling (see the related link below).
  • Simultaneous sampling (S-series) boards have only a sample (scan) clock. Since these boards are not multiplexed, they have no need for a convert (channel) clock.

Channel list (scan list)
List of channels to be sampled.

Scan
A set of samples, one from each channel in the channel list.

Interval scanning
A multi-channel sampling method. This method uses the sample (scan) clock to control when a scan begins and uses the convert (channel) clock to control when each channel in the channel list is sampled.

Sample/Sampling rate (scan rate)
The rate at which one sample per channel is acquired; the rate at which the sample (scan) clock is set. Note that the maximum sampling rate specification for our E Series data acquisition boards refers to the maximum rate at which a single channel can be acquired. For example, the PCI-6071E is capable of a 1.25 MS/s sampling rate. This may consist of 1.25 MS/s on one channel or 250 kS/s on five channels.
Units: Samples per Channel per Second (Scans per Second)

Convert rate (channel rate)
The rate at which the analog-to-digital conversions occur; the rate at which the convert (channel) clock is set.
Units: Conversions per Second (Channels per Second)

Interchannel delay
The amount of time which passes between sampling consecutive channels in the channel list. The convert rate is the reciprocal of the interchannel delay. The interchannel delay must be short enough to allow for sampling all the channels in the channel list within one sample clock period. The greater the interchannel delay, the more time your amplifier is given to settle before the next reading (see the settling time tutorial linked below).

For example code for data acquisition, please refer to the DAQ examples that install with your NI-DAQ installation.

Related Links:
KnowledgeBase 30LDURMV: Difference Between the Scan Clock (Sample Clock) and Channel Clock (Convert Clock)

KnowledgeBase 2XPE1QCW: How is the Convert (Channel) Clock Rate Determined in NI-DAQmx and Traditional NI-DAQ?
KnowledgeBase 1DAIG7W3: What Is the Difference Between Interval Scanning and Round Robin Scanning?

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Report Date: 09/07/2001
Last Updated: 01/20/2017
Document ID: 2D6CTML8

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