Sampling Terminology for NI-DAQmx and Traditional NI-DAQ (Legacy)

Publish Date: Jan 26, 2018 | 0 Ratings | 0.00 out of 5 | Print

Overview

This article explains the vocabulary used to describe the data acquisition process, particularly the vocabulary used by NI-DAQmx and Traditional NI-DAQ (Legacy). It also covers the proprietary terms, and explains why some terminology is different between NI-DAQmx and Traditional NI-DAQ (Legacy).

1. Introduction

Earlier releases of NI-DAQ software included a translational table in order to assist users who were migrating from Traditional NI-DAQ (Legacy) 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.

Note: The following information used to be found in the NI-DAQmx Help.

The following tables translate terms from Traditional NI-DAQ (Legacy) 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 channelproperty/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


Counter 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.

 

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2. Additional Resources

 

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