Various ADC Types Used in NI DAQ Devices

Updated Sep 21, 2018

Reported In

Hardware

  • Multifunction I/O Device
  • C Series Multifunction I/O Module

Issue Details

In the DAQ device specification sheet, there is about a type of ADC(Analog-to-Digital Converters). What types of ADC are used in National Instruments DAQ Devices, such as Multifunction I/O DAQ, DSA or SC Express?

Solution

There are two main types of ADC used in National Instruments DAQ Devices, SAR(Successive-Approximation-Register) and DSA(Delta-Sigma ADC).
 
 SAR typeDSA type
 NI DAQ 
 Devices 
  • NI 63xx X Series devices and modules
  • NI 62xx M Series devices and modules
  • NI 61xx S Series devices and modules (Not all) 
  • NI 60xx E Series devices
  • NI 92xx C Series devices and modules (Not all)
  • NI 44xx DSA devices and modules
  • NI 43xx SC Express devices and modules

The SAR type of ADC is used in most National Instruments Multifunction I/O DAQ devices, not necessarily the case for modular instruments and USB devices. It takes in a continuous analog signal into a discrete format utilizing an approximation register. Also, It utilizes a binary algorithm to convert continuous analog waveform into much smaller discrete outputs.
 
The DSA type of ADC utilize oversampling, decimation filter, and noise shaping to create high resolution and great anti-aliasing filtering applications. Additionally, it is free-running meaning it’s being sampled prior to any trigger conditions. These features allow to be used for vibration and audio signal analysis as well as strain and pressure measurement. Learn more about the DSA ADC here: Benefits of Delta-Sigma Analog-to-Digital Conversion.

Additional Information

Not all the NI 61xx S Series devices and modules are using a SAR type of ADC because some NI 61xx S Series devices and modules are using a pipelined ADC.

Not all the NI 92xx C Series devices and modules are using a DSA type of ADC because only C Series devices and modules for highly accurate measurements are using a DSA type of ADC, such as thermocouple (NI 9211, 9212, 9213), RTD (NI 9217), high voltage and current (NI 9225, 9227, 9229, 9239, 9242, 9244), DSA (NI 9232, 9234), bridge-based measurements (NI 9235, 9236, 9237), and universal (NI 9219).

In the description of the SAR type of ADC, a binary algorithm to convert analog waveform into discrete outputs means that each analog point is checked for being greater than or less than a digital reference point. If greater, the digital bit is set to high, or 1 in binary, then moved to the next bit. If low, the digital bit is set to low, or 0 in binary, then moved to the next bit. This continues until the conversion of the analog point is complete.

For more information on the different types of ADCs, please refer to the Related Links section below.

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