This content is not available in your preferred language.

The content is shown in another available language. Your browser may include features that can help translate the text.

DSA and SC Express Synchronization of PXIe Analog Input Modules

Updated Jun 14, 2024

PXIe Dynamic Signal Acquisition (DSA) modules can be synchronized with each other and with other Data Acquisition modules like SC Express and Multifunction I/O (X Series) modules. Since DSA modules use a Delta-Sigma ADC, there are some important considerations to program a synchronized acquisition successfully with these PXIe modules. 

The purpose of this document is to provide some LabVIEW examples showing how to synchronize PXIe DSA modules, depending on the conditions and hardware used. This document does not pretend to explain in a low level how PXI synchronization works or how Delta-Sigma ADCs work in theory. See the documentation below for more information. 

Additional documentation:

Contents:
1. Multidevice Tasks (using the same sample rate for all the devices).
2. Multirate Synchronization (using different sample rates).
  • Synchronizing two Delta-Sigma devices.
  • Synchronizing Delta-Sigma device with a Legacy Delta-Sigma device.
  • Synchronizing two Legacy Delta-Sigma devices.
  • Synchronizing Delta-Sigma device with a Multifunction I/O device (X Series). 

1. Multidevice Tasks:
This should be the first method considered when synchronizing DSA modules. To simplify the configuration, NI-DAQmx allows multiple Analog Input channels from various modules to be placed in the same task. When you include channels from multiple devices in a task, NI-DAQmx automatically synchronizes the devices and enables trigger skew correction for the devices.
The following initial conditions should be met:
  • To know if the devices can be synchronized using this method, consult the following documentation from the NI-DAQmx Help: DSA, SC Express, and X Series Multidevice Tasks.
  • All channels in a task must be of the same I/O type (analog input or analog output).
  • The sample rate and timing configuration (including triggers) for all the modules will be the same [1].
[1] An exception to this rule is the Slow-Sampled Delta Sigma Modules such as Temperature Input Modules (like PXIe-4353). You can add these modules to the same task even if the supported sample rate in the specifications is slower than the desired sample rate. As they have very low sample rates, they will duplicate the same samples to match the sample rate of the other module, so this won’t be a problem.

To add different modules in the same task, specify multiple channels across different modules in the Physical Channel input to the DAQmx Create Channel VI.
  • Channels from different modules should be included in the same DAQmx Create Channel VI if they are intended to have the same measurement configuration (analog input type, range, units, etc) and the same timing and triggering information.
 
Channel Expansion.PNG
 
  • Channels from different modules that can be channel expanded (according to the requirements mentioned before), but require different measurement configuration (analog input type, range, units, etc), can be added to the same task using different DAQmx Create Channel VIs. Here is an example of a Voltage Input and a Thermocouple Input in the same task sharing the timing and sample rate:
Channel Expansion Different.PNG

2. Multirate Synchronization:
Even though multidevice tasks are the recommended method, there are cases where the application requires modules to be synchronized but running at different sample rates. For these cases, using a Multidevice Task would not be an option, because the timing configuration for each device will be different, which means that multiple tasks are required. Synchronizing these tasks will depend on the combination of hardware used, which can make programming more complex. Here are some common scenarios for Multirate synchronization between different types of Delta-Sigma modules:

Consider the following terminology:
  • Delta-Sigma device: DSA modules like PXIe-4464, PXIe-4466, PXIe-4467, PXIe-4468, PXIe-4480 and SC Express modules with Delta-Sigma ADCs like PXIe-4339.
  • Legacy Delta-Sigma devices: DSA legacy modules like PXI-4461, PXIe-449x. 
  • Multifunction IO device (X Series): Multifunction I/O modules from the X Series family like PXIe-636x.

Multirate Synchronization: Two Delta-Sigma devices:
This example is intended to show low level synchronization of latest generation DSA devices including PXIe-4464 and PXIe-4466, PXIe-4467, PXIe-4468 as well as SC Express devices equipped with Delta-sigma ADCs like the PXIe-4339, for scenarios in which Multi Device Tasks cannot be used.
Notes:
  • If using different sample rates, the Samples per Loop must be equivalent to the same Loop Time on both tasks where Loop Time = Samples per Loop / Sample Rate to avoid buffer overwrite issues. Refer to your hardware documentation for information about the available Sample Rates for your device.
  • For a detailed explanation of how this synchronization works at a lower level, check: Synchronization Explained.
DSAtoDSA1.png
DSAtoDSA2.png
Multirate Synchronization: Delta-Sigma device with Legacy Delta-Sigma device:
This example is intended to show low level synchronization between latest generation DSA devices including PXIe-4464 and PXIe-4466, PXIe-4467, PXIe-4468, as well as SC Express devices equipped with Delta-sigma ADCs like the PXIe-4339, and Legacy DSA devices like the PXI-4461 or PXIe-449x, for scenarios in which Multi Device Tasks cannot be used.
Notes:
  • If using different sample rates, the Samples per Loop must be equivalent to the same Loop Time on both tasks where Loop Time = Samples per Loop / Sample Rate to avoid buffer overwrite issues. Refer to your hardware documentation for information about the available Sample Rates for your device.
  • Not all Legacy DSA devices support reference clock synchronization (for example 447x family). Refer to your hardware device manual for further information on whether this method of synchronization is supported for your device.
  • For a detailed explanation of how this synchronization works at a lower level, check: Synchronization Explained.
DSA-LegacyDSA.PNG

DSA-LegacyDSA2.PNG

Multirate Synchronization: Two Legacy Delta-Sigma devices:
This example is intended to show low level synchronization between two Legacy DSA devices like the PXI-4461 or PXIe-449x, for scenarios in which Multi Device Tasks cannot be used.
Notes:
  • If using different sample rates, the Samples per Loop must be equivalent to the same Loop Time on both tasks where Loop Time = Samples per Loop / Sample Rate to avoid buffer overwrite issues. Refer to your hardware documentation for information about the available Sample Rates for your device.
  • Not all Legacy DSA devices support reference clock synchronization (for example 447x family). Refer to your hardware device manual for further information on whether this method of synchronization is supported for your device.
  • For a detailed explanation of how this synchronization works at a lower level, check: Synchronization Explained.
legacyDSA to legacyDSA1.pnglegacyDSAtolegacyDSA2.PNG

Multirate Synchronization: Delta-Sigma device with Multifunction I/O device (X Series):  
This example is intended to show low level synchronization of DSA or SC Express devices with Multifunction I/O (X Series), for scenarios in which Multi Device Tasks cannot be used.
Notes:
  • If using different sample rates, the Samples per Loop must be equivalent to the same Loop Time on both tasks where Loop Time = Samples per Loop / Sample Rate to avoid buffer overwrite issues. Refer to your hardware documentation for information about the available Sample Rates for your device.
  • For a detailed explanation of how this synchronization works at a lower level, check: Synchronization Explained.
DSA-XSeries1.PNGDSA-XSeries2.PNG
 

Other Support Options

Ask the NI Community

Collaborate with other users in our discussion forums



Request Support from an Engineer

A valid service agreement or active software subscription may be required, and support options vary by country.

Was this information helpful?

Yes

No