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Using a Disabled Channel to Trigger Acquisition with NI-Scope



Hardware: Modular Instruments>>High-Speed Digitizers (Scopes)

Problem:
The 4-channel versions of the PXIe-5160 and PXIe-5162 high-speed digitizers do not have an external trigger terminal (TRIG) on the front panel connector. Do I need to acquire data from an analog input channel in order to use it as analog trigger source, or can I use the channel for external triggers only?

Solution:
The maximum sampling rate of the PXIe-5160 and PXIe-5162 may be limited based on the number of channels you are acquiring from. Furthermore, the device's onboard memory is shared among all channels enabled for acquisition. For these or other reasons, you may want to connect an external trigger to an analog input channel without enabling that channel for acquisition. 

With most NI-SCOPE devices, it is possible to configure an analog reference trigger on a channel that is not enabled. This can be achieved in the NI-SCOPE Soft Front Panel and through the NI-SCOPE API as demonstrated below.

NI-SCOPE Soft Front Panel
On the NI-SCOPE Soft Front Panel, deselect Enabled on the channel you will use to receive an external trigger, then select this channel in the Source drop-down list under Trigger Settings.




NI-SCOPE API
In the NI-SCOPE API, configure the channel you will use to receive an external trigger as the trigger source. It is important to configure the vertical parameters and channel characteristics for the trigger channel separately from the acquisition channels. In LabVIEW, this can be done using the niScope Configure Vertical Parameters and niScope Configure Chan Characteristics VIs, respectively. Also note that the Channel Enabled property must be set to False in order to disable acquisition on the trigger channel. Please refer to the Developer Zone Example: Use Disabled Channel for a Trigger on PXIe-5162 or Other NI-Scope Device for access to the LabVIEW code shown below.




Special Considerations for the NI 5105 8-Channel Digitizer
With the NI 5105 8-channel digitizer, an analog trigger signal must be digitized before being processed by the triggering circuitry. For this reason, a channel that is configured as the source for an analog reference trigger must also be enabled and configured for acquisition. Consequently, data from this channel will also be recorded to onboard memory. Failing to enable a trigger channel will result in Error -201148: Channel you are triggering on is not enabled. 



Related Links:
Developer Zone Example: Use Disabled Channel for a Trigger on PXIe-5162 or Other NI-Scope Device
Product Type Help: NI High-Speed Digitizers Help
Products and Services: Digitizers/Oscilloscopes

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Report Date: 10/04/2012
Last Updated: 09/27/2013
Document ID: 623HEC8P

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