Digital Filtering Considerations for SC Express Devices

NI-DAQmx 18.6 Help


Edition Date: January 2019
Part Number: 370466AH-01
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NI-DAQmx 18.6 Help
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For SC Express devices, you can filter timing/triggering input signals.

You can configure digital filters on the device by choosing three fixed values (90 ns, 5.12 µs, 2.56 ms). For each digital line or input terminal, there are four attributes/properties associated with these digital filters: DI.DigFltr.Enable, DI.DigFltr.MinPulseWidth, DI.DigFltr.TimebaseSrc, and DI.DigFltr.TimebaseRate.

When you set the DI.DigFltr.Enable to true, you must also configure the DI.DigFltr.MinPulseWidth attribute/property. This value represents the minimum value that is guaranteed to be passed into the device. When you select a custom filter value with the DI.DigFltr.MinPulseWidth attribute/property, NI-DAQmx uses an internal 32-bit utility counter to generate the desired filter value.

You can select a custom filter value in addition to the three fixed values mentioned previously. The custom filter value must be the same for all lines across the device. For example, if you choose a filter value of 2 µs for PFI 0, any other filterable line on the device can only be set to one of the three fixed values or the 2 µs value selected for the custom filter.

The following table lists the attributes/properties for terminals that can be digitally filtered.

Type Attribute/Property
Timing Sample Clock Source (SampClk.Src)
Triggering Pause Digital Level Source (Pause.DigLvl.Src)
Reference Analog Edge Source (Ref.AnlgEdge.Src)
Reference Analog Window Source (Ref.AnlgWin.Src)
Reference Digital Edge Source (Ref.DigEdge.Src)
Start Digital Edge Source (Start.DigEdge.Src)

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