Data Acquisition Toolbox™

ClockSource - Specify clock that governs hardware conversion rate

Description

For all supported hardware except Measurement Computing analog output subsystems, ClockSource can be set to Internal, which specifies that the acquisition rate is governed by the internal hardware clock.

For subsystems without a hardware clock, you must use software clocking to govern the sampling rate. Software clocking allows a maximum sampling rate of 500 Hz and a minimum sampling rate of 0.0002 Hz. An error is returned if more than 1 sample of jitter is detected. Note that you might not be able to attain rates over 100 Hz on all systems.

Characteristics

Usage	AI, AO, Common to all channels
Access	Read/write
Data type	String
Read-only when running	Yes

Values

Advantech

`{Internal}`	The internal hardware clock is used (AI only).
`External`	Externally control the channel clock (AI only).
`Software`	The computer clock is used.

Measurement Computing

`{Internal}`	The internal hardware clock is used (AI only).
`External`	Externally control the channel clock (AI only).
`Software`	The computer clock is used.

National Instruments

`{Internal}`	The internal hardware clock is used.
`External`	Externally control the channel clock (AO only).
`ExternalSampleCtrl`	Externally control the channel clock. This value overrides the `ChannelSkew` property value (AI only). This value does not apply to cards with simultaneous sample and hold.
`ExternalScanCtrl`	Externally control the scan clock. This value overrides the `SampleRate` property value (AI only).
`ExternalSampleAndScanCtrl`	Externally control the channel and scan clocks. This value overrides the `ChannelSkew` and `SampleRate` property values (AI only). This value does not apply to cards with simultaneous sample and hold.

Note If you set the ClockSource property to one of the External options, you must also set the SampleRate property to a value close to the external clock rate. SampleRate does not directly affect the external device, and the device will not use SampleRate if you have set an external clock rate, but this ensures that the toolbox configures itself correctly for expected data rates.

Sound Cards

{Internal}

The internal hardware clock is used.