ClockSource (Data Acquisition Toolbox)

Specify the clock used to govern the 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, especially Windows 9X.

Characteristics

Usage
AI, AO, Common

Access
Read/write

Data type
String

Read-only when running
Yes

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

Values

Agilent Technologies

{Internal}
The internal hardware clock is used.

External
The external sample clock, positive true.

Inverted External
The external sample clock, negative true.

VXIBus/3
The VXI bus clock, divided by 3, provided by some other clock master.

VXIBusSample
The VXI bus sample clock.

`{Internal}`	The internal hardware clock is used.
`External`	The external sample clock, positive true.
`Inverted External`	The external sample clock, negative true.
`VXIBus/3`	The VXI bus clock, divided by 3, provided by some other clock master.
`VXIBusSample`	The VXI bus sample clock.

Keithley

{Internal}
The internal hardware clock is used.

External
Externally control the channel clock. Note that
the ChannelSkew property value is honored.

Software
The computer clock is used.

`{Internal}`	The internal hardware clock is used.
`External`	Externally control the channel clock. Note that the `ChannelSkew` property value is honored.
`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.

`{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).

ExternalScan Ctrl
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).

`{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).
`ExternalScan Ctrl`	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).

For an analog output object, a ClockSource value of Internal is analogous to a value of Update.

Sound Cards

{Internal}
The internal hardware clock is used.

`{Internal}`	The internal hardware clock is used.

See Also

Properties

ChannelSkew, SampleRate

ChannelSkewMode DataMissedFcn