NotifyWhenDataAvailableExceeds

Control firing of DataAvailable event

Description

The DataAvailable event is triggered when the number of scans available to the session object exceeds the quantity specified in the NotifyWhenDataAvailableExceeds property.

You cannot set the NotifyWhenDataAvailableExceeds property when the session is in the prepared state, which can happen after running startForeground. In this case, call release on the session before setting this property value.

Values

By default the DataAvailable event triggers when 1/10 second worth of data is available for analysis. To specify a different threshold, change the value of NotifyWhenDataAvailableExceeds.

Examples

Control Firing of Data Available Event

Add an event listener to display the total number of scans acquired and fire the event when the data available exceeds specified amount.

Create the session and add an analog input voltage channel.

s = daq.createSession('ni');
addAnalogInputChannel(s,'Dev4',1,'Voltage');
lh = addlistener(s,'DataAvailable', ...
			@(src, event) disp(s.ScansAcquired));

The default the Rate is 1000 scans per second. The session is automatically configured to fire the DataAvailable notification 10 times per second.

Increase the Rate to 800,000 scans per second, while the DataAvailable notification automatically fires 10 times per second.

s.Rate = 800000;
s.NotifyWhenDataAvailableExceeds

ans =
        80000

Running the acquisition causes the number of scans acquired to be displayed by the callback 10 times.

data = startForeground(s);

               80000

               160000

               240000

               320000

               400000

               480000

               560000

               640000

               720000

               800000

Increase NotifyWhenDataAvailableExceeds to 160,000. NotifyWhenDataAvailableExceeds is no longer configured automatically when the Rate changes.

s.NotifyWhenDataAvailableExceeds = 160000;
s.IsNotifyWhenDataAvailableExceedsAuto

ans =

     0

Start the acquisition. The DataAvailable event is fired only five times per second.

data = startForeground(s);

               160000

               320000

               480000

               640000

               800000

Set IsNotifyWhenDataAvailableExceedsAuto back to true.

s.IsNotifyWhenDataAvailableExceedsAuto = true;
s.NotifyWhenDataAvailableExceeds

ans =
                80000

This causes NotifyWhenDataAvailableExceeds to set automatically when Rate changes.

s.Rate = 50000;
s.NotifyWhenDataAvailableExceeds

ans =
                 5000