Here's an example of adding an external A/D converter for applications needing higher resolution and accuracy than the LabJack's 12-bit A/D inputs provide.

The circuit above uses a Linear Technology LTC2413 24-bit A/D converter.  The LT1019A is a 2.5 volt reference.

The LabJack SPI mode pin-out is shown in the following table.

The following sample code utilizes the LabJackWrapper class to read the A/D.

LabJackWrapper labjack = new LabJackWrapper( -1 );
DecimalFormat fmt = new DecimalFormat( "#0.000000" );

int spiMode = 3;
int spiMsDelay = 0;
int spiHusDelay = 0;
int spiControlCS = 1;		// >1 means we want LabJack to implement and control a chip select pin for us
int spiCsLine = 2;		// '2' means use D2 as the chip select line
int spiCsState = 0;		// specify active state (low) of chip select line, i.e. CSN
int spiConfigD  = 1;		// we want LabJack to configure I/O pins for us
labjack.configSPI( spiMode, spiMsDelay, spiHusDelay, spiControlCS, spiCsLine, spiCsState, spiConfigD );

LTC2413 adc = new LTC2413( 2.5f );	// using 2.5V reference

labjack.addSPI( adc );

while( true )
{
	Thread.sleep( 100 );	// conversion time delay (plus LabJack SPI overhead)

	labjack.updateSPI();

	try
	{
		System.out.println( fmt.format( adc.getVoltage() ) );
	}
	catch( LTC2413Exception ex )
	{
		System.out.println( ex.getMessage() );
	}
}

The LTC2413 class can be found here.