Data Acquisition Toolbox

Input Channel Configuration

You can configure your hardware input channels with the InputType property. The device-specific values for this property are given below.

Table 5-2: InputType Property Values 

Vendor	InputType Value
Agilent Technologies	Differential
Keithley	Differential|{SingleEnded}
Measurement Computing	{Differential}|SingleEnded
National Instruments	{Differential}|SingleEnded| NonReferencedSingleEnded
Sound Cards	AC-Coupled

The InputType value determines the number of hardware channels you can add to a device object. You can return the channel IDs with the daqhwinfo function. For example, suppose you create the analog input object ai for a National Instruments board. To display the differential channel IDs:

• ai = analoginput('nidaq',1);
  hwinfo = daqhwinfo(ai);
  hwinfo.DifferentialIDs
  ans =
       0     1     2     3     4     5     6     7
  

In contrast, the single-ended channel IDs would be numbered 0 through 15.

Note    If the InputType value is changed, and that change decreases the number of channels contained by the analog input object, then a warning is returned and all channels are deleted.

Agilent Technologies Devices

For Agilent Technologies devices, the only valid InputType value is Differential. Channels configured for differential input are not connected to a fixed reference such as earth, and the input signals are measured as the difference between two terminals.

Keithley and Measurement Computing Devices

For Keithley and Measurement Computing devices, InputType can be Differential or SingleEnded. Channels configured for differential input are not connected to a fixed reference such as earth, and the input signals are measured as the difference between two terminals. Channels configured for single-ended input are connected to a common ground, and input signals are measured with respect to this ground.

National Instruments Devices

For National Instruments devices, InputType can be Differential, SingleEnded, or NonReferencedSingleEnded. Channels configured for differential input are not connected to a fixed reference such as earth, and input signals are measured as the difference between two terminals. Channels configured for single-ended input are connected to a common ground, and input signals are measured with respect to this ground. Channels configured for nonreferenced single-ended input are connected to their own ground reference, and input signals are measured with respect to this reference. The ground reference is tied to the negative input of the instrumentation amplifier.

The number of channels that you can add to a device object depends on the InputType property value. Most National Instruments boards have 16 or 64 single-ended inputs and 8 or 32 differential inputs, which are interleaved in banks of 8. This means that for a 64 channel board with single-ended inputs, you can add all 64 channels. However, if the channels are configured for differential input, you can only add channels 0-7, 16-23, 32-39, and 48-55.

Sound Cards

For sound cards, the only valid InputType value is AC-Coupled. When input channels are AC-coupled, they are connected so that constant (DC) signal levels are suppressed, and only nonzero AC signals are measured.

Configuring and Sampling Input Channels

Sampling Rate