National Instruments 321645c-01

Chapter 2 Function Reference — AO_Change_Para meter

NI-DAQ FRM for PC Compatibles 2-32

National Instruments Corporation

Output Enable

On some of the devices, you can disable the output even when the waveform generation is in

progress. You can use this feature to bring the output to a known level at any time.

On DAQArb 5411 devices, there is a relay just in front of the I/O connector. By disabling th e

output, this relay switches so that the I/O connector output shorts to ground. The waveform

generation can still continue, but no signal appears at the I/O connector output. You can

enable or disable the output at any time.

To change the output enable setting, set paramID to ND_OUTPUT_ENABLE.

Output Impedance

On some of the devices, you can select the output impedance to match the impedance of

theload.

Output impedance of 50 Ω is good for testing most of the devices. You can use output

impedance of 75 Ω for video testing. If you select an output impedance of 0 Ω, you should be

driving an unterminated load (that is, a load with a very high input impedance).

To change the output impedance setting, set paramID to ND_IMPEDANCE.

Note The values are set up in milliOhms (mΩ).

Table 2-9. Parameter Setting Information for Output Enable

Device Type Per Channel

Selection Possible Legal Range

for paramValue Default Setting

for paramValue

DAQArb AT-5411

DAQArb PCI-5411

4451 devices

4551 devices

Yes ND_YES and

ND_NO ND_NO

Table 2-10. Parameter Setting Information for Output Impedance

Device Type Per Channel

Selection Possible Legal Range

for paramValue Default Setting

for paramValue

DAQArb AT-5411

DAQArb PCI-5411 Yes 0, 50,000, and

75,000 50,000