National Instruments 321645c-01 用户手册

Chapter 2

Function Reference — AO_Change_Parameter

NI-DAQ FRM for PC Compatibles

2-32

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 National Instruments Corporation

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 the 
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

.

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

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

.

Ω

Table 2-9.  Parameter Setting Information for Output Enable

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

DAQArb AT-5411 
DAQArb PCI-5411

Yes

0, 50,000, and 

75,000

50,000