National Instruments pxi ni 5401 用户手册

Chapter 2

Function Generator Operation

2-10

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NI-FGEN calculates the value of the output attenuation chain, which you 
can control by changing the peak-to-peak amplitude parameter. 0 dB 
attenuation corresponds to an amplitude of 10 V

pk-pk

. The maximum 

attenuation of 73 dB corresponds to an amplitude of 2.24 mV

pk-pk

. Any 

amplitude less then this is coerced to this value.

You can change the output attenuation at any time during waveform generation. 

When you change this setting, the bouncing of electromechanical relays on the NI 5401 
distorts the output signal for about 10 ms. 

As shown in Figure 2-10, before the signal reaches the output connector, 
you can select an output impedance of 50

Ω

 or 75

Ω

. If the load impedance 

is 50

Ω

 and all the attenuators are off (an output attenuation of 0 dB), the 

output levels are ±5 V. 

Most applications use a load impedance of 50

Ω

, but applications such as 

video device testers require 75

Ω

. If the load is a very high-input impedance 

load (~1 M

Ω

), you will see output levels up to ±10 V.

You can change the output impedance at any time during waveform generation. 

When you change this setting, the bouncing of electromechanical relays on the NI 5401 
distorts the output signal for about 10 ms.

You can switch off the waveform generation at the output connector by 
controlling the output enable relay, as shown in Figure 2-8. When the 
output enable relay is off, the output signal level goes to ground level.

Even though the output enable relay is in the off position, the waveform generation 

process continues internally on the NI 5401.

You can use this feature to disconnect and connect different devices to the 
NI 5401 on the fly.

You can change the output enable state at any time during waveform generation. 

When you change this setting, the bouncing of electromechanical relays on the NI 5401 
distorts the output signal for about 10 ms.