National Instruments PXI NI 5401 - Manual (Page 33)

Chapter 2 Function Generator Operation
NI 5401 User Manual 2-10 www.natinst.com
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.
Note 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.
Output Impedance
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.
Note 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.
Output Enable
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.
Note 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.
Note 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.