why use Vac in orcad

[P.Copper]

Hi all

I'm working with a voltage sensor (LV 25-P) to sense the 230V AC, 50Hz supply. Now I've went to LV 25-P datasheet and designed Rm(measurement resistance) such that the output from the sensor is 1.4Volts. Now i wan't to put in a lowpass filter after the sensor. My question is, in orcad i used my source as VAC, what i'm wondering about is do i leave the Vac value as 1(default) or do i use the output from the voltage sensor (1.4 volts in this case). thanks

 

[LvW]

It depends on what you are aiming at.
If you want to simulate the whole circuit, you should use, of course, the correct (realistic) lowpass input voltage.
However, if you want to simulate the filter alone, it does not matter because ac analysis is a small-signal linear analysis.
In such a case, I usually use Vac=1V (effective) and the output voltage (in dB) is identical to the frequency-dependent gain.

 

[P.Copper]

oh and one more thing the output from the sensor is calculated to be 1.4 Volts... is that a Vdc or Vac?, cos in the datasheet for LV25-P they didn't mention in.