Data Aquisition Devices using built in Amplifiers question D

Data Aquisition Devices using built in Amplifiers question:

Data acquisition (DAQ) devices (eg. NI USB 6211) uses built-in amplifiers for measuring transduced signals. The analog input resistance is designed on the order of 10 G Ohm. Explain why?

Solution

Ans) By Thevenin\'s equivalent circuit (Voltage source Vs in series with source resistance Rs)

Vo=Vs*RL/(Rs+RL) ---By Voltage division rule and We know Rs=50; Vs=1

using above equation we have

for RL1=50 Vo=0.5 V

for RL2=1M Vo=0.999950V

for RL3=10 G Vo=0.999999995 V

From the above output voltage trend Vo with increasing in RL we say that drop in voltage from input to output is decreasing with increasing in RL,So to reduce the drop in voltage from input to output analog input resistance is designed in the order of 10 G ohms.As you can observe from the above results the drop is significantly low when RL is 10 G ohms