DC elimination

From: Dr.Prasad
email: clcr@vsnl.com
Model: 7260
Date: 01 Dec 2004

Comments

I measure the harmonic response of our materials to an applied sinusoidal osc.voltage from the lockin. The simple circuit I use involves connecting the lockin (osc.output) to the sample (essentially a dielectric) which in turn gets connected to a capacitor whose other end is earthed. The drop in the voltage across the capacitor is given as the measuring input to the lockin. This works excellent in the AC mode. Now I want to impress upon the sample an external DC voltage. I have two questions in this regard. How do I prevent the large values of DC (up to ± 40V) voltage from (a) affecting the lock-in and (b) saturating the capacitor? I would greatly appreciate a help in this regard. Prasad