DC offset for measuring capacitors

[slashguitar]

Hello,
I want to build an autoranging LCR meter for my graduation thesis (similar to Smart Tweezer). I will use the I-V method described by Dave in his "bonus tutorial".
The problem is that i don't know what to do with polarized capacitors. Do I need an offset voltage or if the ac test signal is small enough(<1Vpp) the capacitor isn't affected?

thanks

[don.r]

You can either bias it with a small DC (make sure its the right direction!) or not bother with DC and let the cap ride the AC. As long as your frequency is high enough there should be zero voltage drop across the cap so no worries. Many audio circuits use polarized electrolytics as decoupling caps.

[Zad]

It shouldn't cause any issues at low voltages. Having said that, the LCR meter the I'm developing has a programmable offset, but that's mostly to trim the drive signal to match the transimpedance amplifier which is internally set at Vcc/2.

Lots more waffle on the subject on my blog starting here:
http://electronicsdesigner.blogspot.com/2011/03/design-for-precision-lcr-meter-aka.html
http://electronicsdesigner.blogspot.com/2011/04/design-for-precision-lcr-meter-part-2.html

I should say that things have moved on since then, and I'm currently writing an update. Are you building a totally from-scratch system or using something like the AD5933?

[Zero999]

I certainlt wouldn't be worried about damaging the capacitor under test. The only reason I can see for a bias voltage is to test the voltage vs capacitance characteristic - some dielectrics vary their permittivity as the bias voltage changes.

[slashguitar]

Thanks for the answers guys

@Zad
I read your blog a while back and really liked the way you explained things. Waiting for part 3 on the LCR meter.
Considering it's a graduation thesis I want to build the LCR meter from scratch so I can "show off" the "analog skills" I acquired during university rather than using an of the shelf IC which does pretty much everything for me(  have to impress the teachers to get a good grade )