Steve,

I never taught you and I will never teach you: "Read!....Learn!" This is a question of respect. That's why I am upset.
Having studied physics I'm very well informed about those numberous, very special 'bridges' and their overwhelming advangtages and limitations.

But here we exclusively speak about Wheatstone-bridge! Remember what Erik stated in his original post:

Why does one excite whetstone bridges with DC?

If one used AC, all problems re offset, drift and such would be eliminated.

So, I was refering to this Wheatstone-bridge. My thesis was, that with standard precision voltage reference and standard precision chopper Opamp it's very easy to achieve very good results. And that with AC bridge excitation more complex circuitry is needed. That this not automatically results in better design, e.g. if one uses square wave excitation, like Russell stated.
Then I thought about a situation, where it's essential to use AC bridge excitation, because signal is buried in noise. Think about Wheatstone-bridges delivering extremely small signals. I wanted to focuse, that then again fast edges are introduced into linear circuitry which makes lot of trouble.

Someone who read my reply at least knows now, that square wave excitation of Wheatstone bridge is not at all a good idea. That's all I wanted to tell the people here, already having discussed square wave excitation (Russell).
Someone having read your reply is only wondering what he is doing wrong because of not achieving this 30bit accuracy.

I again ask: Why should someone use AC bridge excitation when classic DC approach leads to good enough results, is simple, costs less and needs small number of standard chips? That's my individual and direct answer to Erik's question!
People don't use AC bridge excitation in most situation, because DC bridge excitation satisfies their needs.

Heaven, what's wrong with this statement???

If you want to implement Sinus bridge excitation, you need a very stable sinus generator, a detector (may be simple rectifier or more sophisticated synchronous phase detector). But how to produce this stable sinus generator? How much chips are needed? How to control or measure sinus amplitude? How to introduce bandpass filtering, when not using synchronous phase detector? All questions, a developer of a Sinus excited bridge circuit must solve. So, why the hell, not using a simple standard precision voltage source and a standard precision chopper OPamp, when this will also satisfy his needs? He can everytime switch to AC bridge excitation if he needs, and profit from its possible advantages.

That was MY answer to Erik's question. From MY individual point-of-view, with some experience on design of wide dynamic range Lock-in amplifiers.
But instead of giving YOUR individual comment about AC bridge excitation of Wheatstone-bridges you only replied: "This is just WRONG! ... Read! ... Learn!"

I tell you, that such language for me is totally unacceptable! If this is the consequence of discussing with you, then I stop it!

Kai