strain guage execitation

I assume you are actually meaning a Wheatstone bridge. Every one I've seen are DC but there's millions of things that I have never seen so a Wheatstone using AC could be one of them.

http://en.wikipedia.org/wiki/Wheatstone_bridge

AC current excitation has the main advantage as there's self-compensating of zero drift.

Shortcomings of AC are: increased risk for strain gauge insulating and leaks, more complex and pricey PWS.

I saw your answer and want to give you an information. As long as DC was not stable enough HBM build amplifiers using a 5kHz carrying frequency. There was a need to adjust not only resistances but also impedances but it was for the time the most precise measuring equipment.

I got your point.

There is the same dilemma: how accurate and what'll be a price . Everything depends on particular application. If you need extremely high accuracy and distance between excitation source and gauge is short and you have means (time,$,qualification) to deal with complex PWS. Yes, why don't use AC? I said one good to cope with very enemy -- zero drift.

For most of industrial application (at least I've come across) the most of strain gauge's were DC based. For an accuracy range between a few percents to 10th it's enough to use DC. I had a case in my practice when excitation source (12V) had been located 500m off. In case for AC it'll be the mess at least with cable I had at the time.

Today I'm preferring to use DATAFORTH's or like signal normalizers (mV->0-20mA) for gauge's bridge. Very good thing to forget about any problems.

I had a project where'd been used common DC regulator (LM based) but 6 wire's scheme and technique applied when ADC could calibrate itself periodically in depends on measured Exc voltage.

I think it's the case where every party is right at something. For next instance any strain gauge's based scales are believed unacceptable for gems' or precision metals' weighing . String or piezo based sensors is the best option here.