electrodes impdances

[electronic engineer]

I need a clarify for this statement:

Replacement of galvanometers with high-gain amplifiers allowed smaller electrodes with higher impedances to be used and potentials of smaller amplitudes to be recorded .

[dlgoff]

Reference please. What type of electrodes?

[berkeman]

I googled the whole phrase, and got a hit on the Biomedical Engineering Handbook, Chapter 14 on Electrodes -- "Principals of Electromyography":

http://books.google.com/books?id=6bK84ZHFuW4C&pg=PT226&lpg=PT226&dq=Replacement+of+galvanometers+with+high-gain+amplifiers+allowed+smaller+electrodes+with+higher+impedances+to+be+used+and+potentials+of+smaller+amplitudes+to+be+recorded&source=web&ots=_8ZiyA0QI_&sig=zW9FMjKUEyht66Iuvm7j2CQ95ts&hl=en&sa=X&oi=book_result&resnum=4&ct=result

It's about the history of the instrumentation used for Electromyography (EMG), which is measuring the electical potentials generated from muscle contractions.

So to electronic engineer, yes, using an active amplifier instead of just a passive galvanometer was a nice advance in EMG technology in 1929. You can use smaller needles (EMG electrodes) when you use active amplifiers. Kinda' ancient history, though...