c5f8 said:

I have a general question. Electronics articles sometimes state that a

circuit or electronic device such as a sensor has either low input

impedance or high input impedance. The articles never state why it's

important to know what the input impedance is.

I've seen both cases where a product is advertised with the low/high

impedance statement and suggesting that there product is somehow

better because of that statement.

Can someone explain when it's beneficial to have low input impedance

and when it's beneficial to have high input impedance?

To see the answer to your question, imagine you are measuring the

voltage in some part of an electronic circuit (maybe a battery) with a

voltmeter. Now suppose the input impedance of your meter is one ohm.

That would almost always be considered a low impedance (but since low

and high are relative terms, compared to an impedance of 0.001 ohms, one

ohm is high). You'd have a hard time locating a voltmeter with a one ohm

input impedance.

Not many circuits will continue to function with a one ohm impedance

across them, and some might even be destroyed.

Now imagine a voltmeter with a 10 megohm input impedance. It would be

much less likely to interfere with the normal operation of a circuit.

Some voltmeters have an input impedance as much as a million times

higher than 10 megohms for precisely that reason.

I encourage you to continue your study of electronics, and in

particular, the notion of impedance. You will find some interesting

information dealing with maximum power transfer.

Chuck