Electronics > Beginners

Analog multi meter - standard vs FET input

(1/5) > >>

nukie:
Hi all,
I need help in understanding how these FET input based analog meter works. I am thinking of getting one to read average current & voltage from a pulsed source, doesn't need to be very accurate because I will do some calculation.

I really like that FET based analog meter has very high input impedance but does the inclusion of FET circuitry turn it into a digital meter with an analog front end?

Obviously I have zero idea how these FET based meters work, all I can guess that it uses some sort of amplificaiton after the inputs. Should I be buying a standard high sensitivity meter or a FET input based analog meter? Please show me the way.

Kiriakos-GR:
well I need to ask one question up front before I say anything .

How much money do you plan to spend for it ?

Zero999:
I'd assume a FET input just means it has a buffer with a very high input impedance before the meter.

Zero999:

--- Quote from: BoredAtWork on June 03, 2011, 05:59:13 pm ---The classic circuit is two FETs, paired and temperature coupled, to form a differential amplifier.  By todays standard worth a few cent.
--- End quote ---
I would've thought a modern analogue meter would simply use an FET input op-amp because the transistors will be better matched and it's cheaper.

EEVblog:

--- Quote from: nukie on June 03, 2011, 03:20:29 pm ---I really like that FET based analog meter has very high input impedance but does the inclusion of FET circuitry turn it into a digital meter with an analog front end?

--- End quote ---

You could look at it that way, but you do still get that "analog" moving needle performance.
Having the FET input gives it a fixed high input impedance just like a digital meter, and it requires a battery to power it just like a digital meter.
The beauty of an analog meter on the other hand is that it doesn't require a battery (except for ohms), the input signal swings the meter directly.
Some can be quite sensitive actually. I used to have a 100K/volt analog meter.

I have a Tandy/Radio Shack FET meter in the lab.

Dave.

Navigation

[0] Message Index

[#] Next page