# electronic current meter ??????

Discussion in 'Homework Help' started by adn07, Dec 1, 2007.

Sep 25, 2007
17
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i need your help guys ...
i have to design electronic current meter
form nano amper to meli amper
what type of regulators do i need ? what value ?
i realy a preciate any coment...

2. ### recca02 Senior Member

Apr 2, 2007
1,211
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see if this helps.

Sep 25, 2007
17
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thanx recca for quick response ....the link you give dosnt help me with any part of my
project .....but thanx for your time

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Well, we know about something that does not help - but we know nothing about what might help. The more completely you can describe the instrument, the more likely we are to be able to help.

Sep 25, 2007
17
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well , im very happy that i found what i need in our site -if i could say our site-
wich is DC ammeter circuit ..and now i bought gelvanometer (PMMC)
but i faced another problem which is the rang ... i need a rang from nanoamper to
milli amper ....so how can i make this rang??? is the rang determin by the valu of resistors?

6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
The galvanometer is essentially a weak electric motor that tries to turn under the influence of the current through the coil against an opposing force provided by a spring.

The sensitivity of the meter movement is fixed (that is, it's response to current), so the only way to allow it to measure currents above the level which will turn the pointer above the last index mark is to use accurate fixed resistors to limit the current. The value of the ranging resistor has to be calculated with the resistance of the galvanometer's movement in mind, so the scaling of the current is accurate.

At the other end - nanoamps - the galvanometer is not the instrument to use. If the movement is typical, the sensitivity will be in the tens of microamps range. If that is the case, then amplifying the current or using a different instrument will be necessary.

The fascinating thing here is the use of a galvanometer. That is a very old technology, but capable of great precision. At one time, the room in which the galvanometer was installed had a scale painted on the walls, and the movement carried a mirror instead of a needle. The bright line projected on the painted scale gave an improved resolution over a small instrument-mounted scale.

Sep 25, 2007
17
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thanx been there ,,,,
thats what i descover about the galvanometer ....that the rang what i need is diffecult
to make it ....

8. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
That's why galvanometers are not used much anymore.