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How to make a digital ammeter?

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anun

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hi, i want to make a digital ammeter. does anyone know how to make a digital ammeter. is there an ammeter ic???

tnx
 

digital ammeter circuit diagram

Give details. What range of current, AC or DC, frequency range.

The usuall method for an in circuit ammeter is to put the current through a low value resistance so a voltage proportional to the current exists across the resistance.
Eg to measure up to 2A dc you might choose 0.1ohm so that you get a voltage from 0V to 0.2V.
Buffer the voltage and feed into a suitably calibrated voltmeter.

Some multimeters are supplied with circuit diagrams.
 

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    anun

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ammeter ic

Yes, there are "ammeter" circuits. For instance, this one: www.intersil.com/cda/deviceinfo/0,0,ICL7135,0.html
Or the equivalent from TI: https://focus.ti.com/docs/prod/folders/print/tlc7135.html
Or Maxim www.maxim-ic.com/quick_view2.cfm/qv_pk/1496

Intersil make a few other, too. Try Philips, as well. Generally, whenever you see an A/D advertised as having 3 1/2, or 4 1/2 digits, or similar, these are designed specifically for multimeters.

Generally, to measure current, ammeters use shunts and simply measure the voltage across them.
 

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    anun

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digital ammeter circuits

Sorry to hijack the thread, but I am also in the process of trying to design a digital ammeter.

Its for a computer power supply and I am wanting a resolution of a tenth of an amp but the range has to be suitable for whatever current draw will be on perhaps the 12V or 5V rail. i.e 0A -> maybe 40A

I dont particularly want to have to manually switch to a different shunt for higher currents I need it to be done all automatically so its transparent to someone looking at the display.

Im not sure how I would go about making such an ammeter with a high range and fairly good accuracy ?
 

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    anun

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digital ammeter

Here is an article that describes a clamp-on current meter:
 

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    anun

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digital ammeter design

throwaway18 said:
Give details. What range of current, AC or DC, frequency range.

The usuall method for an in circuit ammeter is to put the current through a low value resistance so a voltage proportional to the current exists across the resistance.
Eg to measure up to 2A dc you might choose 0.1ohm so that you get a voltage from 0V to 0.2V.
Buffer the voltage and feed into a suitably calibrated voltmeter.

Some multimeters are supplied with circuit diagrams.
Click to expand...


i am trying to build a digital ammeter that can measure even minute current maybe up to 0.1micro... i was planning of making a regular ammeter and then just amplifying the input current...

Added after 27 minutes:

im going to use it in a dc application
 

ic ammeter

A clamp on meter afaik wont have very accurate resolution right ? Especially at lower currents ?
 

build a digital ammeter

If the current is very small one can wind the wire carrying the current several
turns through the clamp-on meter. E.g. 10 turns will give a tenfold increase in the
output.
 

how to make a digital ammeter

Quiksilv, a 0.001 ohm shunt resistor would give you 0.1A resolution on a 3.5 digit meter, or 0.01A resolution on a 4.5 digit meter.
I grabbed a 100A 0.1% shunt on eBay a few years ago. Here's a different one:
**broken link removed**

I also use an Extech clamp-on DC ammeter that reads up to 40A with a resolution of 0.01A, or up to 400A with a resolution of 0.1A. It reads small currents just fine, but it drifts slightly, so I have to rezero it occasionally (unhook the clamp and press the yellow button). It was somewhat expensive, around $250 US dollars. It's not as accurate as a precision shunt, but it's a lot more convenient.
http://www.extech.com/instrument/products/310_399/380947.html
 

circuit of digital ammeter

Sorry havent checked this thread in a while.

Whats the drawback of using such a large shunt resistor for low currents (~1A) and high currents (~50A) ?

If there are none, then this may be an option to build such a high range and accurate ammeter ?
 

digital ammeter ic

This is an interesting thread. I have the same problem with measuring milliamp current and on top of it there is noise that I have to cancel out. The amp meter I am looking for is called zero resistance amp meter (ZRA) or transimpedance (as i learned recently. Is there anyone out there that have schematics drawing of such circuit. as far as i know there is an op amp and an A/D IC involved but have no idea on which once to use or how to wire them without making the circuit smell funny!!

I would really appreciate any help.
thank you
 

digital ampermeter schematics

Absolute zero resistance ammeters do not exist. You always need even small ammount of resistance for current measurement. Small ammount of power has to be used in measurement. This power can be extremly small when amplifier is used, but there is always signal to noise tradeoff. Things can get even more complicated when large dynamic ratio is required (Large signal to small signal ratio)
For power supply I would suggest log response amplifier and analog meter to show smaller currents and higher currents in enough detail. Sensing resistor does not have to be too small for such application. Size of resistor and required accuracy will dictate tradeoff between small resistance and larger signal/noise or higher resistance and higher heating.
 
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