# Electronic Circuits and Projects Forum

## Multimeter's ammeter accuracy

1. Originally Posted by Ziddik
sorry, but i can't understand that. What do u mean with i should measure the current in series? Please explain
Note the drawing in post #2 of this thread. It shows the current meter in series and the voltmeter in parallel with the load.

Ron

2. Originally Posted by Nigel Goodwin
Isn't that simply because the shunt was inside the negative feedback loop?, it doesn't matter which lead it's in, as long as it's inside the loop.
There are two different and distinct negative feedback loops: one for voltage control and one for current control or current limiting. THe CV (constant voltage) loop senses the output terminals. The CC (constant current) loop senses across the current shunt. The shunt could be in either lead but putting it in the negative line simplifies the design,

3. Originally Posted by bountyhunter
There are two different and distinct negative feedback loops: one for voltage control and one for current control or current limiting. THe CV (constant voltage) loop senses the output terminals. The CC (constant current) loop senses across the current shunt. The shunt could be in either lead but putting it in the negative line simplifies the design,
Yes, it's a standard method in regulated PSU's, and as you say it's often more convenient (for current limiting) to have the shunt in the negative lead.

4. Here is another sketch of a voltmeter and a current meter:

5. Originally Posted by Reloadron
Note the drawing in post #2 of this thread. It shows the current meter in series and the voltmeter in parallel with the load.

Ron
but how to measure the output current of a powersupply if nothing is connected as load?

6. Originally Posted by Ziddik
but how to measure the output current of a powersupply if nothing is connected as load?
There's nothing to measure, current is what something (the load) consumes, with no load nothing is consumed.

7. Originally Posted by Nigel Goodwin
There's nothing to measure, current is what something (the load) consumes, with no load nothing is consumed.
Oh.. my! Thank u

8. I have found the same thing, with various meters. There are some RADARs that require measuring crystal current with a Simpson 260, for just this reason. My recommendation is to get an appropriately sized shunt, and calculate the current using Ohms law. You can find them on ebay and Amazon for 25 to 30 bucks. Granted, at these prices they are not calibrated, but you can send them out for that.

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