All ammeters will introduce a resistance in the circuit that could affect circuit operation.
You'll be better off measuring the voltage drop across a resistor and calculating the current.

In all of my decades of working on circuits, I can't remember when I really needed to actually measure current. Calculating the current was always sufficient.

Indeed you can measure voltages and calculate the current. But what if the resistance is very small?
There ARE Amp meters that have NO resistance (clamp meters). Personally I use a UNI-T UT210E. ($60 - 80) It measures as well AC as DC currents in a range of 0 to 100Amp. DC currents below 20mA are not really accurate. If you need accuracy in this range you'll have to spend at least the ten fold...
There are also the Current to Voltage chips. They transform as well AC and DC. Find/check allegromicro for e.g. ACS 712...
internal resistance : 0,6 MILLI-ohm...

 

It measures as well AC as DC currents in a range of 0 to 100Amp. DC currents below 20mA are not really accurate. If you need accuracy in this range you'll have to spend at least the ten fold...

Or run the wire in which you are measuring the current several times through the clamp.

 

Indeed you can measure voltages and calculate the current. But what if the resistance is very small?
There ARE Amp meters that have NO resistance (clamp meters).

When I worked as an R&D technician, I never used a meter to measure current. We always measured the drop across a resistor and calculated current. If there wasn't a convenient resistor, we inserted one.

We were rarely interested in current in and of itself. Only as it related to correct circuit operation and we could generally verify that by measuring voltages.

For hobby work, I can't remember the last time I needed to measure current. I do it in circuit simulations because it's available without needing a meter, but not in actual circuits.

 

dl324 said:

All ammeters will introduce a resistance in the circuit that could affect circuit operation.
You'll be better off measuring the voltage drop across a resistor and calculating the current.

This is better said as "most Ammeters". The Keithley 480 drops 200 uV. https://www.atecorp.com/products/keithley/480

Generally any measurement disturbs something.

 

Just a quick update in case anyone is looking for something similar. I received these ammeters today and they are pretty impressive. They have a sturdy feel to them and are very simple to use. They are 0.25W. I have tested them through a range of voltages and loads and the readings compare very well with the readings on my power source. In fact when you get below 4mA these ammeters respond better than my power source. I would say there is a discrepany of about half a division which is 1mA. That might even be adjustable because there is a slot in the black hub of the ammeter that I presume is for fine tuning. But these are certainly good enough for my purpose. I will mount them on some kind of bracket and attach a coupe of leads.

 

Normally that adjuster is set so zero current reads zero on the meter.

 

Normally that adjuster is set so zero current reads zero on the meter.

They do.

 

When you set the mechanical zero only rotate the zero set screw clockwise, as you come up on zero slowly bring it up to and set zero. That done back the set screw back counter clockwise just a tad and a tad is a technical term meaning just a few degrees of rotation . Just about all analog meters are the same mechanical affair and look like this.



The front panel screw (mechanical zero adjust) has an offset which fits into that zero adjuster slot as seen above. It's strictly a mechanical zero adjust and on real sensitive meters we would shunt the terminals with a short and then adjust the zero.

Disregard the mention of metal chips as the image was used to show how an analog meter movement could have sticky points along its travel.

Ron