Hi Everybody, as a newbie i have a small question/confirmation that may sound funny for most of you. I am not an technical electrician nor electrical engineer, I am just an engineer who has tiny electric knowlage from High-School lectures. Let's get in to the question:
First of all, I am planing to measure battery capacities (AA rechargable or non-rechargebles on the market) with using 2 multimeters with computer logging capability (UT61+ series). I will add an electric load and I will measure the voltage and current simultaneously with 2 multimeters and finally i will calculate the capacity.
When I was searching for multimeters, I heard about "Burden Voltage" issues of MMs which I was suspect previously cuz' I knew that a DMM measures the current by adding a resistance on the circuit and measures the potential difference from this shunt resistance. Some of comments, it was told that U61E has too much of burden voltage, so i digged a bit more and in an individual comment it was told that this would cause wrong current measurement cuz DMM would dismiss (not take in to account) this shunt resistance and will effect your measurement (also the total Current flow). So briefly in that forum it was told that especially low current measurements will be faulty. And i asked this user with Direct Message he answered that my measurements will be falutly if use about 100 - 200 mA current drain from batteries. I am here to clarify this point, vuz according to my knowledge he/she was wrong.
As far as I know, multimeters add a resistance on the circuit but measures the final current which is a valid value for the total current flow throught the circuit. Let's analyse it with an example:
So when I add an electric load to the circuit (For example 1.2 Ohms) and If let's say I have a 1.2 Volt Ni-MH source. In this curciut without a MM i will have 1.0 Ampere of current. When i add a multimeter in seires with 0,1 ohm shunt resistance at mA measurements (I know they are lower but i gave a value for easier calculation) the total resistance in the circuit will be 1,3 Ohm, So my final and real current will be 0,923 A through the circuit and the MM will measure this value (0,923 A), So in this case my measurement will be correct, what is currrent drained from the battery will be measured by the MM correctly, only the difference the Current that is drained will not be as I planned in the original circuit.
But the guy i mentioned above told that The MM will not take take in to account this shunt resistance drop and measure 1A of current in this circuit. When i said how it is possible, he added "Actually it measures the real current (0,923A) but removes the effect of shunt by calculation and shows you 1A to obtain the circuits real current without the multimeter. And this confused me actually.
If he is right my measurements will be false (The total circuit will drain 0,923 A but the Multimeter will show 1 A )
So, what is the reality?