How to measure DMM's current circuit resistance?

To meet a minimum accuracy spec, a device specifies that the 4-20mA DC current measurement from its 'test' terminals requires a milliamp meter with an impedance of less than 10 ohms. None of the meters in the shop have a current circuit 'resistance' value in the spec sheet.

I assume that a DMM meter's current circuit has a relatively low resistance across which the voltage drop is measured and then converted to a current value.

To measure the resistance of the 20mA milliamp current scale of digital multimeter I was considering using a 1.5V dry cell in series with a 'precision' (0.1%) 100 ohm resistor to get an approximate 15mA current source (not a particularly heavy load on a dry cell).



Measuring the voltage drop across the meter's input terminals (A to B) meter should show the voltage drop across the internal resistor in the DMM under test. That IR drop divided by the 15mA current should tell me the DVM's resistance.

From a physics class 45 years ago, I seem to recall that a battery/cell has an internal resistance. Is that internal resistance large enough to be a consideration for a measurement like this?

Or is there some other (relatively) simple measurement that is I can make?

 

Gentlemen, thank you for your succinct replies.

I read Ted's reply and went, "Duh". Why should I create a milliamp meter from components when I can use a commercial unit to do the same thing? I'm guess I'm showing my age. And thanks for the 'typical' values used for ranges.

I'll re-check spec sheets for the IR drop, Harald.

Thanks again,

Carl