Nassau Community College
Electronics and Telecommunications
Reference Sheet

Current Measurement Techniques


Current measurement requires an entirely different technique than was used in voltage measurement.  To perform a current measurement the ammeter must be placed in series with the component in which the current is being measured.  This involves breaking the circuit and placing the meter across the break, completing the circuit again.

Current Measurement
 
1.    Always check the fuses and the current ranges on the meter, using the test fixture, before beginning!

2.    Connect the leads to the appropriate jacks
        a.    Simpson 270: Red lead >> +, Black lead >> COM  (Except 10A measurement)
        b.    Fluke DMM: Red lead >> 300mA , Black lead >> COM  (Except 10A measurement)

3.    Set the meter to the appropriate range.
        a.    If uncertain, set the meter to the highest current range and work down when measurement is taken.
        b.    Typical setups are shown below.
Simpson 270
Fluke DMM

4.    Find the resistor through which the current is to be measured.
R1


5.    Create a break in the circuit by moving one lead of the resistor.
R1 Break 


6.    Use the meter to jumper across the break.  This puts the meter in series with the component.
R1 Meter


7.    Read the current flowing through the meter.
        a.    Simpson 270 – Find the appropriate scale and determine the reading
        b.    Fluke DMM – Read the LCD panel to determine the current in mA.

8.    Process repeated for a second resistor.
R2 R2 Gap R2 Meter
Determine Resistor  Create the break Put the meter across the break