Current Analyzer

Measuring Current

You can use the Differential analog inputs (CH3/+ and CH4/-) to measure current of your system in your traces.  To do this, you must place a small series resistor in the current path (see below) and measure the voltage drop across the resistor.  We have made an automated dialog to help you with the setup.  Simply press the Gear Icon at the right of the Analog Settings List Box and the following dialog will appear.  Then enter the resistor value near the bottom and press Save.  Your measurements will now show the actual amount of current through the resistor.

The value of the resistor should be small, between 50mOhms and 10 Ohms.  The Voltage Drop across the resistor needs to be large enough to get reasonable resolution, but small enough to not impact your circuit.  A reasonable rule of thumb is to choose a resistor value that causes a voltage drop of 0.1V at your maximum current (V = I * R, R =  V / I).  So for a system that has a maximum current of 200mA, your resistor should be R = 0.1V/0.2A = 500 mOhms. 

Here is a list of suggested Resistor values for various maximum system current with a voltage drop of 0.1V:

Max System Current

Suggested Series Resistor Value

10 mA - 10 Ohms

50 mA - 2 Ohms

100 mA - 1 Ohm

500 mA - 200 mOhms

1 A - 100 mOhms