Measuring Current

Most measurement devices can measure voltages within a certain range. With a resistor, you also can measure the current through an analog input connector. To do so, you must place a known resistance in parallel with the input connector and current source.

You can measure voltage dropped across the resistor and convert it to current using Ohm's Law:

I_(A) = V_(V) / R_(Ω)

where I is the current, V is the voltage, and R is the resistance.

Measuring current is common because many devices generate a 4–20 mA current to represent a physical quantity. For instance, you can use current to measure the level in a tank. Using a level sensor, 4 mA could represent an empty tank, and 20 mA could represent a full tank.