When current is applied to a resistor, voltage drops at both end of the resistor according to Ohm's law. You will get the current value applied to the resistor when you divide the voltage by resistance value. When you adjust the resistance large to make voltage drop large, heating of the resistor would be an issue. To avoid this, current sense should be achieved by using small resistance as possible. When the voltage drop is small, the voltage should be amplified by amplifying circuit.
 

 

The purposes of current sense in a circuit are divided into overcurrent sensing, current control and current Management.

To detect large current of dozens of A, a extreme low ohmic resistor is required. Low ohmic metal film resistor or metal foil resistor are best options. Thick film type resistors are used to detect low current by using comparatively large resistance like a few hundreds miliohm to a few ohm. See our product lineup of current sense low ohm resistors. Thick film resistors are used to detect small current because relatively large resistance from hundreds of mΩ to a few ohm is used for detecting.
 

Current sense low ohm resistors include four-terminal type, with voltage detecting terminals to detect voltage and current terminals to flow current. The advantage of four-terminal is to enable to detect current more precisely, with less error of the detected value by the voltage detecting pattern layout. The disadvantage is the total resistance becomes larger than two-terminal type because its construction makes it easier to produce resistance between voltage detecting terminal and current terminal as well as the resistance to detect current.