There are several different methods for measuring current, each with advantages and disadvantages. Current is defined as the flow of an electrical charge through a component, such as a wire or light bulb. The level of current, usually expressed as amperes or “amps,” is proportional to the amount of electrons that are moving through a device. Devices that are designed to measure current all use Ohm’s Law, which states that current is equal to voltage divided by resistance. While all current sensing methods are based on this principle, the actual design of instruments built for this purpose can vary.
The method chosen by an experimenter for measuring current is often influenced by the task at hand. Bench-top power supplies are often used during the initial design and testing of a new circuit. Handheld multimeters are common for field testing and troubleshooting, while integrated circuits can be installed into a final product for automatic current response.
A bench-top direct current (DC) power supply is one of the most common ways of measuring current. This type of device can be set to produce a specified voltage, and is useful for experimentation. Bench-top supplies typically have several analog or digital readouts, which display both the voltage setting and amount of current being drawn by a circuit. When the power supply is connected to a component, the internal circuitry automatically measures the current. The large readouts and simple controls make a bench supply convenient to work with, but many do not have the ability to record current values.
Digital multimeters can also be used for measuring current. Unlike bench-top equipment, most multimeters are lightweight and compact. This small size allows them to be used in remote locations, but can also make them difficult to read and adjust. Some advanced meters can log current readings and display these saved values on a computer for later analysis. Multimeters are usually not designed to output an adjustable voltage, which limits their ability to power and experiment with new circuits.
Current sensing integrated circuits (ICs) are available for specialized current measuring applications. These small chips do not display current data directly, but are instead designed to be integrated into a larger project. Most integrated circuits designed for measuring current will output the detected value as a voltage amount. This type of chip can be connected to a microcontroller or computer, and allows a device to monitor itself. An industrial robot, for instance, can use a current sensing IC to automatically shut down if a dangerous spike in current is detected.