# Measuring Current

Direct Current Measurement:

Electrical current (i.e. current intensity) is measured using an ammeter. The following graphic shows the circuit symbol of an ammeter. Conventional multimeters normally feature both a voltage measurement mode and an ammeter operating mode with various measurement ranges. To measure the current, the current that needs to be measured must pass through the ammeter. This means a gap needs to be made in the circuit and the ammeter connected in that space. Unlike a voltmeter an ammeter is located in series in the branch for which the current is to be measured. The subsequent animation illustrates this. The following circuit diagram shows various possibilities for integrating the ammeter into the simple circuit previously studied. Since this circuit comprises only one branch and the current is therefore the same at all points, it does not matter where the ammeter is inserted into the circuit. Indirect Current Measurement:

If there is no ammeter available for current measurement, only a voltmeter, then you can still determine the current indirectly by measuring the voltage. To do this we have to utilise the relationship between current and voltage across the load - which we will later encounter as Ohm's law. The principle is based on first inserting a small resistor RM into the circuit instead of an ammeter ("a shunt resistor") purely for the measurement. To ensure that this resistor has little impact on the current to be measured, it must have a very low value (e.g. 1 W). Then we use the voltmeter to measure the voltage UM across this "shunt". This then allows us to determine the current I according to the following relationship. The following circuit diagrams reiterate the principle once again: the graphic on the left shows how the current is measured directly using the ammeter, while the graphic on the right shows the indirect measurement using a measurement shunt RM and a voltmeter. 