Electrical Engineering BMT & UFC › Circuit Analysis 1

Circuit Diagram

If, in another example, a lamp, a pump, a stirrer and a heater are supplied from a battery, we can draw this as a circuit diagram as follows:

The circuit diagram represents a model of reality. The individual components are shown in a greatly simplified form for the electrical analysis. Each has two terminals; current flows into one and out of the other. In the model they are shown in simplified form as pictograms. The circuit diagram contains conductors and switches.

The battery is separated from the rest of the circuit by a main switch, via which the stirrer and heater are connected to the battery. When both the main switch and the lamp switch are switched on, the lamp is also connected to the battery. The same applies to the pump, which can also be switched separately from the other components. The current flows from the positive terminal of the battery with the high potential through the loads to the negative terminal of the battery with the low potential.

The behaviour of the components of the circuit (battery and loads) is modelled. To keep the example simple, the battery is modelled as an ideal voltage source. All loads are modelled as resistors. This means that the battery behaves approximately like an ideal voltage source. Voltage and current at the loads obey Ohm's law U = R ∙ I.

Of course, a stirrer is not an ohmic resistor, but as long as its relationship between voltage and current behaves like that of a resistor, it is modelled as such for simplicity. By reducing it to its electrical properties, we avoid also having to deal with the fluid mechanics of a stirrer when we only want to design a circuit for a stirrer. We can convert the circuit into an even more abstract form of modelling:

Equivalent circuit with voltage source and resistors — Lampe = lamp · Batterie = battery · Pumpe = pump · Rührwerk = stirrer · Heizung = heater

Simple circuits consist of a source and several resistors. The resistors are dimensioned so that the currents and voltages in the circuit take on the desired values. Or, to put it the other way round: the currents and voltages in a circuit can be calculated from the resistance values. The following calculation rules are used for this.