Essential Electrical Signal Parameters Explained

Understanding Period and Frequency

If a signal is repeated over time, it has a frequency (f). Frequency is measured in Hertz (Hz) and equals the number of times the signal repeats in one second (i.e., 1 Hz equals 1 cycle per second). A repeating signal also has another parameter: period (T), defined as the time it takes the signal to complete one cycle. Period and frequency are reciprocals of each other:

What is Voltage?

Voltage is the electrical potential difference between two points in a circuit. Normally, one of these points is usually ground (GND, 0V), but not always. For example, to measure the peak-to-peak voltage (Vpp) of a signal, it's the difference between its maximum and minimum values. The term 'voltage' usually refers to the amplitude difference between the maximum value of a signal and ground.

Understanding Signal Phase

Phase can be better explained by considering the sine waveform. A sine wave can be derived from the movement of a point on a 360-degree circle. A sinusoidal signal cycle covers 360 degrees.

When comparing two sinusoidal signals of the same frequency, they may not be in phase. This means that equivalent points of both signals do not coincide in time. In this case, it is said that both signals are out of phase, and the phase difference can be measured with a simple rule of three:

Where 't' is the time delay between the two signals.

Measuring Electrical Voltages

When we talk about voltage, we are typically referring to the electrical potential difference, expressed in volts, between two points in a circuit. However, one of the points is usually connected to ground (0 volts), simplifying the discussion to 'voltage at point A' (when in reality, it's the potential difference between point A and GND). Voltages can also be measured peak-to-peak (Vpp), representing the difference between the maximum and minimum values of the signal. It is very important to specify what kind of voltage is being measured.

The oscilloscope is a device used to directly measure voltage. Other measurements, such as intensity or power, can be derived from this by simple calculation. Calculations for AC signals can be complicated, but measuring voltage is always the first step before deriving other quantities.

The previous figure illustrates the peak value (Vp), the peak-to-peak value (Vpp), which is usually twice Vp, and the RMS (Root Mean Square) value (Vrms). Vrms is the root of the average squared instantaneous values and is used to calculate the power of an AC signal.