Oscilloscopes

Anyone planning to work or study electronics should become familiar with oscilloscopes. An oscilloscope is a piece of electronic test equipment that allows signal voltages to be viewed by the human eye. This is accomplished as a two-dimensional graph of one or more electrical potential differences (vertical axis) plotted as a function of time (horizontal axis).

Even if you do not think you have seen oscilloscopes in the past, chances are good you have and perhaps did not know it. On the outside, a typical oscilloscope is usually a metal box with a display screen (this is more often than not circular in shape). The box has numerous input connectors, control knobs, and buttons on the front panel. On the face of the screen is a grid called the graticule. This grid is used to help make more accurate measurements. Each square in the grid is known as a division.

In order for oscilloscopes to work they have to have something fed into them. The signal to be measured is fed to one of the input connectors, which is usually a coaxial connector such as a BNC or N type. If the signal source has its own coaxial connector, then a simple coaxial cable is used. If this is not available, a cable called a 'scope probe', which is supplied with the oscilloscope, is used.

A general purpose oscilloscope will have a standardized input resistance of 1 mega-ohm in parallel with a capacitance of around 20 pico-farads. This allows the use of standard oscilloscope probes.

Oscilloscopes that are used with very high frequencies may have 50-ohm inputs, which must be either connected directly to a 50-ohm signal source or used with Z0 or active probes. It is used for measuring voltage.

When oscilloscopes are working properly, you will see what is known as the trace. The trace is a line that is repeatedly drawn across the middle of the screen from left to right. One of the controls, the time base control, sets the speed at which the line is drawn, and is calibrated in seconds per division.

If the input voltage departs from zero, the trace is deflected either upwards or downwards. Another control, the vertical control, sets the scale of the vertical deflection, and is calibrated in volts per division.

The resulting trace is a graph of voltage against time, with the more distant past on the left and the more recent past on the right. In most cases, the trace is shown as a sine wave, also known as an S-wave.

Reading oscilloscopes takes a bit of practice, but it is a skill that you need to learn if you want to work in electronics.