Chelmsford Amateur Radio Society Advanced Course (10) Measurements Part-3 - Oscilloscopes

Oscilloscopes Oscilloscopes can be used for Measuring DC voltages Measuring amplitude Measuring waveform period and frequency Checking waveforms Oscilloscopes contain A CRT or LCD display screen A horizontal timebase A vertical deflection input (or two) A timebase trigger

Oscilloscope Controls Y-axis X-axis Horizontal timebase (ms/div) Y input Vertical gain (V/div) Focus Brightness

Measuring Amplitude Check variable controls are as “cal” Obtain a large trace Read the pk-pk amplitude in divisions. Read the vertical gain (volts/division) Calculate the pk-pk voltage The amplitude is half the pk-pk value The RMS voltage is amplitude x 0.707

Measuring Frequency Check variable controls are as “cal” Display a suitable number of cycles (say 5) Read the total divisions for the cycles Calculate divisions for 1 cycle Read timebase setting (ms/division) Calculate period in seconds Calculate: Frequency = 1 / Period 1 2 3 4 5

Oscilloscope Probes Scope probes reduce input capacitance and divide voltage, usually by 10. This means you must remember to multiply voltage readings by 10. All probes must be adjusted to match the ’scope by connecting to ‘probe cal’ point and tweaking for a level-topped square wave. Trimmer