Operating instructions

University of Saskatchewan

Electrical Engineering Laboratory Equipment Manual

The RS232 setup softkey reveals another set of options. Leave all fields set to their

default values (press the ―Set to defaults‖ softkey); these default values are sufficient for your

needs.

Math Menu

Pressing the math menu button will automatically switch the scope to the math function

currently selected. There are three major functions: addition, subtraction, and FFT (fast fourier

transform or spectrum analysis). Depending upon which function is

active, a different set of softkey choices will be available. However, the

mathematical operation selection softkey is the first available choice for all

three. In the case of addition, no further choices are available—only CH1

+ CH2. For subtraction, there are two choices, CH1 – CH2 or CH2 –

CH1. To turn the math function off, simply press the math menu button

again.

Only the basic instructions regarding the FFT will be presented here. For more

information, consult the TDS200-Series Extension Modules manual.

The fast fourier transform is a mathematical function that takes a set of discrete numbers

as its input. In this case, those numbers are the discrete sampled points of the input waveform.

The FFT requires that the number of samples it receives be a power of 2. The oscilloscope

captures 2500 points per waveform, but only the middle 2048 are used to perform the FFT.

Before you perform an FFT on a waveform, be sure that it is vertically centered in the

display and is as large as possible without clipping (or going off-screen). Also make sure that

several cycles of the waveform are displayed. Now turn on the FFT by pressing the Math menu

button, and selecting the FFT operation. You may select the channel on which to perform the

FFT (CH1 or CH2), the window type to apply to the data, and the FFT zoom level.

There are three window types that you may choose: Rectangular, Hanning, and Flattop.

Without delving into the underlying theory, the following table summarizes the characteristics of

each window type:

Window

Measure

Characteristics

Hanning

Periodic waveforms

Better frequency, poorer magnitude accuracy than

Flattop

Periodic waveforms

Better magnitude, poorer frequency accuracy than

Hanning

VERTICAL

POSITION

MATH

CH 1 CH 2

VOLTS/DIV VOLTS/DIV

2mV

CURSOR 1 CURSOR 2