For what seems to have been forever, the traditional and basic tool in Vocational, Physics, or Basic Electricity programs, have been the Analog Oscilloscope. Instruments extend our senses the oscilloscope lets us see things we normally cannot see. That ability, to visualize, and measure signals is essential to their understanding.
Over the last 5 to 10 years a new type of Oscilloscope has been gaining ground in the “real world” of electronics test – the DSO (Digital Storage Oscilloscope). Driven by the increasing cost of CRT’s, the declining cost of Analog-to-Digital Converters, LCD’s and Microprocessors, Digital Storage Oscilloscopes developments provide significant improvements in performance, functions, and user interface. Recent market data (2006) has the World market for the DSO at $1.2 billion, compared to the analog market at $30 million. When your students enter today’s electronics industry they will be using DSO’s
In education, the DSO has an inherent advantage over Analog Oscilloscopes in its ability to capture, store, and analyze signals and phenomena. An image on an Analog scope is fleeting, unless it is repetitive, you see it, and then it’s gone. If you want to demonstrate what a middle C on the piano looks like (its attack decay, amplitude, duration), you have to keep hitting the key, and hope you have the right time base settings to show a decent display. With the typical CRT at 6”, it is impossible for those seated at the back of the class room to see anything meaningful.
The DSO solves these problems. You strike the key, push the capture button, and viola, the waveform is captured, and stored, and displayed. The display may be analyzed to show the various components. That ability- to store, and show the attack/ decay characteristics of a sound, vibration, or other element of a signal, make it invaluable in teaching. Most DSO’s have RS232, or, USB outputs to send data to a computer. A PC with a large monitor allows the DSO display to be seen at the back of the classroom so no one need be left out.
Most DSO’s have mathematical functions such as: signal addition, subtraction, inversion, multiplication, and FFT (Fast Fourier Transform). With the exception of a sine wave, most signals whether electrical or physical are complex, their time domain display is very difficult to interpret. The FFT converts a complex time varying signal to a frequency vs. amplitude display see Fig. 1 for a screen display of a square wave in the time domain (top) display and its frequency domain display. It’s very easy to demonstrate how a square wave is composed of a fundamental frequency, and its harmonics. The FFT has applications in electrical power cellular telephony, radar signal analysis, and many other electronic phenomena;. You can illustrate why a computer with a 10 MHz clock radiates a signal at 100 MHz and why many household appliances generate radio interference. An FFT is also valuable in evaluating physical phenomena such as vibration, and impulse analysis to name just two.
If you mount an inexpensive accelerometer, on rotating machinery, can show bearing noise, misalignment, and other problems.
When first introduced, DSO’s were expensive – typically 3 or 4 times the cost of the traditional 25 MHz Analog Oscilloscope used by educators. Over time, the learning curve of LCD’s, A/D converters has brought the costs of DSO down to the level of Analog Oscilloscopes. As an example, the Rigol model DS1022C a full featured DSO, sells for $499.00. At that price the user gets a DSO with a 400 Mega sample/ sec real time sample rate ( to capture and display very fast fleeting events) , 1 Meg point storage capability ( allowing detailed analysis of complex signals), TFT display with Ch1 and Ch2 having different colors. Math functions include Add, Subtract, Invert, Multiply and FFT. The unit comes with software so that waveforms and data maybe exported to a PC to create charts, and reports.
From all aspects this powerful tool is limited only by the user’s imagination as to its uses in the class room.
