Types of Oscilloscope

Types of Oscilloscope Points : Types of Oscilloscope, Multiple Beam Oscilloscopes, Double Beam Oscilloscopes, Multiple Trace Oscilloscopes, Sampling Oscilloscopes, Impulse Waveform Oscilloscopes, Scanning Oscilloscopes, Storage type Oscilloscopes, Digital Oscilloscopes As it is stated in the introductory information’s that oscilloscopes are classified as;
i. Free — running oscilloscope
ii. Triggered oscilloscope

But there are a number of types of oscilloscopes which are used for special applications. These are as under:
a) Multiple Beam Oscilloscopes
b) Double Beam Oscilloscopes
c) Multiple Trace Oscilloscopes
d) Sampling Oscilloscopes
e) Impulse Waveform Oscilloscopes
f) Scanning Oscilloscopes
g) Storage type Oscilloscopes
h) Digital Oscilloscopes a) Multiple Beam Oscilloscopes In many cases it becomes necessary to compare one signal with another. In such cases multiple beam. Oscilloscopes are used. These oscilloscopes enclose in a single tube several beam producing systems each with its vertical pair of plates, but mostly with a common time — base. Each Y channel has its own amplifier. The synchronization or triggering is done from the input of a desired Y channel or form an external input voltage. b) Double Beam Oscilloscopes These use two electron guns within the same cathode ray tube. The electron beams of the two channels are completely independent of each other. The same effect may be produced by a single electron gun, the output from it being split into two independently controllable electron beams. c) Multiple Trace Oscilloscopes These oscilloscopes use a single electron gun and produce multiple traces by switching the Y deflection plates from one input signal to another (this means that the Y channel is time shared by many signals). The eye interpret this as a continuous simultaneous display of the input signals although it is a sampled display. This method reduces the cost of manufacturing multi-channel oscilloscopes. d) Sampling Oscilloscopes The oscilloscopes presently available can be used for continuous display for frequencies in the 50-300 MHz range depending upon the design of the oscilloscope. Above this range of frequencies sampling techniques must be employed to obtain satisfactory display. The display may be made up from as many 1000 dots of luminescence. The sampling oscilloscope is able to respond and store rapid bits of information and present them in a continuous display. It is this ability that enables the sampling oscilloscope to side — step the usual limitations in conventional high frequency oscilloscopes which have limited sensitivity and band width and small display size. The sampling oscilloscopes can be used beyond 50 MHz into the UHF range, around 500 MHz and beyond up to 10 0Hz. However, it should be understood that sampling techniques can not be used for the display of transient waveforms. e) Impulse Waveform Oscilloscopes These oscilloscopes are used for investigation of transient non period phenomena which occur at high voltages. The oscilloscopes use special types of CRT wherein the plates are mounted on the sides. The voltage to be measured, is applied to these plates either directly or through capacitive potential dividers. Simultaneously, an impulse is suddenly applied to the cathode voltage. A very bright display is obtained on account of the high voltage and the high beam current which exist for a very short duration. Therefore, photographic records of the display can be obtained even at very high speeds of up to 50 x 10⁶ msec sec. f) Scanning Oscilloscopes The oscilloscopes use television tubes. The data to be measured are applied through intensity modulation on the standardized screen. Several phenomena can be observed simultaneously on a single screen by using this technique. Because of the large number of factors influencing the quality of the recording, experience with the particular camera CR0 combination is usually the best guide. g) Storage type Oscilloscope The storage type CR0 is rapidly becoming one of the most useful tools in the presentation of very slowly swept signals and finds many applications in the mechanical and biomedical fields. In the conventional CRT the resistance of the phosphor ranges from microseconds to perhaps seconds. In applications where the persistence of the screen is smaller than the rate at which the signal sweeps across the screen, the start of the display will have disappeared before the end of the display is written.

With the variable persistence or storage CR0, the slowly swept trace can be kept on display continuously by adjusting the persistence of the CRT screen to match the sweep time. Persistence times much greater than a few seconds or even hours, are available, making it possible to stop events on a CRT screen. The storage CR0 uses a special CRT, called the storage tube. This special CRT contains all the elements of a conventional CRT, such as the electron gun, the deflection plates, and a phosphor screen, but in addition holds a number of special electrodes. h) Digital Oscilloscopes Conceptually, analog and digital oscilloscopes do the same thing they display voltage waveforms. The analog scope uses traditional circuit techniques to display the voltage waveform on a CRT. A digital scope, in contrast, converts the original analog signal to a series of binary numbers which can be then displayed or stored in memory. This means that a digital scope is inherently a storage scope, because the waveform is stored in digital form. Contrast this with the analog scope, where the waveform is a short lived voltage waveform disappears). There are techniques for storing waveforms on an analog display, but they generally are expensive, temper a mental, and have a finite storage time. The ability to store waveforms is especially important when capturing one time events. Without waveform storage, the waveform is plotted across the display and then abruptly disappears. With storage, the waveform remains on the screen so that the user can carefully analyze the data. Another advantage of digital scopes is the ability to display the waveform that occurred before the trigger. This may seem slightly impossible at first glance, but a digital scope can accomplish this by constantly storing the input signal into memory waiting for the trigger to occur. When the trigger occurs, the portion of the waveform that occurred just before the trigger is already stored.

Like other digital instruments, the digital scope is well suited for applications that require transferring waveform data to a computer. Since it stores the waveform internally as digital numbers, the data is already in a form compatible with computers. Also, since the data is in digital form and most digital scopes are microprocessor controlled, the scope can simplify many measurements. For instance, the microprocessor can automatically compute and display the rise time, fall time, frequency etc of waveform, rather than having the user manually do it. A good digital scope can even find the RMS voltage of the waveform by performing a rot-mean — square calculation on the data. The performance of a digital scope is generally limited by the rate at which the analog signal can be converted into digits. The analog waveform must be sampled often enough so that when the digital version of the waveform is reconstructed on the display, it gives a good representation of the actual waveform.