The magnitude of any signal applied to the deflector plates can be calculated by measuring the deflection of the spot against a cross-wires graticule etched on the screen.Ĭhannel: One channel describes the basic subsystem of an electron source, focusing system and deflector plates. The two sets of deflector plates are normally known as the horizontal and vertical deflection plates, according to the respective motion caused to the spot on the screen. Controls of a simple oscilloscope.Īpplication of potentials to two sets of deflector plates mounted at right angles to one another within the tube provide for deflection of the stream of electrons, such that the spot where the electrons are focused on the screen is moved. Every model of oscilloscope has a different layout of control knobs, but the functions provided remain similar irrespective of the layout of the controls with respect to each other.įigure 9.11.
It should be noted that the layout shown is only one example.
These and other typical controls are shown in the illustration of the front panel of a simple oscilloscope given in Figure 9.11. An intensity control varies the cathode heater current and therefore the rate of emission of electrons, and thus adjusts the intensity of the display on the screen. Adjustment of this focusing mechanism is provided by a focus control on the front panel of an oscilloscope.
Smexoscope analog ac dc series#
The stream of electrons is focused onto a well-defined spot on a fluorescent screen by an electrostatic focusing system that consists of a series of metal discs and cylinders charged at various potentials. The cathode consists of a barium and strontium oxide coated, thin, heated filament from which a stream of electrons is emitted. The cathode ray tube within an analog oscilloscope is shown schematically in Figure 9.10.
Interestingly, 12 bit oscilloscopes are beginning to appear (LeCroy), and such an ADC would ideally drive a vertical screen resolution of 4096 pixels (2 12=4096). 240 vertical pixels driven by an 8 bit ADC is half the vertical resolution of 480 pixels driven by a 9 bit ADC, and making the screen diagonal 8.5″ rather than 6.5″ is not going to magically improve it. However, most cheaper oscilloscopes do not maintain pixel size, so ignore the hype about screen diagonal and look instead for the fine detail regarding display pixels, ADC bits, and whether oversampling can be invoked (high-resolution mode). Larger oscilloscope screens are now available, potentially allowing us to see more detail in the waveform provided pixel size remains small. The seminal Tektronix TDS3000 series (introduced in 1998, now on its “C” variant, and much imitated) uses an LCD screen having a 6.5″ diagonal and 640 by 480 pixels, with a 10 cm by 8 cm area available for waveform display from its 9 bit ADCs that was clearly intended to be directly comparable to an analogue oscilloscope. Liquid crystal displays (LCDs) impose no such depth penalty, so modern oscilloscopes have proportions more akin to a handbag. Morgan Jones, in Building Valve Amplifiers (Second Edition), 2014 Screen size and ADC resolutionĪnalogue oscilloscopes typically had a usable screen size of 8 cm by 10 cm because electrostatic deflection CRTs had fixed proportions, and the typical depth was already 40 cm because of the length of the CRT, so a larger screen simply wasn’t feasible.
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