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10-10-2018, 09:41 PM
Oscilloscopes for audio - part-5
One of the features of a CRT scope is that the intensity of the displayed wave form suggests that the wave is stable; the trace is being re-written over and over as the beam is swept across the screen. If there were occasional variations, these appear as "ghosts" behind the solid wave. The first DSOs did not offer this kind of information to the operator of the equipment, but new ones do.
The effect is referred to as "persistence", which is the amount of time that the phosphor glows after the electron beam has left that part of the face of the cathode-ray tube. You can exaggerate the effect by turning up the beam intensity, but this tends to obfuscate details of the wave. Later $$$ CRTs had variable persistence.
There are two ways to achieve a persistence effect with DSOs. The easiest and least expensive method uses the stored wave forms and displays the older ones in a lower intensity than the newest captures. This is accessed in a menu, where the Persist time can be set to 1, 2 or 5 seconds, infinite, or off. There is a Clear button to erase the screen and memory buffer and a new acquisition will begin. This method is used by the OWON XDS2000 and 3000-series DSOs, as well as most of Keysight's line, and many others.
The second method uses additional hardware, which of course adds cost, so these DSOs are called "DPOs" - digital phosphor oscilloscopes. They do not actually have a phosphor display, just a standard LCD; rather, they have a second data path to the display that allows both stored and live waves to be displayed. DPOs tend to be only high-bandwidth scopes.
One of the features of a CRT scope is that the intensity of the displayed wave form suggests that the wave is stable; the trace is being re-written over and over as the beam is swept across the screen. If there were occasional variations, these appear as "ghosts" behind the solid wave. The first DSOs did not offer this kind of information to the operator of the equipment, but new ones do.
The effect is referred to as "persistence", which is the amount of time that the phosphor glows after the electron beam has left that part of the face of the cathode-ray tube. You can exaggerate the effect by turning up the beam intensity, but this tends to obfuscate details of the wave. Later $$$ CRTs had variable persistence.
There are two ways to achieve a persistence effect with DSOs. The easiest and least expensive method uses the stored wave forms and displays the older ones in a lower intensity than the newest captures. This is accessed in a menu, where the Persist time can be set to 1, 2 or 5 seconds, infinite, or off. There is a Clear button to erase the screen and memory buffer and a new acquisition will begin. This method is used by the OWON XDS2000 and 3000-series DSOs, as well as most of Keysight's line, and many others.
The second method uses additional hardware, which of course adds cost, so these DSOs are called "DPOs" - digital phosphor oscilloscopes. They do not actually have a phosphor display, just a standard LCD; rather, they have a second data path to the display that allows both stored and live waves to be displayed. DPOs tend to be only high-bandwidth scopes.
