re oscilloscope triggering in article apr dxcern cern ch jeroen dxcern cern ch jeroen belleman writes in article c vs g ux murdoch acc virginia edu dgj y kelvin seas virginia edu david glen jacobowitz writes is it just me or does anybody else out there not like digital scopes my school has david jacobowitz dgj y virginia edu oh no you re not the only one analogue scopes give you or me at least a fair idea of what s going on in a circuit digital scopes seem to have a habit of inventing a sizable part of it e g even when there are only a few samples per period our hp a displays a continuous waveform complete with non existing overshoots i ve waded through lots of manual pages and menus but i haven t found yet how to turn this off it doesn t show which points have actually been measured as opposed to those which have been interpolated either perhaps you re using the wrong brand sorry all hp fans but i have a hard time being convinced that their scopes match the rest of their excellent gear one of the principal functions i look for when considering a dso is whether you can turn interpolation off the other important feature is to disable repetitive waveform acquisition i e being able to lock the instrument into real time capture mode secondly i don t like menus i want to see all common functions with their own button you ll have guessed i love analogue tek scopes i d choose a knob with printed legend over an on screen display with up down buttons right away the single knob of most digital instruments never seems to be connected to the right function at the right moment i agree with you here the only consolation is that manufacturers are beginning to pay attention to ergonomics when designing the menus however to be fair it seems that first time scope users our students seem to adjust to menus easier than navigating around the twenty or more knobs required of a real scope last but not least you never know if the waveform displayed is old or recent noisy or just incoherently modulated heck you don t even know if it really looks the way it s displayed digital scopes only show you a tiny fraction of what s going on most of the time the re busy computing things this is one area that newer dsos are addressing i recently evaluated the latest box from tek their tds which seems to be a worthy alternative to a standard mhz analogue cro this instrument has a mhz ms s spec meaning that it is always in real time capture mode the pricing also matches equivalent analogue scopes in the range the downer is that the instrument uses menus again but at least they appear to be logically laid out there are only three situations for which i would prefer a digital scope looking at what happened before the trigger looking at rare events and acquiring the data to have my computer play with it let s hope scope manufacturers are listening best regards jeroen belleman jeroen dxcern cern ch one more thing about the new simpler front panels these instruments tend to use digital rotary encoders as knobs now this is a vast improvement over the old oak switch the single most common cause of failure in our scopes other than students blowing up inputs is mechanical wear on these switches i look at the new panels as a great step toward increasing the longevity of the instruments johnh electronics department school of mpce macquarie university sydney australia email johnh mpce mq edu au ph fax
