Analog CRO - One Shot Triggering Use? - Page 1
Forum section: electronics / testgear

author: TomKatt
author_rank: Frequent Contributor
timestamp: February 28, 2023, 02:00:38 pm
content: I've got an old HP 180A analog crt scope. Still running great with a sharp trace despite being nearly as old as I am. I believe this was HP's first "fully transistorized" scope, which is mostly true but does use neon bulb type voltage regulators on a few rails (side note - apparently these neon regulators are actually very stable, which is likely why they were used despite all other active elements going to silicon (or germanium lol).Anyhoo - the 1821A timebase in my scope includes a resettable Single shot mode. As the crt display is not a storage type, I've often wondered if the Single shot trigger was useful for non storage scopes - perhaps using a mounted camera to get a clean waveform image? Or was this feature only applicable to storage scopes? Because otherwise, the Signle shot is about useless as the waveform is gone as soon as it's displayed on the crt.

author: Zero999
author_rank: Super Contributor
timestamp: February 28, 2023, 02:04:50 pm
content: Yes, a camera is necessary for one shot mode. You could use a phone camera to record a video and merge the frames together, or there's probably an app which will do it for you.

author: tggzzz
author_rank: Super Contributor
timestamp: February 28, 2023, 02:35:05 pm
content: Quote from: TomKatt on February 28, 2023, 02:00:38 pmWith skill and imagination, single shot on a non-storage scope can still be useful. It is easier with a (Polaroid film) camera, but possible without. For example, I simply looked at the trace when calibrating a 1953 mechanical camera's shutter speed.You need to have set it up so that the interesting part of the trace will be on the screen. That requires thinking and understanding what will happen, with a little experimentation.You need to understand what small piece of information you want to measure, because you won't be able to remember every feature of the trace. For my example, it was where the second transition occurred on the screen (the first was used as the trigger).You need to have a bright enough trace to be visible, which is a combination of the beam current (i.e. brightness), sweep speed, external illumination, phosphor persistence and retina persistence.But overall, theonlyUSP of early digitising scopes (1980-2000) was their ability to capture single shot events. And even then common digitising scopes had noticeable disadvantages until after, say, 2010.

author: Ian.M
author_rank: Super Contributor
timestamp: February 28, 2023, 03:16:44 pm
content: Back in the day, I used to use one shot mode in a darkened room (or under a black felt hood), with a sheet of acetate cut to fit the display and an OHP pen to trace the trace before it faded.

author: TimFox
author_rank: Super Contributor
timestamp: February 28, 2023, 03:22:05 pm
content: Analog CROs were characterized by their "writing speed" with a given Polaroid film and camera settings to work with single-shot trigger mode.One opened the shutter, armed the trigger, then closed the shutter after the sweep (indicated by panel lights) completed.If I remember correctly, the discovery of the antiproton was done with a CRO and a cine camera to capture multiple single shots, which were then investigated after developing the film to determine the time of flight between two detectors.https://indico.cern.ch/event/104466/attachments/15569/22575/The_Bevatron.pdfSide note: the "B" in Bevatron stands for (American) billion (109). The "BeV" was sometimes called the "Berkeley" or "Brookhaven" eV, while the "GeV" was the "Geneva" eV.

author: TomKatt
author_rank: Frequent Contributor
timestamp: February 28, 2023, 03:39:44 pm
content: Quote from: TimFox on February 28, 2023, 03:22:05 pmI know that the crt tubes were available in a number of different phosphors, some explicitly meant for film camera applications.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 28, 2023, 03:54:15 pm
content: One can use the single shot mode with an anlog scope, but it is limited. I have a single shot mode also with my analog scope (Voltcraft 2040) but I am not sure I have ever really used it.

author: TimFox
author_rank: Super Contributor
timestamp: February 28, 2023, 05:16:57 pm
content: Quote from: TomKatt on February 28, 2023, 03:39:44 pmCorrect. The normal P31 green phosphor (replacing P1) was good for direct human observation, but the blue P5 and P35 phosphors have short decay time and are efficient for film.P7 is a dual-layer phosphor, where the blue layer excites the yellow layer that has a very long persistence. It was used in old-style EKG displays and was useful in single-shot mode CROs with pulsed waveforms.P4 is the normal white phosphor for monochrome TV CRTs.