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DSO 101

Blow the dust off of that scope and unlock its diagnostic power.
Tuesday, August 27, 2013 - 12:27
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Every month, we produce short (15-30 minute) videos on a variety of technical topics. Our June video focused on basic uses of the digital storage oscilloscope (DSO) in an attempt to encourage those of you who have one gathering dust in a corner of your shop to break it out and use it. Judging by the response, many of you are doing just that and have asked us for more scope-related information. Rest assured, we will be adding more material to our video library soon.

These older scope models are still found on sites like EBay and at very reasonable prices.

In the meantime, I thought it appropriate to offer a print primer on scopes and their use as a diagnostic tool. I’m no power user, just an average guy like the rest of you, and if I can make use of this time saving diagnostic tool, I know you can too.

Let’s start with some basic stuff.

Why Use a Scope?
The very first scope I ever used was one of those big box engine analyzers you might recall from the mid-1970s. It was an analog scope, using a cathode-ray tube display and the neon green trace you saw on its screen was in real-time with no capacity to store the information for later viewing or analysis. It typically was used to check secondary ignition patterns and had some neat features. You could show all eight cylinders at the same time in series (the parade pattern), stack them on top of one another (the“raster pattern), or look at one cylinder at a time. This made spotting anomalies in the patterns easy to do and techs with even a rudimentary amount of training could pick out problems in the ignition system after a few minutes of viewing.

This old UEI scope was the first scope I ever personally owned and was a very capable tool.

In the early 1980s, the digital storage oscilloscope (DSO) was born. This new style of scope used an analog to digital converter (ADC) to convert the real-time analog input signal to a digital form that could be stored indefinitely with no degradation in the quality of the signal attributes and later displayed on a variety of screens. Fluke was (and still is) a popular choice for early automotive techs that began experimenting with the use of these scopes as a diagnostic tool.

Some of the distinct advantages offered by the early DSOs were the ability to freeze a capture on the screen, to store that image in a permanent library either in the tool or on a personal PC, and the ability to share that image with other techs. And with the birth of the International Automotive Technicians Forum on something new called the “Internet”, experimenters were able to share their notes with others around the world and not just with those in their hometown.

The majority of the DSOs offered for sale as automotive tools today are more than capable enough of capturing the signals you want and display them with a resolution that almost mirrors on the older analog displays. And with the accessories that have been adapted and developed for automotive diagnostics, our scopes can rise to nearly any diagnostic challenge you care to throw at it. Want to monitor current in a circuit over time, looking for that intermittent cause of the battery drain you’ve been trying to nail down for the last month? A scope can do that. Want to be sure an input sensor signal is reliable? A scope can do that. Want to see if transmission line pressure changes in synch with the variable commands received by the linear solenoid controlling it? A scope can do that. All that, and a whole lot more.

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