Tips to achieve better oscilloscope measurements

Most engineers always have so much to do but not enough time to do them. Thus, they wanted an oscilloscope that will help them reduce the time spent on researching how to make a measurement, and spend more of it in troubleshooting.

Although some high-performance oscilloscopes make it easier for engineers to accomplish simple tasks, providing them with easy access to advanced functionality, this article also offers some tips on how they can increase their effectiveness in making critical measurements.

First, never forget to check the probe. Engineers usually forget to check probe compensation prior to making amplitude measurements on the sinewaves, particularly when their not working with a fast risetime. However, they tend to ignore the fact that risetimes within the measurement system of the oscilloscope also have its effect, which can cause errors when measuring signals.

Second is to find a quick way to troubleshoot mixed hardware/software prototypes. Troubleshooting and designing hardware driven with software commonly requires engineers to look at complex and lengthy bit streams. This is solved by finding an unused I/O pin, which they can use as a trigger point, and inserting the code into the software to easily toggle the pin at the right time. This process help engineers save the trouble of learning complex oscilloscope features, while providing them full control through SW of where the trigger will occur.

The third tip is to use two oscilloscope channels when measuring low frequency signals. To quickly eliminate the noise, users should set one input to ac coupling and the other to dc coupling, while ensuring that both carry similar amplitude range. The oscilloscope should then be set to display CH1 – CH2 (or invert one of the channels and add them), with both probes applied on the test point. This will subtract out the ac component, leaving only the ac component that is lower than the oscilloscope’s ac coupling frequency and the dc component.

The fourth tip is to be intimate with the noise. When chasing unknown intermittent noise source, it helps to know more about it. One useful characteristic is to determine the initial noise transition’s direction. If it is negative-going, the change could be caused by a voltage drop. If it is positive, it could be caused by some kind of inductive surge.

The next tip is to create a “bargain basement” magnetic probe. This is done by connecting the ground lead of the oscilloscope probe to its tip. Engineers can then sniff out oscillations including other sources of the noise on the DUT without even touching it. This will also help engineers check cabinets for EMC leaks and determine optimal cable routing. It should be noted that when snooping, magnetic signals are at their strongest whenever the loop is at 90° to the signal.

Finally, it is worth noting that custom graticules work for almost any oscilloscope. Although oscilloscopes nowadays offer specialized measurements on complex waveforms such as eye diagrams, it is sometimes simpler and faster to work with the device on hand. Consider using easily available and cheap materials such as Chartpak tape as well as transparency materials to make templates that can be taped on the oscilloscope screen. This allows users to work from templates found in specification documents or make templates from “golden waveforms” that were captured on screen.