Analog Signals: Finding Out What You Don't Know
2021-01-08 | 6 min read
Your biggest doubt in declaring a production-ready moment should be that you don’t know what you don’t know. A high-volume production run would be costly to re-work if you find an elusive problem after the fact. Our designs are increasingly digital, but analog signals with infinite resolution will always exist. Since most of us don’t work with an oscilloscope every day, learning and remembering how to set up advanced triggers for analog troubleshooting can seem daunting. Keysight’s Infiniium EXR- and MXR-Series oscilloscopes have a new feature called Fault Hunter, which sets up advanced triggers aimed at finding random, easily missed signal errors. Fault Hunter makes advanced troubleshooting easier.
Analog errors can be trickier to resolve than digital
Infiniium EXR- and MXR-Series scopes can hold up to 7- or 8-instruments in one scope chassis, respectively, which reduces crosstalk (and misplaced equipment). A random or infrequent signal error like a glitch, a runt, or a slow-rising or slow-falling edge is difficult to detect. Fault Hunter sets up advanced triggers that dynamically compare the expected waveform against the present signal. If there’s a signal error, all scope channels freeze, saving evidence for analysis at your convenience.
Fault Hunter is a single button on the front of an EXR-Series oscilloscope and three touch-clicks on an MXR-Series scope menu. Within thirty seconds after starting Fault Hunter, it creates a waveform model based on statistical analysis and automatically looks for an outlier. (Fault Hunter makes some assumptions, but you can override those assumptions if you wish).
Fault Hunter performs six different tests over a user-selected period of one minute to 48 hours. Troubleshooting is like being an electronics detective. Sometimes it’s difficult to determine the root of a problem. For example, perhaps a problem stems from noise caused by a janitor who uses a vacuum cleaner drawing power from the same AC line as your DUT. Fault Hunter captures and time stamps the occasion. On Monday you will have one more clue as to why your prototype fails every weekend.
Figure 1: Fault Hunter automatically finds the most common types of signal faults. It begins by getting statistics on standard measurements and then runs tests to find outliers.
Finding the unknown unknowns
Former U.S. Secretary of Defense Donald Rumsfeld once explained the limits of U.S. intelligence by saying, ”There are known knowns. There are things we know we know. We also know there are known unknowns. That is to say, we know there are some things we do not know. But there are also unknown unknowns, the ones we don't know we don't know.”
The EXR- and MXR-Series oscilloscopes can more than pay for themselves by preventing rework of an entire production run. Fault Hunter searches for faults on one selected channel and provides the results of what happened on all channels. To find out what happened before the error occurred, you can zoom out from the view on your display and search near the record to find the cause. In this case, the scope uses more memory as you zoom out. If you continue to zoom out on the scope’s signal, the scope lowers the sample rate to accommodate the change. If you must maintain high resolution, you can lock an EXR- or MXR-Series scope by manually adjusting it to go no lower than the desired number of samples per second, locking the zoom factor based on the minimum number of samples per second that you set. The EXR-Series scopes have a standard 100 megapoints per channel. The MXR-Series scopes have standard 200 megapoints per channel. Both scope series can be upgraded to 400 megapoints per channel. Fault Hunter can provide more detail with more memory, if you need it.
Fault Hunter also keeps the less experienced from setting up advanced triggers without help from the one advanced scope user in the company. If you are the advanced user, you can tell the supplicant to come back only after they’ve tried Fault Hunter. Oscilloscopes offer a true window into how analog signals behave, but fewer are using scopes as more applications can be accomplished in the digital domain. Keysight’s Fault Hunter lowers the learning curve for those who work primarily in the digital world when analog signals like sensor inputs may be the problem.
To learn more about Fault Hunter, see the application note Infiniium EXR- and MXR-Series Oscilloscopes: Quickly Find and Identify Hidden Signal Errors.