Engineers are said to be skeptics by nature (personally, I'm a little bit skeptical of that statement), but do we really question everything, or just the things we want to question?
When most engineers step into the lab to begin debugging a problem or testing their latest creation, the only thing they rely on to be working perfectly is the test equipment, especially the trusty oscilloscope. Sure, there may be a little skepticism toward the scope until the calibration date is checked, probes are compensated, and all the other things we do to ensure accurate measurements are done.
But is the trusty oscilloscope really working correctly in the lab?
Most labs where I have worked or walked around have a lot of electronics. Most are turned on and doing something, even if that something is not the right something. Lots of times, covers have been removed, ground connections are left unconnected, or other special configurations are running. Then, add in all the RF energy in today's connected world -- radio waves, cellphones, WiFi networks, etc.
Does this sound like an EMI engineer's worst nightmare? Absolutely! The question becomes "Is all this random electronic noise and EMI affecting my trusty o'scope?" How many times do you stop and think about the environment around you and the potential effects on your design or test equipment?
Years ago, I was working on a large project, and we had the luck to have a new lab set up just for us. Some old storage space at the back of the building was cleaned out and combined with other space. Lab benches and supplies were moved in -- even a few pieces of new test equipment! Our excitement was growing as the completion date neared.
Finally, it was time to check out the new lab. As we entered the freshly painted room and stared at the clean lab benches, one engineer suddenly exclaimed, "Hey, what's all that?"
Following his outstretched hand, we all immediately noticed the back wall was actually made of several very large circuit breaker panels. It turns out all of the electric power for the large two-story building entered through our new lab.
We cautiously approached the massive wall of breakers and cutoff switches. Naturally, there was a nice line of caution tape on the floor at the required OSHA distance from the panels. The lab manager, wanting to use every bit of real estate available, had pushed one of the lab benches right up against the tape line. A CRT monitor had been placed on the bench. Switching the monitor on showed the obvious EMI effects -- a nice multicolor display with no input signal.
And did I mention that this particular lab bench, right next to the electrical panels, was intended to test an 800MHz ECL design? Needless to say, some rearranging of workstations occurred that day.
This is an extreme example of how the environment could affect your test equipment, but what about more subtle factors that can go unnoticed? It makes you pause and ask, "Is there some external force affecting my scope?" Rest easy. In most cases, it can still be trusted!
Tell us about any of your experiences with strange factors affecting your trusty oscilloscope.