In-House references and calibration - Page 1
Forum section: electronics / testgear

author: rx8pilot
author_rank: Super Contributor
timestamp: January 13, 2015, 02:29:34 am
content: This is a spin-off of the thread about choosing a professional oscilloscope.https://www.eevblog.com/forum/testgear/professional-scope-purchasing-criteria/The topic went semi-tangent talking about having in-house reference instruments to cross check the measurements being done. I have been doing hobby level electronics all my life (I am 40 now), but about a year ago decided to make a major career move into electronics. I have worn many hats professionally, but mechanical design and manufacturing has dominated the last decade for me. As I have been hard-core studying electronics, I have been surprised at how challenging it is to measure critical circuits accurately. It is clearly WAY more than having an oscilloscope on the bench for sure. I have been designing a number of things, but DC/DC switch mode power supplies have been the most challenging. Fast delicate signals that are easy to damage in the process of measuring.In the previous thread we discussed the merits of various scope features, but this thread is intended to help me understand how to get believable measurements. I started with a typical beginner scope Rigol DS1102E and various random "lab" power supplies, etc. I have made many of the newbie mistakes like using 1x/10x switchable probes in 1x mode to measure high-frequency (FAIL), long ground leads (FAIL), and then chasing these terrible measurements looking for circuit problems (FAIL FAIL FAIL).After what seems like a million hours of reading and experimenting, I have moved up to an almost passable level of capability. I got an old-ish Tek TDS754C 500Mhz/2GS/s and some 500Mhz passive and 750Mhz active probes to step it up a little. These are all used pieces of gear and it immediately becomes necessary to know if these pieces are working properly. TunerSandwich has presented some fantastic info in his posts about capturing useful measurements.I am hoping to learn at least a few things - I don't even know what questions to ask sometimes. Since I am putting together a financing round for my business which will be spending a significant chunk of money on test gear and manufacturing equipment, I need to match that purchase with know-how to get some return on my investment.To get started:How do you best verify the BW and other performance characteristics of a probe?I thought this would be a simple Google search, but I have not found much on the topic. There are plenty of probe tutorials that offer the ABC's of probes, but not necessarily how to best measure the frequency response.Are there any in-house tests that should be done to verify scope accuracy? Especially on an eBay purchased scope.In my previous career machining parts, we kept extremely precise geometry references to cross check our instruments. We were dealing with dimensions down to .0001" - 1/10,000 inch. I would have been losing sleep at night if I could not trust our measurements. What tools and techniques can be used to help verify the scope is capable of telling the truth? High-precision measurements of physical parts is not the task for a beginner, there is subtle technique required on top of having the right calibrated tools. From what I have learned and experienced so far, electricity is tricky to measure as well.I am expecting the discussion of these questions will generate more questions about tools and technique to best understand how to get believable information out of the various instruments on the bench.

author: Fsck
author_rank: Super Contributor
timestamp: January 13, 2015, 02:55:39 am
content: a quick google gives you:http://www.tek.com/dl/60W_18324_0_0.pdffor probe bandwidth.scope absolute accuracy in general doesn't really matter (vs your example of physical dimensions), what we typically care about is relative accuracy.