Do modern DSOs really need calibration? - Page 1
Forum section: electronics / beginners

author: GlowingGhoul
author_rank: Regular Contributor
timestamp: July 28, 2015, 04:47:25 pm
content: What drifts on a modern DSO that would require a lab calibration? Electrolytics in the front end? Probes can get beaten up, but the user cal compensates sufficiently for that.I realize a cal certificate can be a requirement in many situations, but for the personal/hobbyist user, is this really necessary?Keysight recommends a 3 year cal interval.Just wondering if these are more of verification of accuracy to ensure compliance than anything else.

author: leblanc
author_rank: Regular Contributor
timestamp: July 28, 2015, 04:54:54 pm
content: Typically, you're not looking for precision measurements with an oscilloscope. You want to see timings or the general shape of waveforms. Although I have seen many people use DSOs as multimeters....Personally, I wouldn't bother getting my DSO calibrated. I mean I'd run the self-calibration, but nothing more.

author: leblanc
author_rank: Regular Contributor
timestamp: July 28, 2015, 05:14:51 pm
content: The other thing about calibration.... In industry, it's not always so much about adjusting the device. It's often about validating the measurements that were taken with the device since the previous calibration.Let's use a scenario. Let's say you have calibration sticker for Jan 2010 and it "expires" on Jan 2011. In Jan 2010, you know your equipment is in the acceptable range.In June 2010, you take some measurements, put them in a report for a client.In Jan 2011, you get your device calibrated. One of two scenarios happens:1. It's still within bounds. Great! The measurements you took with this equipment between Jan 2010 and Jan 2011 (i.e. June 2010) are okay. You should bring up that report again and indicate that calibration passed before and after the measurements.2. The oscilloscope is out of spec. Bad news. You cannot be certain that the measurements taken between Jan 2010 and Jan 2011 were correct (it could have happened the day after the Jan 2010 calibration for all you know). You need to re-run these tests and update your report (and wait until Jan 2012 to confirm their validity), or at least indicate that the results are not validated.Well organized clients (in particular, industries that follow strict standards, i.e. automotive) will expect this to be done. Any measurement has an associated instrument serial number, date of measurement, date of calibration (before), date of calibration (after), etc. In come cases, even more info is included.For personal/hobby use, none of this applies.

author: mazurov
author_rank: Frequent Contributor
timestamp: July 28, 2015, 06:02:59 pm
content: It's not an instrument that requires calibration but rather the measurement. If you can make all your measurements relative you don't need to calibrate, ever. If you don't care about accuracy you don't need to calibrate. For example, I check batteries by shorting them with my tongue - works very well with no calibration, for more than 40 years.There are also instruments that can be accurate without calibration. GPSDO is one example, this is the other ->http://www.ebay.com/itm/291423957143?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

author: GlowingGhoul
author_rank: Regular Contributor
timestamp: July 28, 2015, 06:42:32 pm
content: OK, so looks like I just need to get some of those "Periodic Check Not Required" stickers, and I'll be good to goSeriously though, of course verification of accuracy would require a cal, I'm really trying to find out how "out of cal" a modern, non-malfunctioning DSO can be expected to get, and why.

author: RogerRowland
author_rank: Regular Contributor
timestamp: July 28, 2015, 06:49:31 pm
content: Quote from: mazurov on July 28, 2015, 06:02:59 pmSo you don't mean car batteries then?

author: GlowingGhoul
author_rank: Regular Contributor
timestamp: July 28, 2015, 06:56:04 pm
content: Quote from: RogerRowland on July 28, 2015, 06:49:31 pmI use car batteries to check the conductivity of screwdrivers.

author: RogerRowland
author_rank: Regular Contributor
timestamp: July 28, 2015, 06:57:11 pm
content: Quote from: GlowingGhoul on July 28, 2015, 06:56:04 pmso you probably get through a lot of screwdrivers too .....

author: mazurov
author_rank: Frequent Contributor
timestamp: July 28, 2015, 07:26:44 pm
content: Quote from: RogerRowland on July 28, 2015, 06:49:31 pmCar battery have 10V across it when dead vs 14 when full. My tongue is not that sensitive. Besides, you can quite thoroughly check car battery using a car, no reason to lick toxic lead sulphate.

author: mazurov
author_rank: Frequent Contributor
timestamp: July 28, 2015, 08:02:09 pm
content: Quote from: GlowingGhoul on July 28, 2015, 06:42:32 pmOn arrival, my (new) Hantek was off on both time and voltage more than most 7000-series plugins I bought as parts unit on eBay. Calibrating modern gear in-house is tedious so Hantek is still off (but stable). On the other hand, my 7000 scopes are now as accurate as new - but I digress.I have HP (AKA AG,KS) cal.facility nearby that calibrates 34401a, among other things. I only go there when I need to produce a signed paper with measurement results. In 10 years of observations, the meter (bearing Hewlett-Packard logo) was never off. You shall expect this kind of stability from a brand-name instrument, scope or otherwise.