DMM # of digits versus ADC bits
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Mark Forums Read

 Equipment & Tools From test equipment to hand tools

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 1st November 2019, 04:47 PM #1 jan.didden   diyAudio Member     Join Date: May 2002 Location: Westende Resort, BE coast DMM # of digits versus ADC bits Hi guys, I was wondering how to compare DMM # of digits versus ADC bits. Let me explain. Suppose I have a 5.5 digit DMM. On the 10V range the last digit would then indicate 00.001V is 1mV. If I have a 16bit ADC that is almost 100dB dynamic range, lets take 100dB for the discussion. That's a factor 10^5, so if I input 10V to the ADC the LSB would be 0.1mV. Is that reasoning correct? Background: I have a 16bit USB scope and the software can also display the signal in a voltmeter format. That voltmeter shows 6 digits, with the last one fluctuating all the time. I can set it to 5 digits and then it is steady. Just trying to get my head around the numbers and accuracy. Jan
 1st November 2019, 05:34 PM #2 BSST   diyAudio Member     Join Date: Jul 2018 The 1/2 digit means that the most significant digit will be either 0 or 1. So the extremes of the DMM readings will range from 000,000 to 19,9999; therefore there are 20,000 possible codes. This would correspond to a little more than 14 binary bits. log(20000)/log(2) = 14.29 bits. I hope I've done this right.
 1st November 2019, 05:47 PM #3 1audio   diyAudio Member   Join Date: Mar 2004 Location: SF Bay Area Jan- you are opening Pandora's box as you know. First the basic reasoning is correct. The bits line up. However for a meter (and for an ADC for audio) its not that useful to just have bits. How many are meaningful? And how do you define that. For audio and other ADC applications there are various measures of accuracy and the issue of noise pops up so you need really clear definitions. If you look at the spec sheet for a 5 1/2 digit DVM its very carefully drawn to show what the manufacturer defined as accurate. That us usually a DC spec with a number of averages under specific conditions. The averaging is a sort of noise filtering which is necessary to get a useable reading. My Keithley 2015 can be almost useless on DC if there is any noise on the DC. Its just a blur of numbers. I would be cautious about even 5 digit DC accuracy with a scope. The probes are not that precise a division. however the magnitude of change may be reasonable accurate. I.E. 1.0015V not really. But a 15 millivolt change under load may be. Audio ADC's usually digitally remove DC making those comparisons impossible. I have 6 1/2 digit and 7 1/2 digit DVMs and an interesting device from QuantAsylum; the QA350, which is a 24 bit ADC with DC precision. Its similar to the DVM's but the lowest bits don't line up and its clear the steps are binary not decimal. However its a great null meter with isolated USB power and data. It also incorporates an interesting RMS function similar to the Keysight 3458. __________________ Demian Martin Product Design Services
jan.didden
diyAudio Member

Join Date: May 2002
Location: Westende Resort, BE coast
Thanks Demian. I also own a 2015 and I noticed that you can select how many digits you want to see. As well as the averaging.

But my new USB scope has a selection of vertical bits versus BW. At the lowest BW, 3MHz, it has 16 bits resolution (250MHz at 8 or 10 bits).

So in the 16 bits resolution setting it should perform at least as good as a 5.5digit DMM, no? No just DC, also AC. And with all the caveats of filtering and averaging, which I believe goes for both cases.

(This is just a demo setting).

Jan
Attached Images
 WS6.PNG (47.6 KB, 119 views)

jan.didden
diyAudio Member

Join Date: May 2002
Location: Westende Resort, BE coast
Quote:
 Originally Posted by BSST The 1/2 digit means that the most significant digit will be either 0 or 1. So the extremes of the DMM readings will range from 000,000 to 19,9999; therefore there are 20,000 possible codes. This would correspond to a little more than 14 binary bits. log(20000)/log(2) = 14.29 bits. I hope I've done this right.
I think it is 200,000 counts, no? 17.x bits?

Jan

 1st November 2019, 07:29 PM #6 jan.didden   diyAudio Member     Join Date: May 2002 Location: Westende Resort, BE coast PS Demian, QA has several interesting devices like the mic preamp that has additional 30dB/10dB low noise preamps. No household should be without one. Thanks for rattling my cage again! Jan
BSST
diyAudio Member

Join Date: Jul 2018
Quote:
 Originally Posted by jan.didden I think it is 200,000 counts, no? 17.x bits? Jan
I believe you're quite correct. I never could count. Yet another brain infarction.

 2nd November 2019, 01:52 AM #8 PRR   diyAudio Member     Join Date: Jun 2003 Location: Maine USA Minor quibbles: The conversion from binary bits to decimal digits seems to be 3.322, so 16 bits ought to be 4.8 digits. A 5-digit DC meter uses all those bits for positive signal. (AD-DC conversion is often done before the ADC.) The 'scope has to handle + and - signal, so only 15 bits on each side. But when you get to this many bits, a lot of it is in the details. Last edited by PRR; 2nd November 2019 at 01:54 AM.
 2nd November 2019, 02:58 AM #9 1audio   diyAudio Member   Join Date: Mar 2004 Location: SF Bay Area The scope uses an averaging algorithm similar to noise shaping to get the additional bits. Useful for some things but not necessarily accurate. It the 15 mV vs 10.015V example above. If its at the hardware level it may be more accurate and useful for looking at noise and artifacts. With FFT you could validate its real accuracy with some low level tones. __________________ Demian Martin Product Design Services
 2nd November 2019, 01:13 PM #10 Speedskater   diyAudio Member     Join Date: Sep 2002 Location: Lakewood, Ohio But a DMM also has a range switch. __________________ Kevin

 Thread Tools

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Room Acoustics & Mods     Music     diyAudio.com Articles     Car Audio     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post Jimmy154 Swap Meet 0 19th May 2017 07:58 PM prasimix Swap Meet 0 22nd July 2016 06:46 AM johnnyb60 Everything Else 4 11th April 2014 02:46 PM Nicola Digital Source 28 21st February 2007 08:09 PM guytou Digital Source 2 9th August 2005 10:40 PM

 New To Site? Need Help?

All times are GMT. The time now is 07:10 AM.

 Home - Contact Us - Advertise - Rules - diyAudio Store - Sponsors - Privacy Statement - Terms of Service - Top - Opt-out policy

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki