20-channel DIY Scanner card for Keithley DMMs and DAQs - Page 1
Forum section: electronics / projects

author: cozdas
author_rank: Contributor
timestamp: December 26, 2019, 05:16:17 am
content: I implemented this some time ago and mentioned that in theDMM6500 topicFew people showed interest in this project thus I wanted to opensource it. You can find the details along with project files and sources inthis github project page.Feel free to ask questions and post comments.Happy holidays.

author: Alexcnc
author_rank: Newbie
timestamp: December 26, 2019, 12:16:12 pm
content: Thank you for bringing the project open source!

author: thm_w
author_rank: Super Contributor
timestamp: December 27, 2019, 01:51:29 am
content: Thanks for the notification, this is really good documentation. Hope to build it.Some photoMOS, first is one OP used:Code:PN Voltage Resistance LeakageTLP3558A - 160V 2R 1uA $1.5-2.50AQY212EH - 60V 2.5R 1uA $0.25+AQY210EH - 350V 25R 1uA $0.25+AQV253A - 250V 8R 1uA $0.8LH1540 - 350V 22R 1uA $0.8PVA1354N - 100V 5R 1nA? $2+ (limited life)PVA3324 - 300V 24R 1nA? $2- Equivalents for AQY: TLP227G, TLP222G, G3VM-351D, LCA110L (6pin, lower R typ) $0.5-3Reed relay- D1A050000 - 200V 0.1R 1nA - $0.60Not sure how much resistance matters? Shame if 25R is too high as there are a ton of surplus ones, probably from telecom gear.Voltage will depend on what circuits you plan to measure. Original spec was ~200V but I'm sure the relays were rated for slightly higher.

author: cozdas
author_rank: Contributor
timestamp: December 27, 2019, 04:04:14 am
content: Quote from: thm_w on December 27, 2019, 01:51:29 amIf you implement it let me know the outcome.My thinking regarding the on-resistance was to keep the loading error less than 1 digit (1ppm). With 10MOhm input impedence, TLP3558A results in ~0.2ppm which is 3.2 LSB of the 24bit ADC.

author: Gregg
author_rank: Super Contributor
timestamp: December 27, 2019, 06:04:13 pm
content: Thank you codzas for your hard work. Now I have another reason to want a DMM6500.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 27, 2019, 06:16:29 pm
content: I would expect the 25 Ohms or even 100 Ohms to be still OK. It may effect the 10 MOhms input impedance ranges a little, but this would be higher than 10 V and usually the lower accuracy ranges anyway.I would be more worried with leakage between the channels. So it may be a good idea to not use the very low resistance ones. At least unused channels should not contribute much to leakage. So the scanner may not be a good choice for high impedance source.

author: thm_w
author_rank: Super Contributor
timestamp: December 27, 2019, 11:53:27 pm
content: Quote from: Kleinstein on December 27, 2019, 06:16:29 pmI added leakage current spec to my post. Seems the mos ones above at least are similar, for their max spec.LCSC has some reed relays for ~$0.60, with better leakage (nA). But of course life is limited (10^8 cycles, about 3 years switching every second). There are also normal relays, and spec for the cheapies is really bad (~5uA, 10^5 life only!). Maybe some value in having a few reed and few photomos or similar.One thing I'm not sure of, what is the purpose of channel 10 on theoriginalscan card? It uses K111 relay and U105 3301 photomos in series, with some 100R resistors. The other channels use a single relay.

author: cozdas
author_rank: Contributor
timestamp: December 29, 2019, 04:28:20 am
content: Quote from: thm_w on December 27, 2019, 11:53:27 pmSCAN-2000 card that I bought from eBay (probably an older revision) doesn't have solid-state switches, just mechanical ones. Although the SCAN-2000 manual doesn't explain the why there are Solid-State Relays (apparently in the newer revisions), SCAN-2001 manual does explain it. I think with a special mode enabled in the DMM, the mechanical relays of both channel 5 and 10 are closed and the fast switching between ch5 & ch10 is achieved by the photo-mosfets.

author: thm_w
author_rank: Super Contributor
timestamp: March 15, 2020, 07:11:05 pm
content: I went to test the card and it looks like I've got the pinout back to frontTime for Rev 2

author: voltsandjolts
author_rank: Unknown
timestamp: March 15, 2020, 08:22:38 pm
content: I have a K2000 DMM (2006 vintage, latest firmware) which probably won't support a 20 channel scan card.I say that because there is a specific version (K2000-20) which does support a 20 channel card.Does anyone know what the differences are between K2000 and K2000-20?Is it just firmware?Cross-reference to 10-channel card which works with K2000 DMM:https://www.eevblog.com/forum/circuit-studio/example-project-relay-scan-card-for-k2000-dmm/

author: voltsandjolts
author_rank: Unknown
timestamp: June 22, 2020, 02:20:36 pm
content: Another option for 20 channel SSR scan card here:https://www.eevblog.com/forum/circuit-studio/example-project-20-channel-solid-state-scan-card-for-k2000-dmm/

author: Anders Petersson
author_rank: Regular Contributor
timestamp: March 16, 2021, 03:49:36 pm
content: I built one (slightly modified). It works with Keithley DMM6500 but is not recognized by Keithley 2010.My original 2000-SCAN card is recognized by Keithley 2010, so it's likely the 2010 doesn't support 20-ch cards, only 10-ch. (Neither the manual of DMM6500 nor 2010 mentions support for 20-ch cards.)EDIT:Looking at voltsandjolts version (https://www.eevblog.com/forum/circuit-studio/example-project-20-channel-solid-state-scan-card-for-k2000-dmm/), I see a suspicious section in the source code:QuotePossibly the Arduino code just needs to do something similar to support K2010.

author: Neuromodulator
author_rank: Regular Contributor
timestamp: May 06, 2021, 08:22:56 am
content: It would be interesting to fabricate the piece that keeps the PCB in place.