Author Topic: Example Project: 20 Channel solid state scan card for K2000 DMM  (Read 24092 times)

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Offline KedasProbe

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #25 on: August 06, 2021, 04:46:25 pm »
Had some free time to work on this
I tested a few G3VM-61VY3 SSR to see if there are outliers that I should not use.
Screenshot below is of 3 SSR. (next to each other in the packaging)

Led current was 5mA 1.26V  (yellow)
Voltage over the output (blue)  serie with 2.1 Ohm and 0.5v supply and 0.3 Ohm wire gives about 0.5 Ohm that is above the typical 0.15 Ohm (max. spec: 2 Ohm), probably some other small resistances in the test setup are making it difficult since it's not a soldered setup.
'Vp-' gives an idea about how equal the resistance is. (assuming the setup stays the same)
'vpp' would be the voltage over the resistor.

Timing ON is about 1.4ms edge to edge but to 'ON' you need to add 0.2ms (see screenshot), that is below the typical 2ms.
Trigger OFF is very fast 0.078ms so that's good, below the typical 0.1, so you don't have to wait before enabling the other relays. (in theory you could do it at the same time without creating shorts, having 1ms margin)

Edit:
With 7.5mA 1.3V Led I get about 1.0+0.2ms on time, off time is the same <0.1ms (there were even a few with 0.90+0.2ms on time.)
7.5mA is also the advised current for this SSR according to the spec sheet.
So for this SSR I will change the 470 Ohm on the PCB to 300 Ohm.

If someone knows what the reason is of this small hiccup near complete open (blue falling edge), feel free to let me know.

Edit2:
1) The hiccup was the power supply who couldn't follow the fast current step. (about 150mA , <1ms)

2) I also did some measurements with 10 Mohm in serie (like Voltage DMM6500, I used the scope probe 10Mohm in serie) with the SSR, Supply 0.5V, then it's faster on:
ON 0.53 ms with 7.5mA led
ON 0.45ms with 10mA led
OFF 0.10 - 0.11ms is typical

Edit3:
17 * G3VM-61VY3,  3 * VOR1142M4T, both 1V 1kOhm load (1mA), 7.5mA led.
yellow is again led voltage, blue is SSR out voltage.
First timing is ON edge time, second timing is OFF edge time.
« Last Edit: September 04, 2021, 05:40:58 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Offline Anders Petersson

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #26 on: August 09, 2021, 07:19:56 am »
Thanks for sharing, Kedas
I use G3VM-61VY2 for 4-wire resistance measurements with good result.
 

Offline KedasProbe

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #27 on: November 06, 2021, 10:21:17 am »
Hi,

I do have a spare PCB but I don't want to go to the trouble of shipping for this price.
Have you tried ordering the PCB? (The price isn't very high, most of the cost is in shipping)
Just upload the provided zip file from the thread starter in https://cart.jlcpcb.com/quote

The pictures I provided are so you would see what you receive.

P.S. 'ghg' Your PM inbox is full.
Not everything that counts can be measured. Not everything that can be measured counts.
[W. Bruce Cameron]
 

Offline ddavidebor

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #28 on: January 19, 2022, 01:39:55 pm »
Hi,

Has anyone been working on the thermocouple card?
David - Professional Engineer - Medical Devices and Tablet Computers at Smartbox AT
Side businesses: Altium Industry Expert writer, http://fermium.ltd.uk (Scientific Equiment), http://chinesecleavers.co.uk (Cutlery),
 
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Online voltsandjoltsTopic starter

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #29 on: January 19, 2022, 03:25:08 pm »
I just use PT100 4W with the standard card.
CJ comp is a bit of a pain because you need an iso-thermal block for the contact block, like the copper one in 2001-TSCAN.
 

Offline aronake

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #30 on: April 22, 2022, 08:47:53 pm »
I am thinking about building a scanning card for DMM6500.

What are experiences from those of you who have built this model? Recommended? Tried any other DIY scan card? How was that in comparison to this?
 

Online voltsandjoltsTopic starter

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #31 on: April 24, 2022, 04:26:58 pm »
Well, I designed it, so I'll leave others to provide critique.
I don't think many have been built, maybe Anders Petersson has some feedback (ping'd him).

I think the 10 channel card (which doesn't need an mcu) is more popular, as long as you don't mind the relay clicking noise.
 
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Offline Anders Petersson

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #32 on: April 24, 2022, 06:21:52 pm »
I actually modified and built another PCB, since that one was drawn in KiCAD so I could cad in an edge connector to plug in a whole set of wires. Here's the one I started from: https://github.com/cozdas/CozScan2020

Mine is working well with DMM6500. It doesn't work with Keithley 2010 however -- possibly solvable with some firmware modification. Maybe voltsandjolts version works with older DMMs.

With lots of channels, even the touchscreen of DMM6500 is inconvenient when setting up channels and navigating the data. I'll make PC scripts instead.

I also have an official 2000-SCAN card with 10 channels and clicking relays. I don't need the electrical advantages of the electromechanic relays and hearing the ticking wearing on the relays gets on my nerves. 2000-SCAN works with Keithley 2010 though.
 
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Offline aronake

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #33 on: April 24, 2022, 10:27:36 pm »
Well, I designed it, so I'll leave others to provide critique.
I don't think many have been built, maybe Anders Petersson has some feedback (ping'd him).

I think the 10 channel card (which doesn't need an mcu) is more popular, as long as you don't mind the relay clicking noise.

Could you elaborate on:
"Switching between 2W and 4W resistance on the same channel causes the channel relay to open.
It works fine changing between channels in 2W and 4W."

In the first post? So possible to do 4W meassurement but need to set up in a certain way?

otherwise all works well for you?
 

Online voltsandjoltsTopic starter

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #34 on: May 03, 2022, 03:55:58 pm »
Quote
"Switching between 2W and 4W resistance on the same channel causes the channel relay to open. It works fine changing between channels in 2W and 4W."

When my PIC firmware receives a command (from the DMM) to open a relay, it opens all relays. I do this because it makes it simple to behave in a safe way and ensure there are no unintended conduction paths between channels.

This method works fine on the K2000 DMM, because it always sends commands to opens all relays before closing any.

But the DMM6500 doesn't do that - it remembers which relays are open and which are closed. So, when changing between 2W and 4W it just sends a command to open or close the sense channel relay. My firmware sees the open command and opens all relays. So its a safe failure mode. Workaround is to select 4W mode, then change to the channel you want to measure.

Firmware can be changed to fix this, but you would be best to do some checks on which relays are closed, to be safe.
It doesn't affect me because I just do 2W voltage scanning, so I did firmware in simplest/safest way which suits me.
 
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Offline aronake

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #35 on: June 25, 2022, 10:43:40 am »
I have been reading though lots of SSR data sheets.

Seems G3VM-81GR1 is a good choice for voltage measurement up to 80 V. Leakage current max 1 nA (close to 0 typically). Downside is resistance up to 25 ohn (16 ohm typical), but that does not matter for voltage.

https://www.mouser.kr/datasheet/2/307/en_g3vm_81gr-2583855.pdf

It also have very low "Capacity between terminals".

For a low ohm version, G3VM-61GR2 seems good. Leak current max 100 nA (0.2 nA typically), 0.7 ohm max and 0.25 ohm typically.

https://omronfs.omron.com/en_US/ecb/products/pdf/en-g3vm_61gr1.pdf

My plan is to make a new card of this kind (already have one with G3VM-61VY3). Short out the sense and 2 wire relays (so signal only go though 1 relay) and have 16 channels with G3VM-81GR1 for voltage measurement and 4 channels with G3VM-61GR2 for temperature (with termistor) and 2 wire ohm measurement
 

Online voltsandjoltsTopic starter

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #36 on: June 25, 2022, 11:37:41 am »
Seems G3VM-81GR1 is a good choice for voltage measurement up to 80 V. Leakage current max 1 nA (close to 0 typically).

Nice find. Indeed the datasheet graph shows typical leakage as 10pA at 80V, 5pA at 40V :-+
 

Offline Doctorandus_P

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #37 on: June 25, 2022, 01:49:52 pm »
Except maybe that some of those G3VM chips go over USD20

https://octopart.com/search?q=g3vm

Is that considered "normal" for a package with two fet's and a diode, or is it a result of the chip shortage?

Ever since "marketing" has been invented some 150 years ago the correlation between what it costs to make something, and what you need to pay that same something has become ever more fuzzier. In these modern times the difference can be all over the place.

But it does not really feel "right" to me that a simple SMPS IC for example costs EUR3 if you buy it form a "western" brand, while a similar chip costs 30ct or less if it's from a local Chinse manufacturer and you buy it from LCSC.
 

Online voltsandjoltsTopic starter

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #38 on: June 25, 2022, 02:02:43 pm »
Yes, expensive now thanks to chipageddon.
But that is being discussed elsewhere, please keep this thread on topic.
 

Offline jrc

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #39 on: July 08, 2022, 08:32:05 am »
voltsandjolts - many thanks again for developing and sharing the design. I ordered some PCBs from PCBWay using your design files. They have now arrived and I will start assembly as soon as the rest of the parts arrive.
One substitution I have made is Toshiba TLP 241B instead of TLP3558A for the relays.
Max voltage drops from 200V to 100V, but current goes from 0.7A to 2A and most interestingly, max resistance drops from 2 ohm to 200 mohm max, 110 mohm typical.
For my applications it's a worthwhile tradeoff, and others might want to check these out too.
One question on the PCB - I noticed there are no solder pads for the small shunt resistors.
Are they meant to be added as an option across the relay terminals, using their existing solder pads? I probably won't use them but would like to know in case I change my mind later.
Thanks again!
 

Online voltsandjoltsTopic starter

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #40 on: July 08, 2022, 10:49:20 am »
One question on the PCB - I noticed there are no solder pads for the small shunt resistors.
Are they meant to be added as an option across the relay terminals, using their existing solder pads?

First post, welcome to the forum, jrc.

Yeh, I was focused on voltage scanning and didn't place footprints for current shunts.
For a low dissipation shunt, you could place a small SMD resistor across the SSR pins, as you suggest.
For higher dissipation, use the screw terminal pin pads on underside of PCB with larger SMD resistors (less heating of the SSR).
I tend to use leaded resistor in the screw terminals - but that could be a pain if you have several channels and shunts (needs insulated legs to prevent shorts).

Have fun with the build - we need pictures, or it didn't happen ;D

 

Offline ozkarah

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #41 on: September 03, 2022, 12:40:32 am »
I have a DMM6500.
Has anyone assembled a few of these cards and has an excess one to sell?
 

Offline wmattias

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #42 on: December 14, 2022, 10:48:00 am »
Hi Anders!

Would you mind sharing the KiCad files for your modified version?
 

Online voltsandjoltsTopic starter

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #43 on: December 14, 2022, 01:17:16 pm »
You might need to PM him as he probably doesn't get notified of new posts here.

I think KiCAD now has an Altium import tool, which should work with the CircuitStudio files in the OP (let us know how it goes if you try it). But maybe you are specifically looking for the KiCAD card by cozdas.
 

Offline Doctorandus_P

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #44 on: January 08, 2023, 11:25:53 am »
I think KiCAD now has an Altium import tool, which should work with the CircuitStudio files in the OP (let us know how it goes if you try it).

KiCad does not import altium "projects", but KiCad can import schematic files and PCB files from altium.
I had a bit of spare time so I gave it a try, and it worked quite well, but not perfect.
I had some trouble organizing the files, but I found out it's mostly my stubborn brain. I kept saving files in different directories and I (or KiCad?) got confused by that. In the 4th try I just created all KiCad files in the unzipped circuitstudio directory and later deleted most of the circuitstudio files. KiCad is also a bit stubborn in that it wants the main project schematic to have the same name as the project.

* Schematic import worked for both schematic files.
* Schematic import of inverted labels does not work. J3 pin 2 is missing the CTS label. U45 pin 30 is missing the 2WIRE label, etc.
* KiCad imports the page layout over it's own page layout, this needs some cleanup.
* KiCad imports the PCB outline on an "Outline" layer, but it has to be on Edge.Cuts for KiCad to recognize it.
* KiCad needs a hierarchical sheet, it cannot have all sheets on the same level.
* KiCad's PCB editor complains about some "zero-sized pad". I have not checked into it.

Overall it worked quite well. KiCad even renders the 3D view of the PCB including the step models. Only the big IDC connector on the left seems to be missing. I've attached the converted project below. I did not do the cleanup.
I did the conversion in KiCad V7.0-rc1 to get some experience with it. This does mean you can not open this project in KiCad V6, but if you want a KiCad V6 project, you can convert it yourself from the circuitstudio project.
« Last Edit: January 08, 2023, 11:30:11 am by Doctorandus_P »
 

Offline Doctorandus_P

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #45 on: January 08, 2023, 04:45:25 pm »
I had a bit more fun with this project, and did some cleanup in the conversion to KiCad.

* Fixed the damaged labels.
* Replaced local labels with global labels (or else KiCad does not recognize the connection.
* Exported PCB footprints to another library.
* Replaced the Ciruitstudio pdf with a KiCad generated one.
* Added link to this website to the schematic.
* Re-linked schematic symbols with PCB footprints, updated the PCB.
* KiCad names the "unnamed nets" differently.
* Re-run ERC and DRC, fixed some more minor issues.
* Deleted the circuitstudio paper and titleblock.

KiCad now recognizes all the PCB tracks and agrees that it's 100% routed.
I did ignore some DRC issues.
I also do not consider this conversion "complete" and you should check it yourself and compare it with the original project.

Overall, it's quite a nice project, but my interest is limited because I do not have a "K2000 DMM".

Some things I noticed:
KiCad flags several "isolated copper" areas and the GND zones around the microcontroller are quite fragmented. I would reassign the uC pins to improve the PCB routing. This would also get rid of the serpentine tracks to some of the relays. I also checked with the original gerber files of this project and under the TPDMM connector, the copper is not touching. One of my (small) annoyances in KiCad is that the THT pads for such connectors are quite big, and I'm relieved to see that KiCad is not the only program here :) My solution is usually to replace the footprints with footprints with oval pads that leave more room for the GND zone to sneak in between pins.

I would probably also have placed all relays on the topside of the PCB for easier assembly.

Why is "STROBE" connected to two uC pins?
« Last Edit: January 08, 2023, 05:33:50 pm by Doctorandus_P »
 

Offline Fabian

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #46 on: August 18, 2023, 09:51:02 am »
Hi everyone! Thanks for the nice project first of all.
I build two of the cards, but they don't work. Maybe someone can kick me in the right direction  ;)
What I did so far: I flashed the PIC with a MPLAB ICD 3 using the MPLAB IPE by setting the device to PIC16F18875, switching to advanced mode, importing the hex file and pressing "Program". The card gets detected by my DMM6500, it is set to 20-Channel mode. The OUTA pins are connected to the rear input jacks (I don't want to use 4W). Nevertheless, the DMM only measures zero volts, while I inject 5V to Channel 1 (and Ch1 is enabled as DCV in the DMM). When I feed the voltage directly into the rear jacks, the DMM shows the correct voltage.
So, I guess the switching is not working properly. Is there anything I am missing? Settings of the DMM? Wiring? Can I easily check that the PIC is doing its thing (I am not a PIC person)?
It is not exactly clear to me if I need the USB-Serial adapter to supply the PIC.
 

Offline Fabian

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #47 on: August 18, 2023, 10:16:40 am »
Update: Ch1-Ch10 are working :) (it was, obviously, my fault and a stupid mistake  ;D)
But Ch11-Ch20 are not working. Switch is set to 20Ch. Any ideas?
 

Offline Fabian

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #48 on: August 18, 2023, 10:53:44 am »
Nevermind, it was a solder issue  |O
 

Offline Doctorandus_P

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Re: Example Project: 20 Channel solid state scan card for K2000 DMM
« Reply #49 on: August 18, 2023, 06:16:43 pm »
Maybe someone can kick me in the right direction  ;)

Now I'm wondering how hard and in which direction you want to be kicked for this soldering mistake.  >:D
« Last Edit: August 18, 2023, 06:19:27 pm by Doctorandus_P »
 


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