Author Topic: Example Project: 20 Channel solid state scan card for K2000 DMM  (Read 13208 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?
Davide Bortolami,
Fermium LTD
 
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Offline voltsandjolts

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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?
 

Offline voltsandjolts

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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?
 

Offline voltsandjolts

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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
 

Offline voltsandjolts

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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.
 

Offline voltsandjolts

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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!
 

Offline voltsandjolts

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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

 


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