Author Topic: Example Project: 20 Channel solid state scan card for K2000 DMM  (Read 7920 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.
[W. Bruce Cameron]
 

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.
 


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