Inputs & outputs & relays ohmic

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23 Apr 2019 02:25 #131592 by islander261
Yes.

If you only need one then a DIN rail mount may be better.

John

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23 Apr 2019 03:08 #131594 by rodw

tommylight wrote:

rodw wrote: You would not believe how hard it is to find reasonably priced components here in Australia. The opto22 brand is quite expensive and not easy to find. I did find this one in a pack of 5. au.rs-online.com/web/p/solid-state-relays/8886843/
Very fast switching times way faster than our servo thread.

It says its DC switching and this article says mosfet can switch both AC and DC.
www.omron.com.au/service_support/FAQ/FAQ02243/index.asp

That is a nice part/price/deal. And yes MosFet's can switch AC and DC, with the AC type having 2 mosfet's inside and DC one only a single one. Mosfet's have a diode inside always so that would let half of the sine wave through even when switched off when using AC, that is why they must have 2 of them wired ....contra !
Mosfet's also have the ability to remain opened by themself ( if the gate is not connected to anything, all it takes to open them is a touch ), but that is very easily dealt with, a single resistor between gate and drain will fix that.
Metal Oxide Semiconductor Field Effect Transistor, full name, i use them a lot, i still have plenty of them on some drives i made just to prove how easy and cheap a stepper motor can be run with Linuxcnc, 4 of them drive a motor, nothing more.
@ John
They can also be used for input sensing, it is basically a relay with no moving parts, and much, much faster.

So I'll order some then.

Thanks Tommy,

I never can understand the distinction between an output module and an input module. To me they are all just a relay and I look at the switching side and the load side to pick one. Perhaps with an SSR, there needs to be a distinction becasue of the differences discussed in the Omron article.

The one I found operates in 250 usec (0.25ms) and the opto 22's are between 5-25 ms so with the mosfets, a change in state will present on the next servo thread cycle. Thats got to be a good thing for Ohmic probing! I might save 5 seconds a day!

JTKnives, I think you are in Australia, let me know if you want one.
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23 Apr 2019 03:55 #131595 by JTknives
So if we are after speed why not go with a G4IDC5K. It’s on/off time is .025ms with 5v out and 2.5-16v in. If you have 12v field voltage then this would handle it right?

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23 Apr 2019 10:15 #131622 by rodw

JTknives wrote: So if we are after speed why not go with a G4IDC5K. It’s on/off time is .025ms with 5v out and 2.5-16v in. If you have 12v field voltage then this would handle it right?


Speed under 1 ms is not useful for us with Linuxcnc as thats the standard servo thread period. But the z axis can move a fair way in 5 ms when probing.. Plus my field power is 24 volt.

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23 Apr 2019 14:20 #131636 by islander261
'03

I must disagree with Rod here, especially if you use a water table. You want the hysterius and slow response of the standard modules to lesson nuisance tripping. This one of the things that set the real input modules apart from using DC output modules backwards besides fitting in I/O racks. The key is to probe slowly, that is why you have a probe height setting so you are only going slow for a short distance.

John
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23 Apr 2019 15:32 #131657 by rodw
But on the other hand, you can use the LinuxCNC debounce component to slow down a fast switching input if this is required. The plasmac config already included debounce components for this purpose.

I googled again but could not find a definitive explanation of the differences between input and output modules but could understand what they might be used for with a PLC or Arduino running say 5 volt logic circuits interacting with the real world.

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23 Apr 2019 16:54 #131669 by JTknives
What kind of relay rack are you guys using. I have seen a few diffrent kinds. One being standard snap in relays like this version.
ELECTRONICS-SALON DIN Rail Mount AC/DC 24V Control 4 DPDT 5Amp Pluggable Power Relay Interface Module. www.amazon.com/dp/B07QV1HXHS/ref=cm_sw_r_cp_api_i_di0VCb3MJWAS1

And another version like this
Electronics-Salon DIN Rail Mount 8 DPDT Signal Relay Interface Module. (Operating Voltage: DC 24V) www.amazon.com/dp/B07CJJ3FYG/ref=cm_sw_r_cp_api_i_Yj0VCbVRGK27P

My issue is my 7i76 is the ED version so it’s outputs are actualy ground syncs. So that’s why I was thinking of going with a bank of normal relays becaus I can wire them how I want.

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23 Apr 2019 20:35 #131687 by islander261
'03

I think the first one you listed will be better given your 7i76ED card. The second one wants voltage sourcing (connection to +v) outputs not voltage sinking (connection to -V or ground) outputs.

John

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26 Apr 2019 03:23 #131919 by JTknives
I ended up getting a relay designed for sinking controllers. 8 channel and 5amp max. That other board had a long less time to get. This one is smaller which is good becaus I’m running out of space. I also got 3 power supply’s. 1 12v@10a for the monitor and pc and a 24v@5a for the 7i76ED and opto22. Also got a 12v@.86a for the ohmic. Plus the opto22 board and optos. Now just need to figure out how to wire in my Estop switch. It’s only rated at 30v5amps. Was going to have it cut power to the steppers but to much load. So can I run it to the 7i76 and controll it that way.

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26 Apr 2019 04:07 #131920 by islander261
You should be fine with your plan for a personal machine. I f you needed a UL or CE stamp you will need a safety rated guided relay to interrupt the power to the stepper drivers. Reality space is if the power to the 7i76ED is interrupted the step signal to the drivers will stop so the steppers will stop. Actually I have never had an uncontrolled movement since I switched to LinuxCNC and my signal only E-stop has worked every time YMMV. In many ways safety control of stepper driven systems is much simpler than analog servos and some digital servos.

John

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