What input should I use for a probe fault.

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09 Jul 2020 22:20 #174151 by oldtech
Sorry, I will include a background in new questions. In any case, it looks like I will need an analog to digital chip for connecting to E-STOP from the probe.

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09 Jul 2020 22:25 #174152 by rodw

oldtech wrote: Sorry, I will include a background in new questions. In any case, it looks like I will need an analog to digital chip for connecting to E-STOP from the probe.


Yes, you probably don't need to use a THCAD as you do not need isolation from the noise of the plasma environment. Tommy's chip should work nice. But you still need an encoder input.. There is not really any other way to do it.

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09 Jul 2020 22:35 #174153 by tommylight

oldtech wrote: In any case, it looks like I will need an analog to digital chip for connecting to E-STOP from the probe.

Hmm ... now i have to ask why?
Use the analogue input on the 7i76, set it in hal as you need and use an output or trigger the e-stop from hal.
No need for any electronics.

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09 Jul 2020 22:44 #174154 by rodw

tommylight wrote:

oldtech wrote: In any case, it looks like I will need an analog to digital chip for connecting to E-STOP from the probe.

Hmm ... now i have to ask why?
Use the analogue input on the 7i76, set it in hal as you need and use an output or trigger the e-stop from hal.
No need for any electronics.


It depends on what accuracy is required. I think Mesa have a different Analog input daughter card PCW has mentioned if its not good enough. Also the analog ins don't have a way to scale them so from memory full scale is 36 volts. You can use a signal amplifier to amplify your signal. I was looking at using them scaled to 24 volt field power but to get full resolution, you'd need a seperate power supply.BUt it could well be enough to experiment with first.

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09 Jul 2020 23:24 #174156 by oldtech
Yep, that was what I was thinking and I'll go ahead with it at least in the experimental stage. Still, its good to know about the analog to digital conversion.

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09 Jul 2020 23:26 #174158 by tommylight
If i remember correctly, if powered by 24V then full scale analogue input would be 24V.
In the Hurco i retrofitted, i used those inputs for servo and spindle load as the drives had an output from 0 to 3.3V for 100% of load with the load going up to 120%, so 4V roughly, had that scaled to have a full display of 0 to 120% load in the PyVCP panel at 12-13% per division, so worked pretty well for that, despite very low voltage.

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10 Jul 2020 01:28 #174167 by rodw
From the 7i76e manual

All field input pins are capable of reading the input voltage. These are not highly
accurate or high resolution but can be useful for things like potentiometer inputs. Input
resolution is 8 bits and input full scale value is 36.3V. Accuracy is +-5%. Software process
data modes 1 and 2 allow reading the analog voltage on inputs 0 through 3,


You can use a LM358 to amplify the signal but to get close to full scale you need a 36 volt power supply. a 24 volt supply will give you 677/1024 steps but the one I bought from memory said that you loose a couple of volts from the full sale reference voltage.
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10 Jul 2020 19:11 #174253 by tommylight
Hmm did not know that, so now happy it worked for me as it did ! :)
Thank you Rod.
And 8 bit is 256 levels, not 1024 as that would be 10 bit.
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