What input should I use for a probe fault.

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.

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.

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.

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.

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.