Scott,

I figure from what you say the ONLY way to get an anaolgue value into mach is via the modbus?? No chance of it via the pp or serial port at the moment?? Obviously if it could be done by either the pp or sp that would make it much easier.

I agree i call bs on 10hz not being fast enough for the z axis, the system was accused of hunting because it was too slow, i think if it hunts its not because its too slow, its because the idea of a simple threshold and no proportional response in terms of a control system is junk, its bound to hunt really. So if you can do us for a pid loop that would be first class.

Personally im very interested in what jp is doing and i do realise trying to do everything in mach has its own limitations but to me its the whole beauty of it so id be keen to keep the processing element in mach, especially if we could improve the quality of the control loop. Im sure a plc could do a better job but for the money i could buy a thc system out of the box, its probably what i should do but a combination of stubborness and interest keeps me at this.

I could sort you out with a screen set, it would probably be a simple mach screenset with an additional tab or two, before i got right down to it id need to spend some time thinking about exactly what i want it to do for me....


I will have a think about itand let you know what i come up with, this would be a great time for anybody else to give some input as to what they want.

Matt

The Vss is connected both to the minus signal of the bridge and to the minus power supply of the PIC (exactly as on my schema)
The PIC itself is powered by a small mobile phone 220V to 5V DC power supply

I appreciate you guys are on a role here but just indulge me one more time if you will. Can you (carefully) take a voltage reading between TRUE ground and Vss whilst the torch is firing and let me know what it is please?

Quote from: freedom2000 on March 27, 2010, 03:56:02 PM

The Vss is connected both to the minus signal of the bridge and to the minus power supply of the PIC (exactly as on my schema)
The PIC itself is powered by a small mobile phone 220V to 5V DC power supply

I appreciate you guys are on a role here but just indulge me one more time if you will. Can you (carefully) take a voltage reading between TRUE ground and Vss whilst the torch is firing and let me know what it is please?

I have not connected the ground to anything... so I cannot do this measure...
The voltage between the plasma "ground" (ie the metal plate) and the troch tip is -300V before cutting and drops to -50 to -200V when cutting.

I will try to monitor this voltage more precisely after ADC conversion and input in my PC via serail link.

JP

I have not connected the ground to anything... so I cannot do this measure...

You just put one probe from your scope or meter to plasma ground and the other probe to Vss - that gives you the potential difference (voltage) accross them.

Quote from: freedom2000 on March 31, 2010, 07:58:14 AM

I have not connected the ground to anything... so I cannot do this measure...

You just put one probe from your scope or meter to plasma ground and the other probe to Vss - that gives you the potential difference (voltage) accross them.

What do you mean by "Ground" ?
Neither the torch tip (torch -) nor the clamp (torch +) are connected with the plasma metal body which is connected to real ground...

JP

The bit that is causing confusion i think is that the plasma clamp which everyone calls the earth clamp is actually the positive side of the circuit and the torch is the negative, meaning that if you connect one side of the meter to true ground (a ground pin into the ground) and the other side to the clamp on the plasma (positive side of the plasma) you will read a few volts positive or negative, maybe 2 or 3, if you move the meter to the torch and true ground you will measure - 300vdc when firing into open air and -80 to -120 volts ish when cutting.

Hope ive confused you some more!!

Matt

Hi all,

Just to be clear on terminology ...

What I call "ground" is the earth of the 220V AC plug connected to the frame of the plasma device
What I call + is the clamp of the plasma connected to the metal to be cut
What I call - is the tip of the torch



The ground is connected to nothing... No measure of voltage possible between earth/ground and + or minus

The voltage between + (clamp) and - (tip torch) is -300V when the arc is off but trigerred
The voltage between + and minus is betwen -50V to -200V when cutting

BTW, my serail connexion from the PIC to the PC is working  
I will be able to monitor voltage on an excel spreadsheet

JP

LOL - I hope the next time I need a tooth pulled the dentist has an easier time than this!
Just for me, like I said - humour me - stick one lead (I don't care which) of your scope/voltmeter on your your "clamp" and the other lead onto your Vss, fire the torch and take the reading. Then stick one lead onto your "plasma metal body" and leave your other lead on your Vss, fire the torch and take the reading. You never know - you might find the results interesting.

LOL - I hope the next time I need a tooth pulled the dentist has an easier time than this!
Just for me, like I said - humour me - stick one lead (I don't care which) of your scope/voltmeter on your your "clamp" and the other lead onto your Vss, fire the torch and take the reading. Then stick one lead onto your "plasma metal body" and leave your other lead on your Vss, fire the torch and take the reading. You never know - you might find the results interesting.

well... I don't know how to say it more clearly...

V"clamp" - Vss = 0V

earth - Vss = nothing (oscillating between -0.xx and +0.xx V --> not a fixed votage)
earth - plasma clamp = nothing
earth- torch tip = nothing

and that's normal as earth is NOT connected to torch tip nor torch ground... (unless you connect the metal part to be cut to earth you will not have a voltage reference between earth and plasma "clamp" or plasma torch tip...)

That's also normal as the power supply for my PIC is not connected to earth.

keep you teeth :-)
JP

Im interested to know what you find when you do it stirling?

Matt