Inputs & outputs & relays ohmic

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21 Apr 2019 04:17 #131368 by JTknives
So as the title says rather cleverly I might add I'm wondering how many realys and Inputs/outputs I need. I have everything with the stepper motors encoders wired up as well as the limit switches. These switched include the X, Y, Z and Z floating head switch.

Now was moving onto the actual control of the plasma its self. I'm going to use a hyperthermia 30XP so I don't have an interface on the plasma to connect to. I'm guessing I'm going to need a relay for the torch start. Does that need to be a DPDT NO. That way the 7i76 knows when it's not triggered by feeding back through the closed leg? I will be using a thcad10 which I know will need some resistors to work with the 30XP. I do have a floating Z with a NC switch. It's set up so when the torch touches off the slide lifts off the switch closing it. It's a very accurate switch designed for tool setters for cnc machines.

The next question is incorporating ohmic and what relays I need for that. I'm guessing I can use the 30XP as it's consumables are shielded except the the fine cut.

I'm guessing there is some clever relay circuitry to incorporate this all together and prevent blasting the 7i76ED with 300v when it fires. And speaking of firing how is the arc ok signal generated for LinuxCNC to see. I would think it would involve an amp reading which is sent back to the analog inputs. But I could be way off.

Thanks guys for any tips or help you can provide. I'm so close to cutting I can taste it lol.
JTknives

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21 Apr 2019 05:32 - 21 Apr 2019 05:34 #131371 by rodw
I think I've ended up with 4 relays on my machine

1. Stepper motor disable on estop (optional but due to having an estop on a wireless pendant)
2. Torch on relay but PCW has suggested using the spindle output on the 7i76 so you might be able to drop it
3. Ohmic enable relay (triggered by an output)
4. Ohmic sensing relay (input)
5. IN4007 1000 volt diode
6. Dedicated 24 volt isolated power supply Meanwell 0.5 amp approx

I think I have it right. For the arc, the torch is negative and the work piece is positive.
So the isolated ohmic power supply (-24v) is earthed to the table
My wire on the torch is 24v positive
The Ohmic sensing relay is triggered when the shield touches the workpiece and sends 24v field power to an input but:
The Enable relay ensures the power to the ohmic sensing relay is only enabled when probing and turned off at other times.
The diode will prevent a reverse current flow if something goes wrong with the arc voltage.

Initially, I had the -24v going through a diode to earth as well but I had some spurious voltage potentials floating around between the torch and the table so took the diode out of the equation.
Last edit: 21 Apr 2019 05:34 by rodw.

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21 Apr 2019 13:41 #131394 by tommylight

JTknives wrote: I'm going to use a hyperthermia 30XP ......

Oh no, not hyperthermia please !!! :)

hy·per·ther·mi·a
/ˌhīpərˈTHərmēə/
nounMedicine
noun: hyperthermia

the condition of having a body temperature greatly above normal.

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21 Apr 2019 15:22 #131400 by JTknives
You can thank my phones auto correct for that one lol.

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21 Apr 2019 16:18 #131405 by JTknives

rodw wrote: I think I've ended up with 4 relays on my machine

1. Stepper motor disable on estop (optional but due to having an estop on a wireless pendant)
2. Torch on relay but PCW has suggested using the spindle output on the 7i76 so you might be able to drop it
3. Ohmic enable relay (triggered by an output)
4. Ohmic sensing relay (input)
5. IN4007 1000 volt diode
6. Dedicated 24 volt isolated power supply Meanwell 0.5 amp approx

I think I have it right. For the arc, the torch is negative and the work piece is positive.
So the isolated ohmic power supply (-24v) is earthed to the table
My wire on the torch is 24v positive
The Ohmic sensing relay is triggered when the shield touches the workpiece and sends 24v field power to an input but:
The Enable relay ensures the power to the ohmic sensing relay is only enabled when probing and turned off at other times.
The diode will prevent a reverse current flow if something goes wrong with the arc voltage.

Initially, I had the -24v going through a diode to earth as well but I had some spurious voltage potentials floating around between the torch and the table so took the diode out of the equation.


Are you saying that pins 5&6 on TB4 can be used to close the torch start switch?

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21 Apr 2019 18:10 #131414 by islander261
1. The use of an opto isolator is strongly advised because it allows probing at much lower voltages and current.
2. The ohmic enable relay is to physically disconnect the sensing circuit from the work piece and torch shield when not probing. This needs to a single Double Pole (DP) or two Single Pole (SP) (what I have) relays.
3. You must be sure the power supply is truly isolated. This causes the most problem for people. Check that the output minus is not internally connected to the safety ground, third wire or DIN rail clamp or to the neutral wire.
4. Please find attached the circuit I have used for several years with no problems.

John

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21 Apr 2019 19:00 #131419 by rodw

JTknives wrote:
Are you saying that pins 5&6 on TB4 can be used to close the torch start switch?


Yes, I believe so.

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21 Apr 2019 19:06 #131420 by rodw

islander261 wrote: 1
2. The ohmic enable relay is to physically disconnect the sensing circuit from the work piece and torch shield when not probing. This needs to a single Double Pole (DP) or two Single Pole (SP) (what I have) relays.


Hmm, thanks, I'll change some wiring on the workpiece side. Something was worrying me.

I know you've shared that circuit several times but when I needed it, I couldn't find it.

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21 Apr 2019 23:40 #131432 by JTknives
OK, looking across the schismatic i see a few things. First your running the 7i76 off 24v field power and the only other supply you have is a 12v supply for the probing. you run the -12v through the opto and then through a NO relay to the shield. relay one and 2 are both triggered by pin22 on TB6. relay 2 connects the +12v to the work. when shield touches the work the opto goes high and sends field voltage to pin12 on tb6. And your torch "on" is ran through relay 4 which is NO and triggered by pin23 on tb6.

now onto the question(s)
Can I just run my probe sensing through a crydom M505012F. I have 2 just laying around and been looking for a use for them. here is their layout. also my 7i76 is the ED version so its outputs are syncing not sourcing.

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22 Apr 2019 00:41 #131435 by tommylight

JTknives wrote: Can I just run my probe sensing through a crydom M505012F.

Unfortunately no, those are SCR used for switching AC, not DC.
The problem with them is that once opened they will remain opened until there is not more current flowing through them and that is something that in AC happens 50 or 60 times per second while in DC it does not until the power is cut off.
Also that is a non isolated type so in the future if you use them, keep that in mind.

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