Controlling a compressor with Linuxcnc.

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05 Nov 2024 06:11 #313795 by Creative25
I have a serious problem with our power company. 
The 60 amps connection to our house is not what they say. I have serious voltage drops between utilities transformer and our house and they will not fix it. Looks like common practice in our area. 

I can reliably cut at 35 amps. 
if I go higher depending how much power my neighbors are using The plasma cutter gets an undervoltage and cuts out. 

So the table happily cuts until the compressor starts. 
Then the plasma cuts out because it gets an undervoltage.  Qtplasmac pauses and gives an arc lost warning. 

If the torch is off during the probing and the compressor kicks in the program keeps running until the compressor cuts out because of undervoltage.

So I can not run plasma and compressor at the same time. 

So I was wandering If I add a relay an electric unloaded valve and a pressure sensor to the compressor. Would it be possible to control the compressor with Linuxcnc.

I was thinking about the following. When pressure drops to a certain level. Well above what the plasma needs the program pauses. Preferably at the end of a cut.
then the compressor starts. When the tank is full the program resumes. 

Is that possible?

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05 Nov 2024 12:27 #313811 by tommylight
Probably yes, it will be a bit tricky to figure out when to stop, one option would be when motion is rapid (going from one cut to another), still, i think you would need another sensor to notify LinuxCNC it is safe to continue.
2 pressure sensors should do just fine, one for low and the other for high, or use the existing one in compressor for the high side, but this complicates wiring and logic a bit more.

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06 Nov 2024 00:31 - 13 Nov 2024 01:00 #313865 by phillc54
EDIT: files changed to suit a pressure sensor on a analog input.

The following should work but has only been tested in a sim. Use a pressure sensor connected to an analog input and change the postgui file hal pin to suit the analog input. Change HIGH_PRESSURE_VALUE and LOW_PRESSURE_VALUE in user_periodic.py to the values you wish to use. All three files need to be in your plasma machine config directory. Due to response times you will need to move the torch to a suitable start point using the cut recovery panel after the job has paused.

custom_postgui.hal
Warning: Spoiler!


qtplasmac_custom.py
Warning: Spoiler!


user_periodic.py
Warning: Spoiler!
Last edit: 13 Nov 2024 01:00 by phillc54. Reason: files changed to suit a pressure sensor on a analog input
The following user(s) said Thank You: tommylight

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06 Nov 2024 08:45 #313881 by meister
i use this sensor to check the compressor pressure,
but you need an analog input for that:

www.amazon.de/gp/product/B07YKZ773Z

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07 Nov 2024 06:35 #313986 by Creative25
Thank you so much 
You come faster than I could work out a concept. 
I do not fully understand the code.

does it stop at the end of a cycle?

Is there any code to start the compressor?

I was thinking of a simple way to use the original pressure switch on the compressor. 

I could add two Relais on the compressor. 
one with a 24V coil in series with the pressure switch.
one with a 220 V coil that closes when the pressure switch wants to start the compressor. 

So when the pressure drops the 220V relay is activated and sends a signal to Linuxcnc. 
linuxcnc pauses the program. And turns on the second relay. To start the compressor. 

Is full the The 220v relay gets turned off by the pressure switch. 

linuxcnc turns off relay2 and resumes cutting. 

The only question is will the Relay with the 220Volt coil turn off when the voltage drops during compressor startup?

 

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07 Nov 2024 06:49 #313987 by tommylight
The whole battle here is to stop LinuxCNC before compressor starts, so you do need another sensor set to trigger at a bit higher than the compressor low pressure, then you can use the existing switch to trigger when compressor stops.

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07 Nov 2024 06:59 #313989 by Creative25
I just gave it a second thought.
a relay with a 220 volt coil on the compressor is a bit risky. 
If your business grows and you employ people an uninformed person could connect 220  volt on the wrong wire and then probably blow the mesa board.

i think I will go with the pressure sensor. 
So far all the analog inputs of the mesa board are free. Advantage I have full control of hysteresis of the compressor as well. Disadvantage I need to put an electric unloaded valve. I guess any normally open pneumatic valve will do.

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07 Nov 2024 07:02 #313990 by phillc54
If you go with a sensor and use a analog input then we can rewrite the code to use a high and low pressure setting.

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07 Nov 2024 17:21 #314026 by Creative25
Thanks for all your efforts.
I am going to order an unloader valve and pressure sensor. 

no hurry with the software side it will take time for me to get all the parts. 

looks like LinuxCnc is really awesome.
 
The following user(s) said Thank You: tommylight

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07 Nov 2024 19:30 #314033 by tommylight


looks like LinuxCnc is really awesome.

 

Yes it is.

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