- Tue Feb 04, 2014 4:42 pm
#168033
Hello Guys,
I'm a bit of a beginner to the Arduino so if I'm talking backwards at any point, feel free to be direct with me.
I've got a plasma cutter for cutting steel plate. To establish the arc, the following happens:
1). A dry relay contact closes and tells the machine to cut.
2). The air solenoid energises (24v DC)
3). The air flow / pressure causes the torch nozzle to move away from the electrode and a pilot arc is struck. This pilot arc "ignites" the main air flow establishing the plasma jet to the steel plate (which has the ground electrode attached).
Regarding 3). I want to data log the arc voltage from the moment the machine gets the signal to start, up to the main plasma jet being established. There's probably a whopping half a second of time for this to happen so my main concern is sampling fast enough to give me a bunch of measurements I can make a graph from.
This arc voltage goes as high as about 230 volts DC so I was thinking of using an isolated supply for the Arduino with a common ground with the arc voltage. As for the sampled arc voltage I would use a resistor network to get 5v at the analogue input pin when the arc voltage was at 230v. I'll probably also throw a zener across this input for extra protection.
Now for the sampling / storing / uploading the data. My sketch would monitor the start signal and when it arrived, sampling would immediately start. I was thinking I could just take the analogue input readings and store them in an array of a given size. The Uno only has 2K of internal memory (SRAM) so I would reduce the resolution of the analogue read to 8 bits instead of the default 10 bits. This way I only need one byte in my array to store one sample, effectively doubling how many samples I can store (8 bit resolution is fine for my needs). Once the array has been filled up, my sketch would send the array values to the PC.
If the sampling rate was too fast and filled up the array before the main plasma arc was established I would simply put a delay between each sample/write to array task.
How does that all sound. I'm still learning the programming so just wanted a general opinion if my methodology is on the right path, before I go and waste my time learning to do something that won't work.
Cheers,
Keith.
I'm a bit of a beginner to the Arduino so if I'm talking backwards at any point, feel free to be direct with me.
I've got a plasma cutter for cutting steel plate. To establish the arc, the following happens:
1). A dry relay contact closes and tells the machine to cut.
2). The air solenoid energises (24v DC)
3). The air flow / pressure causes the torch nozzle to move away from the electrode and a pilot arc is struck. This pilot arc "ignites" the main air flow establishing the plasma jet to the steel plate (which has the ground electrode attached).
Regarding 3). I want to data log the arc voltage from the moment the machine gets the signal to start, up to the main plasma jet being established. There's probably a whopping half a second of time for this to happen so my main concern is sampling fast enough to give me a bunch of measurements I can make a graph from.
This arc voltage goes as high as about 230 volts DC so I was thinking of using an isolated supply for the Arduino with a common ground with the arc voltage. As for the sampled arc voltage I would use a resistor network to get 5v at the analogue input pin when the arc voltage was at 230v. I'll probably also throw a zener across this input for extra protection.
Now for the sampling / storing / uploading the data. My sketch would monitor the start signal and when it arrived, sampling would immediately start. I was thinking I could just take the analogue input readings and store them in an array of a given size. The Uno only has 2K of internal memory (SRAM) so I would reduce the resolution of the analogue read to 8 bits instead of the default 10 bits. This way I only need one byte in my array to store one sample, effectively doubling how many samples I can store (8 bit resolution is fine for my needs). Once the array has been filled up, my sketch would send the array values to the PC.
If the sampling rate was too fast and filled up the array before the main plasma arc was established I would simply put a delay between each sample/write to array task.
How does that all sound. I'm still learning the programming so just wanted a general opinion if my methodology is on the right path, before I go and waste my time learning to do something that won't work.
Cheers,
Keith.