Current monitoring of Laser Power

General discussion of laser machines

Current monitoring of Laser Power

Postby Jack » Fri Jan 08, 2016 5:21 pm

Wondering if someone wouldn't mind informing me of the best way to monitor the current flowing to the laser tube during use. There are a lot of LED / LCD current display modules on EBAY for example, would a garden variety 0-300mA work, or do I need a special high voltage designation? Also, one more question: how can you tell if the laser tube is actually energized, not just the power supply on or the laser system powered up, but the laser tube is actually emitting, albeit a low power beam? Would it be wise to use some sort of indicator feeding off the laser tube feed? What would that look like?

Thanks in advance for any help, here.

Happy lasing!

Jack
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Re: Current monitoring of Laser Power

Postby sshwarts » Fri Jan 08, 2016 6:55 pm

I have a analog ma meter (goes up to 30 ma). I had a digital one for a while but it kept burning out. This is the one I used:
http://www.amazon.com/uxcell-0-30mA-Cur ... 008422PZ4/

You'll see the tube is energized because of the discharge glow in the tube. Don't rely on that for safety though. A switch on the cover is a good idea as is a key switch or something you get in the habit of disabling the laser with.

Scott
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Re: Current monitoring of Laser Power

Postby Jack » Fri Jan 08, 2016 10:23 pm

Thanks Scott, that is very helpful. I'll look up the ammeter as I don't have one less than 1000mA full scale. So the digital ones kept burning out... I wonder if they just couldn't handle the voltage. Did you put your ammeter in series (I assume) on the neg or pos wire? and should I care? Also, if your ammeter is in series on the high tension lines I would think you have to be very careful about insulation and distances around the ammeter and it's connections, right? I know the answers to these questions are probably obvious, but I've never been hurt for making sure.

So there is an, at least, slight glow in the tube when it's energized. That's interesting and I wonder if there is a video or you tube of it where it's discernible. Also, I'm certainly committed to a closed, sealed box as well as multiple interlocks and flashing lights, sirens, etc., (well not really sirens, maybe an intermittent piezo buzzer or something) when the system is energized. I'll also have warning lights and goggle stations at each entry point to the room where the laser is operating. Safety first! (but really, these measures are required if I'm to use the thing in the house and not move it all to the shed....)

Thanks again for your help, Scott.
Jack
 
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Re: Current monitoring of Laser Power

Postby sshwarts » Sat Jan 09, 2016 10:26 pm

If you use a digital ammeter you need to have an isolated power supply (one that isolates both v+ and ground. There are such modules you can by that go from 12 or 24 v to 5v. The meter (be it digital or analog) goes in the ground side of of the tube power supply, never the HV side.

While the analog meter looks old school (which is why I went with digital first), it does have an advantage of being more responsive to changes. The digital ones have a sample rate slower than than what a analog can display.

Scott
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