Laser Current Meter

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parkview
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Laser Current Meter

Post by parkview » Wed Oct 05, 2016 10:53 am

It's handy to monitor a laser tube current. This gives a good indication of the tubes power and if it's being over driven. Yes, mine is being over driven. I think I have a 50W tube in a '60W' system, as it's only 1030mm long and at 100% power, its being driven at 26mA, whereas it should only be driven at around 20mA max. Over driving a laser tube will quickly shorten it's life.

The Chinese/eBay laser unit doesn't come with an tube amp meter, so I made my own. After assessing the few odd meter I have stored away, I selected a 1mA Full Scale Deflection (FSD) meter. This meant I had to come up with a current shunt to shunt most of the current away from the meter. The closest I could come up with using the resistors on hand was a 1.8 ohm shunt. This was made using 2 x 1.2 ohm resistors in parallel and then adding this in series with another 1.2 ohm resistor. Here is my quick test arrangement:
testing resistor shunt values.jpg
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Once I had them worked out, I tested the meter out to find it's new FSD, which worked out to be 32mA. I then imported a photo of the old meter front plate into Inkscape and then used a new layer to draw up a new front plate and used my laser cutter to etch and cut out the paper template.

I used KiCAD to design up a simple circuit and PCB, which was laser etched into a paint covered PCB and etched using Hydrochloric acid and peroxide solution:
finished_pcb_back_sml.jpg
finished_pcb_back_sml.jpg (28.94 KiB) Viewed 2334 times


and the components where transferred from the meter onto the PCB (ok, the ex-TV 1968 capacitor was upgraded to a newer style):
finished_pcb_front_sml.jpg
finished_pcb_front_sml.jpg (28.51 KiB) Viewed 2334 times


The last thing to do was quickly design up a housing for it all and laser cut it out of 3mm MDF:
finished_Meter.3.back_sml.jpg
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and the final product perched on top of the laser cutter:
finished_Meter.2.sml.jpg
finished_Meter.2.sml.jpg (38.28 KiB) Viewed 2334 times


I might redo the front paper to include power levels for my tube. It turns out that safe max power (20mA) is delivered at around 65% tube power. Anything beyond that is pushing the tube.

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BeJay
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Re: Laser Current Meter

Post by BeJay » Sun Oct 16, 2016 9:12 pm

Nice work Paul! Yet another technology I need to investigate :)

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seaton
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Re: Laser Current Meter

Post by seaton » Tue Jul 31, 2018 10:33 am

to continue with this theme....

I had a day off yesterday and finally got around to adding a current meter to mine.

At the moment no box, just hooked it in. I was contemplating a box design, however I think I have enough space on my front control panel and will mount it directly there.

Here is the panel design I came up with for my 80W. This is for a stock 0-1mA Jaycar ammeter, I initially ranged to what resistors I had on hand (2x 10 Ohm 1%) which gave me a nice rounded 0-40Ma Range, but have since re-scaled it down to 0-32mA .

My tube is 80w nominal and 95w Peak as per manufactures data, which equates to 90% - 25mA and 100% - 28mA respectively on the machine setting.

Interestingly when calibrating my meter panel % scale I found it to be rather non-linear for anything below 30%, and very linear for anything over 30%, also interesting that 11%-30% range is my best grey scale engraving mode for MDF at 500mm/Sec. So I can see what lower power lasers are better at engraving. At 10% power settings on my machine I get current but the tube will not fire, while at 11% tube fires, so is my lowest usable setting

I have yet to measure power output with a watt meter, but this will do me for no :)

Anyway I have had some fun and will be a worthwhile addition.

worth noting I had a couple of design and my preference was the bottom one, however while it looked good on the screen, these meters are pretty tiny and was a bit cluttered so have made some adjustments.

2018-07-31_11-40-56.png
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2018-07-30_15-50-16.png
2018-07-30_15-50-16.png (62.24 KiB) Viewed 2309 times

parkview
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Re: Laser Current Meter

Post by parkview » Tue Jul 31, 2018 7:43 pm

Yes, I think that having a mA meter is very handy, in that it gives you an independent view of what's going on with the laser.

What software did you use to design the meter panel display?

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seaton
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Re: Laser Current Meter

Post by seaton » Wed Aug 01, 2018 9:17 am

Its called Meter by tonne software http://www.tonnesoftware.com/meter.html I had a license from way back when I did a job for someone and is not that expensive, there is a basic version that will allow single scale. Software is very clunky and not that user friendly but does a reasonable job.

It has a number of neat features such as linear scales, multiple scales, and you can also characterise the movement and it will adjust scales accordingly.

I'm surprises that there isn't any other web based type of generators out there.

DJCoopes
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Re: Laser Current Meter

Post by DJCoopes » Tue Aug 07, 2018 12:37 pm

for your laser cutter, do you use a 3d printer with the extruder swapped out for a laser, or a dedicated unit?
10 poke 53281,0
20 poke 646,5
30 poke 53280,0
40 poke 647,0
50 print " **** commodore 64 basic v3 ****"
60 print " "
70 print " 64k ram system 38911 basic bytes free"
80 print " "
90 print "ready."

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seaton
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Re: Laser Current Meter

Post by seaton » Tue Aug 07, 2018 6:37 pm

DJCoopes wrote:for your laser cutter, do you use a 3d printer with the extruder swapped out for a laser, or a dedicated unit?


Is a dedicated 80w unit from China that has a working area of 700mm x 500mm, I did a post on commissioning it here http://forum.swmakers.org/viewtopic.php?f=9&t=193. I did have a 3w diode laser that I had intended to install on my 3D printer, however is only really good for cutting paper and thin cardboard or engraving of wood. With my 80w it cuts wood and perspex no problem :D

DJCoopes
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Re: Laser Current Meter

Post by DJCoopes » Wed Aug 08, 2018 11:30 am

with wood engraving, would it be possible to do something like this?
https://blog.adafruit.com/2011/01/05/wo ... nt-traces/
10 poke 53281,0
20 poke 646,5
30 poke 53280,0
40 poke 647,0
50 print " **** commodore 64 basic v3 ****"
60 print " "
70 print " 64k ram system 38911 basic bytes free"
80 print " "
90 print "ready."

parkview
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Re: Laser Current Meter

Post by parkview » Wed Aug 08, 2018 10:10 pm

Sure, if you wanted too. If you just want to do a 'home PCB', I would suggest this method: http://forum.swmakers.org/viewtopic.php?f=12&t=186. I have made many PCB's at home using this method. It's a lot more reliable than laser etching wood or paper then filling in the tracks with a conductive substance. I can do a double sided PCB as well.

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