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DIY CO2 Power Meter

Anthony P

Well-known member
LPF Site Supporter
I would like to get input from everyone on a simple thermocouple CO2 LPM.
I do not know how to enter mathematical symbols on this computer so I will do my best.
d= delta(change in)
T=temp C
t=time seconds
J=joules
m=mass grams
S= specific heat of target (aluminum .89J/Cg)
I am attempting to use a small piece of aluminum as a target attached to DMM temperature probe.

J=SxMxdT
Watt=Joules x Seconds

mass of target=1.912

J=(.89J/Cg)x(1.912g)xdT
Watts=Ans/dt

Measuring temperature change over a period of time should yield watts.

The first question that comes to mind is the effect of ambient temperature.

Cyparagon

Well-known member
Right. Heat from the target is dissipated to the environment through conduction, convection, and radiation. There are formulas for these, but they can be very complex. You'd also need to find the absorption coefficient of the surface of your target, and this will be a function of the spectral distribution of the incident energy.

What you're describing is a calorimeter. Throw that into google and see what pops out. They're not typically ever used with lasers because there are cheaper and simpler options, like thermopiles and photodiodes.

Anthony P

Well-known member
LPF Site Supporter
Time to redesign the wheel.lol. I wonder if a correction factor could be determined experimentally based on ambient temp and response of probe to known temps such as ice or boil. I will research absorption spectrum for Al 10.6 micron, also effects of coating with carbon (candle black the probe). Even if it is unreasonable to expect "accurate" results, at the very least, some degree of precision may be achievable. This would be a useful tool for tuning the laser (mirror alignment, gas pressure and flow rates, voltages, currents, and effects of AC vs full wave DC, 1/2 wave DC, filtering, etc)
The advantage would be that the set-up would be free as most laser builders have a DMM and chunk of Al laying around.

RedCowboy

Well-known member
I saw this a while back.

Anthony P

Well-known member
LPF Site Supporter
Thanks RedCowboy. The videos were very helpful. I figure that by timing a fixed temperature change( 100C) with laser on I get an initial watt value. Then correct for ambient by timing laser off length of time for temperature to transition down over the same range. This is fairly constant as the target releases energy in a consistent manner. Now if I can figure loss due to reflection I should have a ballpark reading of wattage. In the "dohicky" videos they had the advantage of a known power source for calibration. I do not. I am going solely by mathematical rules of chemistry. I have been thinking about purchasing one of those cloudray meters, but more research into them is required.

Anthony P

Well-known member
LPF Site Supporter
OK, I will just ask you guys. Does anyone have experience with the Cloudray company. In particular: handheld CO2 power meter, 40 or 50 watt CO2 tubes, power supplies?

Anthony P

Well-known member
LPF Site Supporter
Thanks Steve. I will study the diagrams in the link.

paul1598419

Well-known member
Many of the recent Chinese CO2 PMs are copies of Peter Laakman's design. Laakman is a Synrad Founder.

Note Novantia, Synrad's parent company has the patent assignment ACTIVE..., which means you can build one for yourself, but don't copy it or sell a board or kit.

Steve
Thanks for this, Steve. I found it interesting how he used a differentiator coupled to a rate of change circuit for both heat up and cool down to give energy and power levels faster, but without the need to time the sample laser. I guess it pays to peruse the patents assigned to these types of new meters as I was unaware of this design.

Anthony P

Well-known member
LPF Site Supporter
Cloudray HLP-200 vs Homemade power meter
After doing multiple tests and collecting data I have determined that the reflectivity on my black anodized aluminum is 49% +/-2%. Ambient correction comes out to 1.8 watts at 18C room temp. Using correction factors, the homemade chunk of Al on thermocouple consistently match the hlp-200 over a variety of test parameters, within a few percent. I would call this experiment a success.
I only have one criticism of the hlp-200. The beginning and ending of the test are indicated by a tone. With water and vacuum pump running it is inaudible. Perhaps a louder tone or LED indicator would be a much better feature.

Cyparagon

Well-known member
49% at what wavelength? With what anodization depth? With what grade of aluminium? With what concentration and type of dye?

Anthony P

Well-known member
LPF Site Supporter
10.6microns CO2. Target Al was just a black TO220 heat sink, weighed on analytical balance. Reflectivity determined by comparing to calibrated meter. If you would like I could repeat experiment with plain uncoated Al or maybe blackened with candle for a more generic figures. This was a proof of concept experiment. Without existing meter to verify results any accuracy would be questionable at best. However, the precision is there. This makes it worthwhile as tuning device for homebuilt CO2 lasers. I would be happy to experiment further if you have suggestions.