Written By: Logan Buchy
Date: March 23, 2016
@KevMacD and I had a pretty successful evening with the laser cutter maintenance.
Thanks to @JohnC and Science World, we were able to borrow a laser power meter. This was invaluable. We measured the optical power output before and after the optical components of the system. The measurement was performed on a Mahoney power meter calibrated to be accurate with a 35 second 'heat up' time. We found the following:
Measurement 1
- Placement: Before Optics
- Measured Power (W): 85
- Duty Cycle: 70%
Measurement 2
- Placement: After Optics
- Measured Power (W): 73
- Duty Cycle: 70%
This means that we are losing about 15% of our power through the optics of the system. This seems high given that Si mirrors should have a reflectivity >99% and will be something that we will be addressing ASAP. We already have components to replace the entire optical system. I suspect the mirrors are getting fairly hot.
The other interesting thing we can learn from this is that the measured power of 85W actually exceeds the tube's specification of 80W. This is a red flag since it suggests that we are over-driving the tube at 70% power. Over-driving the tube can quickly diminish the laser tube's life.
The second thing @KevMacD and I did was install a new current panel meter onto the common leg of the tube. This meter allows us to see how much current is being driven into the tube at a given time. As we suspected, the current through the tube was registering 30mA at 70% power - we are expecting 27mA. I did check the panel meter with a known current before hooking it up to the laser cutter, so I am fairly confident in it's reading. Frankly I am surprised the tube still works, it is certainly not good for it or the power supply. We found 60% is right at 27mA. Therefore, please use a maximum of 60% power for your cuts until further notice.
The laser current is not yet logged onto our stats collection server with this panel meter - we will be looking on how to do this in the future.
Lastly, @KevMacD gave the laser a good clean. It is shiny now and looks gorgeous!