Reshared this because I assigned the wrong category and cannot see how to change it.
Originally shared by Don Kleinschnitz Jr.
Update on the laser response front.
Nothing conclusive yet but made some interesting measurements today.
For some time I have been wanting to measure the lasers output and characterize its response to PWM control.
Looking at the laser light itself has been a bust. Turns out that 10600nm is really out there FAR …DOH!
There isn’t anything electronic and cheap that has sensitivity in that range, and doesn’t get fried. I tried everything including many models of IR sensors and photo-diodes, even avalanche devices .
The most usable device was a thermopile (the type in PIR’s) it will respond at this wavelength but too SLOWLY. I need to measure in the range of 1-10’s microseconds!
Then it dawned on me that I might be able to measure the lasers response indirectly and safely by scoping the tubes current as it responds to PWM pulses.
Could measuring the current in the tube tell us anything reliable about its output?
Does the tubes current response correlate with the tubes optical response?
…
On one hand…
I logic that the light response should be faster than the electric current response curve but likely not slower.
Therefore:
If I can create current pulse responses that meets the benchmark we probably can conclude that the light response meets the benchmark.
On the other hand …
If I cannot show current pulse responses that meet the benchmark then we cannot conclude that the light response does not meet the benchmark unless we can prove the correlation between current and light response.
Now that my K40 conversion is in a reasonable state of use I started to explore this idea of measuring laser light response by measuring its current pulse response.
To benchmark I calculated that the smallest PWM pulse width for reasonable engraving speeds and resolution with a 5% grey shade step increment would be about 11.7us. [another post will show the math]
The tests results shown below were created by looking at the voltage across the current meter in sync with the low going activation of the “Test” button.
…
Annotation of the pictures that follow numbered in successive order:
- This rise time of 1.8us is below the benchmark
- Another capture of a rise time of 1.9us
- A much slower time of 20us captured [no idea why]
- A good look at the internal LPS PWM signal. A period of 408us and a pulse width of 84us at 20% DF.
What does this suggest:
… Sugests that the laser can respond fast enough for reasonable engraving applications. Laser response may be 1.8us or less.
… Its not clear why the response can be slower ie: 20us vs 1.8us
… The internal PWM period of the LPS is 408us which suggests that we could run the smoothies at that same period?? A shorter period is better however.
… Finding fast enough edges suggests that this may be a suitable
method for measuring the lasers response.
… Need to test using the smoothies PWM signal with the LPS PWM maxed out (IN = max).
… The voltage across the laser current meter is very small.
