danger laserpower setting in DSP from Lightobject

[Speedythinker]

It should work on most DSP as there is a seting for the PWM frequency.
The controlling is really depends on the power supply you use. I think that''s why PWM is better than an anlog PS.
I don't know if it works on the original PS that came with the K40

I'll post more info on my forum about. I did check "RF" output as well

See what I found about the PWM Freqency: http://www.lightobject.info/posting.php ... 034&p=3783

Marco

[a542002]

Hi
thats correct as long as the max of 18mA is secured thats the most importand part.
but you said in the intyroduction to the new 2012 DSP that the tube should not be driven over 20.000 hz.
for people who dont have a mA meter I just mentioned that the procentage should not be set higher then 60%
thats about 18mA.
greetings
walt

To clear things up here, I used a scope observe the waveforum and played around with the frequency.
Depends on your power supply, the frequency of the PWM provides an excellence controlling on the power % even if you have 100% set on the system default.

In my case, I set PWM frequency to 50,000HZ and the otuput of the 40W PS never go beyond 18mA. Plus, it provide fine output with 95%,..90%, 85%,80%....

I won't call "danger" here. I would say "hands on"

Marco

[mattrsch]

Hi
thats correct as long as the max of 18mA is secured thats the most importand part.
but you said in the intyroduction to the new 2012 DSP that the tube should not be driven over 20.000 hz.
for people who dont have a mA meter I just mentioned that the procentage should not be set higher then 60%
thats about 18mA.
greetings
walt

What you are saying is not strictly accurate. There are some people on this forum who cross 18 mA at only 30% power, so if they were to follow your advice their tube would be dead in short order. My 40W tube runs at about 15 mA when I set the DSP to 60%. It all depends on the combination of the tube, power supply, and the setup of the DSP. My advice to people who don't have a current meter wold be to go buy a current meter (mine cost me a little over $5). It's a pretty cheap investment compared to burning out a laser tube. At the very least hook your digital multimeter up and step up power until you get close to the limit of your tube, and set your max power accordingly. There's really no need to guestimate like this.

[a542002]

hi
you are funny this is exactly what I just described and claim the whole time.
greetings
walt

Hi
thats correct as long as the max of 18mA is secured thats the most importand part.
but you said in the intyroduction to the new 2012 DSP that the tube should not be driven over 20.000 hz.
for people who dont have a mA meter I just mentioned that the procentage should not be set higher then 60%
thats about 18mA.
greetings
walt

What you are saying is not strictly accurate. There are some people on this forum who cross 18 mA at only 30% power, so if they were to follow your advice their tube would be dead in short order. My 40W tube runs at about 15 mA when I set the DSP to 60%. It all depends on the combination of the tube, power supply, and the setup of the DSP. My advice to people who don't have a current meter wold be to go buy a current meter (mine cost me a little over $5). It's a pretty cheap investment compared to burning out a laser tube. At the very least hook your digital multimeter up and step up power until you get close to the limit of your tube, and set your max power accordingly. There's really no need to guestimate like this.

[Speedythinker]

To clear things up here, I used a scope observe the waveforum and played around with the frequency.
Depends on your power supply, the frequency of the PWM provides an excellence controlling on the power % even if you have 100% set on the system default.

In my case, I set PWM frequency to 50,000HZ and the otuput of the 40W PS never go beyond 18mA. Plus, it provide fine output with 95%,..90%, 85%,80%....

I won't call "danger" here. I would say "hands on"

Marco

Marco,
Is that specific to the newest version of the system or will it work on mine as well (2010)?

Tim:

I found out that that the so called "PWM frequency" isn't right. I changed the number from 10,000 to 100,000 (10K to 100K), the output waveforum stay in the same period with change of pulse witdh. So, I would rather call "Pulse width Control". From what I seem on the scope, the output is 10KHz regardless the setting on the PWM freq. But the % occupancy did change though

l'll take some picture and post it on my fourm

Marco

[Speedythinker]

Forget my last post. Isn't a good solution. After Reset is press, it is actually showing 50% 'frequency' (it's not showing true PWM freq. Will fix it on next release per programmer). The PWM got little effect from the change after Reset press.

After discussion, he said that the Max_Power setting on the System is the best way to control the max output. There are so many kinds of laser power in the market. It's impossible to set current properly for a laser tube without using a current meter monitoring. My PS can output up to 26mA while the K40 can do up to 22~23mA.

Marco

[Speedythinker]

Sorry my last post won't be a solution.

I discussed that matter with the programmer Li after spending two days for testintg and trying to dig out more info with my troubsome Tektronix Scope. Then I did some tests with him for several hrs (chatting by typing, pain as ...). In fact, the card was actually performing it was supposed to be. 70% 3.778V, 95% 5V. So logically, it worked the way it designed. But in reality, it's hard to see much difference after the Max_Power setting is set over 80% . I guess the PS was in saturated mode.

So, my suggestion to the programmer is to rewrite some code to 'fool' the controller. Pretending that 65% was as 100% and add non-linear adjustment to the code. That way, we should be able to see current changing via 65%~100% adjustment, hopefully.

Looking forward to see his new code

Marco

[trwalters001]

Hi All,

Maybe I'm not understanding things correctly...

If what I'm "fixin'" to say isn't correct, please let me know.

I've been reading quite a bit (on Buildlog) about PWM "frequency" as the way to control the laser power.

My understanding of PWM is that it's the duty cycle of the control waveform and not the frequency of the control waveform that does the power control. For instance, if I apply a 1% duty cycle waveform, running at 10kHz to the input of the laser supply, I'll get (for example) 1% power out of the laser. If I put a 1% duty cycle waveform at 100kHz to the input, I'll still get the same 1% power. Same for a 50% duty cycle (50% power out) or 95% duty cycle (95% power out). The frequency of the input waveform doesn't matter as long as it's above the frequency the laser will "see." This is from Wikipedia's "Pulse Width Modulation" page:

The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switchings have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from a few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies.

So, since the PWM signal is integrated to produce the control voltage in the laser power supply, a 100% duty cycle (or high DC level) will produce the maximum output. A 0% duty cycle (or ground) will produce a zero output.

Am I to understand that the power supply that was designed to run a specific laser tube (like my FSE 60W system) will drive enough current through the tube to affect its life?

If I put the rated maximum DC voltage on the laser supply PWM input pin (which corresponds to 100% power), I'll burn out the tube?

It would be nice to hear from Henry on this...

Y'all please elucidate!

Tim

[twehr]

Hi All,

Am I to understand that the power supply that was designed to run a specific laser tube (like my FSE 60W system) will drive enough current through the tube to affect its life?

If I put the rated maximum DC voltage on the laser supply PWM input pin (which corresponds to 100% power), I'll burn out the tube?

Tim

Forgetting all the previous talk about PWM frequency and focusing on the PWM %...

Yes - it is POSSIBLE that 100% (or some other percentage) PWM could cause your PS to overdrive your tube, thereby shortening its life. That is why it is critical that you have a current meter. SOME ps have adjustments for the max output, but the majority don't.

(My examples here is for 40watt laser. You need to know what your max recommended current is for the 60watt laser.)

1. With the meter in line, set your PWM to 50% and manually press and hold the laser test/fire button. See what steady current you get.
2. If over 18 mA (for a 40watt laser), turn it down to 40% and try it again.
3. If it is under the 18 mA (for a 40watt laser), turn it up to 60% PWM and try it again.
4. Keep adjusting as necessary until you know exactly what point you hit the steady current of 18 mA (for a 40watt laser).

Whatever PWM% you end up with is the MAX you would ever want to run a job at.

Even though I have referred to steady current do NOT start believing that you can do photo engraving at a higher value. Just because the meter cannot keep up with the switching on and off, does not mean the current is not exceeding the max. You just do your testing with the steady current to know what the max point is. Then stay under it for all jobs.

[trwalters001]

Thanks for the input, Tim.

I seem to remember that I measured 22mA at full power input. I'll double-check.

I've emailed Henry to find out what the recommended max should be.

Thanks!

Tim