View Full Version : Relationship between Speed and Frequency!

Jiten Patel
09-20-2010, 5:30 AM
Ok so I went down to Trotec on friday to use their 100w Galvo for some samples I need for a magazine advert...They turned out incredible (to me anyway)...(will post pics up soon)

So while up there - bearing in mind I am extremely new to all this, we messed around with the settings and were using it at 30% power (to simulate our 30w laser) and cutting card at around 140-150 speed and with a frequency of 4 KHz running two passes to cleanly cut the card.

Now my question is changing the frequency does what exactly? Speed is self explanitory, but whats the relationship between the two....sorry if this is a ridiculous question, but I couldnt quite get my head around it.

Any help would be grealy appreciated.

paul mott
09-20-2010, 8:28 AM
I think what you are referring to here is the Pulse Repetition Frequency (PRF).
I run my Synrad at a PRF of 5kHz all the time but the operating instructions say that a PRF of up to 20kHz is allowed.
The PRF relates to the storage of particles within the tube which are waiting to be released and has a similar (although not the same) function as the 'Q Switch' used with YAG lasers.
Hope this helps.


Dan Hintz
09-20-2010, 8:53 AM
The pulse-per-inch specifies how often, within a certain distance (let's say 1"), the beam will fire its small spot. At low frequencies (say, 100 ppi), you will fire the laser 100 times as it moves across that 1" of linear travel. If this was paper, you would have a nice perforated line, but it wouldn't be cut completely through.

If you're talking about actual pulse frequency, that specifies how many times the laser will pulse within a specific time period (let's say 1 second). Each pulse has a set amount of energy to impart to the substrate, so more pulses per second mean more total energy. As you move along that line, the higher pulse rate means you're applying more energy to that length of movement.

Jiten Patel
09-20-2010, 9:23 AM
Hey Paul/Dan,

So increasing the frequency in essence is increases the force by adding more pulses from the laser. So there is a fine balance of having the right frequency and speed.

Paul you mention you always run at 4kHz? Is there any advantage of doing this, or is it a simple case of it works so why change it? I found little or no difference changing this setting but the lowest I went was 4kHz. Im just trying to work out the optimal settings for speed and frequency. I guess I will only get to play and experiment once I recieve mine in 5 weeks! Cant really get much out of a 8 hour session.

paul mott
09-20-2010, 9:43 AM
PPI and PRF are two entirely different things and they should not be confused.

I run at 5kHz all the time because that is exactly the same frequency as the tubes tickle pulse. This enables me to generate exact timing of the controlling Pulse Width Modulated (PWM) signal which controls my laser's output power. (I use the 5kHz as my clock frequency).

Increasing the PRF does not necessarily increase output power in fact it often has the opposite effect. When the laser is triggered the output is not linear there is a small but initial burst or surge which then stabilizes. Alteration of the PRF changes the energy available for this initial burst.