Download Checking The Output Of Your Laser Tube

Checking The Output Of Your Laser Tube
INTRODUCTION
This document will outline the steps to confirm that a laser tube is not producing its full rated
output, and to confirm that this is due to the tube itself and not the support circuitry. This
procedure involves three steps: 1) using a power meter to check beam strength AT THE LASER
APERTURE ITSELF -- instead of the table surface -- to eliminate the possibility of dirty or
misaligned mirrors, etc.; 2) testing the primary tube power supply to insure that it is providing the
full rated voltage while the tube is being commanded to fire at 100% power; and 3) testing the
laser firing signal to be sure that it is also at the correct voltage level while the tube is being
commanded to fire at 100% power.
THIS PROCEDURE MAY SEEM COMPLICATED, BUT IT SHOULD TAKE NO MORE THAN
THIRTY MINUTES. PLEASE CALL XENETECH IF YOU HAVE ANY QUESTIONS.
(Note: These instructions are written from the standpoint of our XLT and XLE series lasers. The
procedure for our older 65 IPS and Aurora lasers is basically identical except that front touchpad
commands must be substituted for touch screen commands.)
The materials needed for this procedure are 1) a Q-tip with a long wooden handle, and alcohol or
acetone, for cleaning the laser aperture itself; 2) a thin (1/8"), flat piece of wood or plastic to use
as practice for holding the power meter in front of the laser beam aperture; 3) a laser power meter
(usually provided by Xenetech on a rental basis); and 4) a garden-variety voltmeter set to
measure DC voltages in the range of 0 to 50V.
(Note: If you use acetone as a cleaner, be aware that it is EXTREMELY flammable.)
Note also that this is a two-person operation: one person making the measurements at the back
of the laser machine, and a second person firing the laser beam from the front touch screen when
requested to do so by the person making the measurements.
In preparation for these tests, you should remove the lower rear hatch which runs lengthwise
across the back of the laser machine, thus exposing the laser tube itself. From the front touch
screen, you should also enter "beam alignment mode" (even though these tests have nothing to
do with beam align per se) in order to be able to test fire the laser as needed. The procedure for
entering beam alignment mode is as follows:
1) From the touch screen main menu select the "SERVICE" option.
2) From the service menu select the "BEAM ALIGNMENT" option.
3) In the beam alignment menu set laser power to "100" and set beam firing time to 10 seconds.
4) Each time the "RUNNING MAN" figure is now depressed, the laser beam will be fired for 10
seconds at a requested power level of 100%
TESTING LASER OUTPUT POWER AT THE LASER APERTURE
As you sitting facing the open rear laser hatch, the "business end" of the laser will be facing to
your left. The actual laser "aperture" -- the small window through which the laser beam exits the
laser housing -- is usually recessed some one or two inches into the left laser end plate, so you
will not be able to see it directly. However, the #1 mirror -- which reflects the laser beam up -- is
positioned directly in front of the aperture, so this should help you locate it.
To prove to yourself that you have located the aperture, and by way of practice at holding the
power meter target directly in front of it, you should now practice as follows:
1) Pencil a small circle on one end of your practice piece of wood or plastic.
2) Insert in front of what you think to be the aperture, keeping hands/fingers/face well clear.
3) Give the command to fire the laser.
4) Hold in place for 10 seconds until the laser finishes firing.
5) Remove practice target and confirm that laser has struck within circle.
Once you have located the aperture and gotten the hang of holding a target in front of it, you
should give the aperture a final cleaning by inserting the alcohol or acetone soaked Q-tip into the
aperture recess and swabbing the window at the bottom. (Even though this window is recessed,
it is amazing how much dust can accumulate on it -- enough to reduce transmitted laser power by
30% or more!)
You are now ready to use the power meter to measure actual laser output:
1) Press the button on the power meter handle to start the measurement process.
2) Insert the target area in front of the aperture.
3) Give the command to fire the laser at 100% power.
4) When the power meter beeps, remove quickly.
5) Record the power meter reading.
6) Allow a few minutes for the meter to cool down.
7) Repeat several times until you are able to get a consistent reading.
The laser meter reads directly in watts. For a new laser, the reading at the aperture itself should
be somewhat higher than the rated wattage of your machine. In other words, if you have a new
30 watt laser, you should find that the aperture reading is 32 watts or more. Laser power will, of
course, degrade with age.
TESTING PRIMARY POWER SUPPLY VOLTAGE UNDER LOAD
If you and Xenetech agree that laser power as measured at the aperture is lower than it should
be, you should next check the primary laser power supply to confirm that it is supplying the
correct voltage to the laser tube UNDER LOAD, that is, while the tube is being commanded to fire
at 100% output.
(Note 1: The exact voltage which should be supplied to the tube will vary depending on the tube
type. Coherent/Deos tubes typically require 48V DC; Synrad tubes typically require 30V DC.
Please check with Xenetech to determine the correct value.)
(Note 2: When using a voltmeter, it is critical that the probes be carefully placed and held in place,
such that you do not cause a short circuit -- a process very much like "jumping off" one car from
the battery of another.)
The steps are as follows:
1) Turn on your voltmeter and set it to read DC volts in the proper range.
2) If you are not sure that your voltmeter is working properly, or if you are not sure that you have
set it to the correct range, or if you suspect that its batteries may be running low, test the
voltmeter on your car battery (red probe on positive terminal, black probe on negative terminal).
It should read approximately 12.0V.
3) Locate the two wires providing the primary power supply to the laser tube. These will be
large, relatively thick wires in close association with one another, one red in color and the other
black.
4) Leaving these wires attached to the laser terminal input strip, CAREFULLY place the red
voltmeter probe on the terminal screw for the red wire and place the black voltmeter probe on the
terminal screw for the black wire.
5) CAREFULLY holding the voltmeter leads in place, give the command to fire the laser at 100%
power.
6) During the middle of the 10 second laser firing period, take a voltmeter reading.
7) Repeat until you can get a consistent reading.
If the reading is not as expected, please contact Xenetech immediately. If it is as expected, go on
to the final test following.
TESTING LASER FIRING VOLTAGE
As you know, laser tubes can be commanded to output over a range of power values -- from 0%
up to 100% of their rated power. (I.e., a 60 watt tube outputting at 50% power will be generating
the same output power as a 30 watt tube outputting at 100% power -- 30 watts.)
The output power level is controlled by a "firing voltage", and, if your tube seems not to be
outputting as it should, it is critical to check this voltage level. The steps are as follows:
1) Turn on the voltmeter and set it to measure voltages in the range 0 to 10V.
2) Locate the firing voltage input cable. This will be plugged into the right side of the laser control
box, located behind the lower front door of the laser, and will normally employ a cable TV-style
coaxial plug. (see picture)
Test here
3) Unplug this cable, and, using two hands, CAREFULLY hold the red probe to the bare wire that
extends like a pin from the center of the connector, and hold the black probe to the outer metal
housing of the connector.
4) CAREFULLY holding the voltmeter leads in place, give the command to fire the laser at 100%
power.
5) During the middle of the 10 second laser firing period, take a voltmeter reading. (Note: The
laser will not actually fire at this point because the firing signal has been disconnected.)
6) Repeat until you can get a consistent reading.
The laser firing voltage should be approximately 4.5V. If not, please contact Xenetech.
CONCLUSION
If your laser tube is not producing the correct output wattage at the laser aperture itself, and if the
primary supply voltage and the firing voltage are as they should be, it is likely that the tube needs
to be refurbished. Xenetech has a very economical program for swapping out such a tube with
one which has been newly refurbished and which comes with a warranty. Please contact
Xenetech for details.
(Note: Don't forget to return the laser power meter promptly to Xenetech!)