ALL GONE: Ophir 20C-A-1-Y SOLD!!!!

lasersbee said:

Nice job on building your LPM.

I would make a few suggestions for more accurate readings....

1) the OPHIR Head should be completely out of the enclosure
to have all sides at ambient temperature equilibrium.

2) Pictures #8, #12,#16 and #17 show the Laser's beam profile
OFF the Sensor's active area center. You will get erroneous power
readings if not centered. The OPHIR heads are calibrated by OPHIR
at the exact center of the sensor.

3) In picture #9 you are WAY too close to the Sensor to get an
accurate reading. At that distance and Laser Power you are no
doubt adding radiated heat from the Laser LD and Laser head
to the actual Laser Power reading.

4) the cover was nicely designed but goes back to suggestion 1).



Jerry

Click to expand...

Hi Jerry,

for my answers of the above:

1. I tried to expose as much of the head to ambient as possible. Even having to inset the side panel which is plastic to expose the back side to outside air. The rest are attached to the DIY aluminum chassis which also acts as an additional heatsink to ambient

2. There's no explanation there... other than it's hard to aim the laser using one hand while holding the cam on the other and looking through the camera screen.

3. There was no lens so that was the only way to put as much uncollimated light into the sensor as possible. The laser was from a cold start and had barely enough time to heat up when the pic was taken so there should be minimal effect from the heat. Either way, that was just for curiosity's sake rather than getting an exact power reading. I bet some of the uncollimated light is hitting the inside of the copper module rather than the absorber.

4. The cover is made from aluminum so it also acts as additional heatsinking to ambient which is suggested by Ophir (heatsinking for higher power handling).

But I do appreciate the suggestions and will take them into consideration when taking future measurements. :thanks:

I got my Ophir in the post already! Talk about fast shipping!!

I'll test it for life on Tuesday and let everyone know how it performs!

djQUAN said:

other than it's hard to aim the laser using one hand while holding the cam on the other and looking through the camera screen. :

Click to expand...

Test it out with a stable laser, some Ophir heads are hardly affected at all by not being at the center.

Edit: Diction folks. "Hardly" is extremely vague and can be interrupted as anything from 0.0001%-10%. Some is also vague and can mean anything from 50%-1% of Ophir heads. For the best readings, always take them at the center.

I received mine also. That is fast shipping!

Looks like a nice high quality unit. Time to build a power supply.

BTG, if it helps, I have a build thread on my DIY PS

I would have liked to test it before getting airborn, but I didn't expect to even receive it yet, so oh well.

ARG said:

Test it out with a stable laser, some Ophir heads are hardly affected at all by not being at the center.

Click to expand...

That's strange that OPHIR would produce all the 20C heads with
the same non-linear output when a small beam is not in the center
except for the one you tested.

I wonder why OPHIR even states that the Beam should be at the
center and that is the position they use when calibrating it.

How many OPHIR 20C heads have you actually tested to be linear
on all areas of the Sensors Active area...:thinking:

I've had at least 40 heads pass through my hands in the shop
in the past 2 years and they all exhibited a non-linear output
when not on the center of the Sensor.

Even Trevor posted a chart of the 4 OPHIR 20C heads he had
it clearly showed the non-linearity I referred to in post #21.

I'll try to dig it up...

EDIT.......
Here it is...


Looking at the charts it is easy to see that from the max reading
position to the min reading position there is a variation of:-

Sensor 1 13%

Sensor 2 10.5%

Sensor 3 6.2%

Sensor 4 13.4%

Those reading don't look linear to me. There is not even
any commonality between sensors.


Jerry

ARG said:

Test it out with a stable laser, some Ophir heads are hardly affected at all by not being at the center.

Click to expand...

Unfortunately, I'm not one of the lucky ones. I noticed before that mine changes its output with the position of the laser beam with respect to the center of the absorber. I can't remember how much though but it must be similar to the chart that Jerry posted as the fluctuation isn't that much if I remember correctly.

I am surprised that north gets the most accurate reading? I would have thought it was center?

It is also strange that all readings are below the actual output. Sensor 1 would fail on the accuracy test with 5% deviation. Maybe sensor 4 too.

That's really awkward, they're supposed to be 3% accurate. Even on the center those have a spread of 6.4%, which shouldn't happen even if one were at +3% of the real vealue and the other at -3%.

The numbers on the chart should be used for reference only.
Trevor's North position is not my North position when I test
these Heads. It was shown later on that the Brand New Coherent
Cube Laser that Tevor used to make that chart was in actual
fact outputting only 73mW (~9% low).

The fact remains that the active area of the OPHIR Heads is
NOT linear over it's surface area even though some LPM builders
try to state otherwise.

All readings should be compared to the center position and the
3% OPHIR head error stated on the Forum isin fact +/-3% of
true power as stated by OPHIR.


Jerry

lasersbee said:

The numbers on the chart should be used for reference only.
Trevor's North position is not my North position when I test
these Heads. It was shown later on that the Brand New Coherent
Cube Laser that Tevor used to make that chart was in actual
fact outputting only 73mW (~9% low).

The fact remains that the active area of the OPHIR Heads is
NOT linear over it's surface area even though some LPM builders
try to state otherwise.

All readings should be compared to the center position and the
3% OPHIR head error stated on the Forum isin fact +/-3% of
true power as stated by OPHIR.


Jerry

Click to expand...

For what it's worth, my "North" position is oriented such that the label on the back of the sensor is right-side-up. Seems like Ophir considers that "North" also.

Small correction - I had assumed the laser was brand new, but because it was given to me by Coherent, I suspect it wasn't. I think I've said that before, but it's worth mentioning here.

I also think you mean "uniform" rather than "linear." We're not yet sure whether or not the sensor exhibits linearity over its full range at each of the four compass positions, but we do know that a given power will not read uniformly across the active area.

It's a quibble, but if we want to be scientific we need to use the right words to describe what we're talking about.

Trevor

So, out of curiosity, I decided to check how much it deviates.

I used my 405nm labby laser which is quite stable. Ophir label in the back side oriented right side up.

center: 176mW
north: 180mW
east: 176mW
south: 167mW
west: 174mW

Trevor said:

I also think you mean "uniform" rather than "linear." We're not yet sure whether or not the sensor exhibits linearity over its full range at each of the four compass positions, but we do know that a given power will not read uniformly across the active area.

It's a quibble, but if we want to be scientific we need to use the right words to describe what we're talking about.

Trevor

Click to expand...

Agreed... "uniform" readings across the active area of the Sensor
is a more accurate definition...:beer:
But you get my drift...


Jerry

And...! Another one comes and another ones comes and another one bites the dust! Missed out again Well i have plenty of time to save up for one because i don't think they will be selling cheap anytime soon.