Easy LPM Calibration

[loreadarkshade]

This thread will help you calibrate your laser power meter in a quick and dirty way to get approximate LPM readings (I would guesstimate +/−5% accuracy).

Please note that this method is VERY quick and dirty, and should only be used as a last resort, and is in no way more reliable than purchasing a new laser power meter or having one calibrated professionally.

What you will need:
-One of the diodes included in the list below
-An accurate constant current source (any bench power supply will do)

How it works:
Set the power supply in constant current mode, and supply the laser diode with any matching current as in this list, and then adjust your LPM calibration according to the (W) output of the diode at that specific current.

Spoiler: The list:

Laser Calibration

Sheet1 Diode,Voltage (V),Current (A),Power (W),Info / Reference Sanwu Pocket 520nm 50mW,N/A,N/A,0.055,Measured by Loreadarkshade with Ophir 20C-A-1-Y GH05C01A9G G8 Lens,?,1.62,0.967,Measured by Giannis_TDM on Gentec EO PS-310WBv2 LPM - <a href="https://laserpointerforums.com/members/giannis_tdm....

docs.google.com

Thanks to DTR (https://sites.google.com/site/dtrslasershop/home) for taking his time to measure these diodes for us.

Feel free to post your commercially available laser pointer (eg. sanwu color and power) measured on your own calibrated LPM down below, I will add it to theh list for reference.

 

[RedCowboy]

The diodes such as NDB7A75 is no longer in production, but even when it was the output varied quite a lot, some would do 5W @ 3.5A and some would do 6W at the same 3.5A and now that a lot of what's for sale is used the output is even less reliable.

Also the nubm44 you buy today will likely be used and could be a V1 or a V2 and with unknown hours of runtime.

Also as DTR was in the business of selling these diodes, he would test the higher binned diodes at the time they 1st came out, yes people do test and bin diodes from the same batch, because there are variations with some being " freaks " that test extra high and as a specific diode is produced they get better at making them, there are improvements along the way and they typically get stronger over the production lifetime, just like the nubm44's that came in v2 projectors were stronger than the nubm44's that came in v1 projectors.

If I was going to calibrate this way, I would use a lower output diode with a more reliable output, but not the nubm's and not at over-driven values which vary quite a bit, easily ( 15% ).

 

[Giannis_TDM]

This thread will help you calibrate your laser power meter in a quick and dirty way to get approximate LPM readings (I would guesstimate +/−5% accuracy).

Please note that this method is VERY quick and dirty, and should only be used as a last resort, and is in no way more reliable than purchasing a new laser power meter or having one calibrated professionally.

What you will need:
-One of the diodes included in the list below
-An accurate constant current source (any bench power supply will do)

How it works:
Set the power supply in constant current mode, and supply the laser diode with any matching current as in this list, and then adjust your LPM calibration according to the (W) output of the diode at that specific current.

Spoiler: The list:

Laser Calibration

Sheet1 Diode,Voltage (V),Current (A),Power (W),Info / Reference Sanwu Pocket 520nm 50mW,N/A,N/A,0.055,Measured by Loreadarkshade with Ophir 20C-A-1-Y GH05C01A9G G8 Lens,?,1.62,0.967,Measured by Giannis_TDM on Gentec EO PS-310WBv2 LPM - <a href="https://laserpointerforums.com/members/giannis_tdm....

docs.google.com

Thanks to DTR (https://sites.google.com/site/dtrslasershop/home) for taking his time to measure these diodes for us.

Feel free to post your commercially available laser pointer (eg. sanwu color and power) measured on your own calibrated LPM down below, I will add it to theh list for reference.

I HEAVILY disagree with using that as calibration due to it more like being +-60%, Kindly note that both the lens and more importantly the diode are factors, why I am saying 60 is because I happen to have a cyan diode that I just bought last month that does 160mW at 200mA, a normal one does 100mW at 200mA with a g2, I was using a less efficient G8 but that is besides the point, due to the inherent features of semiconductor manufacturing you can never trust a diode. hence why most 'proper' pointers are not powered by just CC, they are using the diode's internal photodiode to enable CW(constant wattage) regulation.

 

[Darktron]

Honestly I prefer to messure raw power of a diode with only exception being the glass window(or gball) in the TO package. Why? Well optics just add more to the complexity. You can buy a G2 rated at >95% transmission and a different seller can sell the same lens stating a >98% transmission. And like others metioned before you can get a "Freak" (I call them Prime) diode literally in the same block or batch. So I would test them at threshold current or slightly above.

 

[Giannis_TDM]

Honestly I prefer to messure raw power of a diode with only exception being the glass window(or gball) in the TO package. Why? Well optics just add more to the complexity. You can buy a G2 rated at >95% transmission and a different seller can sell the same lens stating a >98% transmission. And like others metioned before you can get "Freak" (I call them Prime) diodes literally in the same block or batch. So I would test them at threshold current or slightly above.

That would be even worse since the diode will need to be so close that the heat radiating from it would more than significantly alter the readings, also the threshold current and power at that current also varies greatly.

 

[Darktron]

That would be even worse since the diode will need to be so close that the heat radiating from it would more than significantly alter the readings, also the threshold current and power at that current also varies greatly.

It should be enough distance if it is a gball diode. At least to get a 10mW reading accuracy? How would you go about this in optics wise beside the diodes difference?

 

[Giannis_TDM]

It should be enough distance if it is a gball diode. At least to get a 10mW reading accuracy? How would you go about this in optics wise beside the diodes difference?

I would just use a G8 for everything since it's typical efficiency is known as around 92% and that does not really vary between lenses.

 

[Darktron]

I would just use a G8 for everything since it's typically efficiency is known as around 92% and that does not really vary between lenses.

Is a great choice but yet again I see claims from >90% to >98% on different sellers.

 

[Giannis_TDM]

Is a great choice but yet again I see claims from >90% to >98% on different sellers.

Simple solution, just buy the known efficiency dtr one, Even if its called G8 by another ebay shop it wont be the same lens most likely so for the 92% 'gurantee' just buy a dtr one and use it only for that purpose.

 

[RedCowboy]

The longer focal length G8 is a great lens, but for power testing the short focal length G2 is the best because you don't have the edge clipping issue which is more profound with higher divergence diodes so you get the highest possible reading other than no lens at all.

 

[ashwaganda]

1. Understand Your Device: Before starting, make sure you understand the specific calibration requirements for your LPM device. Different devices might have different procedures.
2. Gather Necessary Equipment: You’ll need a standard or reference device against which you can calibrate your LPM. This reference should be more accurate and should have a known and certified flow rate.
3. Set Up in a Controlled Environment: Perform the calibration in a stable environment where factors like temperature and pressure are controlled and consistent, as these can affect the readings.
4. Connect the LPM to the Reference Device: Ensure a secure and leak-free connection between your LPM and the reference device.
5. Run the Fluid or Gas: Allow the fluid or gas to flow through the LPM at a known rate (from your reference device). It’s often recommended to test at multiple flow rates - low, medium, and high.
6. Record the Readings: Carefully record the readings from both your LPM and the reference device.
7. Adjust Calibration if Necessary: If there’s a discrepancy between your LPM and the reference, adjust the calibration settings on your LPM accordingly. This process will vary depending on the specific LPM model.
8. Repeat the Test: After adjustments, repeat the test to ensure that the calibration is accurate across different flow rates.
9. Document the Calibration: Record the results of your calibration, including the date, conditions, and any adjustments made. This documentation is crucial for future reference and for maintaining consistent measurement standards.
10. Regular Checks: Regularly recalibrate and check your LPM to ensure ongoing accuracy, especially if it’s used frequently or in varying conditions.

 

[Unown (WILD)]

Ashwaganda or whatever has been banned for spamming. Was probably a bot. The darn thing also reported a post just to say it was a good post. WTF

 

[Giannis_TDM]

Ashwaganda or whatever has been banned for spamming. Was probably a bot. The darn thing also reported a post just to say it was a good post. WTF

You know what I just realized? it was a bot and it was using chat gpt. A numbered list like one above is very typical of chat gpt

 

[Unown (WILD)]

One of the most greatest achievements in technology and it's used for spamming. So sad

 

[lasersbee]

You could use the Sun on a clear day at a predetermined date and time
at your specific location on the globe knowing the about of radiation at
that specific time of day.

You would need to thermally isolate the LPM/s Heatsink from seeing the
Sun and only allow the sun to hit the entire Sensor's surface ONLY.

Doing some simple math will get you an Idea of the Power falling on the
sensor in Watts. I would estimate a 10-20% accuracy if no errors were made.

Jerry

 

[paul1598419]

You could use the Sun on a clear day at a predetermined date and time
at your specific location on the globe knowing the about of radiation at
that specific time of day.

You would need to thermally isolate the LPM/s Heatsink from seeing the
Sun and only allow the sun to hit the entire Sensor's surface ONLY.

Doing some simple math will get you an Idea of the Power falling on the
sensor in Watts. I would estimate a 10-20% accuracy if no errors were made.

Jerry

It never occurred to me to use the sun. When I was buying calibrated LPMs they were most often calibrated using an IR laser source unless I got to ask that it be calibrated using a green wavelength.....which I have done.