I want to say that I am not trying to bash any products out there, I think it's great that there are low cost meters on the market made by forum members, these are a great asset to the community.

I have seen a lot of people on the forum asking how to calibrate a home made power meter or saying they have tested something with a calibrated meter made by a forum member. The truth is, it's not calibrated.

When a meter is calibrated, it is setup in a temperature and humidity controlled environment and the detector is tested at several wavelengths each at several powers using a know good power/energy meter which is certified by NIST. Every laser is checked before and after testing on the detector in question. Every detector is different and every one gets a different calibration curve, and ratios.

Sometimes you may find a meter on ebay that was calibrated several years ago and has not been used for a while, you may thing it will still be calibrated and accurate, this is not the case. There are many things that can lead to a detector becoming inaccurate. The thermal detectors have specific coatings which allow them to absorb a set amount of light, silicon detectors have a limited lifetime, parts degrade including insulation, thermal compounds, and other materials. The detectors may appear to be fine and may work fine, but they are not calibrated unless they are still within the calibration period.

Every major company understands the reasons to have test equipment regularly calibrated, it's so they can insure consistency and repeatability in their products and be able to give customers exactly what they buy. In some cases, it can cause a lot of problems if you end up selling a product that does not meat the same specifications as you state when selling it.

Some people say that just because the calibration has expired does not mean that accuracy is off. It's the same as saying, just because the safety on my gun is broken doesn't mean it's going to shoot someone accidentally, it just makes it way more likely.

I would encourage people on the forum who own meters from companies who are still around to have their meters calibrated. It usually does not cost much money, I received my meter and head back from Coherent from calibration, it cost about $250 plus shipping. It is worth having done as you can be sure of whatever you measure.

Again, I am not trying to bash anything out there, I am just saying you cannot call it calibrated unless it is NIST traceable.

The calibration of rulers is is also especially important.

Mine is NIST traceable. I should know, I did it myself

You don't necessarily need lasers to calibrate a thermal head, but like ben said you do need a temperature controlled chamber (in which the TC and temperature reading device is also calibrated) and having a calibrated power meter makes things a lot easier (because it can be used as a standard)


Just in case anyone was wondering, I am an ASQ/ISO 17025 certified calibration tech. I'm in charge of alllllll calibration for a large aerospace company.

Finally a thread where I can REALLY say I know what I'm talking about

For me having a LaserBee was good enough. If was fairly accurate and regardless of it's calibration relative to other meters it still gave me a means of comparing my different lasers.

400th post

-Tony

Only a few people even would have a need for a meter that's properly calibrated. It's not like the day the "calibration period" ends the readings go off completely. The might only be off by a tiny fraction most of the time. Professionals probably should be concerned with having their meters calibrated to this degree of accuracy, but the hobbyist really only needs a close ballpark.

let's say my meter was calibrated long ago and now is reading 5mW under the real power. is it really worth 250$ to fix it?