FieldBest Optical Power Meter
Yesterday I looked at an optical spectrometer, these are great tools for measuring the wavelength of a light source. For example determining the output wavelength of an unmarked laser.
What they’re not really useful for is measuring the output power of a laser. For this, you need an optical power meter. For lower power measurements these use photodiodes. Photodiode based power sensors can sometimes also be with optical attenuators to measure higher power lasers, but are generally limited to a few milliWatts.
Thermopile based sensors are generally used for higher powers. Essentially a thermopile is a number of thermocouples in series.
I’ve been wanting to test the power output of the various lasers I have in the 10mW to 10W range. New Newport meters are a bit too expensive for me, costing ~$3000.
So I picked up 3 cheap power meters. A LaserBee (which is made by a small company), and FieldBest (which is a cheap Shenzhen meter) and an old Newport 818P-110-19 which was ~10 years out of calibration.
This post is about the FieldBest meter, but I’ll discuss the Newport and LaserBee in future posts. I quickly compared the three units using a couple of the lasers I have:
Without a lab standard it’s difficult to draw any strong conclusions from the numbers above. But on the ~1W laser the FieldBest matches the Newport well. On the low end the 30mW measurement matches the LaserBee well. The low power laser seems to be below the detection threshold of the Newport (which has a 100W range).
So, of the 3 meters I have the FieldBest seems to be reasonably accurate, and has the most useful range (for me).
I obviously decided to open it up, and see what the build quality was like. The construction is pretty basic, but quite tidy:
It’s driven by a MCU sitting on its own PCB. This looks like a generic MCU module and uses what is quite possibly a real STM32F103:
The analogue circuitry also seems fairly basic, at some point it would be interesting to draw out the schematic for this, but it looks like simple voltage gain stage followed by either a second gain stage or a buffer to me:
I also took the cover off the sensor. Unfortunately, this doesn’t really reveal very much:
Due to its accuracy, I suspect this is a low range thermopile sensor. Perhaps if I can find a broken FieldBest unit at some point I’ll be able to pull apart one of these sensors.
Overall, I’ve been pretty happy with these FieldBest units, particularly considering that they cost a tenth of a similar Newport meter.
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