How does this LPM work?

[loreadarkshade]

I just purchased a Coherent Laser Power Meter (PM150-50A).

I can see 4 pins on it.
+15v, Ground, -15v, and OUT

As far as I understand, I can apply DC 30v across the +15v and -15v, and when I connect my DMM to Ground and OUT, all I have to do is subtract 15v from my reading correct?

I just don't want to fry this thing applying 30v to it. (+15v, -15v is relatively the same thing as +30v across both pins correct?)
I also saw another that was connected to a power amplifier board, do I even need that?

Thanks in advance!

Here is the listing

2.8'' TFT PM2.5 Detector Air Quality Tester Meter Monitor Sensor PMS5003 | eBay

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[loreadarkshade]

All good, I found the datasheet!
I am bummed after finding out it has 30mW resolution :/ Does this mean it is 30+- mw close to the real value?

http://52ebad10ee97eea25d5e-d7d40819259e7d3022d9ad53e3694148.r84.cf3.rackcdn.com/UK_Z22-COHERENT_OEM-Thermopile-Sensors_DS.pdf

 

[RedCowboy]

My ophir head takes +12 and -12 which is basically 6 lipos in series with a center tap between the 3rd and 4th cells.

 

[loreadarkshade]

My ophir head takes +12 and -12 which is basically 6 lipos in series with a center tap between the 3rd and 4th cells.

Thank you! I was wondering how the hell to get a + and - power supply, good idea!

 

[loreadarkshade]

My ophir head takes +12 and -12 which is basically 6 lipos in series with a center tap between the 3rd and 4th cells.

Is your head a 30mW model? I'm wondering what kind of sensitivity i can get out of this one.

 

[RedCowboy]

No mines a 10W

Looks like you have 150W capable head with 30mw resolution.

 

[loreadarkshade]

No mines a 10W

Looks like you have 150W capable head with 30mw resolution.

Wanna swap? Haha , I dont need such a brute as i mostly measure sub watt lasers.

 

[Anthony P]

Just like powering an OP amp.

 

[Giannis_TDM]

Just like powering an OP amp.

Yes and no, single rail opamps exist. (single supply)

 

[Giannis_TDM]

Wanna swap? Haha , I dont need such a brute as i mostly measure sub watt lasers.

In terms of reading, you don't subtract anything, I'd recommend an Arduino with a 16bit or higher ADC and a low noise jfet based frontend with a PGA, you can subtract the small offset by the jfet amp in your code, then you need to find a general spectral correction factor on the LPM head datasheet, apply that to the measurement and then apply the W/V factor. After all that you should have a working LPM (Note: If you want the PCB to be a bit cheaper, you could try either an opamp (as a comparator) going into the jfet with a vref on one end and an Arduino controlled DAC on the other, would give you lots of range options. For optimal performance isolate the head thermally)


If you don't wanna turn this into a whole project, search ebay for a compatible monitor.

PS: Thankfully, yours looks like the 40mv/w version, will make your live a bit easier but 1mw is still 400uV so you better be experienced in signal theory and analogue frontend design, won't be all that hard but small errors matter in the uV range, good luck!