DIY PAR Meter Question

TheEngineer · Oct 5, 2017

I have the sensor from an MQ-200 Apogee PAR Meter. It belongs to my local club. Someone dropped the whole darn thing into their tank and the main unit is shot. I'm hoping I can get it replaced, but in the meanwhile I wanted to play around with the sensor.

I've seen that you can just wire it up to a multimeter and do a simple calculation to back into PAR. Essentially you take mV * 5 * 1.08 (submersion factor?) and you get PAR. Problem is that I'm getting readings of around 1100mV just under my Radion running at 60%. Clearly I'm not actually putting off nearly 6,000 PAR.

I guess this sensor could have a different voltage range. Anyone know which sensor was attached to the MQ-200?

zachxlutz · Oct 5, 2017

Following. I have the PMK from Neptune and I'd love to be able to hook it directly to a multimeter and get quick PAR numbers without having to hook it back up to the Apex.

saltyfilmfolks · Oct 5, 2017

@Dana Riddle

Hitmans reef · Oct 5, 2017

Here’s a link for apogee their page their equations
https://www.apogeeinstruments.com/conversion-ppf-to-lux/

TheEngineer · Oct 5, 2017

I pulled out the ole lux meter to see if I could make some sense of the numbers I'm seeing.

The par sensor reads 1160mV at the same spot the lux meter reads 28,000 lux. Let's use 60 as the conversion factor and that's about 466 PAR. Dividing 1160 by 466 gives 2.5 (rounding). Maybe this sensor puts out double the voltage of the one most people use?

Dana Riddle · Oct 5, 2017

What does 'just under' mean? I checked the output of a Kessil (about 4 inches from the array in air) with an Apogee and pegged the meter out at of PPFD 4,000 micromole/m2/sec. Repeated the procedure with a LiCor (calibrated for 'air' readings) and got 7,200.

TheEngineer · Oct 5, 2017

Dana Riddle said:
What does 'just under' mean? I checked the output of a Kessil (about 4 inches from the array in air) with an Apogee and pegged the meter out at of PPFD 4,000 micromole/m2/sec. Repeated the procedure with a LiCor (calibrated for 'air' readings) and got 7,200.

Just under meaning I was just holding it under the middle of the light. It’s about 9” from the sensor to the light. In air, not water. 460 par with the XR15 gen 4 at 60% in air seemed reasonable. I know this sensor is no good for LEDs. I’m just trying to salvage it for the club.

Dana Riddle · Oct 5, 2017

I don't have a Radion to compare, so the old adage applies: If you're happy with the number, it's right. If not....

TheEngineer · Oct 5, 2017

Dana Riddle said:
I don't have a Radion to compare, so the old adage applies: If you're happy with the number, it's right. If not....

lol. I’m just trying to figure out a conversion factor. Those numbers I listed (1160) are mV not micromole/m2/sec. I’m hooking it up to a multimeter.

saltyfilmfolks · Oct 5, 2017

Perhaps a simple sun calulation.

Lux meter outside. Divide by 53.
Use par meter. See what you get. Compare.

I'm just a simple country Dr Jim.

TheEngineer · Oct 5, 2017

saltyfilmfolks said:
Perhaps a simple sun calulation.

Lux meter outside. Divide by 53.
Use par meter. See what you get. Compare.

I'm just a simple country Dr Jim.

I’ll try that in the AM. It’s currently dark here on the right coast.

saltyfilmfolks · Oct 5, 2017

TheEngineer said:
I’ll try that in the AM. It’s currently dark here on the right coast.

What you are looking for as well is the Mv output from the meter however as well to convert that number to par. Correct?

What I give you is just a way to claibrate it or rather , insure its calibration.

TheEngineer · Oct 5, 2017

saltyfilmfolks said:
What you are looking for as well is the Mv output from the meter however as well to convert that number to par. Correct?

What I give you is just a way to claibrate it or rather , insure its calibration.

Yep