DIY PAR meter, Yeah you heard me - Page 35 - The Planted Tank Forum
 
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post #511 of 731 (permalink) Old 04-05-2013, 01:31 PM
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Skimmed the thread and I have a few questions. Some you guys are probably sick of answering but I guess I missed em so forgive me.

The parts list in the first post claims to be updated 9-25-12, is that the most current information? I see a 27k resistor on the low side of the jack, I'm assuming that's the resistance that's being discussed recently as far as calibration (someone mentioned a 15k resistor and 15k pot, I think?)

What light source are you all calibrating to?

Are you all just using a pair of wires for the cable to the sensor? Has anyone had interference or noise issues and switched to shielded cable?

Ironic that you're using 2447 as the diffuser. That's what my overflow box and ATS scaffolds and a bunch of other nicknacks on my tanks are built from, and I have lots of it around the shop.
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post #512 of 731 (permalink) Old 04-05-2013, 02:53 PM Thread Starter
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i saw you offered to calibrate another member's par meter, is that an open offer? when i build mine would you be willing to do the same for me?
Sorry, I'm busy with other projects and won't have time to calibrate your meter. Set the resistor to 24.7K and hope for the best.

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What light source are you all calibrating to?
A regular white spiral bulb.

And use the smallest guage wire you can find. I'm using an ethernet cable. There are lots of variables if you use different materials so that's why having a PAR meter to calibrate against is good.

I'm getting PMs from science people who aren't even in planted tanks wanting to measure sunlight for their tomato plants I think it works even better for sunlight since light bulbs are so varied and low in output compared to the sun.

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post #513 of 731 (permalink) Old 04-05-2013, 05:41 PM
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Sorry, I'm busy with other projects and won't have time to calibrate your meter. Set the resistor to 24.7K and hope for the best.


A regular white spiral bulb.

And use the smallest guage wire you can find. I'm using an ethernet cable. There are lots of variables if you use different materials so that's why having a PAR meter to calibrate against is good.

I'm getting PMs from science people who aren't even in planted tanks wanting to measure sunlight for their tomato plants I think it works even better for sunlight since light bulbs are so varied and low in output compared to the sun.
I stumbled onto this a few days ago: http://www.apogeeinstruments.com/apo...l-information/ The Quantum PAR meter isn't perfect either. Unless a PAR meter is made with multiple photodiodes, each measuring a portion of the spectrum, the meter will have various errors when measuring light from different sources. For the Quantum meter, it is pretty accurate with typical fluorescent aquarium lighting, but not that accurate with sunlight.

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post #514 of 731 (permalink) Old 04-05-2013, 05:52 PM Thread Starter
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I stumbled onto this a few days ago: http://www.apogeeinstruments.com/apo...l-information/ The Quantum PAR meter isn't perfect either. Unless a PAR meter is made with multiple photodiodes, each measuring a portion of the spectrum, the meter will have various errors when measuring light from different sources. For the Quantum meter, it is pretty accurate with typical fluorescent aquarium lighting, but not that accurate with sunlight.
yup, you have to ask apogee to calibrate your sensor for indoor or outdoor light. There's a 10% difference.

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post #515 of 731 (permalink) Old 04-14-2013, 05:26 AM
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i was wondering why you used a photodiode vs a phototransistor? i was looking threw products and it looks like this one:
http://www.alliedelec.com/search/pro...9988#tab=specs
has an very similar responce to wavelengths as the graph in your first post, its a bit cheaper too...

Last edited by genocdex; 04-14-2013 at 05:30 AM. Reason: edited for price correction
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post #516 of 731 (permalink) Old 04-14-2013, 03:05 PM Thread Starter
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DIY PAR meter, Yeah you heard me

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Originally Posted by genocdex View Post
i was wondering why you used a photodiode vs a phototransistor? i was looking threw products and it looks like this one:
http://www.alliedelec.com/search/pro...9988#tab=specs
has an very similar responce to wavelengths as the graph in your first post, its a bit cheaper too...

Phototransistor output is usually too small in term of resolution to have it be meaningful. The spectral response for the transistor you showed is similar but not quite.


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post #517 of 731 (permalink) Old 04-17-2013, 01:17 AM
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Hi you guys still selling these? I would love to buy one. Thanks
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post #518 of 731 (permalink) Old 04-17-2013, 01:26 AM Thread Starter
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DIY PAR meter, Yeah you heard me

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Hi you guys still selling these? I would love to buy one. Thanks
Yeah, will be making some this weekend.


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post #519 of 731 (permalink) Old 04-17-2013, 01:48 AM
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Are you calibrating these prior to shipment? Looking at similar data from others, mine seems to be reading at least double sometimes triple what would be expected. Any ideas?
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post #520 of 731 (permalink) Old 04-17-2013, 02:47 AM Thread Starter
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DIY PAR meter, Yeah you heard me

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Are you calibrating these prior to shipment? Looking at similar data from others, mine seems to be reading at least double sometimes triple what would be expected. Any ideas?
It is matched to an apogee sensor. If you feel the readings are too high, you can adjust it by fiddling with the pot (blue thingy), counter clockwise to bring down the reading.


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post #521 of 731 (permalink) Old 04-17-2013, 01:33 PM
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It is matched to an apogee sensor. If you feel the readings are too high, you can adjust it by fiddling with the pot (blue thingy), counter clockwise to bring down the reading.


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Can you walk me through your calibration process? There is another guy in my local club that bought one too and is having similar issues. It almost seems like you calibrated to a low data value and the error just gets larger the farther we go towards the high end. I also noticed that outside it is invariably reading 1391 no matter what. Please advise.
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post #522 of 731 (permalink) Old 04-17-2013, 02:50 PM Thread Starter
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DIY PAR meter, Yeah you heard me

I match reading again a spiral cf ranging from 160 - 50 par by varying distance.

Your 1300 par reading sounds right. The par is calibrated for indoor light. It's the beginning of spring. You should get 1800-2000 at noon around July, remember the earth is on an axis.


I'll try a different light source next round just to make sure. I have a feeling it's slightly high but x2 or x3 is too much. Again, if you feel it's too much, change the pot to your liking.

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post #523 of 731 (permalink) Old 04-17-2013, 07:50 PM
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DIY PAR meter, Yeah you heard me

Used one of your DIY par meters I'm impressed, I hope I used it correctly, flat end towards the light right? Put my light at about 116-130 par at 40"
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post #524 of 731 (permalink) Old 04-21-2013, 07:40 AM
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I match reading again a spiral cf ranging from 160 - 50 par by varying distance.

Your 1300 par reading sounds right. The par is calibrated for indoor light. It's the beginning of spring. You should get 1800-2000 at noon around July, remember the earth is on an axis.


I'll try a different light source next round just to make sure. I have a feeling it's slightly high but x2 or x3 is too much. Again, if you feel it's too much, change the pot to your liking.

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This meter pegs out at 1391 no matter how bright it is outside. Readings are two to three times greater than what a real par meter is showing me. Buyer beware, this meter is not legit. Sorry bro, I gave you a chance to come correct and you failed.
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post #525 of 731 (permalink) Old 04-21-2013, 02:22 PM Thread Starter
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DIY PAR meter, Yeah you heard me

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This meter pegs out at 1391 no matter how bright it is outside. Readings are two to three times greater than what a real par meter is showing me. Buyer beware, this meter is not legit. Sorry bro, I gave you a chance to come correct and you failed.
Sure, people should get all the info before they buy. I'll make some today and see if your problem is showing up.

What par meter are You using btw and how old is it?
What is the reading from the par meter to sunlight?

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