|Topic Review (Newest First)|
|10-22-2015 12:59 PM|
Originally Posted by rubenhak View Post
I've also added spectral light filters to the diode to further help with PAR calculations. You can find it here
AquaticTechTank.net ? View topic - DIY PAR meter
|10-22-2015 06:10 AM|
Originally Posted by mistergreen View Post
I see you've been through a long journey of building a PAR sensor. May I ask if you have complete instructions on hand? If yes I'd really appreciate if you could share them.
If not, could you give me few pointers. I have few questions here. What is the purpose of Cosine diffuser and how do you use it? Is the Photodiode VTB8441BH submersible? I was thinking to put the sensor into the aquarium for constant monitoring. Will this work with Miniature Solar Cell - BPW34? I'd prefer to use the latter one since it is much smaller.
Also, what is the algorithm to calculate the PAR value from the sensor reading?
Thanks a lot,
|07-02-2015 02:13 AM|
|rottison||mistergreen now that I have my par meter built I need to calibrate it my local club has a apogee meter I can use. Do you do any thing special to calibrate? And how do you calibrate the par meter normaly?|
|06-11-2015 02:54 AM|
|rottison||that is how I thought it went also just wanted to make sure before it was glued down|
|06-11-2015 01:39 AM|
I believe that the diffuser goes into the bottom of the jar first, then you put the filters between the acrylic diffuser and the photo diode, so that light passes first through the diffuser, then through the filters, where it hits the screen of the photo diode. Correct me if I'm wrong Mistergreen.
Originally Posted by rottison View Post
|06-11-2015 12:16 AM|
|rottison||so in the morning I will make it more permanent but I have 3 colored ronco disk cut to fit the jar and just dropped in then I will glue the photo optic to the diffuser and drop that in and dab a bit of silicon on the edges to hold it in place few hours drying time I should be almost done.|
|06-10-2015 10:42 PM|
|mistergreen||The order of the light filters doesn't matter but I would put the diffuser on top.|
|06-10-2015 07:48 PM|
|rottison||mistergreen does it matter what filter or disk goes to the bottom of the jar fist or in what order|
|06-07-2015 02:35 PM|
hmm, interesting. The only thing I can think of is the variance on the voltage regulator and resistors in that chain to the atmega that would give us different results. So it would vary from batch to batch.
The regulator is outputting to 4.99V (middle & right pin)and the resistor by the atmega is 10.05K.
Yeah, there might be too many variance to get an exact number. I guess the only way to calibrate is to use another calibrated CEP with light sensor or a PAR sensor.
|06-07-2015 12:40 PM|
I think that O2Surplus envisioned that any calibrated CEP, once calibrated to a PAR meter, and the values known, will calibrate exactly the same way each time via the 10K resistor method, the 10K resistor eliminating the variability of the sensor itself. Then, because of the standardization of the sensor input to 10K, only one calibrated CEP would be necessary for anyone to calibrate their individual CEP using the 10K resistor method.
But, having taken some readings from my own CEP, the theory does not seem to correlate to readings Mistergreen obtained from his calibrated CEP.
I confirmed the value of my 10K ohm resistor that was put across the sensor terminals, and it is 9.97K ohms. Close enough, tolerance of about 3%, but it occurs to me that there may be variabilites in all the components within the circuits of individual CEPs to make universal calibration through a mathematical formula almost impossible as these variabilities add up...unless there is some kind of conversion factor that can be used to acount for the actual values of components used in individual CEPs. Take my 15K ohm resistor for example. Mine reads 11.94K, and not 15K.
|06-07-2015 12:10 PM|
Here are the results...
I was very fortunate, in that I had an Electronics Rainbow kit for my grandson that I was able to find a 10K ohm resistor.
So, I wrapped black electrical tape around the leads of the resistor so that my holding it did not change the resistance.
First, I tested the CEP that had been calibrated to Mistergreen's commercially produced PAR meter, we will call it CEP #1, and got the following result on the LDC screen of the CEP:
Indoor = 3813
Outdoor = 3458
(Note Mistergreen's reading was 4357, an almost identical reversal of the 1st two numbers above on my Outdoor reading)
I tested several ways, from the soldered pins of the jack, and also from the two terminals of the green block where the Sensor wires connect, holding the resistor with my fingers, making sure to only hold the resistor through the black electrical tape I applied to the resistor. I also took readings holding the resistor with a set of tweezers grasping the black tape area. But, I don't have a set of plastic tweezers, which would have been preferable to perform this test. So, I hope that the black electrical tape did the job to isolate the resistor from any effects from my touching it. The readings were taken multiple times, and the results were always consistent.
I also tested the two CEPs that have only been calibrated by me using the resistance method, and not through a light emitter via a commercially produced PAR meter. These CEPs were calibrated by putting a probe on the top pad of the 15K ohm resistor, and touching the other probe to pin #1 and #2 on the 10K POT. You may recal that CEP #2 calibrated
to 27.46 ohms, and CEP #3 calibrated to 27.5K ohms using this method, and were calibrated to closely match the results using this method from CEP #1, which had been calibrated using a PAR meter by Mistergreen.
When using the 10K ohm resistor touched to the input of the sensor terminals, the CEPs returned the following values on the LCD screen:
CEP #2 previously calibrated to 27.46K using the resistance method between the 15K resistor and terminals 1 & 2 at the POT:
LCD Reading =
Indoor = 3813 using 10K resistor at the input terminals of the sensor
Outdoor = 3458 using 10K resistor at the input terminals of the sensor
CEP #3 calibrated to 27.5K using the resistance method between the 15K resistor and terminals 1 & 2 at the POT:
LCD Reading =
Indoor = 3819 using 10K resistor at the input terminals of the sensor
Outdoor = 3463 using 10K resistor at the input terminals of the sensor
CEO #2 and CEP #3 are consistent with the results returned from CEP #1, the one calibrated to Mistergreen's PAR meter, but slightly off from one another because the POT is pretty touchy, and it's hard to get that fine of an exact adjustment using a screw driver.
I did not change the POT adjustments of CEP 2 & 3 because they appeared to mimmick the adjustment I made via the top resistor pad and the POT terminals previously made, versus the 10K resistor method, so I left them alone, right where they were.
I don't know why the values I obtained versus the values obtained by Mistergreen on his CEP using the 10K resistor at the sensor terminals are so far off from one another.
Could it have anything to do with my 15K resistor value being measured at 11.94K versus 15K? If so, then perhaps a reading of the 15K resistor would be in order before calibrating using the 10K resistor method, and some kind of conversion factor could be applied to acheive actual calibration based on the actual 15K resistor value of any random CEP.
|06-07-2015 02:49 AM|
I'll try this as soon as I can. Because I live in a rural area, it may take a few days to come up with a 10K resistor. They just closed our Radio Shack for good. I'll check my stash to see if I have one, but if not, then I'll have to order one from Mouser. So, it may be a few days before I can get back to you guys. But, if it works, it's a wonderful stroke of genious!
Now, one question, regarding my calibrated CEP, the PCB is permanently stuck to the back wall of a plastic cabinet via double stick tape, and can not be removed, it's like concrete. The photo diode is connected to the PCB via a power jack/plug via wire extensions between the jack and the input for the sensor at the PCB. See the white wire on the left? The sensor connects to the PCB through the jack. Power, is the Red/Black wire on the right, connected to power on the PCB through a power plug/jack.
Can I just unplug the sensor, unplug power, and put the 10K resistor across the center pin and ground at the sensor's jack terminals, and be good to go, or will having the jack in the mix throw things off with respect to the jack and wire extenstions to the PCB adding resistance? And, if accessing the sensor terminals through the jack is a problem, technically speaking, then it just makes it a little more difficult to access the sensor terminals inside the cabinet to make the connections, due to the confined space inside the cabinet, and because the CEP can't be removed. It can be done, no problem, but it would make it easier and quicker to connect at the jack if it won't throw everything off.
What are the anticipated electrical varitions (ie:tolerances) between the photo diodes with respect to photo diode specs? Anybody know the percentages?
Originally Posted by O2surplus View Post
|06-07-2015 12:49 AM|
Originally Posted by rottison View Post
|06-07-2015 12:22 AM|
|rottison||so if quizcat gets that can I plug that into mine and call it calibrated|
|06-06-2015 07:04 PM|
Originally Posted by mistergreen View Post
LOL- I knew there had to be a dirt simple solution......Just had to stare at the circuit for awhile to see it.
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