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Old 09-21-2012, 08:58 AM   #121
drhemlock2
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seems like this is not going to leave you alone until you get it the way it should be this is good news. i am at the stage now where i am designing my lighting using your info as well as others. so many choices . i have found the lux meter on the ebay and hope to get after it later on once i figure out the type of photo diode you end up using as well as the filters along with it.
thanks for your work.
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Old 09-21-2012, 05:21 PM   #122
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This morning I rechecked the reading vs a Quantum PAR meter. It read 21 with the PAR meter reading 24-25. Close enough for my purpose. I will recheck it again in a few days to verify that the reading is stable.

I also made another try at selecting filters the give a more even spectral response. It came out worse than what I used. The difficulties are finding a filter to knock off the near infrared and near UV, without distorting the rest of the spectrum too much. Then finding another combination to even out the response, without getting too many peaks, and still another combination to drop the sensitivity sufficiently without really exaggerating the peaks. I keep thinking it can be done better, but I'm out of ideas now. My "obsession" has about run its course now.
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Old 09-21-2012, 09:20 PM   #123
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Quote:
Originally Posted by sowNreap View Post
Your way over my capabilities now! LOL

But I do wish I had a waterproof one. I moved and altered my lighting setup a bit and now need to know what it's reading in the tank itself.

If you decide you want to make a couple let us know. I'd like to buy one. I think I could do the adapter part to be able to switch between this sensor and lux sensor. But like I said this mod is beyond my ability.
It is really an easy mod, especially if you have good vision and steady hands, both of which I am a bit short of. The only tools I used were a hacksaw to cut the acrylic tubing, a utility knife to score the flat acrylic for breaking off a strip, a soldering iron to connect the wires to the diode, an electric drill (cordless) to drill for the electric cable in the piece of tubing, scissors to cut circles of filters, a pair of wire strippers for the electric cable wires a sheet of fine sand paper, to flatten and square the ends of the tubing, toothpicks to manipulate the filters and diode, and some masking tape to act as a third hand at times.

You can PM Ductapemaster to urge him to make some, too.
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Old 09-21-2012, 09:54 PM   #124
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Appreciate all your hard work on this, Hoppy.

I've got all the tools, just not the skill to use them very good. I had a hard enough time just trying to solder a headphone cable to a new jack today. But I might see what I can do when I get some spare time.

Otherwise I'll check with Ductapemaster (I'm really good at using duct tape to mod things ) to see what we can work out.
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Old 09-22-2012, 04:42 AM   #125
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Quote:
Originally Posted by sowNreap View Post
Appreciate all your hard work on this, Hoppy.

I've got all the tools, just not the skill to use them very good. I had a hard enough time just trying to solder a headphone cable to a new jack today. But I might see what I can do when I get some spare time.

Otherwise I'll check with Ductapemaster (I'm really good at using duct tape to mod things ) to see what we can work out.
Remember our difficulties measuring PAR for CFL bulbs? I think the problem may be related to the need for those lux meters to be turned on with the sensor covered. That lets the electronics set an accurate zero for the readout. I was shocked when I first turned on my meter with the new waterproof probe, and it read around 1300 instead of 25! I noticed that the reading kept rising and falling too. Then I remembered that these are supposed to be self adjusting on the zero point, so I turned it off, laid the original sensor black-out cap over the sensor. Then turned it on again. When I removed the cap, it read 21, and the reading was steady. I'm not sure this fouled up your lux meter readings before, but it might have.
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Old 09-22-2012, 05:32 AM   #126
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It's possible that's what happened. I think I usually took the cover off first then turned it on. Later I uncovered and turned on and then made final height adjustments to give a bit of time for the sensor to stabilize. Finally on the last few tests using the aquarium hood, I just left in on and uncovered because it didn't take that long to get the height adjustment right.

Good to know though. In the future I'll make sure to turn on, then uncover.

If I get time I may test those spiral CFL's again. Just to see if I can get more consistent readings.
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Old 09-22-2012, 07:04 PM   #127
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OK, the way we learn is from our mistakes! Today I tried my new waterproof sensor in the noon sun. It doesn't work well. The acrylic half sphere on the end is much too sensitive to the angle to the light. I could rock the sensor back and forth towards the sun and a little off from towards the sun, and it made a big difference in the reading, ranging from about 450 to 1500 with only maybe 20-30 degrees of movement. That makes it unusable if any accuracy is needed.

If I had listened to mistergreen I wouldn't have used the half sphere, but used just a flat disc as the measuring end of the sensor. One other bad effect of the half sphere is the magnification it gives, which just adds to the difficulty in reducing the reading by a factor of 60 to get it to read PAR instead of lux. I now think that it would work best to get a white acrylic 1/8" thick end for the sensor. But, I don't really need a waterproof sensor, so I may just let this go. (But, I may also get the PAR fever again and try one more time later!)

EDIT: Well the fever came back in about 3 hours! I realized I might be able to hacksaw off the top of the sensor, and reuse the rest of it with a flat top. So, I successfully removed the top, found the guts all in good shape, and then searched again for a better arrangement of filters. I now have it back together with new filters, a flat acrylic top, painted white with nail polish on the inside and lightly sanded to eliminate most reflection from the top.

When I did the final assembly and glued the top on, I accidentally left one filter out, so it reads high now, 35 instead of 25. I think I can glue another flat top on it, with another filter sandwitched between them to get back to the right reading. That will be tomorrow's project.
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Last edited by Hoppy; 09-23-2012 at 02:56 AM.. Reason: Added more info
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Old 09-23-2012, 06:28 PM   #128
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I cut another disc of 1/8 acrylic, lightly sanded one face to stop reflections, sandwitched a couple of filters between that and the existing top of the sensor, glueing it in place around the outer edge with Weldon #16. Now it reads 21 instead of 25, and the non-waterproof sensor reads 27. Both are close enough. When the sun comes out I will try a full sun reading again.
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Old 09-23-2012, 09:55 PM   #129
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Default way to go hoppy

i knew it would not keep ya down keep plugging away and let us know what you find this seems like a weekend project to me....
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Old 09-23-2012, 10:50 PM   #130
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I think it is well worth the effort to convert the original sensor to read in PAR, and it is about as easy as it could be to do it. Once we know what the optimum set of filter squares is, to use the minimum number and have the best response curve, it is about a one hour job, at most. (I may make a few more calculations to try to find the best set of filters.)

Making a waterproof sensor is probably not worth the effort, and, while the last design I used was fairly easy to assemble, any mistake is very hard to correct, since it is all glued together. But, it does work. If you decide to do a waterproof sensor you almost have to use a disconnect fitting so you can use the original sensor to calibrate the new sensor. So, I think that is worth the effort too.
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Old 09-25-2012, 05:41 PM   #131
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This is my last try - I mean it this time!

Yesterday I tried a different technique for selecting filters to get the PAR correction on the Mastech sensor. I tried to visualize the appearance of the sensitivity plot needed to make the change to the sensor sensitivity I wanted. Then I searched until I found one that looked like it should, and calculated the sensitivity with that filter in place. Then I just repeated this process until I was near the amount of attenuation of the output that I needed, and assembled the sensor with those filters to see how close I was. That let me calculate the % transmission I needed in one last filter. After several tries I got the spectral sensitivity near what I wanted, and the readout very near what I wanted. I ended up using 6 filters - Roscolux #17, 36, 55, 363, 4430, and 3304.

Two more discoveries: Most important, the conversion from lux to PAR for this meter isn't dividing lux by 61, as I have been saying, but it is dividing lux by 76 - big mistake on my part. This is the reason the data we got for CFL bulbs was so far off from the older data. Then I find that the Mastech sensor electronics are easily confused. Every time I open the sensor case and replace it, the readout goes crazy for a few minutes, before settling down to read correctly. This is probably because of the cheap way it is made.

The sensitivity chart for this final sensor looks like:


When I check this against the Quantum PAR meter I get 32 PAR with the Mastech meter and 29 with the Quantum meter. In the sunlight, the Mastech meter reads appropriately. (I wasn't looking for exact readings for that much light)

I found the easiest way to add these filters to the Mastech sensor is to just lay the stack of .5 inch square filters on top of the circular housing for the diode, and use a couple of strips of Scotch tape across opposite corners to hold them in place. That part is extremely easy. If a correction is needed it is easy to remove the stack and substitute for one of the .5 inch squares.

When you stack filters it tends to result in exaggerated peaks and valleys in the response curve. First, the sensitivity is cut by a factor of 76, and the filters that are appropriate tend to have peaks and valleys in roughly the same places, which quickly amplifies the magnitude of those peaks and valleys. One would think that neutral gray filters wouldn't have those peaks and valleys, but they do, and the darker they are, the bigger the peaks and valleys. Filters that are the darkest also tend to totally block certain parts of the spectra, which isn't good at all, so multiple different filters are necessary.
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Old 10-06-2012, 01:35 AM   #132
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I'm sure no one will be surprised that I am still working on this. I'm still not satisfied, and it is a very challenging problem.

This week I made a couple of "breakthroughs". First, the Mastech LX1010B luxmeter I have has a very easy to modify sensor, because the photodiode is enclosed in a cylinder of plastic almost exactly 1.25 inches in diameter, so it will fit well inside a 1.5 inch diameter acrylic tube. Also, the assembly is very easy to take apart and put back together. Plus, the cosine filter "dome" is just a bit bigger than 1.5 inches in diameter, and isn't permanently attached to the housing - it pops out. So, the photodiode and cosine filter are easy to fit into a short piece of 1.5 inch acrylic tube, which is easy to buy in one foot lengths on Ebay.

Next, after a week of trying to find a combination of Roscolux filters that will convert the lux readings to PAR readings it finally occurred to me that I don't need to do that. I can just convert it to read 10XPAR instead, which takes far fewer filters, making it much easier to find a set that do exactly what I want. And, when a sensor good for reading 20,000 in its indicator is going to be marginal for accurately reading 20 on that indicator. By shooting for 10XPAR, it will be reading 200, or 10% of the lowest scale, and by putting the scale selector on the 20,000 range, it reads PAR with no conversion needed.

Today I found a workable method for selecting the filters, and got it down to only 4 filters. Those make it read exactly the same as the Quantum PAR meter, and the spectral response is also good:


By requiring only 4 different filters, the Rosco sample book goes a lot farther for modifying these. I can get at least 4 sets of filters from one book, or buy just 4 sheets of filters, and have enough for 100+ PAR meters.

By the middle of next week I will have my 1.5 inch tubing, and be ready to work out the last details for converting it to a true, waterproof PAR meter. One absolute rule for this is to do nothing to interfere with the optical path in the sensor, besides adding the filters.

I have also finally figured out that my connectors that allow me to switch sensors aren't a workable idea. When working with such low voltages and currents, the contact resistance in the connectors is too big a problem and a variable one at that. Also, there is no reason to use more than one sensor, if I do this well.

My biggest problem will be finding another equally interesting project when I finish this.
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Old 10-06-2012, 06:38 AM   #133
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Default hello my friend

still at it i see let me know what i need to do with the sensor and what link did you use for the acrylic tube i need some also. are you going to use the cosine filter "dome" on the tube? let me know.
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Old 10-07-2012, 02:42 AM   #134
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This is a sketch of what I plan to do. Notice that the optical path will be the same as the original sensor.

For the acrylic tube, go to Ebay and search for acrylic tube. You will find numerous listings, all using the same illustration of a bunch of clear plastic tubes. Click that sellers "store" and you will find a listing for 1.5 inch tube. It would be cheaper at Tap Plastic, but they won't sell less than a 6 foot length, and that costs more than one foot plus shipping on Ebay. I get my sheet acrylic from Home Depot. It is cheaper at Tap Plastics, but I have to drive 20 miles, and that costs gas! HD is very close to me.
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Old 10-07-2012, 06:44 PM   #135
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I have now checked, double checked, and triple checked my dimensions and I'm convinced this will work. I also visited Harbor Freight and bought a Dremel type rotary tool, not the toy one, but the $20 one. Ready to start!!
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