For the PAR inclined . Apogee upgraded sensor

[theatrus]

Ordered a stack of PCBs from China - I'll report back once I've tested it in a few weeks likely.

As for the sensor, I probably will find some time to play with light sources and it this weekend. I have LEDs, an old 250W SE MH setup with an old Hamilton 14k and XM10k bulbs, and T5 actinics + blue+. I can do some spot comparisons to my existing SQ-120.

[dread240]

I'd definitely like to pickup one of your boards if you have the spares. I was a day or two away from buying the USB 200 version until I saw this thread.

[theatrus]

Initial testing of the SQ-500 vs the SQ-120, as read by a Fluke 87V in high res mode:

The sensor, on its side with the protective cap installed:




For these tests, I zipped tied the two sensors together and kept their positioning fixed.

First tes, a 14k 250MH electric ballast used Hamilton 14k MH bulb in an average reflector:



SQ-120 PAR: 146.7
SQ-500 PAR: 145

Very close

Next up is a 100W Royal Blue multichip on my bench, there due to other testing:





These results are... very different.

SQ-120: 860 PAR
SQ-500: 670 PAR

Yes, backwards from what I expect...

I did a few other tests, on my LEDBrick units installed. This is a violet + RB + blue + cyan + coolwhite + (very limited PC amber, green, red).

SQ-120 PAR: 960 (at the water line, its very diffuse and a nice 250 midway)
SQ-500 PAR: 820

Again, different direction than I would expect.

Its dark outside so I can't baseline it against the sky.

If the SQ-500 was consistently low I'd expect something, but the MH result being a good match doesn't imply its direct measurement error. Ambient light in all cases was off or minimized.

[dread240]

Yea I would have absolutely expected heavy blue fixtures to increase in par, not decrease.

I'm interested in how they compare against sunlight.

I did a few more reads though and the li-cor (which most people say is the gold standard for par metering) almost always read lower then the apogee when tested with LED's, so I'm curious if we're finding out that they're not as powerful as we thought they were?

I'm looking forward to getting a hold of one of these and using our clubs older meter now since all my led channels will be seperate. I can see the difference in measurement per channel

[oreo57]

Stupid tablets...

[oreo57]

MH w their complex spectrum could create offsetting errors. Calibrate w a green LED. Both should measure the same. If the 500 is Sig off that might give you a clue.
To be honest, I wouldn't really expect them to output equal uA. Different filter pack in the 500 would most likely create a "darker" sensor. Not to mention a different photodiode.
In other words you need a different conversion factor.
Theoretically the 500 will be low here as well. Correct the "blue centric" by the ratio.
As a side note, Apogee States they need to correct the software in the meter body. May just be a change in a scaler.

[theatrus]

Conversion factor is different. From a voltage output standpoint, the mV to PAR multiplier of the SQ-500 is 100x, while the SQ-120 is 5x.

[theatrus]

Originally Posted by dread240

Yea I would have absolutely expected heavy blue fixtures to increase in par, not decrease.

I'm interested in how they compare against sunlight.

I did a few more reads though and the li-cor (which most people say is the gold standard for par metering) almost always read lower then the apogee when tested with LED's, so I'm curious if we're finding out that they're not as powerful as we thought they were?

I'm looking forward to getting a hold of one of these and using our clubs older meter now since all my led channels will be seperate. I can see the difference in measurement per channel

Possible! I'm all for more accuracy

Still waiting for the amplifier boards and parts to land. If your multimeter has a 10uV range you can just use that

[oreo57]

Originally Posted by theatrus

Conversion factor is different. From a voltage output standpoint, the mV to PAR multiplier of the SQ-500 is 100x, while the SQ-120 is 5x.

I understand that.

0.01 mV per μmol m-2 s-

Humor me.. Test the green diode..
Specs and reality can be 2 different things.. That is why one has "calibration"..
490-500nm diode would be best..
how many diodes have the exact same response??
It is "off" for a reason, just need to find it...Even assuming your Apogee is correct is a leap of faith..

Reference:
http://www.advancedaquarist.com/2005/7/review/view
http://www.apogeeinstruments.com/con...April-2009.pdf
http://www.apogeeinstruments.com/con...ember-2012.pdf

Spectral errors were typically smaller for common electric lights relative to LEDs, where
spectral errors for all quantum sensors were less than 4 % for common electric lights and
less than 11 % for LEDs.
• Spectral errors were typically smaller for mixed and broadband (white) LEDs relative to
single color LEDs, where spectral errors for all quantum sensors were less than 4 % for
mixed LEDs.
• Quantum sensors can be a very practical means of measuring PPF from LEDs, but spectral
errors must be considered. Errors presented in the table above can be used as correction
factors for different electric light sources.

sorry, just lots of related stuff..

I DO see where you are coming from though..

Calibration Traceability
Apogee Instruments SQ-500 series quantum sensors are calibrated through side-by-side comparison to the mean of four
Apogee model SQ-500 transfer standard quantum sensors under high output T5 cool white fluorescent lamps. The transfer
standard quantum sensors are calibrated through side-by-side comparison to the mean of at least three LI-COR model
LI-190 reference quantum sensors under high output T5 cool white fluorescent lamps.

It should be simple.. BUT....

[dread240]

Originally Posted by theatrus

Possible! I'm all for more accuracy

Still waiting for the amplifier boards and parts to land. If your multimeter has a 10uV range you can just use that

It doesn't I have a fluke 1587 which has the nice 1000v insulation tests and all built in, but it misses out on some of the finer readings of like an 87v and it's accuracy isn't as tight in those applications...

Kind of a waste these days too as all I do is switchgear, so 24vdc controls basically

[K.C.]

I've always considered my Apogee meter a reference and haven't felt it needed to be completely accurate. Dana Riddle has said that allowing for an error of 5% with LEDs gave him enough information to judge.

The greater range of the new sensor seems inconsequential given the number of other factors that could affect it, IMO.

I'm happy to be corrected with factual research !

[007Bond]

[QUOTE=K.C.;24379838]I've always considered my Apogee meter a reference and haven't felt it needed to be completely accurate. Dana Riddle has said that allowing for an error of 5% with LEDs gave him enough information to judge.

Agree,...I have a 200,...I measure new bulbs when installed and at various times to determine their output. For my leds,...again just a reference,...if I upgraded to a 500 for me still a reference,...for my purposes its a "tool" I appreciate having

[theatrus]

If your goal is local delta measurements, then by all means the original works great.

PAR measurements were over 10% out under a real LED lighting system, which makes the older unit a poor standard for that application.

[007Bond]

Yeah for me just a reference point with a multiplier in the back of my mind and notes as to locations that various corals seem to like. For my purpose I would rather spend an additional 200 dollars needed to upgrade my existing unit on some new corals,...a lot of reefers have no reference at all,.... I think a par meter is a very useful tool to have especially when you are using led lighting.

[oreo57]

Bump as a reminder..

[theatrus]

Amp boards showed up despite DHL's best attempt to not deliver it

Don't have all the parts yet, probably by this weekend.

[dread240]

anxiously awaiting results

[theatrus]

Good news!

It works great, at least in initial testing. Well within specification for a 100x amp.

Here is the front (mounted on a Fluke 87V):



And mounted on the cheapest meter I have, some Mastech:



Backside:



I've only assembled one, but have parts for a some more. As part of a beta test with anyone interested, I'm happy to let some go at cost (which is low, but I haven't computed it yet) - feel free to PM me.

[RobbyG]

Really nice looking board, I am not sure but you seem to be using Altium designer like me. While I like your idea, I think your going to find that this is not as easy as you may have thought. your going to have a lot of problems working with op amps in the uV range and accuracy is going to be really hard to achieve. Good luck, I made a complete meter for my older apogee unit, that multiplied the voltage by 5 then I used a regular Chinese LCD voltmeter display that reads up to 2V max. When pointed at direct sunlight at noon I get about 1.980V or 1980 PAR which is close to the 2000 they suggest. My fluke 87V shows that the circuit works well, but it did require a bit of work even in the mV range to get it to have an even slope across the input range and I had to fiddle with the resistor values to get the gain exactly right and the offset. I suspect yours will be a lot harder to get just right. Good luck, it's nice to see some other EE's on the forum.

Rob

[theatrus]

Yup, Altium. Once locked in, forever maintenance fees.

I opted for some spendy (relatively) parts in order to keep the input offset voltage an order of magnitude below the meter resolution (1-2uV, chopper op-amp), and using precision resistors for the feedback (to avoid needing to calibrate each one)

I'm still stepping through the full range, but from my calibrated benchtop DMM the gain is tracking as expected (error < 1 PAR, or < 1mV after gain).

Op-amp:
https://www.maximintegrated.com/en/p...s/MAX9617.html

A virtual ground is used to minimize the classic "rail to rail isn't actually really rail to rail" problem of op-amps

[RobbyG]

Excellent work. You might want to make a second revision and just add in the display and case. Of course you will need to add a 9v battery to power the display but you could ditch the other battery and just build a small DC-DC converter to power the existing circuit, also it makes the unit become an independent meter like the original. They use to have some nice cases on eBay that have a 9v battery compartment and a cut out area for the display.

BTW if your not opposed to the idea, please post the schematic, it's good when stuff like this is archived for people who might want to build one.

Rob

[theatrus]

Nothing particularly magic in the schematic

[karimwassef]

looks like it needs to become an Arduino PAR shield! I'm not just saying that because it would enable DIY data acquisition, control, storage and wireless alerts...

[theatrus]

Originally Posted by karimwassef

looks like it needs to become an Arduino PAR shield! I'm not just saying that because it would enable DIY data acquisition, control, storage and wireless alerts...

Stacking shields and such always seemed like a PITA. Maybe an inline interface board?

[karimwassef]

Sure. Just need to get the data into a controller architecture to take action or raise flags.