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Using Apogee PAR Sensor and mVMeter

14K views 101 replies 10 participants last post by  jeffkrol 
#1 ·
Has anyone tried to use a cheap digital mV meter and an Apogee SQ222, self powered sensor, to make a semi-DIY PAR meter? I received one of those sensors as a gift, and bought a cheap 200 mV digital meter to use as a readout. So far I haven't been able to make it work. I get a reading around 160 no matter if the sensor is illuminated or blacked out.

Using this version of the sensor requires supplying DC voltage to the sensor, and it gives a 1 mV per PAR unit readout (if it works). The sensor uses a common ground as the negative lead for both the supplied DC voltage and the DC mV output. The mV meter has 4 wires - two for the supplied voltage and two for the output voltage. I wired it with the common ground connected to both negative leads. Does that seem like the right way? I'm using a 9V battery for power, with the negative lead as the common ground.
 
#3 · (Edited)
I'm look at the spec and it has 3 wires.

Green: Positive (signal from sensor)
White: Input power
Clear: Ground (for sensor signal and input power)

So you need to create a circuit for the signal to be read I assume.

White go to positive of the 9V, clear to negative of 9V. Positive lead of meter to green and ground lead of meter to negative of 9V.


I have the SQ-120 I use with a volt meter.
 
#4 ·
Yes, that's how it is hooked up, but the meter has 4 leads, red for battery +, black for battery -, green for signal +, and blue for signal -. I have the blue and black connected to the sensor ground (transparent), and the green to the sensor green.

I used my multimeter to try to measure the voltage across the green and blue wires, and got zero voltage. The 200 mV meter is: https://www.amazon.com/gp/product/B008M0CIHS/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
 
#7 · (Edited)
AFAICT the output signal of the Apogee is 0-2.5V..
your box is 0- 200mV...
you can't measure (peg the circuit ) at more than 200PAR
1mV = 1PAR
https://www.google.com/url?sa=t&rct...xDPiDw5sg&sig2=TMobrLqbLcRn9ysx_HrV-g&cad=rja
All you need is a standard VOM w/ one probe on neg.. the other on signal..
At least that is how I see it..
OR a simple voltmeter gauge

Point of the powered sensor is the low level signal is amplified..

better...
https://www.amazon.com/bayite-wires...100729&sr=1-2&keywords=digital+voltmeter+0-30

Wiring:
Red wire: Power supply +
Black wire:power supply -, Measured Voltage -
White wire: Measured Voltage +


Link for meter PDF:
https://www.google.com/url?sa=t&rct...4pYFo12Hg&sig2=DrqC-85ZCgRQkuSDQCsiMA&cad=rja

red/black power to the meter
green/blue what you want to measure..

My guess is you would need 2 power supplies..
 
#11 · (Edited)
Different sensor...not amplified.. passive..well depending.. and who knows how the meter internal wiring works..

Bump:
Why wouldn't a single battery work? I have the diode in parallel with the meter power leads. That should be exactly the same as two separate batteries. The "ground" is not connected to any real ground, so it is just a common negative terminal. I realize I'm missing something, but what?

I haven't tried the simple diode yet, but may get to it tonight.
From the spec sheet of the 4 wire device..
No no power supply needed for a diode.. it is self powered..so technically you have 2 power supplies..

If you stick the photodiode on blue/green and 9v on red/black it will work..or should if the signal is strong enough
As to your other sensor.. Different animal.. built in circuitry (amp) which needs power..
You meter looks to be "isolated" so to speak and again NOT enough range for over 200PAR..

Happy to be proven wrong.. but don't see it..

Depends on the sensor..


FIND what is wrong w/ the above vs the below:




(tired..;))
 
#12 ·
I hooked up a simple photodiode to the meter, and it worked fine. So, the problem is in how I'm using the powered sensor, but as far as I can understand, I am using it as it is designed to be used. Tomorrow I think I will disassemble all of my connections and do them again from scratch. I'm tired too!
 
#15 · (Edited)
It is a very simple circuit, so breadboard isn't needed. Here is the circuit:



And, I think I found my wiring mistake! As I recall, I had the two green wires connected. That wouldn't work at all. So, I will follow my plan and take it apart and rewire it.

It is back together again, and I'm 99% sure the connections are correct, but it now indicates -0.8 PAR at all times, no matter how much light it is sensing. Perhaps a solder joint isn't good, but I will wait awhile before checking it again.

 
#16 ·
Oh! I just thought of something. If it's still not working for you, you might need a drop down or up resistor on your signal lead.

I have a thermo sensor that needs a drop down on the signal. Without it, it'll be full voltage/signal all the time. Try a 5-10K resistor. Pull out the breadboard :)
 
#19 ·
Hoppy's meter will read a max of 200 PAR since that's the limit. 2.5V is basically 2500 PAR. 2000 PAR is mid day summer sun. He's not measuring the sun.

I just saw the pictures, try a pull down resistor.
Why limit the sensor so...........Current LED's can exceed 200PAR at almost any depth..


seems ridiculous since you could have a much larger range w/ "apparently" much less hassle hooking an analog voltmeter to it..

and these "module" apparently has 3 ranges possible

0-200mV , 0-20V and 0-200V

At 200PAR it is really easy to "peg" the meter..
 
#21 · (Edited)
The sensor does not have anything on it to allow you to change the calibration, so it is factory adjusted to yield 1 mV per PAR unit. I am a planted tank hobbyist. I will never in my remaining lifetime use more than 100 PAR lighting, so I have zero interest in any readings above 200 PAR. The 200 mV digital volt meter also has nothing that is user adjustable, without also destroying the factory set calibration. My goal is a 0-200 micromoles per square meter per second PAR meter.

Nothing in either Apogee's information sheet, or the Chinese manufacturer of the voltmeter's information sheet says a word about using a resistor in the signal lead. Wouldn't that change the calibration in an unknown way?

When I looked at all of my soldered connections all I found was a very poorly soldered connection to the switch on one terminal. I fixed that, but of course it had no effect at all. I think the sensor may be damaged. The voltage reading doesn't change between moderate shade outdoors and complete blackout. When I tried this with a multimeter measuring the sensor output it did show sensitivity to changes in light, which suggests that the voltmeter is where the problem is.

I got the sensor from a fellow member here, who preferred not to be named, because he had bought it a few years ago, hoping to do what I'm trying to do, but never got around to it, and, like me, realized that there is a time when you have to accept that some of your plans just aren't going to happen. So, he offered it to me. But, during the time it was sitting around waiting to be used it is possible that something damaged it. I have no way to test it in any definitive way so I may have to just accept that my project, which looks absolutely great, may never actually be usable. Only if someone can find an alternative way to connect it to the voltmeter that is theoretically sound will I have any chance to make it work. I'm not even close to being an expert on this.
 
#22 ·
Hey,
try getting a reading from the sensor leads without powering it. You should get some voltage from light just like your generic photodiode. If you're not getting anything then it's possible broken. You can send it to me to play with if you have a feeling it's not broken.

I don't think a drop down interferes with the signal. The drop down/up could be in the apogee meter. I don't think they would tell you. I would try it anyway just to see if you get ANY signal. The only thing for sure are the self powered ones like SQ-110,120 etc...
 
#23 · (Edited)
I have no way to test it in any definitive way
Huh? A 9v battery Upon (further review, see below, VOM and a light source will test it..
I have no way to test it in any definitive way so I may have to just accept that my project, which looks absolutely great, may never actually be usable.
Unless someone put more than 24V though it it should be fine.
Send it to me.. I'll pay shipping..



you guys are making this way too complicated.. It is apparently a passive sensor w/ a built in amplifier..
See highlighted above..

These sensors have been designed to have all the circuitry inside the head, the same as our non-amplified sensors. This means they are rugged and there is no worry about water damage to the circuit board. The circuitry is a basic non-inverting configuration of an operational amplifier (op-amp). The op-amp has been specifically chosen to have a low voltage offset and be physically small enough to fit inside of our current sensor body head. The op-amp has a max voltage specified at 5 V which is why the maximum output of our amplified sensors is 5 V. Included in the circuitry is a Zener diode that will short to ground if a voltage higher than 6 V is applied. This keeps the main circuitry from getting destroyed if the sensor is wired incorrectly
http://www.apogeeinstruments.com/amplified-sensors-explained/

More "anomolies"..

One sheet says ps 5-24V this says 5 go figure..
Use a phone charger as a power supply..
 
#24 ·
The Apogee PAR meters, like the ones we are familiar with, don't use a sensor that is adjusted to give 1 mV per PAR unit. The electronics that drive the digital readout module are in the readout module, not the sensor. This sensor, which I didn't realize even existed, is designed to be used with any mV meter and the meter reading will be the PAR value. It is designed to operate with any DC supply between 5 and 24 VDC. It gives a readout of 0 to 2500 mV (0 to 2500 PAR). On the surface it is perfect for DIYers like me, or at least DIYers who have more knowledge of digital circuits than I have.

My gut feeling is that I have made a simple mistake that people with more experience wouldn't even know they were avoiding.

If this ends up just frustrating me I will probably do a RAOK in that forum, or, sell it for the $20 it would cost to pay my parts cost and the shipping cost. Hobbies are supposed to be fun, not sources of frustration!
 
#25 · (Edited)
there are dozens of digital voltmeters. Some w 3 wires. Why did youpick that one.
btw there is an amp buyable that would allow the new
apogee to work w/ any digital vom.
https://blueacro.com/?gclid=CKfxk5n6u9ECFQiMaQoddncB6w
the much better sensor to go with it is only $100 more and $30 for the amp just add vom.
also calibrated.

 
#28 · (Edited)
#33 ·
It looks like the MQ510 comes with a meter and MQ500 doesn't.
I personally wouldn't buy one. GO the cheaper SQ 120 or MQ210. Sure it might be a bit less accurate but why spend all that money for something you'll use a few times. It might be worth it for a club where members can share.
 
#36 ·
MQ-510 (meter plus sensor) is actually listed under "aquarium use" (PAR METER, aquarium) and is the same price as the MQ-500.


Sensors only are SQ-XXX Probably would pick the 520...USB attachment to computer..
 
#39 ·
Yes, I noticed that, and I assumed that that pdf was published before the SQ222 model was available, then was not updated to include the 222 version. Lots of assumptions!

I may use a voltage divider to get a 5 volt supply from the 9 volt battery, just to see what the effect is. But, I would need to go buy a couple of resistors, and they are sold in packages of 10 each (?), so that does discourage me.
 
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