Hi All,

I am trying to measure particle in water using IR LED and photodiode ( reflective), the circuit I use limited the current by resistor 39 ohm and 5 volt so its around 100 mA that drive the LED,

I need your recommendation of what type of LED, Photodiode and lens I can use. the market is full of LEDs and I am lost, I need a proper LED (960 nm) I guess and photodiode and lens to test my circuit.

Thank you very much and I am looking forward to hear from you.
Maj

 

Make sure the optical wavelength of the sensor matches that of the source. Lasers would give more optical power.
You may want to try various optical wavelengths besides infra-red. You would need quartz glass since ordinary glass is not transparent to IR.
You also want to examine optical polarization, i.e. the effects of horizontal and vertical polarization.

 

Make sure the optical wavelength of the sensor matches that of the source. Lasers would give more optical power.
You may want to try various optical wavelengths besides infra-red. You would need quartz glass since ordinary glass is not transparent to IR.
You also want to examine optical polarization, i.e. the effects of horizontal and vertical polarization.

Thank you very much, any recommended sources that I can buy from them lenses and leds?
I am going to try different wavelength , and I don't understand what do you mean y optical polarization ?

 

Thank you very much, any recommended sources that I can buy from them lenses and leds?
I am going to try different wavelength , and I don't understand what do you mean y optical polarization ?

The amount of back scattering depends on whether the original source light is vertically polarized or horizontally polarized.
What are you trying to determine?

 

The amount of back scattering depends on whether the original source light is vertically polarized or horizontally polarized.
What are you trying to determine?

I would like to measure turbidity/ concentration of water, as the particle increase as I get more light back.

I am going to install this in pipe line ( dark).

the original source you mean the IR LED? if so I am looking for integrated IR LED with Photodiode.

hope that's clear and excuse my knowledge as I am new in this field.

Many Thanks
Maj

 

Correction on what I wrote before.

You're in luck. This is research I did as an undergrad for a final year project in Engineering Physics. The light source used was a 1mW He-Ne laser (wavelenght of 632.8nm). The back scattering was split into horizontal and vertical polarized components. The two components were detected using two Siliconix P238 photo-FET (400-1000nm, peaking at 850nm), amplified and filtered.
The ratio of horizontal to vertical components, H/V was calculated and plotted against log(mass concentration) for different particle sizes. This was found to be the least dependent on particle size compared with all other measurements.

The He-Ne laser beam was physically chopped at 225Hz using a motorized fan blade to avoid DC drifts.
If I were to do this today, I would use a solid-state laser diode and modulate the signal. You want your modulation frequency to be well away from AC line frequency and its harmonics.

 

Correction on what I wrote before.

You're in luck. This is research I did as an undergrad for a final year project in Engineering Physics. The light source used was a 1mW He-Ne laser (wavelenght of 632.8nm). The back scattering was split into horizontal and vertical polarized components. The two components were detected using two Siliconix P238 photo-FET (400-1000nm, peaking at 850nm), amplified and filtered.
The ratio of horizontal to vertical components, H/V was calculated and plotted against log(mass concentration) for different particle sizes. This was found to be the least dependent on particle size compared with all other measurements.

The He-Ne laser beam was physically chopped at 225Hz using a motorized fan blade to avoid DC drifts.
If I were to do this today, I would use a solid-state laser diode and modulate the signal. You want your modulation frequency to be well away from AC line frequency and its harmonics.

Thank you very much for this valuable information,
as i understand you use laser (visible light)? if so is it possible to measure up to 6% suspended solid ? i think its too dens.

also i don't understand the AC part,

please see the attached pictures, its the same what i am looking for, i tried this sensor but it doesn't work, its 12 volt supply and i still receive 5 volt from signal wire but its doesn't change when i put an objective in front of the lens or if i put it in water still no signal change so i am thinking is it IR LED fault? also could you provide me where i can find IR led, detector and lens like in the pictures, something with similar specification as its built in and i ca not find anymore information ?

thank you very much and i am really looking forward to hear from you.

much appreciate it

 

the circuit I use limited the current by resistor 39 ohm and 5 volt so its around 100 mA that drive the LED,

Please correct me if I'm wrong, but the TS calculations look wonky to me.

He stated that the supply voltage was 5v and the resistor was 39Ω. To calculate the current we need Vf of his LED.
Vf was not given, but with the specs provided, it can be calculated.

(5-Vf)=.1A*39Ω
(5-Vf)=3.9V
5V/3.9 - Vf/3.9=1V
1.28V - 1V = Vf / 3.9
0.28V = Vf/3.9V
3.9V * 0.28V = Vf
Vf = 1.09V

Vf looks a little low. But if it works ...

 

so do you mean the circuit has problem ?

 

Ummm, yes. I would like to know where you decided the current in the LED was 100mA?

Also, where did you decide you needed 39Ω!

What's "wonky" is those component valued results in, IMHO, a Vf that I had difficulty finding online.

I'm not sure, because you refer to a 5V supply. Oh wait, later you say a 12V supply. Which is it?

 

Ummm, yes. I would like to know where you decided the current in the LED was 100mA?

Also, where did you decide you needed 39Ω!

What's "wonky" is those component valued results in, IMHO, a Vf that I had difficulty finding online.

I'm not sure, because you refer to a 5V supply. Oh wait, later you say a 12V supply. Which is it?

Hi,
I didn't decise its 100mA, I have the board and its has 39 ohm and the voltage is pass through is 5 volt so from I=V/R its around 120 mA,
the power supply for the whole circuit is 12 volt.

thank you and hope this is more clear

 

Hi,
I am looking for an LED with around 950nm and driving current approximately 120mA, detector for this LED and lens , I want to use this in water utilities, your advise please as I really confused and too much in the market.

is there an integrated IR LED with multi-detector and lens ? if so from where I can purchase them.

Thank you very much

 

Hi,
I am looking for an LED with around 950nm and driving current approximately 120mA, detector for this LED and lens , I want to use this in water utilities, your advise please as I really confused and too much in the market.

is there an integrated IR LED with multi-detector and lens ? if so from where I can purchase them.

Thank you very much

Check Farnell and search for infrared LED.
Most are at 850nm.

Here are examples at 940nm.
http://uk.farnell.com/sharp/gl100mn1mp1/ir-emitter-smd-940nm/dp/9707824

http://uk.farnell.com/vishay/vslb3940/ir-emitting-diode-940nm-t-1-thd/dp/2504156

 

Some at 950nm

http://uk.farnell.com/search?st=infrared emitter 950nm

 

Cheap plastic lenses available from WWW.ANCHOROPTICS.COM, I used some for near IR. For anything optical try WWW.EDMUNDOPTICS.COM .
Reps world wide. What country are you I?

 

Why use IR for suspended solids? Most turbidometers use visible light I think, and measure both transmitance on axis as well as scattered light 90 degrees off axis. Reflectance isn’t really the same thing although I suppose it might be useful.