Ultra Violet Radation Meter

[Olihou]

I have the interest to build a UVB meter for measuring the ultraviolet radiation intensity in the wavelength range from 280 to 320 nanometer. It will be used in my reptile house. The reptiles need UVB light for making vitamin D for bone health, but over doze will hurt them.

UV meters are available as laboratory instruments and are quite expensive (hundreds of dollars).

I think I can meet my target with a simple circuit. What I need is a UVB detector diode plus a high gain current amplifier. May be a budget of $50 will suffice?

Any advice please, on the detector diodes and circuits?

 

[akg]

startwith the datasheets of some photodiodes..

 

[Hero999]

RS sis do some UV photodiodes perhapps you should start there.

 

[Tarsil]

About the diode try this:**broken link removed**
https://www.scitec.uk.com/uvphotodiodes/
About the first link..it describes a UV photodiode with integrated amplifier which I've seen in a industrial made apliance.
U might manage to go under 50$ for the gadget. But u'l stil need to borow a industrial made one for comparing&adjusting readings.

 

[Tarsil]

I've also seen some more cheaper&available Osram photodiodes.

 

[Olihou]

Hi every body

At last I have been able to find locally a supply of UV sensor diodes OS100 from Orion Semiconductor: **broken link removed**

I have tried it out, giving a few mV output when shined with a small UV lamp used for checking bank notes.

Will look for suitable circuits to make a handy UVB Meter.

Again any advice please with regard to the circuits, the curent amplifiers....and how to calibrate it evetually ....... ?????

 

[jpanhalt]

One can classify methods to determine the amount of light into three categories: 1)Those that convert the light to heat and measure the temperature change (thermopiles); 2) Those that use a chemical reaction with a known quantum yield (i.e., molecules of product per photon of light)(actinometer); and 3) Comparison with a reference meter or reference source.

Since I don't know anything about the resources you have available, it is hard to advise. If there is a nearby medical university, you may check with the dermatology department to find out if they have a reference instrument you can use.

If you cannot find a reference instrument, then actinometry is considerably easier to use than constructing your own thermopile. The most popular actinometric system is based on the photochemical conversion of ferrioxalate to ferrous ion. You will need access to a spectrophotometer to measure the product yield.

Good luck. John

References:
1) Hatchard and Parker, Proc Roy Soc (London) A235, 518 (1956).
2) https://www.electro-tech-online.com/custompdfs/2006/10/E136uvpaper.pdf
3) The Iodide/Iodate Actinometer in UV Disinfection: Determination of the Fluence Rate Distribution in UV Reactors. Photochem Photobiol. 2006 Mar-Apr;82(2):611-5.

 

[Tarsil]

Hi every body

At last I have been able to find locally a supply of UV sensor diodes OS100 from Orion Semiconductor: **broken link removed**

I have tried it out, giving a few mV output when shined with a small UV lamp used for checking bank notes.

Will look for suitable circuits to make a handy UVB Meter.

Again any advice please with regard to the circuits, the curent amplifiers....and how to calibrate it evetually ....... ?????

U'l need a voltage amplifier and a opamp or a couple of transistors (I'd use a FET or MOS-FET cause of much higher imput impedance) will do. U'l need to amplify the voltage like 300X or so. The output of that amp goes to the analog imput of a uC (wich wil take care of the display to).
U'l need to compare the instrument to a industrial one.Just get some UV intensity (read on the ind meter) =f(V) ..voltage read at the autput of the amplifier. After that get de UVi=f(V) function (u can use a software designed for that) and let the uC do the math. U might get around 50$ if u use a LED display.
Keep me posted.

 

[Hero999]

I have tried it out, giving a few mV output when shined with a small UV lamp used for checking bank notes.

Probably because it's a UVA/Visible violet source, but UVB. If it's UVA you're after then most UV LEDs will work quite well as photodiodes.

 

[philba]

I'm not sure of this but you might be able to use the sun on a clear day. You should be able to compute the amount of UV based on latitude. maybe a local college's meteorology dept could help you out there.

 

[Olihou]

Thank you all for the wonderful suggestions.

I think I will use a high-input-impedance operational amplifier to amplify the tiny current from the UVB sensor diode (only 250 nA at 35 uW/cm2). TL081 is a possible choice but probably it will not work well at a supply voltage of 3 volt, which I intend to. I wonder if there is any better OP Amp for this purpose ?

For display I will just use a small microammeter or simply a DVM to start with.

As for calibration I will use a reference meter, if I can get one. The thermopile and the chemical methods are beyond my capability indeed.

"You should be able to compute the amount of UV based on latitude" --- that is very interesting, philba. Can you advise how this is calculated ? by a formula ?

 

[philba]

You should be able to compute the amount of UV based on latitude" --- that is very interesting, philba. Can you advise how this is calculated ? by a formula ?

sorry, I don't know the formulas. google might help. I just know that the angle of the sun (actually amount of air the sunlight passes through) will change the amount of UV. I've seen charts that show UV radiation at the surface by time of day.

 

[Tarsil]

sorry, I don't know the formulas. google might help. I just know that the angle of the sun (actually amount of air the sunlight passes through) will change the amount of UV. I've seen charts that show UV radiation at the surface by time of day.

Those charts are about average intensity (think!?)> The UV level is afected by how much smog, humidity, air temp etc. so that won't be much accurate.

 

[Tarsil]

BTW...Why only 3V..that low voltage only increases the dificulties. U could use a 9V bat or so because that meter uses only 20-30mA Max (with display) and isn't used continous....Isn't it?

 

[jpanhalt]

Actually, I was impressed by the suggestion of using a clear day as a standard from someone who lives in Seattle.

It seems to be an excellent idea. Since your artificial lights are probably less intense than sunlight, if you can devise a way to block a known portion of the light, you can obtain a two-point calibration curve to refine your measurements. Obviously, great precision is not required, but we have no idea how non-linear the response may be or whether the response is saturated in direct sunlight. I used to use "neutral density" filters, which can be made from particle suspensions or even solid materials with holes that represent a known percentage of the total area. I would suggest an optical density of 1.0 (i.e., something that blocks 90% of the light) for obtaining your second calibration point. If you have contacts in a meteorology dept as suggested by Philba, they may have filters you could borrow. John

 

[Tarsil]

Actually, I was impressed by the suggestion of using a clear day as a standard from someone who lives in Seattle.

It seems to be an excellent idea. Since your artificial lights are probably less intense than sunlight, if you can devise a way to block a known portion of the light, you can obtain a two-point calibration curve to refine your measurements. Obviously, great precision is not required, but we have no idea how non-linear the response may be or whether the response is saturated in direct sunlight. I used to use "neutral density" filters, which can be made from particle suspensions or even solid materials with holes that represent a known percentage of the total area. I would suggest an optical density of 1.0 (i.e., something that blocks 90% of the light) for obtaining your second calibration point. If you have contacts in a meteorology dept as suggested by Philba, they may have filters you could borrow. John

Those charts represent average values! U'l just have a calibration curve related to a sunny day with...a unknown UV intensity. 2 point calibration curve? ...beter hope that the sensor has a realy linear response and u don't manage to get 2 wrong points.

 

[philba]

Those charts are about average intensity (think!?)> The UV level is afected by how much smog, humidity, air temp etc. so that won't be much accurate.

yes, that's why I suggested a univ dept of meteorology - they usually model that stuff. a calibrated meter is the best choice, though.

 

[Olihou]

BTW...Why only 3V..that low voltage only increases the dificulties. U could use a 9V bat or so because that meter uses only 20-30mA Max (with display) and isn't used continous....Isn't it?

Well I am keen to make a handy meter that could be placed in my pocket, or any spot in the reptile house. I will use a 3V button battery like CR2032. Power consumption shohld be in the order of 1 to 2 mA, to drive a 100 uA microammeter, say.

Indeed I am making things difficult, but it is fun to make something that is useful but not just "me too".

So far I have not been able to get any suitable Op Amp local for 3 volt operation. I will try the TL081 first for a 9 volt design this week end. Just can't wait !

 

[audioguru]

The minimum operating voltage for an LM358 dual opamp or LM324 quad opamp is 3V. They are fairly low power.
An MC33171 single, MC33172 dual or MC33174 quad opamps also operate with a supply down to 3V and use less power.

The minimum recommended operating voltage for a TL081 is 7V.

 

[Tarsil]

It's a interesting ideea. About using a low voltage....Something like AD795, LMV 821 (2,4) can do the trick. Those aren't very expensive but if u don't gt them....