GUVA-S12SD sensor board calculations

Breakout boards, sensors, other Adafruit kits, etc.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
irvingwashington
 
Posts: 14
Joined: Thu Oct 03, 2013 2:33 pm

GUVA-S12SD sensor board calculations

Post by irvingwashington »

Howdy all-

First, thanks for posting the schematic for the board in another thread, very helpful! (http://forums.adafruit.com/viewtopic.ph ... va#p286893)

Next, I'm attempting to resolve some discrepancy between the datasheet and the board description in the calculation of UVI. Bear with me, hopefully I've just made a dumb mistake in my math...

I'm powering the board with 3.3V.

From the DS, 1e-6A ~= 9mW/cm2. Using our good old friend from grade school y=mx+b, the line for UVA power is ~ y = (1.1088e-7)x

It looks like from the UVI graph the line is y = (2.1e-8)x + 7.3e-8. This is using UVI 6 = 2.0e-7A and UVI 15 = 3.9e-7A, but this doesn't really jive with the DS Iph value above the graph of 2.6e-8A for UVI 1. Just eyeballing their graph, UVI 1 ~= 1.0e-7, so this makes no sense to me at all.

From the schematic, the opamp is set to a gain of 1e6, correct (R1)? So 1e-9A input would give an output of 0.001V, or 1V/uA gain.

If the gain is 1V/1uA then I'm not sure how the formula given for the breakout board makes sense: Vo = 4.3 * Diode-Current-in-uA

Do R2 and R3 effect the gain calculation, or are they signal filters?

Here are my calculations based on my line equation for the UVI, where the heck am I going wrong?

THANKS!
Z

Code: Select all

UVI	Photocurrent(A)	output voltage V @1V/uA
0	7.30E-008	0.073
1	9.40E-008	0.094
2	1.15E-007  0.115
3	1.36E-007	0.136
4	1.57E-007	0.157
5	1.78E-007	0.178
6	1.99E-007	0.199
7	2.20E-007	0.22
8	2.41E-007	0.241
9	2.62E-007	0.262
10	2.83E-007	0.283
11	3.04E-007	0.304
12	3.25E-007	0.325
13	3.46E-007	0.346
14	3.67E-007	0.367
15	3.88E-007	0.388

User avatar
adafruit2
 
Posts: 22148
Joined: Fri Mar 11, 2005 7:36 pm

Re: GUVA-S12SD sensor board calculations

Post by adafruit2 »

Not sure - we used an 'eval board' schematic and verified it against the weather report...it isnt a full-UV spectrum sensor so the calculation may be off due to hand-tweaking of the schematic to adjust for the actual UVI?

irvingwashington
 
Posts: 14
Joined: Thu Oct 03, 2013 2:33 pm

Re: GUVA-S12SD sensor board calculations

Post by irvingwashington »

That's okay, I know it's going to be slightly different from the UV report from the weather service.

I'm more interested in where the "4.3x" multiplier comes from, since at least as I see the circuit, you're looking at a straight 1V/1uA gain. The slope of the UVI line, at least from their graph, is slightly less than the number given in the datasheet, ~21nA vs ~26nA, so I can't get the numbers to work!

Z

Locked
Please be positive and constructive with your questions and comments.

Return to “Other Products from Adafruit”