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Posts: 7
Registered: ‎03-15-2017

Si1133 UVI calculation

UV index = 0.0187(0.00391 Input^2 + Input)

 

I want to use given equation to measure UVI, but datasheet doesn't mention what exactly is Input.

 

 

My channel 0 configuration is following, other values are default 0.

SI_CH0.ADCCONFIG.S.ADCMUX = am_UV;
SI_CH0.ADCCONFIG.S.DECIMRATE = dr_4096;
SI_CH0.ADCPOST.S.RES24BIT=1;
SI_CH0.ADCSENS.S.HW_GAIN = 9;

 

With these settings i'am using Force command to measure what?

One reading witch means "Input"? 512 consecutive measurements added? averaged?

Is it:

fx(raw_value)==Input?

raw_value==Input?

 

I guess i need to do some arithmetics with raw values to get Input. Please help me to put on right track.

 

Posts: 25
Registered: ‎04-09-2015

Re: Si1133 UVI calculation

Hi, 

 

The input is the raw_value read from the sensor. To use that equation, you should set DECIM_RATE to 512.

 

Regards,

Tony

Posts: 7
Registered: ‎03-15-2017

Re: Si1133 UVI calculation

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I plotted equation result. Is it normal having 0-250 raw value working range?

I expected different equation which would use at least ~16 bits of 24 bits available range.

 

Please confirm that this result is normal.

Posts: 7
Registered: ‎03-15-2017

Re: Si1133 UVI calculation

Thank you for previous response. I have additional question ahead.

Should i expect any reasonable UVI without diffuser?

Posts: 25
Registered: ‎04-09-2015

Re: Si1133 UVI calculation

The shape of the curve applies to the case with diffuser. Without diffuser, the result won't be as accurate.

 

If you change the configuration, you can scale the result accordingly to fit in the same curve.

 

Regards,

Tony