OPT3004: OPT3004

Hi Mark,

I understand questions are related to rotating the IC and seeing light level reading change. How did you ensure that the unit is in the exact same position when it is rotated? A small change in the position or if the sensor is tilted to face towards or away from the light source even slightly can have an impact on readings in this type of test. Also is the room completely dark except for this light source? 

Best,

Alex

Hi Alex,

As you can see I have the units mounted in a box, and rotating the box is all I had done.  The units are not perfectly level in that box, so as they get rotated the angle to the light source is most likely changing as well.  Yes, the room was completely dark aside from the light source above the units.

Now, as to the units remaining in the same position while adjusting the brightness of the source (pages 8-11 in the doc), please let me know your thoughts on the variance in the readings as the brightness increases.

Thanks!

Mark

Hi Mark,

What is the x-axis on this graphs on the pages 8-11? What does the setting 2,4,6,8 mean?

Best,

Alex

Hi Alex,

The x-axis in the charts is the lux reading of the OPT3004 while underneath the LED light source.  The settings 2,4,6,8 are the brightness settings of the LED light source, 2 being dim and 8 being full brightness.

Mark

Hi Mark,

Is the y-axis not the OPT reading? If opt reading is x axis, what is the y-axis?

Best,

Alex

Yes, you're right, y-axis is the OPT reading.  The x-axis is time.

Hi Mark,

Understood. So what is causing the light level to change over time? I see there are separate plots for different LED settings but seems if LED setting is fixed for each plot the light level should not be changing over time in the plot.

Best,

Alex

Hi Alex,

The light level remains constant after the brightness is adjusted.  I'm more concerned with the difference between the light readings at each of the brightness settings.  Each colored line is an Agriculture Sensor using the OPT3004.  To illustrate, from 20:00 to 22:00 in time, a reading was taken at 20:52:13 and the readings were 21114, 23439, 27371 and 27904.  Why the big difference in lux, nearly 6800 from minimum to maximum?  That's what I'm most concerned with.  Do these readings fall within the accuracy of the OP3004?

Mark

Hi Mark,

Will follow up on this by this week.

Best,

Alex

Hi Mark,

No this is not expected as device to device variation on OPT3004 is spec'd at max +/-10% and I see up to 25% difference in your min and max responding device. Because units are placed in different locations relative to the light source it is possible this could be coming from the setup.

Best,

Alex

Hi Mark,

Are you able to replicate one of the setups described in this app note? https://www.ti.com/lit/an/sbea002a/sbea002a.pdf

section 2.1 Attenuation Compensation. This is specifically geared to measuring attenuation due to a window, but the same setup can be used to measure this type of device to device variation. You can see in the setup that position relative to light source is controlled and stable light source used.

Best,

Alex

Hi Alex,

So does this mean you recommend a piece of glass overtop of the light sensor to decrease the unit-to-unit variation?  That the OPT3004 just out in the open with nothing in between it and the light source will have the variation that I'm seeing in my testing?  I think you're also trying to point out that the X,Y,Z position of the light sensor in relation to the light source needs to be tightly controlled when looking at the light readings between units, is that correct?

Mark

Hi Mark,

No, I am not recommending to add a dark glass on top. This app note was specifically geared to this application, but the same setup minus the dark glass (lux meter, tightly control XYZ position of light source and DUT) will apply to the type of test you are doing. Please let me know of anything still unclear here.

Best,

Alex