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OPT4048: Guidance for calibration?

angelo trivelli
Prodigy 10 points
Part Number: OPT4048

Tool/software:

I am evaluating the use of the OPT4048 for a color detection application where a strip of paper will be illuminated with a white LED and the OPT4048 will then generate a color reading. 

This application does not have critical accuracy requirements and the sensor seems to produce the "correct" reading as far as I can tell. However, I have not yet evaluated more than one sensor and I suspect that I might need to perform individual calibration on these sensors. 

How that should be performed?

I see the datasheet provides a matrix (in section 9.2.4) to take the four ADC readings and convert them to tristimulus [X,Y,Z] coordinates. But what about calibration? Somehow, we need to come up with another matrix, a 3x3, to convert the [X,Y,Z] to new [X',Y',Z'] coordinates that give correct readout for one (or maybe two or three) reference color(s)?

Is there a prescription for how to do this? Has anyone done it? I suspect it's just a linear algebra exercise but I would feel more confident about it if we had some guidance from TI. 

Thank you!

  • 0
    TI__Expert 4300 points

    Hello Angello,

    Thank you for posting to the sensors forum,

    We currently do not have a guide for obtaining a new matrix - we would have to generate a new matrix using our lab setup. Are your sensor readings in accordance with the datasheet spec? Are you looking to calibrate the sensors for your white LED light source?

    Thank you,

    Daniel Balmaceda

  • 0 in reply to Daniel Balmaceda
    Prodigy 10 points

    I am trying to come up with a process for calibrating the sensor such that different OPT4048's will give the same (CIE_x,CIE_y) readings when I illuminate some color reference paper (within some reasonable tolerance).

    I am hoping that maybe I can just use the matrix given in 9.2.4 of the datasheet and not need to do anything further but I won't know until I start testing more OPT4048's. So far, with the one EVM kit I have it seems to be "OK" but I don't know yet how much variance I can expect across different OPT4048's. 

    Is the expectation that we are supposed to come up with our own matrices? Or use the one from the datasheet? Or use the one from the datasheet and then multiply by another matrix for calibration?

  • +1 in reply to angelo trivelli
    TI__Expert 4300 points

    Hi Angelo,

    The datasheet matrix provided should give good performance for all devices in this case. Calibration is really for sensors that need to be adjusted for cover glass; otherwise, no adjustment of the matrix is needed. Are you using a cover glass for your application?

    Thank you,

    Daniel Balmaceda

  • 0 in reply to Daniel Balmaceda
    Prodigy 10 points

    Thanks! 

    I don't expect to need any covering in this application.