Version 2 sample solder for 3ml cuvette and calibration +- .05 pH unit

Tested V2 of the cuvette sample holder on May 3 2017 with a calibration run in the lab.  The first trial measurements of absorption ratios confirmed that the 3 ml cuvette would work so this second prototype was built and tested in the lab against the bench spectrophotometer.  We got the enough RB to RN calibration data to provide good indication that the device is working.

Below the results of the calibration done with the Version 2 cuvette holder.  The V2 holder also used different LED and TSL257 components.  Subsequent test runs on the workbench with a bottle of filtered seawater and supply of mCP at 50ul / 3ml show a sample variation of up to .05 pH units, which does not meet a .01 pH measurment accuracy requirement.  However, this V2 build, validation of the 3ml cuvette sample holder, and the lab calibration run shows that we’re on track and moves the build focus to producing a reproduceable cuvette holder.

Calibration3May17.PNG

Rn to pH :  This curve is computed for a narrow-band spectrometer from Eq.(4) of Yang et al.

RNeq4

Rb to pH: Computed from   the Rb to Rn calibration equation and Eq (4).
Rn = .4565 Rb + 0.4901

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