Sample Holder Version 3, +- .01 pH

Above.   V3 is based on a lab quality cuvette holder from a surplus HP8452 spectrophotometer.   To get it working, I made additional mounting components from 3mm plastic material.  After hooking up and with bench testing, this unit verifies that a  +- .01 pH unit is possible with the v2 controller I have now.  We want to get this in the lab asap for calibration and this provides the baseline for going forward with a DIY make of a cuvette holder – the next one being V4.

 

2.3 Bench tests

  • The blue 434 nm and green 578 nm LEDs are both down on brightness as measured in the blank shot.
  • Sample to sample variation translate to  ± .002 pH units or better. This meets the ± .01 pH unit target requiremen

Construction notes: 24 may 2017

Cuvette holder:  reposition the LED holder for a shorter path length and increase LED intensity.

Controller:
moved green LED to Arduino uno pin 9 and reflashed- determined the problem is not the pin but the 1k trim potentiometer.
bypassed 1kR led series resistor for green 578nm.  1kR remains for blue 434nm.
add two 4-40 bracket stabilizer screws on TSL257 board
wiring harness- swapped colors of wiring to match led color /blue/green/
green pot adjustment is difficult – ok now, fixed needed
optics signal cable male header pins move – OK now, fix needed

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