Oil testing kit Beta programme - Technical adjustments to Public Lab Spectrometer 3.0

Date: 4/Nov/2015

Here I document my experience making adjustments to the Public Lab Spectrometer 3.0, which was assembled using these instructions.

Propping-up the cuvette holder and aligning the spectrometer

When I started scanning the Mineral Oil sample [ HYPERLINK HERE ] no light was being captured. I separated the cuvette frame and spectrometer and I noticed that the laser beam was not passing through the centre of the 'viewing window' in the cuvette holder:

I then noticed that the slit in the slit card of the spectrometer did not aligning correctly to the 'viewing window':

I devised a support structure to prop-up the cuvette holder using small Lego parts:

I inserted the Lego structure under the cuvette holder…

…so that the cardboard rests between the Lego brick 'protrusions' (what are these circular things called?)

Propped-up, the cuvette frame now looks like this:

The final adjustment - due to lack of time - was to keep the cuvette frame and spectrometer holding tightly and steadily together. I used mammoth tape, which does not stretch nor damage the cardboard yet can still be easily removed.

I taped the cuvette lid. I also taped the cuvette frame to the spectrometer in two places: on the side and at the bottom (not pictured here):

Issues which I have not tackled:

1) The cuvette holder has enough room for the cuvette to move around. When I pushed the cuvette all the way to one side (left side looking towards the slit card from the cable feed) I got this…

…and when moved to the other side (right side looking towards the slit card from the cable feed):

2) The second issue is that the cuvette itself is ribbed on two sides and smooth on the other two. The spectrometer receives the light coming out from the ribbed side. I wondered if this makes a difference and it does: if the laser enters the sample through the ribbed side and the spectrometer captures the light coming out from the smooth side, more frequencies seem to be captured. I would like to test this further and post some photos in the future. For now I just wanted to point this out and ask if it this was perceived as non-problematic when choosing the cuvettes and/or the design of the spectrometer and cuvette frame and the way they fit together.

Related research notes:

Oil testing kit Beta programme - Package content

Oil testing kit Beta programme - Assembly: cuvette frame

Oil testing kit Beta programme - Assembly: spectrometer

Oil testing kit Beta programme - Calibration

Oil testing kit Beta programme - Scanning OTK samples