Public Lab Research note


Oil testing kit Beta programme - Technical adjustments (hack!)

by cindy_excites | | 2,173 views | 2 comments |

Read more: unstable.publiclab.org/n/12368


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:

IMG_4166_misalligned.JPG

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

IMG_4167.JPG

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

Technical_issues--_IMG_4160_-_lego_piece.JPG

I inserted the Lego structure under the cuvette holder…

Technical_issues--_IMG_4162_-_lego_placement.JPG

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

Technical_issues--_IMG_4163_-_lego_piece_in_place.JPG

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

Technical_issues--_IMG_4158_-_lego_final_look.JPG

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):

Technical_issues--_IMG_4164_-_frame_tape.JPG

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…

Technical_issues--cuvette_positioned_left.png

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

Technical_issues--cuvette_positioned_right.png

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


2 Comments

I had the same problem of ribbed cuvettes. I found some cuvettes that do not have ribs and so I use those all the time now.

Reply to this comment...


I love the lego hack! Maybe we should make one entirely of lego. They're very precise.

@Guillaume123 - if I understand correctly, Cindy said it worked better with the ribbed side, which I'm glad to hear as I'd suspected that would be helpful:

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

Did you find that not to be true?

Is this a question? Click here to post it to the Questions page.

Reply to this comment...


Login to comment.