Laser Scale

[allenn]

Picture 1: A laser pointer is hot glued to my scale. At the beam pivot point I super glued with the help of a small square a 1/2 by 5/8 mirror.
Picture 2: The laser beam is reflected 79 inches to a scale or chart hanging on the wall. The marks on the scale are 1-1/4 inches apart, equaling, or very close to 1/10 of a grain.
Picture 3: For fun, but not necessary, a web cam was pointed at the scale on the wall. This picture shows the results.
Picture 4: This picture shows how far the laser dot moves when I drop one kernel of Varget into the pan. Compare pictures 3 & 4 to see the difference. You can see the laser dot move 1/4 inch when you drop one kernel of Varget.

link to video http://youtu.be/fvlCOP7fwdc

 

[BoydAllen]

I like it! Can we see a picture of the scale?

 

[BoydAllen]

I can see the pictures. It looks like you have built in light beam cutoff setup into the scale, to control the trickling of the charge. Did I come close?

 

[allenn]

Yep, the light beam cutoff is the one made by Omega. It works good but is tricky to set up.

 

[Webster]

I think the accuracy of the scale is inherent to its design. Using devices to read the beam movement more accurately doesn't change the inherent accuracy of the system. You have probably increased the repeatability not the accuracy. Nothing wrong with what you are doing. Repeatability is what you want. If you zero the scale and get the beam moving does it always stop at the same place or close to the same place on your laser wall chart? If it doesn't I wouldn't think you have improved anything. The dampener and pivot friction influence wear the beam stops moving. They act as a brake.

To make up an example: If you have a 6” ruler the divisions are located with a certain accuracy. You cannot make the ruler more accurate than the divisions are placed on the ruler by using a magnifier. If you measure 10 things with the same ruler and magnifier they are close to the same length but you have not increased the true accuracy of the length.

 

[BoydAllen]

Webster,
Reloading balance scales can be tuned up to be a lot more sensitive than they are out of the box. If you have no experience with this, and you have such a scale, you are in for a treat, if you learn how to tune one, or have one done. The latest one that I tuned will move when a single piece of Varget is placed on the pan, without bumping the pan to get the scale to react. The problem that this clever idea addresses is that although my scale is sensitive, and repeatable the amount of beam movement that results from a small weight difference is difficult to read. The way that I have handled this is to use an inexpensive, manual focus web cam to take a macro shot of the end of the beam, and the scale. This image is displayed on my computer's monitor. What he has done is take this one step more, and made what the camera sees larger, or as an option he could simply read the results from the wall where the laser beam is projected onto the paper scale. The long and short of this is that we can only read a scale to as fine a division as we can see, and properly tuned, they are better than we can easily see.

 

[1066]

Good work Webster, nice to see another experimenter. I've used this method myself but now use a camera. As Boyd says, tune up your scale a bit and you will have even better results.

Also interesting to see you have the Omega optical switch mounted "upside down" although, of course, it works just the same, never thought about using it that way. (And I designed the system )

 

[allenn]

Boyd, thank you. I think you are the only one that understands what I was trying to do. Take a look at the video link.