Freshly encouraged by data gathering via Node-RED with serial communications, I investigated getting another set of data points. In the packing bubble squish experiment I could see pressure data from the load cell, which showed me the bubble relaxing (and thus reducing pressure) over time. What I could not see was the physical displacement corresponding to that reduction in pressure. I assume the Z-axis carriage did not move, so the reduction likely took the form of flex in the acrylic plate. How might I measure that kind of data for future experiments?
An answer could be found from the field of machining, indicators are used to measure linear displacement precisely. How precise? In the world of machining, I can have any precision I want, but precision costs money. How precise do I want to afford for this project? I started by looking at cheap electronic indicators like Harbor Freight item #63613. ($30) But while the manual hinted at a data output port, there’s no further information about it.
I started looking further and further up the food chain and, while I could find indicators with digital output, they have the similar problem of either a poorly documented or proprietary undisclosed format. Eventually I passed the $100 mark and I started getting discouraged. I was not willing to spend that kind of money on an instrument made by a company I have not known for quality precision.
And that’s when a brand I have known for quality precision popped up in my search: Mitutoyo. I know that name well from my machining course and other precision contexts, but they have all been very expensive at several hundred dollars and up. I didn’t know they made a low-end model (with corresponding lower precision) available at around $150. Certainly many times more than the Harbor Freight item, but it is a name I trust to be precise, and popular enough that details of their data port (called SPC or Statistical Process Control port) would be documented somewhere.
For extra reassurance I decided to pay a little extra to buy from known vendor McMaster-Carr, and when it arrived I got my first surprise: the data port interface instructions were in the box! This was a great good start to a successful project connecting Mitutoyo SPC data port.