Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-L] Sonometer, What Do You Think of the PASCO Model?

On 7/29/2014 9:41 PM, Bernard Cleyet wrote:
On 2014, Jul 29, , at 17:26, John Denker <> wrote:

On 07/29/2014 04:00 PM, Bill Norwood wrote:

- Has anyone considered the bass guitar with 4 tensile strain gauges just
past a "frictionless" bridge on the tuning end? /snip/ I have no idea of the dimensions of, or how to shop for, such strain
I suspect you want to measure force i.e. stress, not strain.
The magic word here is "load cell".
Once you know the magic word, the shopping becomes easy.
Use "google shopping" (as opposed to regular google web search):

Making a load cell from a resistance module was one of the exercises at a recent Vernier engineering workshop. (or was it calibrating?)

I thought such measured the resistance due to the strain experience by a resistor.*** e.g. pencil lead on paper. The stress is inferred by the spring constant.

One use early in UCSC’s history was a resistance module glued to an Al rod. It detected a sound pulse. (At least that’s my interpretation of a bunch of them surplussed back before 1984.)

The load cell (force transducer) Vernier cells is too big for a string instrument, but would work (unnecessary) on a sonometer.

*** an early version used a plate w/ a magnet and a Hall detector, IIRC!

bc, may be engaging in his favo. occupation.***

***Jumping to false conclusions.
I think BC has it about right. Engineers infer stress from the strain experienced by thin film resistors (often in a rosette pattern) when a member to which this strain gauge is glued is then strained. Load cells are often fabricated by applying strain gauges to a compact material structure of known properties. Undergraduate labs sometimes use a coke can as an interesting test structure, though a piece of spring steel in bending or tension ("feeler gauge stock") makes a usable force meter when a strain gauge is applied. The small differential resistive change is applied to an instrumentation amplifier which is a glorified operational amplifier. Strain gauges are supplied on paper like substrates smaller than a postage stamp. They are glued to the structure of interest with epoxy or cyanoacrylates. They cost several dollars each in the usual run of things. Serious strain gauge amplifiers may cost $hundreds however.

Brian Whatcott Altus OK