How Does QVLA Work?
Flood two different sized volumes with light sources of equal intensity.
Measure the light intensity within each volume.
The disparity between light intensities inside the volumes reveals the difference in volumes (X-Y).
Experimentation proves light intensities accurately measure volume.
Bellows expansion and/or retraction, fluctuating fluid levels and mechanical movement of walls are all examples of volume changes measurable by QVLA®.
The light emitter must be uniform in its output unaffected by time, temperature or changing ambient light levels. The light emitter is synonymous with a ruler. Presently, the patented QVLA® light emitter has a frequency response > 15,000 Hz. Lifetime is calculated at greater than 100 years.
Reading the ruler is cost critical. Applying only what is needed for an application is important; analog solutions are least expensive, digital solutions with communications protocols can cost more
QVLA Infinite Resolution
For discussion, imagine having a QVLA® emitter inside an air cylinder. For every movement of the rod there is a corresponding change in light intensity inside the volume as depicted to the right. Light intensity is lowest at maximum rod extension/greatest volume as shown with the top volume to the right. The bottom volume represents less rod extension and brighter internal volume.
In the top configuration the rate of light intensity change per correlating stroke or volume change is the smallest. This is the point to establish resolution.
Using a reference voltage of 4.096 volts with 16 bits of resolution yields increments of .0000625 volts (4.096 ÷ 65,536 = .0000625).
A 2½ in. bore air cylinder with a 10 inch stroke has a light intensity variance of .0172 volts at the last inch of stroke. Dividing .0172 by our resolution of .0000625 we get 275.2. Divide 1 by 275.2 we get a theoretical resolution of .0036 inch for the last inch of travel. Considerably higher resolutions are possible with shorter stroke cylinder/smaller volume or closer to the light source.
Experimentation with light intensity, reference voltage, resolution bit choice and analog circuitry will yield substantial results for surprisingly good value.