LED Based Position Volume Sensor

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.

Maximum Rod Extension ≡ Greatest Volume ≡ Least Light
Maximum Rod Extension ≡ Greatest Volume ≡ Least Light
Medium Rod Extension
Medium Rod Extension
Minimum Rod Extension ≡ Smallest Volume ≡ Greatest Light
Minimum Rod Extension ≡ Smallest Volume ≡ Greatest Light
QVLA Changing Volume
This 1/x curve approximates light intensity in a changing volume.