The same spindle supports the photoelectric cell or "eye" so this rotates too; it is always "looking" in the direction in which the model is moving.
These amplify the response of the photoelectric cell to light so that, when a moderate light is seen, the relay in the plate circuit of the second tube closes.
It determines the density of a sample placed between the light source and the photoelectric cell from differences in the readings.
The densitometer is basically a light source aimed at a photoelectric cell.
Each globule is very active photoelectrically and constitutes, to all intents and purposes, a minute individual photoelectric cell.
The detector, which is located at a fixed distance from the projector, uses a photoelectric cell pointing vertically.
The light pen itself had a small photoelectric cell in its tip.
A photoelectric cell collects the light which passes through the cuvette.
