In through-beam counting, durations of the received-light and beam-interruption states: light time for a clear beam and dark time for an obscured beam.
Also called: light time; dark time; light-dark timing; beam-blocked duration; beam-clear interval.
Are dark time and Dark-ON the same thing?
No. In through-beam counting, dark time is the interval when product sufficiently obscures the beam; light time is the clear-beam interval. Dark-ON and Light-ON select which optical state energizes the output, rather than how long that state lasts.
In reflective sensing, a present object may return light rather than block it. State the optical arrangement before interpreting light/dark labels. If a recipe measures electrical pulses instead of the optical input, identify its start and end events rather than assuming identical intervals.
Why must the interval between products be considered?
Both products and gaps have to be distinguishable. A short interval between objects can be more restrictive than the time one object is sensed. The following simplified example illustrates the geometry; it does not model accelerating or tumbling tablets.
A dark-time limit is a classification criterion within the specified system. A configured detector may accept a product only when its measured dark interval falls between selected limits. That rule does not establish a universal duration or show that completely overlapping products can be distinguished.
Assess whether other presentations can produce a similar interval, including overlapping products. The product, sensor arrangement and response to those cases define what the timing limits can distinguish.