conveyor — count_cycles (photo-eye)
Physics
Section titled “Physics”Parts or pallets moving along a conveyor pass a fixed point on the belt/roller path one at a time, each briefly interrupting a through-beam photoelectric sensor aimed across the conveying surface at a height that only the product (not the belt or rollers) breaks. Each product gives exactly one beam-break pulse as its leading-to-trailing edge crosses the beam, so counting debounced beam-breaks counts units passing the point. The fastest realistic event is set by the smallest product spacing at maximum belt speed: a fast case/pallet line at 60 m/min (1 m/s) belt speed with 0.3 m minimum product gap gives a worst-case pulse rate of roughly 3 Hz; sampling the digital sensor output at 500 Hz gives >150x margin over Nyquist for that rate and resolves the shortest realistic beam-break pulse width (tens of milliseconds for a fast-moving small part) without merging two closely-spaced products into one pulse.
Sensor
Section titled “Sensor”- Spec: through-beam or retro-reflective photoelectric sensor, digital, NPN/PNP, NO
- Signal: counter ({count}), range n/a
Example parts
Section titled “Example parts”- SICK WL4-3P200 retro-reflective photoelectric sensor (PNP, 200 mm range)
- Banner Engineering Q45VR6LV retro-reflective photoelectric sensor (visible red, PNP)
- ifm electronic O5D100 through-beam photoelectric sensor pair
Mounting
Section titled “Mounting”Mount the sensor (or through-beam emitter/receiver pair) on a rigid bracket off the conveyor frame, aimed across the belt or roller path at a height that intercepts every product’s leading edge but clears the belt surface, idlers, and any guide rails at all points, positioned at a straight run with stable product orientation (not at a merge, diverter, or incline where products can overlap or tip).
Wiring
Section titled “Wiring”3-wire DC (24 V, 0 V, signal) to a digital input / counter channel on the edge box’s I/O module; route the cable along the conveyor’s existing cable tray, clear of the drive motor’s VFD cabling to avoid induced noise on the signal line.
Validation
Section titled “Validation”run 50 manually-counted units past the sensor at normal line speed and compare the detector’s counter delta over the same window
Expected: counted units exactly equal to the manual count (a correctly positioned beam sensor on a single-file straight run gives an exact 1:1 count)
Safety notes
Section titled “Safety notes”- de-energize and lock out the conveyor drive (LOTO) before reaching near the belt, rollers, or pinch points to install the mounting bracket
- mount the bracket and sensor body clear of the belt’s travel path, any roller nip points, and the drive pulley guard at all times
- verify the sensor’s voltage rating matches the 24 V DC supply and keep its cable away from the conveyor’s line-voltage drive wiring
25–95 USD, difficulty 1/5, ~15 min install downtime.