conveyor — scrap_weight (load-cell-scrap-bin)
Physics
Section titled “Physics”Rejected parts discharged from a conveyor line accumulate in a scrap/reject collection bin. Load cells supporting that bin’s frame form a strain-gauge bridge whose output voltage is proportional to the bin’s total weight; a weight transmitter converts that bridge signal into an engineering-unit weight reading. Differencing successive weight readings and dividing each weight increment by a known average single-part weight converts cumulative bin weight into an estimated cumulative reject count, without needing a discrete sensor on each rejected part. That derived reject count, paired with a good- output count from an upstream count_cycles recipe on the same line, feeds the SPC p-chart detector exactly as a direct good/reject counter pair would. Because the bin fills in discrete dumps (one part landing at a time) rather than continuously, the signal only needs to be sampled fast enough to resolve one discharge event settling before the next: for a line discharging rejects at up to 1/s with a load cell/transmitter settling time of under 100 ms per event, sampling the transmitter’s output at 50 Hz gives ample margin above the discharge rate’s Nyquist requirement while letting the processing chain apply a settling-time filter per discrete weight step rather than averaging through transients.
Sensor
Section titled “Sensor”- Spec: compression load cell under scrap bin frame, strain-gauge bridge, with weight transmitter, 4-20 mA or digital output
- Signal: scalar (kg), range n/a
Example parts
Section titled “Example parts”- Mettler-Toledo PBK load cell kit with IND246 weight transmitter
- Hardy Process Solutions HI 6300 weight processor with Hardy load cells
- Vishay Precision Group (Celtron) LCD compression disk/canister load cell with a Siemens SIWAREX WT231 weight transmitter
Mounting
Section titled “Mounting”Mount 3-4 compression load cells under the scrap bin’s support frame (one per corner or leg) so the bin’s full weight bears squarely on the cells with no side-loading, using the load cell manufacturer’s mounting kit to keep the bin free to settle vertically while constrained horizontally. Position the bin under the conveyor’s reject discharge chute so parts fall directly into it without striking the bin’s edge or the load cells’ wiring.
Wiring
Section titled “Wiring”Each load cell’s bridge output to the weight transmitter’s summing junction box, then the transmitter’s calibrated 4-20 mA or digital output to the edge box’s DAQ or digital input module; route cabling away from the conveyor drive motor and discharge-chute vibrator (if fitted) and ground the shield at the transmitter end only.
Validation
Section titled “Validation”manually drop 20 known parts of consistent weight into the empty, tared bin one at a time at a normal discharge pace, and compare the edge system’s derived reject count against the known count of 20
Expected: derived reject count within +/-1 of the known count of 20 once the average single-part weight constant is calibrated against the actual part’s measured weight
Safety notes
Section titled “Safety notes”- de-energize and lock out the conveyor drive (LOTO) before working near the discharge chute or belt to install the bin and load cells
- keep hands clear of the discharge chute and the moving conveyor’s pinch points (belt- to-roller nip, chute pivot points) whenever the line is powered, including during bin load-cell calibration
- verify the weight transmitter’s supply voltage matches its rating before wiring; do not wire a DC-rated transmitter to an AC supply, and lock out the transmitter’s power feed before opening its junction box
800–4500 USD, difficulty 3/5, ~75 min install downtime.