Load cells for checkweighing and inline sorting
Checkweighing is a speed problem wearing a weighing problem's clothes. The cell has to settle fast enough for the reject mechanism to act before the product is already in the wrong bin.
On a checkweighing line the cell is asked two things at once: measure accurately, and settle fast. Those two requirements pull in opposite directions, and the balance between them is set by the sampling rate and the mechanical design of the conveyor.
What actually goes wrong
These are the failure modes we see repeatedly in checkweighing and sorting installations. In most of them, better hardware would not have helped.
Settling time versus filtering
Heavy filtering gives a clean reading but a slow response. On a fast line, an over-filtered signal means the reject mechanism fires after the product has moved on.
Vibration from the conveyor
A conveyor running at speed transmits its own frequency into the load path. Near the line frequency, this shows up as a stable but wrong reading.
Product impact
Product dropping onto the scale is a shock load well above the static weight. The cell must survive the impact without shifting its zero.
Airflow and temperature drift
Open-air sections of the line see rapid temperature swings. An uncovered cell in a cold store or a hot filling hall will drift through the shift.
Models used in this application
These are the models our engineers usually start from for checkweighing and sorting. The specification on each product page is the full one — no abbreviated versions.
SP-200
Single-point
5 kg / 10 kg / 20 kg / 50 kg / 100 kg / 200 kg / 300 kg
- Accuracy
- C3
- Protection
- IP65
- Combined error
- ≤ 0.02 %F.S
- Creep
- ≤ 0.015 %F.S
SB-200
Single-ended shear beam
25 kg / 50 kg / 100 kg / 200 kg / 500 kg / 1 t / 2 t
- Accuracy
- C3
- Protection
- IP67
- Combined error
- ≤ 0.02 %F.S
- Creep
- ≤ 0.015 %F.S
MI-50
Miniature
50 g / 100 g / 200 g / 500 g / 1 kg / 2 kg / 5 kg
- Accuracy
- C6
- Protection
- IP65
- Combined error
- ≤ 0.005 %F.S
- Creep
- ≤ 0.008 %F.S
Selection notes
- Single point for platform scales up to a few hundred kg — it tolerates off-centre product placement
- Keep the filtering low and the mechanical design rigid — a compliant conveyor will not settle
- Specify the sampling rate you need before you specify the cell
- Shielded cable and a junction box away from the drive motors
Checkweighing and sorting questions
What sampling rate do I need for checkweighing?
Most lines run at 100–300 samples per second with 2–10 Hz filtering. That gives a stable reading within 20–50 ms of the product settling. Below about 50 samples per second the reject mechanism starts to lag the product position.
Why does my checkweigher reading drift over a shift?
Almost always temperature. An exposed cell in an open-air section drifts as the ambient temperature moves, and the drift looks identical to a load change. Shield the cell, use a temperature-compensated model, and take a zero reference at a known temperature.
Can I use the same cell for checkweighing and platform weighing?
For light product in a small pan, yes — a single point cell is the standard choice. For heavier product, or where the product does not land centrally, use a shear beam, because single point cells lose accuracy with off-centre load.
How do I handle product impact on the scale?
Expect shock loads of two to three times the static weight. Specify the safe overload accordingly, keep the product drop height as low as the line allows, and confirm the cell is mounted on a rigid base rather than a compliant frame.
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