An in-line machine that weighs every pack as it moves past and rejects the ones outside tolerance.
01 / Definition
What a Checkweigher is
A checkweigher weighs every pack on a moving line and removes the ones outside tolerance. It sits between two conveyors: packs arrive on the infeed, cross a short weigh belt supported on load cells, and leave on the outfeed. Anything underweight or overweight is pushed off downstream.
The hard part is that the pack is never still. The load cell sees the weight plus every vibration from the conveyor, the motor and the factory floor. The controller samples the signal over the brief window the pack is fully on the weigh belt, filters out the noise, and settles on a number — often inside 200 milliseconds. Belt speed, pack spacing and filter settings therefore matter as much as the load cell itself.
Also called
02 / Anatomy
The parts that matter
The components a technician reaches for when this machine stops working.
Weigh belt and frame
A short conveyor isolated from the rest of the line so only the pack's weight reaches the cells.
Load cells
Usually strain-gauge or electromagnetic force restoration. EMFR settles faster and suits high line speeds.
Digital filter
Removes conveyor and ambient vibration from the raw signal. Over-filtering slows settling; under-filtering gives scatter.
Infeed and outfeed conveyors
Set pack spacing. Packs arriving too close together overlap on the weigh belt and corrupt both readings.
Reject mechanism
An air blast, pusher or diverter arm, triggered on a delay timed to the belt speed.
Controller and display
Holds the target weight and tolerance band, logs results, and drives the reject output.
03 / Applications
Where it is used
Legal-metrology compliance and giveaway control on food, pharma and FMCG lines.
04 / Failure modes
How it fails
What actually goes wrong on Indian shop floors, and what each fault looks like to the operator.
FM_01
Readings scatter run to run
Vibration reaching the weigh frame — a worn conveyor bearing, a loose guard, or the frame touching adjacent structure.
FM_02
Consistent offset from the true weight
Calibration drift, or something resting on the weigh platform such as a cable, a product guide or build-up underneath.
FM_03
Rejects missing the pack
Reject delay no longer matches belt speed, usually after a speed change nobody re-timed.
FM_04
Packs touching on the weigh belt
Infeed spacing too tight for the line speed, so two packs are briefly on the belt at once and both readings are wrong.
FM_05
Load cell damage
From impact or overload — a dropped pack or a jam can exceed the cell rating and leave a permanent zero shift.
05 / Onsite
What our technician checks
A methodical path to root cause, not a scattergun of part swaps.
- 01Run a certified test weight repeatedly and record scatter as well as average — scatter and offset have different causes
- 02With the line running empty, watch for signal movement that indicates vibration reaching the frame
- 03Check nothing bridges the weigh platform to the fixed frame: cables, guards, product guides or spilled material
- 04Measure actual pack spacing at line speed and confirm only one pack is on the weigh belt at a time
- 05Time the reject against a known failing pack and adjust the delay for the current belt speed
- 06Inspect load cell cable glands and connections for moisture, the usual cause of slow drift in wash-down areas
06 / Get it fixed
Related services
The MachineryFix services that cover this equipment.
07 / Questions
Frequently asked questions
Why do readings vary when the same pack goes through twice?+
Scatter means vibration is reaching the weigh frame or packs are too close together. Check for a worn conveyor bearing, a loose guard, contact between the weigh frame and surrounding structure, and confirm only one pack is on the belt at a time.
Does a checkweigher need legal calibration?+
If you use it to ensure packs meet declared weight, it falls under legal metrology and needs verification by an authorised agency at the required interval. Internal test-weight checks are good practice between those verifications but do not replace them.
How fast can a checkweigher work?+
It depends on pack length, belt speed and the settling time of the load cell technology. Electromagnetic force restoration cells settle faster than strain gauge, which is why high-speed lines use them. The practical limit is usually pack spacing, not the cell.
Why is every pack reading slightly heavy?+
A consistent offset is calibration or something resting on the platform — a cable, a guide rail touching, or material built up underneath the weigh belt. Clean under the belt and re-zero before recalibrating.
Written & reviewed by MachineryFix — last reviewed — questions? Call +91 70133 33007