A bench or floor scale that reads the wrong weight is rarely broken. In most service calls the load cell is still healthy and the fault sits somewhere between the platform, the mounting frame and the calibration. The difficulty is that every fault looks the same from the operator’s side: a number that cannot be trusted. This guide separates those faults by what you can observe on site, before anything is opened or replaced.
Start with one question: where is it wrong?
Put a known test weight on the platform and move it around. The answer splits the problem into three very different repairs.
Wrong by the same amount everywhere
The scale is consistent but off. This is a span or calibration problem, not a mechanical one.
Changes when the weight moves
Corner error. The most common complaint, and the one this article covers in detail.
Drifts with nothing on it
Look at the environment and the mounting first, not at the electronics.
Reading the symptom
The table below is the shortest path from what the operator reports to what you should check first. Work down the “first check” column before deciding anything needs replacing.
| What you see | What it usually means | First check |
| Reading changes as the load moves across the platform | Corner error, or the platform is touching something it should not | Run the four-corner test described below |
| Reading is proportionally wrong at every position | Span drift, or calibration performed with an inaccurate weight | Recalibrate with a certified test weight |
| Display will not return to zero after unloading | Mechanical binding, debris under the platform, or a load cell strained past its limit | Lift the platform and clear everything underneath |
| Reading wanders with no load applied | Moisture in the cable or junction box, temperature swing, nearby vibration | Inspect cable entry and terminals for water and corrosion |
| Reading is unstable only when other equipment runs | Electrical interference, or shield not grounded at one end | Check shield termination and route the cable away from motor lines |
| Non-linear: accurate at low load, wrong at high load | Support frame flexing under load, or the load cell has been overloaded | Check the frame stiffness before touching calibration |
Why the frame matters more than people expect
A load cell measures the deformation of a metal body. It cannot tell the difference between the weight you intended to apply and the force the structure around it passes through. If the support frame flexes, part of the load never reaches the cell, and the amount that goes missing changes with how much you load.
That produces the most misleading symptom of all: a scale that passes a light test weight and fails at working load. Calibration cannot fix it, because the error is not constant. Recalibrating simply moves the error to a different part of the range.
Check the frame before anything else when the error grows with load. A weak or corroded support will defeat any adjustment made downstream.
The four-corner test
This is the measurement that turns a vague complaint into a number you can act on. It takes a few minutes and needs only one test weight.
Procedure
- Calibrate the scale roughly first, so you are reading real deviations.
- Use a test weight of about one third of maximum capacity.
- Place it over each corner in turn, then at the centre. Press ZERO between positions.
- Write down all five readings. Do not rely on memory.
Acceptance: all four corners and the centre should agree within one division. If they do, the corners are not your problem — go back to the symptom table.
Corner adjustment by filing
Read this before you pick up a file
Filing removes metal permanently. There is no way back if you take off too much, and a ruined load cell costs more than the service call. This method applies to single-point load cells in bench and platform scales. Do not use it on truck scale or tank weighing installations — there, corner differences are corrected in the indicator, not with a file.
If the scale is under legal metrology control, any mechanical work on the load cell will break the verification seal and the scale must be re-verified afterwards.
Removing a small amount of metal at the designated point makes that section deform slightly more under the same force, which raises the output from the corner that was reading low. The work is done in very small steps, measuring after every one.
1 Find the low corner. From your five readings, identify the corner showing the lowest value. That is the one to work on.
2 File lightly. Use a sharp file with light pressure at the designated point. On the first pass, take almost nothing off — you are learning how fast the material responds.
3 Measure again. Press ZERO and repeat the full four-corner test. Never file twice without measuring in between.
4 Repeat, then recalibrate. Continue until all corners and the centre agree within one division, then calibrate the scale properly.
Keep the filing force well below the rated capacity of the load cell. Pressing hard with a file can apply more force to the sensing element than the load it was built to measure.
When to stop and replace instead
If the corners still disagree significantly after several careful rounds, the fault is inside the load cell — usually permanent deformation from an earlier overload. More filing will not recover it. Replace the cell and check what caused the overload before putting the scale back into service.
What the load cell is actually doing
A load cell is a metal body with strain gauges bonded to it. Each gauge is a thin metal track laid in a zigzag pattern on an elastic backing, and its resistance follows the geometry of that track:
R = ρ · L / S
where R is resistance, ρ the resistivity of the material, L the track length and S its cross-section.
Load the cell and the body deforms. Gauges in tension get longer and their resistance rises; gauges in compression do the opposite. The bridge turns that small imbalance into a millivolt signal, the converter digitises it, and the indicator displays a weight. Everything downstream depends on that deformation being repeatable — which is exactly what a flexing frame or a bent platform destroys.
Reference: capacity and wiring
Two things worth confirming before a replacement: the load cell capacity that belongs with the scale model, and the wiring colours of the cell you are fitting. Colour codes are not standardised across manufacturers, and a swapped signal pair produces a reading that falls when it should rise.
Load cell capacity by scale model — Jadever JCE / JWE
| Scale model | ZEMIC | TEDEA | MAVIN |
| JCE/JWE-3K | 5 kgf | 5 kgf | 4.5 kgf |
| JCE/JWE-6K | 10 kgf | 10 kgf | 7.5 kgf |
| JCE/JWE-15K | 20 kgf | 20 kgf | 20 kgf |
| JCE/JWE-30K | 40 kgf | 50 kgf | 45 kgf |
Single-point load cells from KALA
KALA Sensority Technology supplies its own aluminium parallel-beam range, from laboratory capacities up to platform and bagging systems.
| Model | Capacity | Notes |
| KSPS | 0.5 – 3 kgf | Low capacity, IP60 anodized aluminium; laboratory, counting and small OEM platforms up to 200 × 200 mm |
| KSPM | 50 – 500 kgf | Compact body for smaller platforms and hopper scales |
| KSPA | 300 – 500 kgf | IP67, built with CASC manufacturing support; bagging and automatic weighing |
| KSP | 50 – 2000 kgf | Widest range; pricing, counting, platform, conveyor and dosing scales |
For the small bench sizes in the table above, ask us which cell suits your platform — rated capacity alone does not decide it.
Wiring colours
| Load cell | Exc+ | Exc− | Sig+ | Sig− | Shield |
| KALA, ZEMIC or MAVIN | Red | Black | Green | White | Yellow |
| TEDEA | Green | Black | Red | White | Yellow |
Note the excitation and signal pairs swap between these two makes. Always confirm against the label on the cell itself before wiring.
Field service note
KALA Technical Notes
Corner adjustment is a repair of last resort on a scale that is otherwise sound. If the readings will not settle after the checks above, send us the scale model, the load cell type and your five corner readings — that is usually enough for our technicians to tell you whether the cell is recoverable or should be replaced.
● Load cells, indicators and replacement parts for bench, floor and platform scales.