Load cell selection reference for industrial weighing: strain-gauge (bonded foil), compression (canister, disk), tension (S-beam, in-line), single-point (platform scale), shear-beam, double-ended shear-beam (weighbridge), and hydraulic. Includes OIML accuracy classes (C3, C4, C6), IP rating relevance, temperature coefficient, output signal (mV/V vs digital), and cable / summing-box wiring diagrams for 4-load-cell and 6-load-cell installations.
| Topology | Loading mode | Capacity range | Typical use |
|---|---|---|---|
| Single-point | Off-centre compression | 1 - 500 kg | Platform / bench scales |
| S-beam | Tension or compression | 50 kg - 20 t | Hopper suspension, tension weighing |
| Shear beam | Bending / shear | 250 kg - 10 t | Silo, tank, floor scales |
| Double-ended shear beam | Bending, symmetric mount | 5 - 100 t | Weighbridge, rail scales |
| Compression canister | Axial compression | 5 - 500 t | Heavy silo, industrial press |
| Compression disk (button) | Axial compression | 100 kg - 500 t | Force calibration, press-fit measurement |
| Ring torsion | Radial + axial | 500 kg - 200 t | Rail, road weighbridge |
| Hydraulic | Fluid pressure | 1 - 1000 t | Legacy weighbridge, hazardous area |
OIML R60 assigns load cells to accuracy classes based on maximum divisions nmax and combined-error envelope. The class name (C3, C6, etc.) states the maximum number of thousand divisions the cell supports for legal-for-trade weighing.
| Class | nmax | Combined error | Typical use |
|---|---|---|---|
| C1 | 1 000 | ±0.10% FS | Process control, not legal-for-trade |
| C2 | 2 000 | ±0.06% FS | Non-approved industrial weighing |
| C3 | 3 000 | ±0.023% FS | Legal-for-trade platform, hopper |
| C4 | 4 000 | ±0.017% FS | Legal-for-trade weighbridge |
| C6 | 6 000 | ±0.010% FS | High-accuracy legal-for-trade |
Analogue strain-gauge cells output a differential voltage proportional to the excitation and the applied load. Standard sensitivity is 2 mV/V — a 10 V excitation gives 20 mV full-scale output, well below the standard 24-bit ADC noise floor. Higher-sensitivity cells (3 mV/V, 4 mV/V) trade linearity for output level. Digital cells (RS-485 output, sometimes CAN or PROFIBUS) integrate the ADC into the cell body and eliminate summing-box wiring — required for large weighbridges with cable runs over 30 m.
4-wire cabling supplies excitation and measures the signal on two twisted pairs. 6-wire cabling adds sense lines that measure the voltage actually present at the cell's excitation terminals, allowing the indicator to compensate for voltage drop across the cable — mandatory on cable runs over 5 m or where temperature swings change the cable resistance seasonally. All modern OIML-approved cells ship with the 6-wire terminal block populated.
Multi-cell installations (4-load-cell platform, 6-load-cell weighbridge) route every cell's output through a summing box before entering the indicator. The summing box paralleles the excitation, sums the signals and, on trim-pot versions, allows corner adjustment of each cell's contribution to correct for uneven load distribution. Sealed IP68 summing boxes are mandatory outdoors and in washdown areas.
| IP rating | Water | Dust | Typical use |
|---|---|---|---|
| IP65 | Low-pressure jets | Dust-tight | Indoor industrial |
| IP67 | 1 m immersion 30 min | Dust-tight | Outdoor, occasional flooding |
| IP68 | Continuous immersion | Dust-tight | Buried weighbridge, marine deck |
| IP69K | High-pressure high-temp wash | Dust-tight | Food processing, pharma washdown |