Load cell scale

01

Size load cell capacity from dead load, live load and supports

Mettler Toledo's weigh module guidance says load cells measure both dead load and net load, and that using load cells larger than needed is not recommended because accuracy suffers. For scales where the goods sit centred over the supports, such as tanks, silos and vessels, it gives C ≥ sf × (TDL + SC) ÷ N; for four-cell floor, small-vehicle and conveyor scales with off-centre loads, C ≥ sf × (TDL ÷ 4 + SC ÷ 2), where C is load cell or weigh module capacity, TDL total dead load, SC scale capacity, N the number of cells and sf a safety factor, which Mettler Toledo gives as 1.25. [1]

Editorial calculation: a tank with 800 kg dead load and 2,000 kg scale capacity on 3 weigh modules needs C ≥ 1.25 × (800 + 2,000) ÷ 3 ≈ 1,170 kg per module; on 4 modules, about 875 kg. Choose the nearest standard capacity at or above the result rather than a much larger cell. [1] The dead and live loads here are illustrative.

Mettler Toledo describes tank, hopper and vessel applications as static loading with little horizontal shear on the cells, while conveyors, pipe racks and high-powered mixers impose dynamic loads that need suitable modules. [1]

Give the supplier the vessel drawing, empty and full weights, number and position of supports, product and process (agitation, heating, pressure), required resolution and accuracy, piping and connections, environment (washdown, hazardous area, outdoor wind or seismic), indicator outputs and calibration method.

02

Choose the accuracy class, wiring and installation

OIML R 60 ranks load cells in classes A, B, C and D by the maximum number of verification intervals: class C covers 500 to 10,000 intervals, for example C3 for 3,000; class B 5,000 to 100,000; class D 100 to 1,000. Its maximum permissible errors are an apportioning factor (0.7 unless declared) times 0.5, 1.0 or 1.5 verification intervals depending on load. The Recommendation notes that a load cell need not be of the same class as the measuring system it is used in. [2]

On wiring, Mettler Toledo says each cell's cable runs to a junction box that sums the signals for the indicator, an analog junction box sums up to four cells, cables should not be shortened or lengthened in the field because that changes the output, and 6-wire cells add sense lines that help where the indicator is far from the scale. Its handbook treats tank piping-connection design together with the support structure and foundation. [1]

Pipework is where a well-chosen cell loses accuracy. At the European Commission's Joint Research Centre in Ispra, a 400 dm³ D-shaped product tank on a weighing system for nuclear material accountancy was chosen for an accuracy potential of 1 in 10⁵ and to avoid density, dip-tube and temperature problems of volume methods. The team commissioned it first with no pipes attached, then measured the influence of pipe connections and of off-centre loading as the centre of gravity moved during filling; after modifying the pipework, optimising its clamping and recalibrating, initial results with process pipework attached showed a repeatability of ±0.006% of 400 kg, the liquid weight in the tank. [4]

Editorial calculation: ±0.006% of 400 kg is ±24 g; for comparison, a 3,000-interval scale (OIML class C3 cells) on a 400 kg span has an interval of about 133 g, so the JRC result after pipe clamping and recalibration sits well inside one such interval. [4] [2]

03

Understand how a shear beam load cell senses load

Flintec's US patent 6,172,309 (filed 6 April 2000, granted 9 January 2001) describes the shear beam cell used in weigh modules: a rectangular beam of load-cell-quality aluminium, steel or stainless steel alloy, bolted at one end as a cantilever and loaded through a vertical hole at the free end. Between the two, opposed lateral recesses leave an I-section with a thin vertical web; strain gauges bonded to both sides of the web measure principal strain due to shear and are connected in a bridge circuit. [3]

The patent explains that the vertical shear force is the same in every cross section between the support edge and the loading hole, so shear stress varies inversely with the cross section; capacity ratings in a range are set by changing the web thickness while the blank and recess sizes stay constant. Known shear beam designs, it says, give high accuracy with low sensitivity to off-centre loads, torque and horizontal forces at the load point. [3]

Its design cuts the web pockets with a side-cutting tool so the web thickens gradually away from a flat centre where the gauges sit, giving more uniform shear strain there and lower off-centre load sensitivity, and reduces machining from five set-ups for the prior design to one. [3] Editorial note: for a weigh module, ask the supplier for the cell type (shear beam, bending beam, column), body material and sealing, the OIML R 60 class and the off-centre load test results, alongside the capacity worked out with Mettler Toledo's formula. [2] [1]

04

Compare what suppliers offer

Suppliers linked to this page list load cells, weigh modules or indicators for weighing systems; each card links to the page reviewed.

Zhihe lists pancake, shear beam and tension load cells with weigh modules, junction boxes and indicators; Hongli lists OIML/NTEP shear beam load cells and weighing modules with junction boxes and indicators; Top Sensor lists load cells, weight indicators and load cell amplifiers; Kuanyi lists load cells, weighing indicators and junction boxes with scales.

05

Trace the system components

This is a functional reference built from the sources cited; it is not one maker's parts list.

06

Fill the specification fields with values for your vessel

A weighing system quotation needs values for your vessel and process. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the vessel, load and accuracy data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Vessel: [drawing; supports; empty weight; full weight]
Process: [static or dynamic; agitator; temperature; pressure]
Accuracy: [resolution; class; legal-for-trade or not]
Installation: [piping connections; support structure; wind/seismic]
Electronics: [junction box; indicator; outputs; cable lengths]
Calibration: [test weights; method; certificate]

See manufacturer records Send an enquiry through CNFX