Weighing Load Cell

Function

Each load cell uses the shear-beam principle: a precision-machined alloy-steel beam contains a through-hole that concentrates shear strain within a defined gauge zone. Four resistive strain gauges are bonded in a full Wheatstone-bridge configuration in that zone; applied load deforms the beam, unbalancing the bridge and generating a millivolt output proportional to the applied force. The bridge output — typically 2–3 mV/V — is ratiometric to the excitation voltage, making the reading independent of minor supply fluctuations. In the plant tower environment, IP-rated sealing and transient-voltage surge protection are critical, as the weighing deck is exposed to mixer vibration, dust ingress, water from aggregate washdown and occasional pressure-washing. On plants with long cable runs from tower to control cabin, digital cells with on-board analogue-to-digital conversion and RS-485 output eliminate ground-loop and cable-resistance errors that degrade system accuracy.

Construction & quality

Load cell bodies are precision-machined from EN24T (AISI 4340 equivalent) alloy steel, heat-treated to 900–1,000 MPa tensile strength, then surface-ground on all mounting faces to ±0.02 mm flatness. The strain-gauge pocket is machined to a controlled depth; each full-bridge strain-gauge set is bonded with two-part epoxy adhesive and the bridge is temperature-compensated over a −10 °C to +70 °C operating range. After bonding, each cell is laser-trimmed for zero balance and span, then subjected to a full creep and hysteresis measurement cycle. The complete assembly is hermetically sealed: the cable exit is overmoulded in polyurethane and the body sealed to IP67 as standard. Cells for the heated bitumen vessel are supplied with a stainless-steel check rod to accommodate the vessel's thermal expansion whilst remaining within the cell's side-load tolerance. Mounting hardware — stainless-steel load-button pins, rocker pins and limit-stop plates — is supplied as a matched kit. Cell bodies are zinc-plated or nickel-plated for plant-environment corrosion resistance.

When to replace

• Persistent tare drift — the displayed empty-hopper weight creeps across shifts despite repeated manual re-zeroing
• Batch-to-batch ingredient-weight scatter exceeding ±0.5% of setpoint on a stable aggregate feed and unchanged recipe
• Weigh controller reporting a single-channel signal fault or an abnormal imbalance between cells in the summing junction box
• Visible corrosion pitting, cable damage or physical deformation of the cell body discovered during scheduled inspection
• Hopper physically contacting support steelwork and overloading one cell — identified by one channel reading disproportionately high relative to the others during an empty-hopper check