OHAUS Defender Series Service Manual

Also see for DEFENDER SERIES: Assembly instructions Instruction manual Instruction manual Instruction manual User guide

Contents

OHAUS Defender Series Service Manual Manual pdf 10 page image

9 Defender™ Series Bases Service Manual1.10 How Load Cells OperateLoad Cells convert force into a signal. The Defender Series Bases have a Strain Gauge Load Cell, which ismade from a metal beam with holes drilled in it. Strain gauges are affixed to the beam at the top and bottom tomeasure changes in the beam due to deflection. The gauges are bonded very securely to the metal, wherethey sense very small deflections in the metal caused by the load being applied to the cell. Because the signallevels are very small, the circuit is protected from all outside influences such as moisture, physical damage, orelectrical interference.Figure 1-1. Typical Strain Gauge Load Cell.The strain gauges are wired into a Wheatstone Bridge Circuit. (See Figure 1-2.)Figure 1-2. Downward force on the Platform bends the beam, causing two gauges to stretch andtwo to compress in opposition, changing the electrical resistance of the circuit.At zero load, all strain gauges are unstressed. Weight placed on the Platform bends the beam, causingtwo gauges to stretch and two to compress in opposition, changing the electrical resistance of the circuit.The difference in the output signal before and after the mass was placed on the platform is measured,interpreted and displayed.ForceWheatstone Bridge CircuitStrain Gauge++Strain Gauge–Strain GaugeStrain Gauge–Printed Circuit Board (PCB )completing WheatstoneBridge circuitStrain GaugesInternal PCBBeamAttachmentpoints toPlatform