How Load Cells Operate; Typical Strain Gauge Load Cell; Downward Force On The Platform Bends The Beam - OHAUS Defender D30BR Service Manual

CHAPTER 1 INTRODUCTION
1.8

HOW LOAD CELLS OPERATE

Load Cells convert force into a signal. The Defender B-V Series Bases have a Strain Gauge
Load Cell, which is made from a metal beam with holes drilled in it. Strain gauges are affixed to
the beam at the top and bottom to measure changes in the beam due to deflection. The gauges
are bonded very securely to the metal, where they sense very small deflections in the metal
caused by the load being applied to the cell. Because the signal levels are very small, the
circuit is protected from all outside influences such as moisture, physical damage, or electrical
interference.
Beam
Internal PCB
The strain gauges are wired into a Wheatstone Bridge Circuit. (See Figure 1-2.)
Printed Circuit Board (PCB )
completing Wheatstone
Bridge circuit
Figure 1-2. Downward force on the Platform bends the beam, causing two gauges to stretch
and two 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, causing two gauges to stretch and two to compress in opposition, changing the
electrical resistance of the circuit.
1.8 HOW LOAD CELLS OPERATE
The difference in the output signal before and after the mass was placed on the platform is
measured, interpreted and displayed.
Ohaus Corporation www.ohaus.com
Strain Gauges
Figure 1-1. Typical Strain Gauge Load Cell.
Force
1-4
+
Strain Gauge
Strain Gauge
–
Wheatstone Bridge Circuit
Defender™ B & V Series Service Manual
Attachment
points to
Platform
–
Strain Gauge
Strain Gauge
+