This article describes load cell, the devise used for the measurement of large tensile and compressive forces and pressures.
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What is the Load Cell?
Load cell is the device that is used for measurement of very high compressive and tensile force, high pressures, and weights. There are five types of the load cells depending on the primary and secondary element that is used to sense the force. These are: strain gauge type load cells, hydraulic load cells, diaphragm load cells, spool type load cells and ring type load cells.
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Strain Gauge Type of Load Cells
One of the most popularly used types of the load cells is the strain gauge load cell. In fact amongst all the types of load cells, the strain gauge type ones are used most commonly. These load cells are used for the measurement of very large compressive and tensile forces. This load cell is the special application of the strain gauges.
In the strain gauge load cells the strain gauge is connected to the steel column (load column) or the member on which the applied tensile or compressive force is to be measured. This member could also act as the primary member absorbing the force from other component on which the force is applied.
All the parts of devise including the steel column and the strain gauge are enclosed in a very strong, rigid and heavy iron casing. There are two wiring connections to the strain gauge for which special holes are made in the iron casing.
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How the Strain Gauge Load Cell Works?
In the beginning the force or pressure is applied to the load column due to which it gets compressed and its length gets reduced. This column acts as the primary transducer since it converts the applied force into change in length, however this change in length is not measured directly. At the same time, the strain gauge connected to the load column gets compressed. This strain gauge acts as the secondary transducer since it records the displacement of the load column.
Since the strain gauge is compressed, its length gets reduced, which depends on the magnitude of the applied force on the top of the load cell. As we know the resistance of the strain gauge changes when its length changes. This change in resistance can be recorded by the wires connected to the strain gauge. The resistance change is calibrated against the applied force, thus the recorder directly gives the value of the applied pressure or the force.
For the measurement of the tensile force, usually the bonded wire type of strain gauge is used. While in case of the compressive force, the length of the strain gauge reduces, in case of the tensile applied force its length increases.
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1) Book: Mechanical and Industrial Measurements by R.K. Jain, Khanna Publishers.