“A Load cell is a force transducer which converts forces such as tension, compression, pressure, toque, weight etc. into an electrical signal that can be used to measure such forces. Or simply it is used for the measurement of different types of forces as mentioned. The main purpose of load cell sensor is measure weight or to check amount of load transferred.”

A simple load cell diagram is shown below-

Most common type of the cell transducer is electric type that is based on strain gauge. So here we will discuss working principle of strain gauge type. Since we know that strain gauge is a variable resistive transducer which converts physical variable such as force, pressure or weight into change in electrical resistance and here change in resistance produces change in form of voltage of current when gauge is connected to bridge circuits thus the amount of force delivered to the cell is proportional to the change in voltage, therefore the amount of force can be calculated from the cell’s output or an scale can be calibrated directly to measure physical quantity such as force, load or weight. a diagram to illustrate its working principle is shown below-

A simple cell diagram using strain gauges is shown in figure. Here 4 identical strain gauges (i.e. having same no load electrical resistance) are attached or bonded to a metallic cylinder directly. These gauges outputs are connected to wheat stone bridge circuit arms. When there is no load upon cell, bridge circuit will be balanced and there is no current flowing through galvanometer i.e. zero output. Now when weight, load or force (to be measured) is applied to the cell, gauges R1, R4 undergo through compressive load where as gauges R2, R3 undergo through tensile load, which results into change in resistance of gauges. Since gauges are connected to wheat stone bridge, bridge gets unbalanced showing current in galvanometer which can be read and calibrated in terms of applied force or load or weight to be measured.

There are basically 4 main types, based on their working principle as mentioned as-

• Pneumatic type
• Hydraulic type
• Strain gauge type
• piezoelectric type

To ensure that the these cells can handle the expected service, some performance parameters must be developed and stated. Some common terms that should be specified, are given below-

• Full Scale Output (FSO) or rated output
• Operating Range (in kN)
• Cell sensitivity
• Gross error (measured in % of the full scale output) or Calibration accuracy
• Maximum working load or weight
• Recommended supply voltage
• Cable type and its length,
• Over range handling capacity
• Zero balance (Offset)
• Operating temperature range
• Input and output resistance
• Enclosure type and ATEX protection
• Cell material
• Linearity
• Hysteresis
• Repeatability, etc.

In industries, these cell are widely used to measure weight. They can be mounted on hoppers, reactors, and other equipment to control their weight capacity, which is typically crucial in industrial processes. Some of their practical applications are mentioned below-

• Force Gauges
• Torque gauges
• Hopper scales
• Belt scales
• Pallet weighing
• Weigh bridges
• Platform weighing