Load Cells:
Load cells are utilized in nearly every electronic weighing system.
In understanding load cells, you’ll be better able to comprehend the systems in which
they are used. 
The following is a brief summary of the inner workings of a load
cell. While this explanation does not answer every question, it can provide the basic
framework for understanding load cells.
System Components:
In contemporary control applications, weighing systems are used in
both static and dynamic applications. Some systems are technologically advanced,
interfacing with computers for database integration and using micro-processor based
techniques to proportion material inputs and feed rates. To send the weight information to
computers, signal conditioners are utilized to permit direct communication from the load
cell via conversion of the load cell’s analog signal to a digital signal.
An entire system can be constructed, one piece at a time, from
basic modules.
Parts of a system can include:
- Load cells
- Cable
- Junction Box (summing up the load cell signals up
to one output),
- Instrumentation (indicators, signal conditioners, etc),
- Peripheral Equipment (printers, scoreboards, etc.)
Fundamentals:
A load cell is classified as a force transducer. This device
converts force or weight into an electrical signal.
 The strain gage is the heart of a load cell. A strain gage
is a device that changes resistance when it is stressed. The gages are developed from an
ultra-thin heat-treated metallic foil and are chemically bonded to a thin dielectric
layer. "Gage patches" are then mounted to the strain element with specially
formulated adhesives. The precise positioning of the gage, the mounting procedure, and the
materials used all have a measurable effect on overall performance of the load cell.
 Each gage patch consists of one or
more fine wires cemented to the surface of a beam, ring, or column (the strain element)
within a load cell. As the surface to which the gage is attached becomes strained, the
wires stretch or compress changing their resistance proportional to the applied load. One
or more strain gages are used in the making of a load cell.
Multiple strain gages are connected to create the four legs of a
Wheatstone-bridge configuration. When an input voltage is applied to the bridge, the
output becomes a voltage proportional to the force on the cell. This output can be
amplified and processed by conventional electrical instrumentation.
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