Since the advent of the automotive industry, the importance of a correct weighing system has grown significantly. Although it was important before then to weigh objects, it wasn’t until the last 19th century that the concept of a “load cell” was even introduced.
They are of extreme importance in various industries around the world.
A load cell, by basic definition, is a transducer that emits an electrical signal directly proportional to the force being pressed on it. To get a better idea of a transducer, imagine an antenna.
The antenna converts electromagnetic waves into electrical signals, for the use of radio, television, and other components. The antenna is a transducer for that energy transfer.
A load cell operates the same way a transducer operates, according to physics principles. The idea behind it is the same: It converts energy from one form to another.
Load cells can be used in any number of industries; in fact, you’ve probably encountered one already. One common type of load cell is the kind used in grocery stores to electronically weigh items. When you place you fruit or vegetables on the weight machine, it emits an electrical signal that shows how much it weighs.
Loads cells are also used often in pharmaceutical industries and laboratories, where the importance of weighing thinks as close to exact as possible is high. They are also used in the automotive industry for calibrations of equipment, specifically when it comes to determining the load bearing of vehicles or parts of vehicles.
There are five types of 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. Here is at two of the most common: the strain gauge load cells and the hydraulic load cells.
The strain gauge type load cells utilize a “strain gauge” to determine the amount of force bearing down on the object. The strain gauge was invented in the early 1900s by Edward Simmons and Arthur Ruge. It operates according to a mechanical metal foil pattern that is supported in the back and has adhesive. When the metal foil pattern bends under pressure, it changes the electrical resistance and thereby signals force.
Strain gauge load cells are the most common type used in the industry. These load cells are stiff, have very long lifespans when in comes to applications, and have very good resonance values. When the force is placed on the strain gauge, it converts the electrical resistance into an electrical value which is proportional to the force being placed.
Hydraulic load cells uses a conventional piston and cylinder arrangement. The piston is placed in a thin elastic diaphragm, which never actually comes into contact with the load cell.
The load cell is filled with oil. When force is applied to the piston, it displaces a certain amount of oil, which is pushed through a hose and converted to a hydraulic pressure gauge. Because this type of load cell does not have any electrical components, it is used most often in hazardous areas and outdoor environments.
Load cells face a particular challenges when it comes to the mechanical operation of load cells and the environment in which they are placed in. Mounting is an issue, particularly when it comes to friction. An overload can cause a plastic deformation. Wiring may develop high resistance due to corrosion. And electrical currents (like lightning) cause problems.
Whereas load cells measure the amount of force placed on an object, a torque sensor measures the amount of torque (i.e. force applied to a circular motion) on an object. Torque sensors are used to measure the torque of any rotating object, including an engine, crankshaft, gearbox, transmission, rotor, bicycle crank, and much more.
Both load cells and torque sensor units are designed to operate in a wide temperature range of -452 degrees Fahrenheit to 450 degrees Fahrenheit.
And often, like the standard strain gauge load cells, the torque sensor units also use strain gauge technology. Unfortunately, while static torque is easy to measure, dynamic torque is not.