Force transducers convert forces into output signals that can be used by gauges, controllers, or data loggers. They can be hydraulic, pneumatic, or based on strain gauge sensors. Load cells are highly accurate and used in various industries. They have analog or digital outputs and can be connected to computers or data highways. Force transducers can be as small as a pinhead or as large as a bridge column.
A force transducer converts measured forces representing force, weight and pressure into transmitted output signals. These signals can be fed to computer-connected gauges, controllers, or data loggers. Most force transducers have analog or digital electronic, pneumatic or hydraulic outputs, depending on the needs of the application. A force transducer can be as small as the head of a pin, measuring a mere gram of force (1/28 of an ounce), or as large as a bridge column, measuring hundreds of tons (1 ton equals 2000 pounds or 909 kilograms). .
The first force transducers were hydraulic. Cylinders, bellows or diaphragms converted forces into pressure signals which were read off gauges. One advantage of hydraulics is that indicators in different locations on the same line allowed multiple people to obtain and use information at the same time. Another is that plumbing systems are inherently sealed systems, making them generally rugged, reliable, and impervious to water and other contaminants.
Later, force transducer systems with pneumatic outputs came into use, allowing for easy integration into pneumatic process control systems using the universal 3-15 psi output convention. Many users of hydraulic systems have simply installed a pneumatic pressure transmitter into the hydraulic hose from the hydraulic force transducer already in place. Pneumatic force transducers have also been widely used to directly control winding tension brakes on rolling machines in the paper industry.
Advances in the art of strain gauge sensors since the 1950s changed the way forces would be measured. The sensing element was based on the relationship between electrical resistance and the stretching, twisting, or other physical distortion of a conductive wire, foil, or thin film from its normal rest position. When these conductors were connected to beams, studs, shafts or plates, they enabled the implementation of highly accurate, repeatable and robust force transducer systems called load cells. They would be applied to every area of human enterprise, from industry and commerce to transportation, health care, scientific research, and personal electronics. They are used in weighing scales, scales and for medical measurements such as blood pressure.
Force transducer systems based on strain gauge sensors or load cells are generally inexpensive to manufacture. They include voltage excitation for the sensor and balance bridge circuit, an amplifier section, scaling, and conditioning electronics for the output. Analog outputs can range from direct current (DC) voltages that predominate scientific, medical, and defense applications, to standard 4-20 milliampere DC current outputs for industrial control systems. Force transducers connected directly to computers and multiplexers can incorporate RS-232 serial interfaces, Universal Serial Bus (USB) connections, and industrial data highways such as Modbus®. Food scales in dieters’ kitchens or digital tire pressure gauges on keychains both incorporate miniature force transducers with simple liquid crystal displays (LCDs).
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