Load cell

A load cell is an electronic device (transducer) that is used to convert a force into an electrical signal. This conversion is indirect and happens in two stages. Through a mechanical arrangement, the force being sensed deforms a strain gauge. The strain gauge converts the deformation (strain) to electrical signals. A load cell usually consists of four strain gauges in a Wheatstone bridge configuration. Load cells of one or two strain gauges are also available. The electrical signal output is typically in the order of a few millivolts and requires amplification by an instrumentation amplifier before it can be used. The output of the transducer is plugged into an algorithm to calculate the force applied to the transducer.

Although strain gauge load cells are the most common, there are other types of load cells as well. In industrial applications, hydraulic (or hydrostatic) is probably the second most common, and these are utilized to eliminate some problems with strain gauge load cell devices. As an example, a hydraulic load cell is immune to transient voltages (lightning) so might be a more effective device in outdoor environments.

Other types include piezo-electric load cells (useful for dynamic measurements of force), and vibrating wire load cells, which are useful in geomechanical applications due to low amounts of drift.

Every load cell is subject to "ringing" when subjected to abrupt load changes. This stems from the spring-like behavior of load cells. In order to measure the loads, they have to deform. As such, a load cell of finite stiffness must have spring-like behavior, exhibiting vibrations at its natural frequency. An oscillating data pattern can be the result of ringing. Ringing can be suppressed in a limited fashion by passive means. Alternatively, a control system can use an actuator to actively damp out the ringing of a load cell. This method offers better performance at a cost of significant increase in complexity.

Load cell types

* double ended shear beam
* single ended shear beam
* single column
* multi column
* membrane
* torsion ring
* bending ring
* pancake
* digital ElectroMotive Force

Applications

* electronic crane scales
* finding the center of gravity of an object by weight
* force measurement
* Force gauge
* hopper, tank and vessel weighing
* onboard weighing
* railcar weighing
* structural health monitoring
* tension measurement
* in- motion dynamic check weighers check weigher
* truck weighing
* wireless crane scales
* "S" Type

References

External links

* [http://www.lcmsystems.com/glossary_of_terms.html Load cell glossary of terms]
* [http://www.omega.com/prodinfo/loadcells.html Introduction to Load Cells]
* [http://www.rdpe.com/ex/hiw-sglc.htm How it works (interactive)]
* [http://www.societyofrobots.com/sensors_forcetorque.shtml Load cell tutorial]
* [http://www.futek.com/apps_load.aspx Diagrams of load cell applications]
* [http://www.loadcelltheory.com/loadCellTheory.html What is a Load Cell?]
* [http://www.loadstarsensors.com/capacitance.html Capacitive Load Cell Technology]
* [http://www.pulselectronic.com Load Cell Technology]
* [http://www.puls.com.tr Load Cell Technology by PulsElectronic]
* [http://www.apdataweigh.com Load Cell Applications]
* [http://www.wipotec.com/main.php?file=technik/technik_main.dat How Electromotive Force Restoration Works]