Load cell
A load cell is typically 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 to be sensed is deforming a strain gauge. The strain gauge converts the deformation (strain) to electrical signals. Normally, a load cell consists of four strain gauges in a wheatstone bridge configuration, but are also available with one or two strain gauges. The electrical signal output is normally 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 is of finite stiffness and has 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 bending beam
- shear beam
- column
- membrane
- ring torsion
- bending ring
- double shear beam
- pancake
- "S" beam
Applications
- truck weighing
- tension measurement
- force measurement
- railcar weighing
- hopper, tank and vessel weighing
- onboard Weighing
- electronic Crane Scales
- wireless Crane Scales
- structural health monitoring
