There are different types of load cells which are used to convert a force to electric signals. The force conversion is indirect and it occurs in two ways. The mechanical placement deforms the force into a strain gauge. It measures the strain (deformation) as a signal as a result of the effect of the strain on the electrical resistance. The different types of load cells are usually made of 4 distinct gauges in bridge configuration. There are also load cells of half bridges (two strain gauges) or a quarter bridge (one strain gauge). The signal electrical outputs are arranged in order of millivolts and need the amplification of instrumentation amplifier to operate successfully. The transducer output can also be weighted to ascertain the extent of force used on the transducer. The different types of load cells in use include strain gauge cells, pneumatic load cells, and hydraulic load cells.
Hydraulic load cell
In these types of load cells , the piston is usually kept in an elastic diaphragm but does not have a direct contact with the load cell. There are mechanical stops kept in place to stop too much pressure on the diaphragm in situations where the load exceeds certain limits. On the application of load on the piston, the progression of the diaphragm and the piston arrangement leads to an increased pressure of the oil. When this happens, it creates a change in the bourdon tube linked to the load cells.
Pneumatic load cell
In these types of load cells , there is an automatic regulation to balance pressure. One side of the diaphragm is pressurized with air and it passes through the nozzle at the base of the load cell. To take measurements inside the cell, air gauge is usually placed at the load cell. When the diaphragm deflects, it affects the pressure of the chamber and the nozzle.
Strain gauge load cell
These are the most common types of load cells , though other cells are equally frequently used. For example, the hydraulic load cell is the second most widely used types of load cells in industrial applications behind strain gauge cells. They are normally used to reduce the risk of using strain gauge cells. There are some conditions that will require the use of strain cells and there are some other conditions that will require the use of hydraulic cells. For instance, where lightning (transient voltage) is prevalent, it is best to use hydraulic load cells because they are immune to their effects.
Other types of load cells
Apart from the cells mentioned above, there are also other types of load cells, including wire and vibrating load cells and piezoelectric load cells. The piezoelectric load cells are used in the dynamic measurement of force. On the other hand, the wire load cells are very useful in geo-mechanical applications as a result of low rate of drifts.
All the different types of load cells pass through a stage known as ringing when they are kept in quick load changes. This is the result of the spring-like characteristics of the load cell.