A load cell is a sensor that detects force such as tension, compression, pressure, or torque. There are 3 types of load cells, hydraulic, pneumatic, and strain gauge. The relation between the varying parameter in the load cell and the applied force is used to measure the force. You have already seen their application in your daily life, be it a weight machine at a local store or in your car.
How does it work?
Strain Guage Load Cell
Strain gauges are the most common type of load cells. Strain gauges are secured in an aluminum or steel body of the load cell. The load cell body is elastic and thus called a spring element. Tension on the spring stretches the body, whereas compression contracts the body. Hence, the body reacts to any force and deform.
The spring gauge detects this deformation and their resistance change due to the deformity. But, the change is very small. To get a measurable value, 4 spring gauges in a Wheatstone bridge combination is used. This way, the change in the output voltage is measured. The output voltage is directly proportional to the applied force.
Hydraulic Load Cell
A hydraulic load cell is a conventional piston-cylinder system. The hydraulic fluid pressure inside the sensor changes with the applied pressure. The pressure change is directly proportional to the applied force.
Pneumatic Load Cell
A pneumatic load cell uses the force-balance method, as a hydraulic load cell. However, instead of fluid, it uses either regulated air or nitrogen.
Advantages and Applications
Strain gauge load cells are highly accurate and precise. They feature linear measurement as well. Due to fewer moving parts than the other load cells, they tend to last longer. Also, they are smaller than the other load cells. They find applications on our daily uses to aerospace industries. Strain gauge load cells are used in airplanes to measure wing deflection. They are used in cable bridges to verify design parameters and make sure that the design is capable of handling the stress.
Hydraulic load cells are used for hazardous applications. Lack of electronic circuitry allows it to be deployed in any hazardous environment, without risking an explosion. However, there are chances of fluid leakage over time.
A pneumatic load cell is best suited for places in which cleanliness is a prime concern. They are also very precise and used to measure small weights. There is no fluid in the sensor even if the chamber breaks, the air is released into the atmosphere.