Load cells are widely used in many industries because of their accuracy and precision. Many electronic weighing scales now use load cells to weigh various types of objects. Depending on the type of load cell used, it can weigh the smallest pill or even the largest railroad cards.
How does load cells work?
Load cells are categorised as transducers. Essentially, they convert force into weight outputs. When force is applied, the sensors will transmit the data to the load cells which converts this to electronic data values. The converted data is then sent to the indicators where you can read the weight of the object.
To further understand how load cells work, let's discuss each working principle involved in the use of load cells.
1. Strain Gauge
The strain gauge is a metal foil that provides varying electrical resistance when force, pressure, torque or compression is applied. The converted resistance is then measured producing the weight output of the object causing such force tension.
The strain gauge is securely attached to a zigzag-shaped film that stretches or contracts to cause the changes in resistance. When this happens, the weight results based on the strain applied in load cells, that is, the changes in resistance of the electrical conductors or strain gauge.
2. Force Sensor
The force sensor is the metal body, typically referred to as flexure, that is bonded to the strain gauge. This is made of aluminium or stainless steel that offers durability and strength to withstand heavy loads. It is also characterised by the flexibility to ensure that it will return to its original form when the force or load is removed.
When tension or pressure is applied, the force sensor acts like a spring that flexes. This, in turn, provides changes in the electrical resistance creating voltage differentials.
3. Wheatstone Bridge Circuit
The Wheatstone bridge circuit is a series of strain gauges arranged in a loop circuit. It ensures that the measuring grid is aligned consistently and correctly. When it receives the voltage differentials, it works according to the changes in voltage coming from the physical force applied to the force sensor.
4. Load Cell Amplifier Module
Load cell amplifier modules are converters that regulate excitation voltage to the Wheatstone bridge circuit. It converts the electrical signals or the millivolts per volt output to data that is more understandable by the users or weight readers.
The Importance of Load Sensitivity and Accuracy
Two of the most important concepts in load cells are sensitivity and accuracy which are collectively known as force sensor accuracy. It rests mainly on the consistency of capturing every rational force variation.
In essence, force sensor accuracy is the minutest amount of force that can be applied to the load cell causing the linear and verifiable voltage differentials. The higher the accuracy, the better.
Are there factors that can affect the accuracy of load cells?
Every type of load cell is engineered to meet the accuracy that your business needs but some outside factors can also affect its accuracy.
● Side and Eccentric Loads
When your load cells receive tension, force or weight from different angles, their accuracy may be impacted over time. If you are not using a single point load cell, it may be best to ensure that you prevent placing weight off-centre.
It is noteworthy to remember that load cells typically measure force in the same direction. Placing pressure from various angles can impact not just its precision but also distort weight readings.
Due to the load cell’s sensitivity, the air temperature or climate can impact its accuracy. Some load cells are designed to withstand extreme temperatures, hence, always check the operating temperature in the datasheet before purchasing.
Another factor that can hugely impact the accuracy of your load cell is how you mount it. Similar to side and eccentric loads, mounting your load cell off-centre can impact its accuracy and precision.
The imbalance in the mounting angle and location can cause unequal distribution of weight in your load cell. It is best to follow the mounting instructions that come with your load cell. If you are unsure of the mounting process or if you are doubtful about where to mount it, it may be best to ask your load cell provider to help you install it.
Just like temperature, humidity can also affect the accuracy of load cells over time. If your working environment is a high-humid place, it is advisable to find a load cell engineered for this condition. A good load cell for this type of environment has IP protection of at least IP61 such as stainless steel load cells and compression load cells.
Creep is the result of constant and repetitive use as time goes by. It is the change in its accuracy resulting from the load cell’s monotonous usage while environmental factors remain the same. Any material deformity in the load cell composition can lead to creep that impacts its accuracy over time.
Load cells come in many styles, types and sizes. It may be best to know what type of working place you have, environmental considerations and the kind of force, pressure, torque or tension it will receive.
Contact Meltrons Australia to learn more about load cells!