Load cells are measuring devices that monitor and gauge forces of compression, tension and shear. They are a type of transducer that converts sensed mechanical force into electrical signals for measurement used in mechanical testing, ongoing system monitoring and as components in devices such as industrial scales.
Of the three major categories by which load cells measure force, compression and tension are the most commonly employed. Sometimes a load cell will measure an object through both of these applications, rather then one or the other. Both compression and tension loadcells often use strain gauges; strain gauges are very small devices that measure the strain of an object by converting internal deformation into electrical signals, precisely measuring weight, force or strain. Force gauges use strain gauges in push-pull testing and flow measurement. While most load cells measure and test with strain gages, some use piezoelectric sensors, which utilize piezoelectric crystals to measure weight, strain, movement and vibrations. Pressure sensors and force sensors are transducers very similar to load cells that measure pressure, applied force and strain in gas pressure, altitude and liquid pressure. These sensors are often piezoelectric sensors. Many of these sensors, although quite small, are built to support or to hold as much as several tons; miniature load cells are built to provide precise measurements for much smaller applications. Equipment such as force transducers, torque sensors and load sensors all sustain strain gauges or load cells that measure and convert energy. Digital load cell technology is the most popular way to access the information gained through the sensors.
Various types of load cells, pressure sensors and gauges are used in manufacturing, processing and testing industries. Pressure sensors and load cells are used in food processing industries to precisely measure ingredients and to properly distribute the products during packaging. In industrial warehouse environments, where pallets of inventory are shuffled around, load cells are often used to determine the precise weight of loaded pallets, which is crucial for the filling and accepting of orders. Other load cell applications include the testing of bridge building materials such as beams for tension strength, as well as in railcar weighing and truck scales. Load cells are essential components in many calibration systems, as well as for fatigue testing in research and development laboratories. With reading accuracies within 0.25%, load cells, sensors and gauges provide accurate mass, weight and pressure measurement of very small loads to loads of several thousand tons.
After load cells transduce mechanical stress into electrical energy, the information that loadcells monitor is then signaled to a recorder or other computerized data collection system. Analog or digital load cell technology is used for the recording and transferring of information. Digital load cells have become more popular than analog load cells in recent years because they work faster, have a higher accuracy rate and better resolution. When load cells are used to measure any variance in certain ongoing systems, the load cells can sound an alarm or shut down the system itself until the discrepancy is corrected. Load cells can vary greatly in size and shape depending on the industrial arena they will be utilized in. The two basic components of a load cell are the sensing element and circuit. The sensing element is most often a strain gauge, which is comprised of coil. However, it can also be a piezoelectric sensor that utilizes crystals. The circuit is the connection of these gauges or sensors throughout the load cell.
Load cell outputs include analog voltage, analog current, analog frequency, switch or alarm, serial and parallel. The most basic designs consist of four gauges, which make up the measuring circuit. More complex and detailed cells can have up to thirty gauges as part of the measuring circuit. The arrangement of gauges is usually done according to the Wheatstone bridge equation, which was developed in 1833 by Samuel Hunter Christie. It was not until ten years later though that the equations' namesake improved upon it and made it popular. The more gauges inside the load cell, the more sensitive the cell is in recording and monitoring variance in measurement. In calculating capacity of a load cell, factors that must be considered are: the maximum force value, the dynamics of the system (i.e. frequency response), the effect that placing the transducer in the force path will have and the maximum extraneous loads that the load cell will handle. When mounting load cells, such factors must be considered: whether the load cell be in the primary load path or whether it will see the forces indirectly; whether there are any physical constraints that should be met for size and mounting; what level of accuracy is required, and what environmental elements the load cell will be subjected to that may cause special problems. These complexities are necessary to have the correct measuring force load cell in place, to ensure the safety and productivity of the industries employing them.
Compression load cells - Strainsert Company
Load Cells - Strainsert Company
Mini load cells - Cooper Instruments & Systems
Load Cells - Strainsert Company
Mini load cells - Cooper Instruments & Systems
Load Cells - Strainsert Company
A load cell is a force transducer that is most commonly used in weighing scales and other manufacturing equipment. The key objective of a load cell is to help the user measure the physical quantity or mass. More technically, a load cell is an electromechanical tool used across industries, from medical to architecture and from domestic to scientific research.
The use of load cells can be found in many appliances, such as security systems, weighing scales, personal scales, machines in the defense sector, weighing equipment in research laboratory and pharmaceutical production, industrial automation, submarine pressure sensing, and material testing. In the construction industry, weight measuring machines are used to test the strength of the structure.
Load sensors can be found in thermometers, as well as electrical weighing scales, and even in underwater submarines. They are a must-have tool for small and heavy scale manufacturing industries. Load sensors play a very significant role in automation precision. Additionally, security systems are all designed on the working principles of transducers.
How do load cells work?
As a load is applied onto a surface, the sensor changes its shape or physical status. The job of the sensor is to measure that shift, stress, tension, or compression on its surface.
There are different types of load cells, each work based on different principles. These types include:
Some other types of force or energy measurement and conversion tools include elastic systems, vibration systems, magneto-elastic devices, and dynamic balance devices. All of these classifications are not very technical, rather they more closely follow the traditional methods of measurement.
Capacity-based load cells are also available and provide low capacity, mid capacity, and high capacity output options. The low capacity machines are ideal for home use, while the mid and high capacity versions are used within more complex manufacturing systems.
Currently, strain gauge based force transducers are also widely used. The measurement output depends on the recommendations of the Wheatstone Bridge circuit concept. This circuit, however, did not have a diagram or scheme for the strain gauge system. The inventor had anticipated that a change in the resistance of an object is directly proportional to the force, load or pressure applied to it. The transducer makes the amount of force or pressure visible or readable for the user.
The technical definition of a load cell is often tough to comprehend. A load cell is a transducer, using an engine which generates electrical signals of a certain magnitude. A transducer is a mechanical device that works as a converter between two forms of energy. Therefore, a load cell converts energy from one medium to another.
To put it simply, a load cell is a mechanism that is devised on an electronic weighing scale. It works as a sensor that responds to the weight applied on the upper surface of a machine. That sensor then sends the interpreted data to the LED screen of the machine, which displays the accurate weight applied. The importance of correct weight measurement is undeniable. Load cells are highly accurate transducer mechanisms that give highly important information to the user.
The force or energy applied on the surface of a machine is converted and sent as a signal to the LED indicator of the weighing scale.
Different Types of Load Cells
The function of load cell transducers is not just limited to weighing. As stated earlier, these devices convert force or energy into another form and can be used in many other applications. Load cells can efficiently translate between different forms of energy, such as force, torque, light, motion, etc. Also known as load transducers, load cells are used in a number of automation, sensor, and control systems across industries.
How Load Cells Function
Load cell instruments aim to highlight the actual mass of a material. They are produced based on the principles of mass measurement under fluid pressure, elasticity, magnetic effect, piezoelectric and zero environments.
Load cells can efficiently perform precise and linear measurement, without showing any differences in data caused by changes in the environment or medium. Today's advanced load cells typically offer a very long life due to their sustainable design. Their design includes no moving parts that decrease the chances of machine damage.
Simply put, electric weighing scales are machines that manufacturers use to check the weight of an item. Scales can be found in households, stores, manufacturing units, and research laboratories. These objects use different types of weighing machines, all have unique and dissimilar capacities.
In today's society, the efficacy and accuracy of balancing scales are at their best. Scientific explorations have made it possible for us to accurately assess the weight even to the hundredth and thousandth of a decimal. There are no chances of inaccuracy when measuring the weight of an item on an electric scale.
However, there are a number of factors, whether intended or not, that may have an effect on the accuracy of scales. These include:
Load Cell Types
- The load
applied to the length of, or parallel to, the primary axis with which it shares
a common axis.
- Load cells output comparison against standard test loads.
- The output change of load cells that occurs over time while the load cell is under load, while all environmental conditions and other variables have remained constant.
- The volume inside the pressure port of force sensors, or transducers, at room temperature and barometric pressure.
- The change of length along the primary axis of load cells involving no-load and rated-load conditions.
- The membrane part of force sensors that changes its value under pressure-induced displacement.
- An unexpected change in output under constant load conditions.
- A steel tube with a u-joint at each end of load cells that transfer torque from the output of the transfer case to the axle.
- A load, which is applied parallel to, but not having a common axis with, the primary axis of load cells.
-The current or voltage that is applied to the input terminals of a transducer.
- A sensing device of load cells that is located on the very end of a transducer with no pressure port.
- The amount produced equivalent to the maximum load for a specific load cell application or test.
- The numerical distinction between the least output and the rated capacity of load cells.
- The greatest difference between load cell output readings for the same applied load. One load cell reading is obtained by escalating the load from zero, the other load cell reading by lessening the load from rated output.
- The resistance measured across the excitation terminals of a transducer at room temperature at the point where there is no load applied and the load cell output terminals are open-circuited.
- The force, weight or torque that is applied to the transducer, load cell or force sensors.
- The round shape of the top surface of load cells, transducers or load sensors where the load is applied.
- The physical number, property or circumstance that is measured by load cells, such as acceleration, force, mass or torque.
- The change in resistance caused by an applied strain of the load cell diaphragm.
- The geometric centerline (axis) along which load cells are designed to be loaded.
- An attachment to load cells, which allows tension or compression forces to be directed at the center line of load cells through a threaded center hole.
- The maximum pressure or load that may be applied to the transducer, load cells or force sensors without causing permanent damage or a change in the load cell performance specifications.
- Force that tends to divide an object along a plane parallel to the opposing stresses within load cells.
- The ratio of the change of the length of a structure when force is applied to it to the dimension of the original length.
- The output signal rated excitation of load cells with no load applied, usually expressed in percent of rated output.