Load cell

This elasticity gives rise to the term "spring element", referring to the body of the load cell.

When force is exerted on the load cell, the spring element is slightly deformed, and unless overloaded, always returns to its original shape.

A strain gauge is constructed of very fine wire, or foil, set up in a grid pattern and attached to a flexible backing.

The wire or foil in the strain gauge is arranged in a way that, when force is applied in one direction, a linear change in resistance results.

Tension force stretches a strain gauge, causing it to get thinner and longer, resulting in an increase in resistance.

The strain gauge is attached to a flexible backing enabling it to be easily applied to a load cell, mirroring the minute changes to be measured.

Increasing the number of strain gauges applied collectively magnifies these small changes into something more measurable.

In a load cell, the resistors are replaced with strain gauges and arranged in alternating tension and compression formation.

When force is exerted on the load cell, the structure and resistance of the strain gauges changes and

[3] This allows for simple installation of the load cells without expensive and complicated mounting kits, stay rods, or overload protection devices, which in turn eliminates the need for maintenance.

The material used for the elastic element is normally aluminum or stainless steel for load cells used in corrosive industrial applications.

The low strained element combined with the fact that a capacitive sensor is non-contacting, provides the very high shock resistance and overload capability of the capacitive load cell compared to the strain gage load cell.

This is an obvious advantage in industrial environments and especially for the lower capacity load cells where the risk of damage because of shocks and overloads is high.

Air pressure is applied to one end of the diaphragm and it escapes through the nozzle placed at the bottom of the load cell.

[5] Typical hydraulic load cell applications include tank, bin, and hopper weighing.

The piezoelectric effect is dynamic, that is, the electrical output of a gauge is an impulse function and is not static.

Another advantage of Piezoelectric load cells conditioned with a charge amplifier is the wide measuring range that can be achieved.

Users can choose a load cell with a range of hundred of kilonewtons and use it for measuring few newtons of force with the same signal-to-noise ratio; again this is possible only with the use of a charge amplifier for conditioning.

With these additional signals, the controller can compensate for the change in wire resistance due to external factors, e.g. temperature fluctuations.

The sensing elements are in close proximity and in good mutual thermal contact, to avoid differential signals caused by temperature differences.

As such, a load cell of finite stiffness must have spring-like behavior, exhibiting vibrations at its natural frequency.

Alternatively, a control system can use an actuator to actively damp out the ringing of a load cell.

[12] From 1993 the British Antarctic Survey installed load cells in glass fibre nests to weigh albatross chicks.

[13] Load cells are used in a wide variety of items such as the seven-post shaker which is often used to set up race cars.

They can be installed on hoppers, reactors, etc., to control their weight capacity, which is often of critical importance for an industrial process.

Some performance characteristics of the load cells must be defined and specified to make sure they will cope with the expected service.

Among those design characteristics are: The electrical, physical, and environmental specifications of a load cell help to determine which applications it is appropriate for.

Over time, load cells will drift, age and misalign; therefore, they will need to be calibrated regularly to ensure accurate results are maintained.

[15] ISO9000 and most other standards specify a maximum period of around 18 months to 2 years between re-calibration procedures, dependent on the level of load cell deterioration.

Annual re-calibration is considered best practice by many load cell users for ensuring the most accurate measurements.