Scales and balances are used to measure static or dynamic loads for a wide range of industrial applications. They are used to weigh small packages, the contents of hoppers, and extremely heavy loads that are hauled by trucks or trains. Performance specifications for scales and balances include measurement type, rated load, and accuracy. There are three basic measurement types: compression, shear, and tension. Compression squeezes contents along the same axis. Shear is compression along the offset axes. Tension weigh modules are used to convert a suspended tank or hopper into a scale. To provide reliable measurements, mounting hardware is used to ensure that only the vertical load is measured. Rated load is the maximum load that scales and balances can handle without sustaining permanent damage. Accuracy is the limit tolerance or average deviation between the actual output and the theoretical output.
Scales and balances provide analog outputs and differ in terms of display type and user interface. Many devices can output a voltage signal or current signal in proportion to the strain on the sensor. Common voltage ranges include 0 – 5 VDC and 1 – 5 VDC. The most common analog current loop is 4 – 20 mA. Devices with a switch or relay that operates at set point are also available. Scales and balances display values with analog meters, digital readouts, or video display terminals. Analog meters include a needle or light emitting diode (LED). Digital readouts are numerical or application-specific. Video display terminals (VDT) include cathode ray tubes (CRT) and flat panel displays (FPD). Some scales and balances include an analog front panel with potentiometers, dials, and switches. Others have a digital front panel. Larger, more complex systems can often be controlled remotely with a computer interface and include application software.
Scales and balances differ in terms of applications and features. Benchtop devices are relatively small and measure a limited range of loads. Conveyor scales weigh items as the pass along an assembly line. Truck, rail, and axle scales are placed under a vehicle’s tire. Floor scales align the measuring platform with the main floor and are suitable for shipping heavy freight and animals. Dynamometers measure the amount of power applied. Counting systems, crane scales, hopper or tank scales, weigh checks, and general-purpose industrial scales are also available. In terms of features, some scales and balances have a built-in audible or visual alarm. Others are waterproof, washdown-capable, or ruggedized for harsh environ