Gravimetric means having to do with the measurement of mass. Mass measurement includes the use of scales, balances and mass flow meters. It also includes the calibration or comparison of a weight to a standard.
Modern scales use transducers known as load cells. The vast majority of these cells utilize strain guage technology. There are however certain applications where other load sensing means are used such as hydraulics, LVDT's, vibrating wire and even radiation emitting. These transducers may be used to support the load receiving element (scale deck) directly, or may be used to sense the load transferred through a lever or levers to the load cell. In the latter case, the scales are referred to as electro-mechanical scales.
Scales can range in capacity from very small laboratory or precious metal scales with low capacities in the 1 gram range all the way up to very large scales designed to weigh fully loaded vehicles or rail cars. These scales may have capacities in the 100 metric tonne range or more. In addition, there are several types of special purpose scales. These include conveyor belt scales (integration over time), in-motion railway scales, hi-speed in motion packaging systems, bagging scales etc.
Scales are generally categorized as either non-automatic or automatic. Non-automatic are by far the most common scale type and consist of all scales where an operator places the load on the scale, takes a reading then removes the load. These are the scales you will see in your local grocery store or deli. Automatic scales are less common and are almost always located in commercial or industrial environments. These scales are designed to operate automatically and continuously. Examples include conveyor belt scales used to load ships or rail cars, bulk weighers used to ship or receive grain or other bulk commodities and in motion rail scales which weigh entire unit trains while they are in motion.
What is the difference between a scale and a balance. Although the terminology is often used interchangeably, strictly speaking a scale will provide a reading of the weight, either directly (automatic indicating) through a weight display, or indirectly (non-automatic indicating) through the reading of a beam or beams. A balance will indicate a balanced condition when the load on one pan counteracts the load on the other pan. These are usually equal arm balances, but may also be unequal arm, in which case the load on one pan is either a fraction or multiple of the load on the other pan.