GLOSSARY OF TERMS
VPG is involved in the business of measurement, display, and control of physical parameters ranging from relatively simple measurement of electrical current and surface strain (unit displacement) to the more complex measurement of weight and force and ultimately to the control of industrial processes and weighing in-motion. Through an acquisition strategy based upon vertical integration, VPG has built on its core technology in resistive metal foils to achieve a high standard of precision in all our business units.
Resistive Foil Technology: Resistive foil technology pertains to manufacturing process expertise in metal alloys used in foil resistors and foil strain gages. Aspects of the technology range from metallurgical considerations to micro-electronic processing know-how to sensor design to end use application.
Resistors: Resistors are electrical components that oppose the flow of current. They are used to protect, operate, or control circuits. In addition to being supplied as individual components of a single resistance value, resistors can also be supplied as pre-configured resistor networks with multiple resistors inside a common package. Voltages can be reduced with individual resistors or divided into separate voltages with the use of resistor networks. Performance specifications to consider when searching for resistors include resistance range, tolerance, power rating, continuous operating voltage, temperature coefficient, (TCR), Resistance change due to power (PCR), and operating temperature.
Current Sensing Resistors: Current sensing resistors convert the current flowing through them to a voltage drop. Monitoring or measuring this voltage drop allows the current through the resistor to be measured. Typical uses for current sensing resistors include electric motor control, surge protection circuits for electronic products, energy optimization in battery powered portable products, high precision weight measurements, control of X-Y displacement, and many other applications.
Strain Gages: Strain gages are resistive sensors whose resistance is a function of applied strain (unit deformation). Stress is calculated from the strain information. Typically a strain gage is attached to a structure and when such a structure is deformed (tension, compression, shear), the resistive strands in the strain gage follow the structure deformation which causes an electrical resistance change. The resistance change is then expressed in units of strain or stress. Strain gages are used in transducers that convert force, pressure, tension, etc., into an electrical signal. They are also used for measuring strain in structures (stress analysis) such as airplanes, cars, machines, bridges and other structures. Performance specifications to consider when searching for strain gages include operating temperature, the state of the strain (including gradient, direction, magnitude, and time dependence), and the stability required by the application.
Load Cells: Load cells are mechanical components which act as force sensors by employing strain gages to provide an electrical output proportional to the applied force. Typically the electrical output is either analog (voltage or current) or digital. Load cells have specific mechanical packaging and sensing orientation to fit into electronic scales, and testing and monitoring systems. Load cells can be used for tension, compression, and/or shear measurement. Tension load cells are used for measuring forces that are in-line and "pull apart". Compression load cells are used to measure forces that are in-line and "push together". Shear load cells are used to measure tension or compression forces that are offset (not in-line). When selecting load cells, there are many form factors or packages to choose from to insure their physical size is compatible with space available for the application, such as inside an electronic weighing scale.
Weigh Modules: Weigh modules are subassemblies designed to be mounted to tanks, trucks, bins, silos and other applications requiring an integrated weighing system. There are two basic types of weigh modules: compression and tension. Compression weigh modules are used to convert static loading applications such as tanks, or dynamic applications such as conveyors, into a scale. In tanks and other static structures, the weigh modules mount under the legs or supporting structure. Tension weigh modules convert a suspended tank or hopper into a scale. Mounting hardware ensures that only vertical load is measured, providing reliable weighing.
Scales and Balances: Scales and balances are used to measure static or dynamic loads for a wide variety of industrial applications. Typically a scale consists of a mechanical structure or platform supported by load cells whose electrical output is displayed to indicate the weight being measured. Scales include bench top devices which are relatively small and measure a limited range of loads. Conveyor scales weigh items as they pass over a specific point on the conveyor. 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 weighing heavy freight and animals. Dynamometers measure the amount of power applied by an engine. There are also scales for counting systems which are useful when items are nearly identical in size or weight. Scales for material handling such as crane scales and fork-lift scales can eliminate the need to take items to a stationary scale.
Web Tension Sensors and Controllers: Web tension sensors and controllers are used on continuous processing machinery for applications such as paper and roofing material production, printing, metal rolling, cutting, embossing, punching and forming. Typically, force sensors are placed at each end of an idler roll that is part of a machine frame and over which the web travels in the process. Thereby, the idler roll equipped with sensors measures the force placed upon the roller from the web. The output signal from the sensor can be used to control such parameters as the magnitude of the web tension, the speed of the web, the alignment of the web; or to detect breakage in the processing of the web.
Onboard Weighing System: An onboard weighing system is used to weigh a load carried by a vehicle with the system being wholly contained within the vehicle. The system is used not only for measuring the weight of a load as it is being placed on a vehicle; it is also used to weigh portions of a load being removed from a vehicle. Typically this occurs where a vehicle is used to transport a load of material to various locations and at each location some of the load is removed. There are onboard weighing models available for tractor-trailers and vocational trucks in a variety of applications, including trash collection, dump trucks, and concrete mixers. The biggest benefits to truck operators are reduced loading and adjustment times, since onboard scales allow for loading the vehicle to the maximum legal limit on-site. In addition, they allow for maximized payloads on every trip and the elimination of overweight fines.
Data Acquisition Instrumentation: Data acquisition instrumentation is used to sample real world physical conditions and conversion of the resulting samples into digital numeric values that can be manipulated by a computer. The components of data acquisition systems include sensors that convert physical parameters to electrical signals, signal conditioning circuitry to convert analog waveforms into digital values for processing, and software programs using various general purpose programming languages.
Weighing Indicators and Controllers: Weighing indicators and controllers are electronic instruments used for a range of applications from simple weight displays and data collection to control of an entire automated process including adding multiple ingredients to a batch recipe formulation, turning on a motor, or starting a conveyor. Weighing indicators and controllers are also used for inventory management and traceability. Typically controllers are supplied with programmable software.