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Metrology, standardization and certification |Метрология, стандартизация и сертификация

Lesson 7

Read the text: Microelectromechanical systems and electrical power distribution and control

A mite less than 1 mm on a MEMS device.Microelectromechanical systems (MEMS) is the technology of the very small, and merges at the nano-scale into nanoelectromechanical systems (NEMS) and Nanotechnology. MEMS are also referred to as micro machines, or Micro Systems Technology (MST). MEMS are separate and distinct from the hypothetical vision of Molecular nanotechnology or Molecular Electronics. MEMS generally range in size from a micrometer (a millionth of a meter) to a millimeter (thousandth of a meter). At these size scales, the standard constructs of classical physics do not always hold true. Due to MEMS' large surface area to volume ratio, surface effects such as electrostatics and wetting dominate volume effects such as inertia or thermal mass. Finite element analysis is an important part of MEMS design.

The potential of very small machines was appreciated long before the technology existed that could make them—see, for example, Feynmann's famous 1959 lecture There's Plenty of Room at the Bottom. MEMS became practical once they could be fabricated using modified semiconductor fabrication technologies, normally used to make electronics. These include molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro discharge machining (EDM), and other technologies capable of manufacturing very small devices.

Companies with strong MEMS programs come in many sizes. The larger firms specialize in manufacturing high volume inexpensive components or packaged solutions for end markets such as automobiles, biomedical, and electronics. The successful small firms provide value in innovative solutions and absorb the expense of custom fabrication with high sales margins. In addition, both large and small companies work in R&D to explore MEMS technology. Complexity and performance of advanced MEMS based sensors are described by different MEMS sensor generations.

  MEMS description.

Developments in the field of semiconductors are leading to integrated circuits with three-dimensional features and even moving parts. Such devices, called MicroElectroMechanical Systems (MEMS), can resolve many problems that a microprocessor plus software or hardwired ASIC(Application Specific Integrated Chip) cannot.MEMS technology can be implemented using a number of different materials and manufacturing techniques; the choice of which will depend on the device being created and the market sector in which it has to operate.

Electrical power  distribution and control

The EPDC subsystem distributes 28-volt dc electrical power and generates and distributes 115-volt, three-phase, 400-hertz ac electrical power to all of the space shuttle systems' electrical equipment throughout all mission phases. The EPDC subsystem consists of a three-bus system that distributes electrical power to the forward, mid-, and aft sections of the orbiter for equipment used in those areas. The three main dc buses are main A (MNA), main B (MNB) and main C (MNC). Three ac buses, AC1, AC2 and AC3, supply ac power to the ac loads. Three essential buses, ESS1BC, ESS2CA and ESS3AB, supply control power to selected flight crew controls and operational power to electrical loads that are deemed essential. Nine control buses, CNTL AB1, 2, 3; CNTL BC1, 2, 3; and CNTL CA1, 2, 3, are used only to supply control power to flight crew controls. Two preflight buses, PREFLT 1 and PREFLT 2, are used only during ground operations.

Electrical power is controlled and distributed by assemblies. Each assembly-main distribution assembly, power controller assembly, load controller assembly and motor controller assembly-is an electrical equipment container or box.

The dc power generated by each of the fuel cell power plants is supplied to a corresponding DA. Fuel cell power plant 1 is supplied to DA 1, FCP 2 to DA 2 and FCP 3 to DA 3. Each DA contains remotely controlled motor-driven switches called power contactors used for loads larger than 125 amps. The power contactors are rated at 500 amps and control and distribute dc power to a corresponding mid power controller assembly, forward power controller assembly and aft power controller assembly. Power contactors are also located in the APCAs to control and distribute GSE 28-volt dc power to the orbiter through the T-0 umbilical before the fuel cell power plants take over the supply of orbiter dc power.

1. Match the left part with the right:

2. Complete the sentences with the suggested words: inexpensive, sizes, specialize, solutions

Companies with strong MEMS programs come in many _______. The larger firms _______ in manufacturing high volume _______ components or packaged _______ for end markets such as automobiles, biomedical, and electronics.