Electronic pressure control devices

Consideration of Flow Devices—Positive Attributes of Modern Electronic Pressure Control Devices... 

The pressure at the head of the column (several tens to hundreds of kPa) is stabilized either mechanically or through an electronic pressure control (EPC) in order that the flow rate remains constant at its optimal value. This device is valuable because if the analysis is performed with temperature programming, the viscosity of the stationary phase and by consequence the loss of charge in the column, increase with temperature. Therefore to maintain the carrier gas flow constant, the pressure must be finely tuned to compensate this effect. The result is a faster analysis and a longer life for the column. 

Vacuum system. Components associated with lowering the pressure within a mass spectrometer. A vacuum system includes not only the various pumping components but also valves, gauges, and associated electronic or other control devices the chamber in which ions are formed and detected and the vacuum envelope. 

Some proportional detectors are combined in the same instrument with a suitable transducer which can perform some of the functions of a controller. For example, for pneumatic systems the primary sensing element actuates a variable air jet, thus modulating an air pressure which is transmitted to a further controller or direct to the controlled device. Electric and electronic detectors such as the infrared detector include the sensing and amplifying circuits of the instrument. 

Thermoelectric flame failure detection Analog burner control systems Safety temperature cut-out Mechanical pressure switch Mechanic/pneumatic gas-air-ration control Thermoelectric flame supervision Thermal combustion products, discharge safety devices Electronic safety pilot Electronic burner control systems Electronic cut-out with NTC Electronic pressure sensor/transmitter Electronic gas-air-ration control with ionisation signal or 02 sensor Ionisation flame supervision Electronic combustions product discharge safety device... 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Electronics for controlling instrument-operating parameters, such as temperature and pressure, have contributed to more stable operation. This produces better repeatability of the system for multiple cycles leading to higher precision of component isolation. Advantage of improved measurement devices can be realized once the sample preparation function is resolved. Computer hardware and software provide expanded capability for signal processing and data manipulation. Stable and precise sample preparation and measurement systems allow accurate analytical information provided that adequate maintenance and calibration practices are applied,... 

As previously mentioned, the SFE pump should produce a constant pressure of supercritical fluid with a rate controlled by a flow restrictor after the extraction vessel. There are a number of types of flow control devices, including a capillary made from fused silica, a pinched stainless steel tube, or a variable orifice allowing for electronic control of the pressure. 

Many micro energy conversion systems require a host of auxiliary components along with the core elements mentioned above. These can include micro heat exchangers and combustors to provide heat valves and flow regulators to control the flow of fuel or coolant temperature, pressure, or speed sensors along with electronics to control the device operation as well as power electronics and electrical energy storage. 

If the GC is equipped with some type of electronic pressure or flow control system, the flow rate variations can be reduced to negligible values. In such devices the column length and diameter, type of carrier gas and desired average linear velocity are inputted into the GC software. The GC automatically determines the current column temperature during temperature programming (see below) and adjusts the column head pressure so that the desired u gj. is obtained. A more rigorous approach to measuring volume flow rate and linear velocity (Hinshaw 2002) explicitly considers the effects of gas compressibility. 

This process uses a beam of high-energy electrons from a device called an accelerator to initiate resin cure in place of the usual autoclave that applies heat and pressure. EB curing is suitable for composite parts as thick as 5 cm. Parts are cured by spraying these electrons onto the composite part. The cure is controlled through the application rate of the electrons and the total number of electrons or dose applied to the part. It is conducted at room temperature so that normal thermal stresses associated with heat curing are minimized across the part however, local residual stresses are induced due to the localized curing that occurs only within the exposure area. 

Electro-pneumatic valve positioners are used with diaphragm-actuated, sliding-stem control valves. The electro-pneumatic valve positioner receives an electronic input signal from a control device and modulates the supply pressure to the control valve actuator, providing an accurate valve stem position [25]. 

---