Sensors pressure

We next consider a small (linear) deflection of a clamped circular diaphragm under a distributed load as an example of a pressure sensor. The deflection d at the center of a stress-free clamped circular diaphragm with radius r is given by 

For a square membrane with sides of length L, the deflection d at the center of the membrane would be 

For a 1.5 pm thick polysilicon membrane with sides that are 100 pm long, 

Device layer (silicon) Handle wafer (silicon) Metal (gold) 

1 http //scienceworld.wolfram.com/physics/SpringsTwoSpringsmParallel.html 

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Special uses iaclude oxygen for fuels iatended for long-term unattended service (13). Candles are fired on demand by a pressure sensor ia the oxygen accumulator. Chlorate candles were iacorporated iato backpacks designed for use ia the ApoUo moon missions (14). 

Absolute pressure is pressure measured relative to a perfect vacuum, an absolute 2ero of pressure (2). Like the absolute 2ero of temperature, perfect vacuum is never reali2ed in a real world system but provides a convenient reference for pressure measurement. The acceptance of strain gauge technology in the fabrication of pressure sensors is resulting in the increased use of absolute pressure measurement in the CPI (see Sensors). The pressure reference... 

Fig. 8. Reluctance-type pressure sensor. The E-cote corresponds to the area where the magnetic fields ate produced.

Fig. 10. Cross-section of meter body having a pie2oresistive pressure sensor.

Fig. 11. Capacitive pressure sensor in the differential measurement configuration. Courtesy of Rosemount, Inc.

The pressure sensors discussed herein are reasonably accurate for measurement into the low vacuum region. Upon some modification, these sensors can be extended into the lower end of the range, to approximately 1.3 x 10 Pa (10 torr). Vacuum gauges ate required for accurate measurement of lower pressures. 

Doping of the siHcon can have a large effect on the etch rate, and layers of different materials such as Si02 and Si N can have different etch rates. Eor pressure sensors, thin diaphragms of Si or related materials are etched into the wafer (see Pressure measurements). 

Many of the variations developed to make pressure sensors and accelerometers for a wide variety of appHcations have been reviewed (5). These sensors can be made in very large batches using photoHthographic techniques that keep unit manufacturing costs low and ensure part-to-part uniformity. A pressure differential across these thin diaphragms causes mechanical deformation that can be monitored in several ways piezoresistors implanted on the diaphragm are one way changes in electrical capacitance are another. 

Fig. 2. Digital pressure sensor on a 6 x 4.8 mm chip, fabricated at the Technical University of Berlin (5). See text.

Dynamic explosion detectors use a piezoresistive pressure sensor installed behind the large-area, gas-tight, welded membrane. To ensure optimum pressure transference from the membrane to the active sensor element, the space between the membrane and the sensor is filled with a special, highly elastic oil. The construc tion is such that the dynamic explosion detec tor can withstand overpressures of 10 bar without any damage or effect on its setup characteristic. The operational range is adjustable between 0 and 5 bar abs. Dynamic explo-... 

You should install pressure sensors that transmit a message to shut-off the pump, sound an alarm, or indicate to the operator that the moment to change the filter has arrived. With a new filter installed, the pump begins operating again to the right of the BEP within the sweet zone and slowly over time proceeds moving toward the other end of the sweet zone. 

To obtain the benefits of this seal, it is necessary to install a gauge indicating the actual seal chamber pressure. Sensors and transmitters can be used to monitor and act on a pressure change. One of the two seals can fail without product loss or fugitive emissions. This seal would be connected to a pumping unit seen later in this chapter. 

Turbomaehinery operating pressures, temperatures, and speeds are very important parameters. Obtaining aeeurate pressures and temperatures will depend not only on the type and quality of the transdueers seleeted, but also on their loeation in the gas path of the maehine. These faetors should be earefully evaluated. The aeeuraey of pressure and temperature measurements required will depend on the analysis and diagnosties that need to be performed. Table 19-2 presents some eriteria for seleetion of aerothermai instrumentation of pressure and temperature sensors for measurement of eompressor effieieney. Note that the pereentage aeeuraey requirements are more eritieal for temperature sensors than pressure sensors. The requirements are also dependent on the eompressor pressure ratio. 

PCT may be used for the production of electronic and automotive components such as circuit board components, connectors, switches and relays, and alternator armatures and pressure sensors. The main application has been in the fabrication of surface-mount connectors that can withstand infrared reflow soldering operations. 

Step 5. Cake Discharge - At this point the air pressure is released, the cake outlet is opened and the leaf stack is vibrated to discharge the cake. The cake outlet opening must be interlocked with a pressure sensor to avoid opening under pressure. On some filters the cloth or mesh screen may be backwashed with water after cake discharge to dislodge and remove any cake residue that adhered to the medium. 

A pressure sensor giving a continuous indication which is displayed on the control panel and can be observed by the operator. The sensor has a high pressure safety interlock set at a predetermined pressure that activates an emergency shutdown system. 

Design alternative 1 is inherently safer because the pressure sensor provides continuous feedback to the operator. The operator has some confidence that the pressure sensor is working (although not complete... 

Pressure sensor A recording or measuring device that corrects the pressure of a fluid when it varies by a given amount I rom its design set point. 

Provide a sensor that detects the upset and shuts-in the process before an identified source of condition develops. For example, it the jiiessure controller fails and the pressure increases, provide a hiati-pressure sensor to shut-in the process. If there is a leak and the [ires-sure decreases, provide a low-pressure sensor to shut-in the proce.ss. 

Assemble the components into the process system and apply FMEA techniques to determine if protection devices on some components provide redundant protection to other components. For example, if there are two separators in series, and they are both designed for the same pressure, the devices protecting one from overpressure will also protect the other. Therefore, there may be no need for two sets of high pressure sensors. 

The application of this procedure is best seen by performing an FMEA on a simple two-phase separator. Table 14-3 lists those process upsets that can be sensed before an undesirable event leading to a source of condition occurs. For overpressure, primary protection is provided by a high pressure sensor that shuts in the inlet (PSH). If this device fails, secondary protection is provided by a relief valve (PSV). 

A large leak of gas is detected by a low-pressure sensor (PSL) that shuts in the inlet, and a check valve (FSV) keeps gas from downstreant components from flowing backward to the leak. Similarly, a large oil leak is detected by a low-level sensor (LSL) and a check valve. Back-up protection is provided by a sump tank and its high-level sensor (LSH) for an oil leak. That is, before an oil spill becomes pollution there must be a... 

High Pressure Sensor Pressure Safety High ... 

The component failure rate data used as input to the fault tree model came from four basic sources plant records from Peach Bottom (a plant of similar design to Limerick), actual nuclear plant operating experience data as reported in LERs (to produce demand failure rates evaluated for pumps, diesels, and valves), General Electric BWR operating experience data on a wide variety of components (e.g., safety relief SRV valves, level sensors containment pressure sensors), and WASH-1400 assessed median values. 

Premature disk failure Operator error Pump motor failure Reaction inliibitor system failure Coolant system failure Outlet piping obstruction Motor alann failure Pressure sensor failure... 

A more serious limit to this implementation is due to the volume of the recycling pump and associated equipment such as flowmeters and pressure sensors. As the pump moves with respect to the zones, its volume leads to a dead volume dissymmetry, which can lead to a decrease extract and raffinate purities. This decrease can be significant for SMB with short columns and/or compounds with low retention. However, it can be easily overcome by using a shorter column or asynchronous shift of the inlets/outlets [54, 55]. This last solution is extremely efficient and does not induce extra costs because it is a purely software solution. 

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