Gages pressure sensors

Figure 2.6 (a) An unbonded strain gage pressure sensor. The diaphragm is directly coupled by an armature to an unbonded strain-gage system. With increasing pressure, the strain on gage pair B and C is increased, while that on gage pair A and D is decreased. 

Glass-Polymer Bonding, Figure 1 Experimental setup for leak tests. The bonded chip Is mounted on top of an Inverted light microscope for optical leak detection. The pressure is generated with a syringe pump at the chip inlet side and measured at the outlet side with a MEMS gage pressure sensor... 

It is also interesting to briefly consider online measurements of variables different from temperature [5], Since pressure is defined as the normal force per unit area exerted by a fluid on a surface, the relevant measurements are usually based on the effects deriving from deformation of a proper device. The most common pressure sensors are piezoresistive sensors or strain gages, which exploit the change in electric resistance of a stressed material, and the capacitive sensors, which exploit the deformation of an element of a capacitor. Both these sensors can guarantee an accuracy better than 0.1 percent of the full scale, even if strain gages are temperature sensitive. 

The sensitivity of a piezoresistive pressure sensor depends on the piezoresistive coefficient. Silicon crystal face selection and gage layout on the crystal face are important because of the anisotropy of the piezoresistive effect. Silicon (100) and (110) are often used with P-type diffused resistors to achieve a desired sensitivity. The next consideration is the thermal stress effect originating from the silicon crystal face. Fig. 7.3.5 shows the stress-distribution maps for silicon (100) and silicon (110) by the finite element method (FEM). 

Fig. 7.3.20 shows the results of prototype evaluation for Nip, TNO, and TNS of the pressure sensor with the optimal gage layout on its (100) silicon element. Nip, TNO, and TNS are nearly zero, as expected. 

Figure 2.8 Typical semiconductor strain gage units (a) unbonded, uniformly doped (b) diffused p-type gage (c) integrated pressure sensor (d) integrated cantilever beam force sensor. (From R S C Cobbold Transducers for Medical Measurements Application and Design, copyright 1974, John Wiley and Sons, Inc.)...

The requirement for use of IS devices does not restrict a designer. Rather it directs them to certain choices of equipment which have been designed for and are certified by lEC as available for use in hazardous areas with intrinsically safe barriers including 4—20 milliamp (mA) DC two-wire transmitters, thermocouples, resistance temperature detectors (RTDs), strain gages, pressure, flow, level switches, current/ pneumatic (l/P) converters, solenoid valves, proximity switches, infrared temperature sensors, potentiometers, EED indicating lights, and flowmeters with magnetic pickups. 

A North Sea field wave setup experiment was conducted on the Island of Sylt by Hansen. Utilizing a combination of ultrasonic wave gages and pressure sensor wave gages out to a distance of 1280m from shore (10m depth), Hansen found good correspondence of data to an empirical expression provided by ... 

Lentz and Raubenheimer ° report on a field experiment at the U.S. Army Field Research Pier in Duck, NC, USA where 11 pressure sensor gages and 10 sonar altimeters extended across the surf zone from 2 to 8 m of water depth. Close agreement with Longuet-Higgins radiation stress theory for wave setup was noted... 

Use of many different approaches to measure/evaluate setup (i.e., videos, pressure sensors, runup gages, manometers, etc.). 

A series of tests showed the pressure sensors checked within their calibration accuracies when readings from these gages were compared to load cell data which was used as the standard. Since these tests confirmed basic calibration accuracies, we concluded the strain gage pressure cell would provide the more accurate and reliable data for propellant loading within the i 1/2 per cent required by one missile manufacturer. 

Note 7—Refer to Annex A6 of Test Method D 2892 for ftirther details concerning the calibration of pressure sensors and McLeod gages. 

Nozzle pressure and temperature were measured by pressure/temperature sensor (type 4083A from Kistler). The nozzle sensor was installed at a proper installation hole machined in the nozzle ad tor. A pressure sensor was installed just in front of the gate in toe runner. The pressure sensor in toe runner was type 6157B from Kistler. A pressure/tenperature sensor in toe cavity was installed just after toe gate. The pressme/temperature sensor was type 6190A from Kistler. The sensors in toe cavity and in the runner are piezoelectric type, and toe sensor in the nozzle is strain gage type. 

Fig. 7.3.1 shows the principle of the piezoresistive sensor. Diffused resistors (gages) are formed on the thin-walled section called the diaphragm. An applied pressure is detected via the piezoresistive effect, which is the change in electrical resistance when a stress is applied to the diaphragm. The sensitivity is determined by the material, diameter, and thickness of the diaphragm. The thin-film piezoresistive sensor offers low sensitivity because the piezoresistive coefficient of thin-film silicon is less than one-third of that of single-crystal silicon. 

The silicon piezoresistive sensor detects distortion. Therefore diffused resistor (gage) layout and diaphragm geometry design have a profound effect on the sensor characteristics. We utilize simulation technology for pressure-sensing element design. 

This final section on physical sensors describes their use for measurements of blood pressure. Different kinds of sensor element may be used for this purpose they include strain gages, LVDTs, variable inductances, variable capacitances, optoelectronics and piezoelectric and semiconductor devices. The principles of... 

An automated data collection system (DCS) of approximately 6(XX) channels continuously records the readings of the various sensors on an hourly basis. The DCS scans and records the readings of temperature, humidity, pressure, MPBXs, strain gages, convergence monitors, and current and voltage for heater power. The measurements made by the DCS are referred to as passive monitoring. Other measurements such as ERT, neutron logging, GPR, acoustic emissions, REKA probe, and others are made periodically (every few weeks to few... 

Electronic sensors are elements used to measure and record a host of quantities of importance to engineering systems. These include sensors to measure force, torque, acceleration, pressure, strain, temperature, humidity, etc. In addition to wire resistance strain gages used to measure static strains, the piezoelectric effect is used to measure d5mamic strains. 

A3.1 Principle—The calibration of vacuum sensors is based upon the use of the McLeod gage, which is the only practical primary gage suitable for this pressure range. 

A vacuum sensor shall be connected to the sidearm of the trap. The sensor must be capable of reading the pressure with a precision equal to or letter than 1 % of the pressure employed, or equi to or better than 0.00133 kPa (0.01 mm Hg), whichever is greater. The McLeod gage can achieve this accuracy when properly used, but a mercury manometer will permit this accuracy only down to a pressure of about 1 kPa and then only when read with a good cathetometer (an instrument based on a telescope mounted on a vernier scale to determine levels very accurately). An electronic gage such as the Baratron is satisfactory when... 

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