Diaphragm-type Pressure Transducer Research Articles

Toward Integrated Pressure Sensors for Temperatures up to 600°C

The main objective of this study is to develop pressure-sensing systems by integrating pressure transducers with the interface circuitry in one package that can withstand harsh environments, particularly high temperatures up to 600°C. To achieve that, both pressure transducer and interface circuitry are individually required to operate and survive up to 600°C with acceptable degrees of reliability. This article reports performance evaluation of fabricated 4H-SiC Junction Field Effect Transistors along with differential pairs for use in the interface circuitry. The test results are very promising and show stable performances from 25°C up to 600°C. Moreover, design, fabrication, and early test (from 25°C up to 100°C) of an SiC-based circular diaphragm-type pressure transducer are also reported.

Towards Integrated Sensors for Environments with Temperatures up to 600 °C

Abstract The main objective is to develop sensing systems by integrating transducers such as pressure sensing elements with the interface circuitry in one package that can withstand harsh environments, particularly high temperatures up to 600 °C. To achieve that, both pressure transducer and interface circuitry are individually required to operate and survive up to 600 °C with acceptable degrees of reliability. This paper reports performance evaluation of fabricated 4H-SiC JFETs along with differential pairs for use in the interface circuitry. The test results are very promising and show stable performances from 25 °C up to 600 °C. Moreover, design, fabrication, and early test of a SiC based circular diaphragm type pressure transducer is also reported.

Tongue Pressure Changes Before, During and After Crib Appliance Therapy

To describe tongue pressure changes before, during, and after crib appliance therapy in mixed dentition open bite cases. A crib appliance was applied to each of the 13 patients in the study group. The control group consisted of six patients. Tongue pressures were measured using a diaphragm-type pressure transducer during rest position and swallowing in changing intervals for 12 months in both groups. Tongue pressures were performed on the upper first molar, upper and lower central incisors, and on the middle spur of the crib appliance. In the study group, the initial resting tongue pressure on the upper molar increased after appliance insertion and was followed by a decreasing trend for 12 months. The resting tongue pressures on the upper and lower incisors remained lower than initial values at the end of 12 months. Swallowing pressures returned to initial values at the end of 12 months, and the changes were insignificant. The resting and swallowing tongue pressures on the middle spur of the crib appliance decreased gradually during the 10 months (P < .05). Pressure changes in the control group were insignificant for all measurements. Open bite values in the study group increased significantly by the end of 12 months. Measurements performed on the crib confirm the tongue adaptation to environmental changes. Resting tongue pressures at the 12th month remained lower than the initial values. These findings indicate adaptive behavior of the tongue to open bite closure and the new position of the incisors.

Design and performance of an immersable low-temperature pressure gauge

A sensitive diaphragm-type pressure transducer, suitable for use at low temperature is described. This device was optimized for pressure up to 3.5 MPa. The external pressure deflects two CuBe disks, which form the electrodes of a capacitor. The transducer sensitivity at 3.43 MPa is about 25 pF/MPa. No hysteresis was detected within the accuracy of the piezoelectric pressure transducer used in the calibration procedure.

Low-cost thin film pressure transducer

A flat diaphragm type pressure transducer with an anodised insulating layer and thin Pt-film as a strain gauge has been designed and made. The paper gives details of the diaphragm and the information on the anodisation process employed. Sputtering was used for the deposition of the Pt-film strain gauge sensors. Observations on the behaviour of the transducer are presented which include, stability of the gauge resistance with pressure and time, linearity and hysteresis, and the insulation resistance of the anodised base layer. It was concluded that although this type of transducer can be adopted for measuring pressure in the lower range up to 10 bars, creep effect was at a noticeable level in the output. However, the transducer is attractive for its low-cost and weight.

Diaphragm-type sputtered platinum thin film strain gauge pressure transducer

A diaphragm-type pressure transducer with a sputtered platinum film strain gauge (sensing film) has been designed and fabricated. The various steps followed to prepare thin film strain gauges on the diaphragm are described. M-bond 450 adhesive (Measurements Group, USA) has been employed as the insulating layer. A detailed procedure to cure this layer is given. A d.c. sputtering method is employed to prepare the platinum films. This paper also includes details of the strain gauge pattern and its location on the diaphragm. A description of the output characteristics and overall behaviour of the platinum thin film pressure transducer is reported.

Correcting for Response Lag in Unsteady Pressure Measurements in Water

There is not much information available on the use of diaphragm-type pressure transducers for the measurement of unsteady pressures in liquids. A procedure for measuring the dynamic response of a pressure transducer in such applications and correcting for its inadequate response is discussed in this report. An example of the successful use of this method to determine unsteady surface pressures on a pitching airfoil in a water channel is presented.

Dynamic pressures on a large vertical cylinder due to random waves

The hydrodynamic pressures due to random waves on a large vertical cylinder, resting on a flume bed and piercing above the free surface has been investigated experimentally in constant water depth. The test cylinder was fixed with diaphragm-type pressure transducers at nine different pressure ports with one of them at the still water level (S.W.L.) itself. The cylinder was rotated about its own axis to study the pressure distribution around its circumference. The time histories of the water surface elevation and the corresponding dynamic pressures exerted on the cylinder have been analysed in the frequency domain. The experimental results are compared with the theoretical results based on the linear diffraction theory of MacCamy and Fuchs and the agreement is satisfactory. Finally, the hydrodynamic pressure coefficients obtained from random wave tests are compared with those from regular wave tests.

Diffracted wave field and dynamic pressures around a vertical cylinder

Investigations on the hydrodynamic pressures due to regular and random waves exerted on a large vertical cylinder in a constant water depth are reported in this paper. In the experimental investigation, the test cylinder embedded with diaphragm-type pressure transducers at nine different elevations was rotated about its axis to measure the dynamic pressure around its circumference. The wave field in the neighbourhood of the cylinder was measured at six different locations. The results of the experiments are compared with the linear diffraction theory of MacCamy, R. C. and Fuchs, R. A. [(1954) Wave forces on piles: a diffraction theory. U.S. Army Beach Erosion Board, Technical Memorandum No. 69]. In general, the agreement between the theoretical and experimental results is found to be satisfactory. A comparison between the regular and random wave test results is also presented and discussed.

New method for measurement of surface pressure using magnetic tape

A new method of surface pressure measurement has been developed using magnetic tape as a sensor—instead of the usual strain gage, piezogage or semiconductor —within a diaphragm-type pressure transducer. The method is based on the idea that a pressure value applied to the diaphragm is related to the deflection of the diaphragm, and the deflection can be related to the value of magnetization strength sensed in the tape. The merit of the new method is that it can be easily applied for measurement of pressure distributions on model surfaces because many pressure transducers are contained in a single sheet only about 1-mm thickness. The proposed method can be used in the high-temperature, short-duration measurement conditions, and so it is well suited to hypersonic wind-tunnel use. The sheet can be bonded onto a model surface. In this study, experiments using the new pressure sensor were performed in a hypersonic gun tunnel at a Mach number of 10 for a duration time of 10 ~2 s. Pressure distributions around two models in hypersonic flow were measured successfully.

Dynamic pressure distribution on a cylinder due to wave diffraction

The experimental investigations on the dynamic pressure distribution around a large vertical cylinder resting on a flume bed and piercing the free surface subjected to regular waves have been carried out in a 4-m wide wave flume in a constant water depth of 2.5 m at Ocean Engineering Centre, Indian Institute of Technology, Madras, India. The cylinder of diameter 400 mm was fixed with diaphragm type pressure transducers at eight different locations below the still water level along with one at the still water level. In addition to this, to study the effect of nonlinearity, one pressure transducer was located above the still water level. The experimental results pertaining to mostly deep water conditions are compared with MacCamy and Fuchs theory and the agreement is found to be good. In order to account for the effects of nonlinearities the above said theory has been modified the results of which are found to be in better agreement.

Small sensitive pressure transducer for use at low temperatures

A sensitive diaphragm-type pressure transducer suitable for use at very low temperatures is described. This device was optimized for pressures up to 3.5 MPa, but sensors for other pressure ranges can be readily manufactured. The external pressure deflects two sapphire disks which causes a change in capacitance between the platinum electrodes sputtered on the disks. The transducer can easily resolve changes of 1 Pa at 3.5 MPa, while reproducibility and hysteresis, though not fully tested yet, are better than 10 Pa. The transducer is 610 μm thick and 8 mm diameter.

Development of variable capacitance pressure transducers for vacuum applications

The development of variable capacitance diaphragm-type pressure transducer systems for vacuum applications is described in detail. This technology area is an interesting and challenging problem of design and manufacturing engineering and incorporates an interdisciplinary mixture of material science, and state-of-the-art techniques in electronics. Since the measurement system must be usable for a wide variety of applications in vacuum science ranging from very high accuracy metrology transfer standards to general-purpose vacuum measurements under very demanding environmental conditions, many conflicting factors must be considered in the design. For all practical purposes, this technology has evolved over a 35 yr period from 1949 to 1984 within which there have been several distinct developmental time periods; 1949–1969, 1970–1975, 1975–1980, 1981–1984. This paper will review the technology, considering the chronological development of sensors, signal conditioners, and overall transducer systems. Some very recent advances will be discussed as well as projections for the future.

Investigation of Squeeze Film Damper Forces Produced by Circular Centered Orbits

This paper presents the results of an experimental and analytical investigation of the dynamic forces generated by a squeeze film bearing damper constrained to move in circular centered orbits. These orbits were mechanically produced in a specially designed, end sealed, test rig. Aircraft engine damper geometry and operating conditions were simulated. The effect of journal speed, oil viscosity, inlet pressure, and eccentricity ratio on the damper performance was studied. The pressure distributions about the journal were measured for each test condition by high-response diaphragm-type pressure transducers. These pressure profiles were numerically integrated to determine the force components of the squeeze film. Experimental results were compared to an analysis which is summarized in this paper and included the effects of inlet and cavitation pressures. The “long bearing theory” was found to be reasonably accurate in predicting the shape and magnitude of the pressure distribution. Considerable emphasis was directed to the study of the circumferential pressure distributions between 180 deg and 360 deg since aircraft engine dampers generally operate in this region. For the cavitated film (i.e., pressure distributions less than 360 deg), accurate prediction of the damper forces was found to be critically dependent on the effect of inlet and cavitation pressures.

Measuremets of the Thermal Transpiration Effects of NO at 90 K and of CO, N2, O2, CH4, and He at 77 K

Abstract The thermal transpiration effect of the title gases was measured by a relative method by using a diaphragm-type pressure transducer. The data fit the Takaishi-Sensui equation [P1⁄P2=(AX2+BX+C\sqrtX+\sqrtT1⁄T2)⁄AX2+BX+C\sqrtX+1)] quite well in the region of X(=P2d2) higher than 0.03 mmHg mm. The values for A, B, and C are 25.5, 9.3, and 0.6 for NO at 90 K, 28.5, 10.5, and 0.6 for CO and N2, 24.0, 9.2, and 0.8 for O2, 44.0, 11.4, and 1.2 for CH4, and 2.96, 0.6, and 1.6 for He at 77 k respectively. The values for the temperature-independent constants, A*, B*, and C* deduced from the values for A, B, and C above, were in agreement with the literature values and/or the estimated values.

An omnidirectional pressure transducer

Diaphragm type pressure transducers are inadequate in the measurement of pressures in deforming media such as soil, because they are too rigid and uniform pressure application is difficult. The omnidirectional pressure transducer is designed to overcome these shortcomings by encasing a cell in a hollow flexible walled sphere filled with an incompressible liquid.

Fused quartz diaphragm-type pressure transducer

A diaphragm-type pressure transducer made of fused quartz is described for use particularly in the range 0-1.333 kPa (0-10 torr) with a resolution of 0.7 mPa (5 mu torr). Its particular features are its high mechanical and thermal stability.

A Sensitive Nonmagnetic Pressure Transducer for Use at Very Low Temperatures

A sensitive diaphragm-type pressure transducer suitable for use at very low temperatures is described. The device is useful over the differential pressure range of −200–+200 Torr at ambient pressures up to 20 atm. Differential pressure deflects the prestressed diaphragm causing a change in capacitance between a gold layer on the diaphragm and a fixed plate. The transducer can easily resolve changes of 10−3 Torr in pressure. The method of constructing the device is described in detail.

Direct-Reading Diaphragm-Type Pressure Transducers

An analysis is given of a direct-reading system for micron range differential-capacity type diaphragm manometers. It is shown that electrostatic compensation of diaphragm displacement by feedback produces a linear pressure calibration when control system gain is sufficient. It is also shown that adjustment can be provided for unavoidable inequalities in the manometer capacities without changing the calibration. An experimental direct-reading gauge is described with deviations from linearity less than 1% in the pressure range 0 to 500 μ.

Sensitive Diaphragm Type Pressure Transducer

A simple diaphragm type transducer for small differences in gas pressures is described together with a suitable electronic arrangement for using it as a control element. The sensitivity of the arrangement is limited by ambient temperature effects on the diaphragm. A zero stability of about 0.1 μ Hg has been achieved and this could probably be improved on by sufficiently good thermostating. An important feature of the diaphragm is that it may be subjected to large unbalanced pressures without damage, although such pressures will produce zero shifts equivalent to a few microns of mercury.