An artificial neural network-based smart capacitive pressure sensor

A smart capacitive pressure sensor (CPS) using a multi-layer artificial neural network is proposed in this paper. A switched capacitor circuit (SCC) converts change in capacitance of the CPS due to applied pressure into a proportional voltage. The nonlinear characteristics of the CPS make the SCC output nonlinear. Further, due to dependence of the CPS characteristics on ambient temperature, the SCC output becomes quite complex for obtaining correct digital output of the applied pressure, especially when the ambient temperature varies with time and/or place.

To circumvent this difficulty, an ANN is employed to model the sensor. By training the ANN model suitably, the digital readout of the applied pressure can be obtained which is independent of ambient temperature. A new idea for collecting temperature information from the sensor characteristics themselves, and automatic feeding of this information into the ANN-based CPS model is proposed. From the simulation results it is verified that the ANN model can give correct readout of the applied pressure within ±1% error (FS) over a wide range of temperature variation starting from −20°C to 70°C. This modeling technique of the CPS provides greater flexibility and accuracy in a changing environment.     

ANN-based intelligent pressure sensor in noisy environment

A novel artificial neural network (ANN)-based intelligent capacitive pressure sensor (CPS) in noisy environment is proposed in this paper. A switched capacitor circuit (SCC) is used to convert the change in capacitance of the CPS due to applied pressure into a proportional voltage which is then applied to the ANN model to estimate the pressure. Because of the nonlinear response characteristics of the CPS and its temperature dependence, complex signal processing of the SCC output is required to estimate the applied pressure accurately, especially when the room temperature changes with time, place, or both. The situation becomes further complicated when the CPS encounters random noise, as is the case in many practical situations.

To alleviate these difficulties in estimation of unknown applied pressure in a CPS, a multilayer perceptron (MLP) has been utilized to model the CPS characteristics over a wide temperature range with noise. By training the MLP model suitably, a direct digital readout of the applied pressure can be obtained. From the simulation studies it was verified that the performance of this model is quite satisfactory for a wide variation of temperature, starting from −20°C to 70°C, and for a signal-to-noise ratio (SNR) of 40 dB and above. This modeling technique provides greater flexibility and accuracy in a changing and noisy environment.     

A temperature and pressure controlled calibration system for pressure sensors

A data acquisition and experiment control system has been developed to characterize and calibrate prototype pressure sensors capable of operation in a cryogenic environment. The system consists of: a personal computer for acquisition of sensor output voltage, sensor operating parameters, and data processing including numerically derived corrections for sensor thermal offset, sensitivity variations, and thermal errors; an environmental chamber capable of controlling temperature to within 1 °C over a −184 °C to 220 °C range; a pressure standard capable of generating pressures to within 1 part in 100,000 over a 0 to 344.74 kPa range; and a data logger for recording outputs from system multimeters, precision resistance temperature devices, thermocouples, and power supplies. The system utilizes a modified, commercially available interface board to allow the demultiplexing, digitation, and input of remotely multiplexed, pulse amplitude modulated pressure signals from pressure sensor arrays to the PC bus. System software is discussed and includes: sensor data acquisition, algorithms for numerically derived thermal offset and sensitivity correction, and operation of the environmental chamber and pressure standard.     

Wireless sensor marking and temperature measurement with SAW-identification tags

A wireless sensor marking system based on surface acoustic wave (SAW) identification tags is presented. The proposed solution is compatible with existing measurement systems and can be applied directly in the sensor or by means of a unique sensor identification cable (SIC). The SAW tag operates completely passive, and withstands temperatures up to 400 °C as well as shocks up to 35 000 m/s². It contains a unique serial identification number, which is encoded on the high-temperature stable SAW device by means of metallic reflector gratings. The interrogation unit uses the sensor cable for transmission but is not directly connected to it, thus the identification system can be even used with high impedance measurement equipment, e.g. charge amplifiers. Interrogation is done in frequency-domain based on well-known radar principles and is realized in a low-cost add-on circuit to the existing sensor evaluation circuitry. Furthermore, by simply enhancing the evaluation software, a temperature measurement of the SAW tag itself, and thus often of the sensor or the sensor environment can be done without additional hardware requirements.     

Development of an air servo displacement sensor

This paper introduces a new type of displacement sensor called an “air servo displacement sensor.” The sensor’s piston automatically follows a measured object using a pneumatic servomechanism with a nozzle-flapper that acts as a detecting device. Because the piston is supported by an aerostatic bearing, it experiences almost no friction. An optical linear scale mounted on the piston is used to measure the displacement of the measured object because the gap between the nozzle and the measured object is maintained at a constant level. As a result, this new sensor can successfully perform non-contact displacement measurements over a much longer measuring range, when compared to the traditional air micrometer. The optimal parameters for the sensor structure were obtained using simulations and experiments. Performance accuracy tests with a micrometer showed a repeatability error below ±0.5 μm and a linearity error below ±2 μm, with a measuring range beyond 10 mm. It has been verified that that the sensor exhibits a sufficient level of accuracy for the operational requirements.     

Modeling and development of an ANN-based smart pressure sensor in a dynamic environment

In many engineering applications, a capacitive pressure sensor (CPS) is placed in a dynamic environment in which the temperature variation is quite large. Since the response characteristics of a CPS are highly nonlinear and temperature dependent, in such situations, complex signal processing techniques are needed to obtain correct readout of the applied pressure. We have proposed an artificial neural network (ANN)-based smart capacitive pressure sensor, whose response characteristics can be estimated within an accuracy of ±1% error over a wide variation of temperature starting from −50°C to 150°C. This modeling scheme automatically takes care of all the nonidealities, such as, nonlinearity, offset, gain and temperature dependence, of the sensor. A novel idea of automatic collection of temperature information and its feeding into the ANN model is also proposed. In the practical implementation of this scheme, the hardware complexity poses a serious impairment. Since the tanh() functions are needed for implementation in the ANN-based model, to reduce the hardware requirement, we provide a simple scheme for computation of tanh(). Sensitivity analysis of the model with respect to the finite word-length constraint on the final stored weight values, and number of terms used in the implementation of tanh() function, have been carried out. A microcontroller-based implementation scheme for the ANN-based model is also suggested.     

A miniaturised sensor for deep hole diameter measurement

A miniaturised displacement senor for deep hole measurement is reported in this paper. By exploiting the induced eddy current effects detected by chip coils, the sensor generates a ’digital’ signal. The sensor chip coil can be manufactured by the similar processes to those used for manufacturing a printed circuit board (PCB) which allows them to be miniaturised. The paper elaborates on the construction and mechanism by which the displacement is directly transferred to a frequency output. It also reports on the transducer, which uses two contact probes for transmitting the displacement to a noncontact sensing element. Experimental results demonstrate the stability, linearity, measurement range and accuracy of the sensor system.     

Computer-controlled testing system for investigating the dynamic characteristics of contactors with A.C. electromagnet drives

An original computer-controlled measurement system with electrodynamic sensor is presented in this paper. The system was used to examine simultaneously dependencies of time related electromagnet coil current, electromagnet coil voltage, electric power supplied to electromagnet coil, voltage across contacts, acceleration, speed, path and kinetic energy of contactor moving element. An additional software allows diagrams of the following parameters to be obtained: maximum and minimum acceleration, maximum speed and kinetic energy of contactor moving element, electric energy supplied to electromagnet coil and times typical of alternating current electromagnetic drive for selected values of the coil supply voltages and various switching on angles of this voltage (within the range 0–170°). Results of the investigation enable also to take a view on such parameters of the designed equipment as, for example, making time or rebounds of the contactor contacts. The system is very useful to verify the results of investigation of computer simulated contactor closing.     

智能温室多点温度检测系统的设计

针对传统温度测量系统测量精度低、不具有数字通信和网络通信功能等缺点,利用数字温度传感器DS18B20、微控制芯片AT89C51设计温度测量系统,实现多点测温,经实验验证测温精度高,能实现温度的远程自动控制。     

Thermal resistances resulting from commonly used inserts between stainless steel static bearing surfaces

A review of the sources of previously published information on inserts is presented. The thermal resistances of thin (<3.5 mm) Melinex, Perspex, Tufnol, PTFE and mica inserts, used successively between flat stainless steel (type EN58B) bearing surfaces in the absence of any grease or lubricant, have been measured in high vacua (of better than 10⁻³ N m⁻²) in the range 20–80°C. The presence of such non-metallic shims led to the resistance of the steel-to-steel contact system increasing by a factor of between 10 and 1000. The introduction of a second similar thin insert adjacent to and in series with the first produced only a slight (<10%) increase in the overall resistance of the assembly.     

Modeling and characterization of piezoelectric cantilever in fluids at different temperatures

This paper introduces measurement and modeling of a piezoelectric beam used as a sensor in different types of liquids. It is immersed in different fluids at temperatures increasing from 20 °C to 50 °C. The working principle is based on detecting different resonance frequencies of the cantilever in different solutions. The oscillation of piezoelectric beam is measured using a vector network analyzer. An electrical equivalent circuit derived from a resonator model is used to simulate the experimental data. These calculated circuit constants have been related to physical properties of liquids under test. The combination of these liquids which includes non-conducting and conducting solutions, exhibiting low and high viscosity covers a good range of common physical properties of fluids. Main focus of this research is to explore the capability of piezoelectric cantilever as a liquid sensor with the influence of temperature. The equivalent circuit model has been proved to be viable to fit experimental data in non-conducting solution but less effective in conducting solution.     

Fatigue of bitumen and bituminous mixes

This paper gives details of an investigation into the fundamental fatigue properties of bitumen and bituminous mixes. Fatigue tests carried out under constant bending stress, at varying temperatures between −13·5°C and +25°C, show that the material exhibits fatigue properties over wide ranges of stress and that for a particular temperature and speed of loading the log stress-log number of cycles to failure relationship is linear between 10⁴ and 10⁸ cycles. The life under constant stress is highly dependent on the temperature of the test, a low temperature giving a longer life at a particular stress; it is also dependent to some extent on the speed of loading, but taking into account the stiffness of the material which depends on temperature, speed of loading, rheological characteristics and composition of the mix, it has been found that when the logarithm of the strain is plotted against the logarithm of the number of cycles to failure all experimental results at different speeds and temperatures for one mix lie with a certain amount of scatter about a straight line. It appears therefore that the factor affecting the fatigue life is one of strain rather than stress, and the effects of temperature and speed can be accounted for by their effect on the stiffness of the specimen. This has been confirmed by tests under constant torsional strain at different temperatures between −20°C and +40°C, but at the higher temperatures under this type of loading the fatigue life includes a considerable crack-propagation time. Similar results have been obtained from mixes containing different amounts of aggregate, but as the quantity of aggregate in the mix is reduced so the life for a given strain increases, suggesting that the criterion of failure may be one of tensile strain in the bitumen present in the mix. Some tests have also been carried out on pure bitumen specimens at different temperatures.

Careful examination of the fatigue cracks and failure surfaces shows that in nearly all cases failure originates on the principal tensile plane. The effects of such factors as surface conditions, void content and rest periods have also been studied.     

Shape measurement based on fiber-optic technique for complex internal surface

Reverse engineering based on fiber-optic technique is a very new topic in CAD/CAM fields. A novel single-mode fiber-optic sensor is presented based on the principle of beam reflection to implement the digitizing of complex surface shape. The fibers in the sensor probe are arranged like a spoke with eight symmetrically cross-arranged receiving fibers and one centered emitting fiber. Thus, the sensor can compensate for the offsets caused by fluctuations of surface reflectivity and light power and is fit for application under rough and formidable conditions with noncontact, fast shape measurement. A prototype was developed based on the simulation results to verify the feasibility. With the GRIN lens on the exit end of the single-mode emitting fiber, the lateral resolution was greatly improved compared with former multimode fiber-optic displacement sensors. Preliminary experiments indicated that the estimated uncertainty of displacement measurement was better than ±2 μm, and the uncertainty of ±5.6 μm can be obtained when measuring a MJ20×1.5 thread.     

光纤温度传感器的应用及发展

详细地分析了国内外主要光纤测温方法的原理及特点，给出了不同方法的温度测量范围和性能指标，在此基础上提出了一种适用于燃气轮机工作温度测量的新型光纤温度传感器的结构设计和工作原理。     

Influence of grain refinement on the high temperature fretting behaviour of IN 738 LC

The wear and friction behaviour of Inconel 738 LC in contact with SiSiC was studied for the case of oscillating sliding motion. The test temperature was varied in the range from room temperature up to 700 °C. A large-grain IN 738 LC and a grain-refined modification were compared. In both cases, the wear dropped drastically at temperatures above 400–500 °C and remained low for the grain-refined modification, but increased again for the large-grain modification at temperatures above 600 °C. The high wear/low wear transition was accompanied by a transfer of metal on the ceramic surface.     

A novel technique for calibration of polygon angles with non-integer subdivision of indexing table

Polygons are basic angle standards for angle measurement, particularly used for calibration of rotary angular indexing, and for measuring equipment such as dividing heads and tables. A main application in daily life is in bar-code readers. Calibration of such angle standards is required for traceability and at the highest accuracy it is a responsibility of national metrology institutes. In order to investigate uncertainty parameters on polygon calibration and to establish the capabilities of national metrology institutes, intercomparision measurements in the name of EUROMET project 371 “angle calibration on precision polygons” between 12 European countries have been carried out. Two precise polygons with 7 and 24 faces have been calibrated by the participants. Difficulties arose for precise calibration of seven-sided polygon for those institutes, which do not have a high-resolution angle comparator or two autocollimators. UME, the National Metrology Institute of Turkey, has applied an alternative technique for precise calibration of seven-sided polygon without using high-resolution angle comparators (i.e., indexing tables or angle dividers) or two autocollimators. The technique is based on the circle closure principle. The pitch and cumulative angles of the polygon are extracted from the angle measurement between some polygon faces (such as one and four (1/4), analogous 2/5, 3/6, 4/7, 5/1, 6/2 and 7/3) the angle of which can be generated close enough by the indexing table. This means that the polygon can be regarded as unfolded in seven 3-pitch angle intervals of 3×360°/7≈154°17′, making up 1080° in total. The method gives the differences between these seven intervals; with the closure condition (the sum must be zero) this gives all absolute angles. A full uncertainty evaluation is given that is based on the model function which relates the measured values to the polygon angles. For the calibration actually carried out, this yielded an uncertainty of 0.24″. Within this uncertainty the measured polygon angles corresponded very well with the reference values of the intercomparison. The method is of use for laboratories which do not have a high-resolution angle comparator (i.e., an indexing table or angle divider) or two autocollimators for the calibration of such angle standards.     

Optimization and temperature mapping of an ultra-high thermal stability environmental enclosure

Precision metrology, lithography and machining systems will soon require sub-nanometer tolerances in order to meet the evolving needs of industry. This, in turn, requires thermal control of large environmental enclosures with sub-millidegree single-point stability and control of temperature gradients to several millidegrees. In order to optimize the system's thermal controls, it is essential to measure the open-loop transfer function. We report a technique that obtains the open-loop transfer function by utilizing a dynamic signal analyzer to perform a closed-loop frequency response measurement of the thermal system. Based on the transfer function, we designed a PI-lead compensation controller and achieved one-sigma air temperature stability of less than 1 m°C at a single point over 2 h. In order to rapidly map temperature gradients over large regions inside the 7 m³-volume enclosure, we have developed a measurement scheme that involves mechanically scanning a network of thermistors. Accurate cross calibration of the thermistors and a study of self-heating effects on temperature measurement in moving air have also been performed, which assures the relative accuracy of the thermistors is less than 1 m°C. Comparing temperature gradient maps taken before and after control improvements shows improved temperature stability over the mapped volumes.     

A new automatic reference and switching unit for calibration of high value resistors in the range 100 kΩ to 10 TΩ

We describe a Reference and Switching Unit (RSU), that, with a digital multimeter (DMM) and a dc voltage calibrator, constitutes a system for calibration of standard resistors in the range 100 kΩ–10 TΩ at measurement voltages up to 1000 V. This system represents an implementation of a DMM-based system already developed at IEN. We report the characteristics of the DMM-based system, the metrological and electronic features of the RSU, the uncertainty levels that can be achieved with the DMM-based and whit the RSU-based systems. Finally, we show the obtained results in order to check the compatibility of the two systems in the calibration of standard resistors in the range 1 GΩ–1 TΩ. The 2σ best measurement capabilities of the RSU-based system span from 6.3×10⁻⁶ for the calibration of a 100 kΩ standard resistor at 10 V, to 1.2×10⁻³ for the calibration of 10 TΩ standard resistor at 1000 V.     

Adaptive calibration of a capacitance tomography system for imaging water droplet distribution

A highly sensitive electrical capacitance tomography (ECT) system based on an HP4284 impedance analyser has been developed and used to quantify low concentration multi-phase flows in wet gas separation processes. The system hardware provides high accuracy (0.05%) and high resolution (10⁻¹⁷ F). The sensor was calibrated in an environmental chamber with solid samples of known permittivity over ranges of temperature and humidity. Adaptive calibration and adjacent electrode pair correction techniques were applied to image very low concentration profiles. This paper describes the techniques used and presents the experimental results obtained from a test flow rig called Twister, which has been designed to separate liquid droplets from wet gas streams. The test results over a range of operating conditions (20–95% humidity) demonstrate that the ECT system is capable of reconstructing clear images of the droplet distribution inside Twister. Changes as small as 1 gWater/kgAir in the form of liquid droplets were detectable. It has also been shown that the concentration of the condensable phase can be estimated quantitatively within 20% in comparison with the reference measurements.     

EXPERIMENTAL ANALYSIS OF TEMPERATURE IN GRINDING AT THE GLOBAL AND LOCAL SCALES

The purpose of the article is the experimental estimation of the global and local heat fluxes and the corresponding energy partition to the workpiece for regular grinding of 100Cr6 steel with aluminium oxide wheel. By using a grindable thermocouple, the temperature and the real contact length allow determination of the global heat flux and the partition ratio at the wheel scale. The high frequency analysis of the signal has shown maximum flash temperatures of about 1000°C corresponding to the local temperature under the chip-grain unit with very high heating speed of about 100°C/µs. The comparison between theoretical temperature decay and experimental cooling has demonstrated that the time response of the sensor is fast enough for the estimation of the local temperature and power due to the sliding of grain and to the plastic strain of ground materials.