Pyroelectric Transducers for the Measurement of Heat Transfer under Conditions of Hypersonic Flow

Pyroelectric detectors have been fabricated from polycrystalline samples of barium titanate. These detectors were mounted in a model for tests in a hypersonic wind tunnel and calibrated. The method of calibration is discussed and tables of calibration data are included. Thermocouples were mounted in the model to evaluate the detectors. The detectors were tested and results of the tests are discussed. Advantages of pyroelectric detectors are presented and typical output traces from both the pyroelectric detectors and the thermocouples are shown.     

Measurement of the Discrete Modulation Transfer Function

Abstract

The development of a unique discrete modulation transfer function (DMTF) [1] has solved the previous problem of multivalued modulation transfer function associated with the non-isoplanatic nature of discrete systems. This paper proposes two methods for the measurement of the DMTF and shows that the use of the DMTF makes the performance analysis and measurement of discrete systems easier.     

Minimizing the Dynamic Error of Measurement Transducers

A method is proposed for reducing the dynamic error of a measurement transducer of stochastic signals by introducing correcting networks into the structure of the instrument. An analytical expression is obtained for the dynamic error in the case when the transducer takes the form of a first-order inertial network while a correcting network is made in the form of a modified differentiating cell.     

Definition of the Measurement Function of the Modulus of the Vibration Acceleration Vector of Three-Component Vibration Transducers

Measurement Techniques - The measurement function is calculated for the modulus of the vibration acceleration vector of three-component vibration transducers by means of a unicomponent calibrating...     

Transfer Function Measurement Using Analog Modeling Techniques

Analog models provide a cheap and effective method for identification and checkout of a wide range of physical systems via the transfer function concept. This paper reviews the excitation of series, parallel, and pi mode analog models by deterministic stimuli. Errors between the system and model responses may be displayed on a cathode-ray tube, or on an instrument measuring mean-error modulus. Novel methods of tuning the model coefficients by observing the error displays are described and evaluated experimentally. The checkout strategy is particularly suitable for use by technicians since reliable repeatable models are obtained independent of the level of operator understanding of the system under test. These models may then be used as input data for quality control of production items and for preventive maintenance schemes during the life of the system under test. A low-order model is shown to be perfectly adequate for dynamic performance checkout of a complex noisy nonlinear system. Intermediate access points then permit elemental modeling down to replaceable units. For adequate confidence in system dynamic performance, checkout tolerances placed on the model coefficients must be conditional and a suitable tolerance flow chart is included. Although presented on the basis of manual instrumentation, the methodology is suitable for automation and is applicable to self-adaptive systems in which system dynamics change slowly with time.     

Hot-Wire Measurements of the Heat Transfer in a Partially Magnetized Potassium Plasma

A hot-wire device designed as a gas-loaded heat pipe has been used to study the axial magnetic field influence on the heat transfer in a potassium vapor plasma at low vapor pressures p _K=400 to 1200 Pa, temperatures T _w of the tungsten filament in the range 2000 to 2800 K, and magnetic field intensity B=0.182 to 0.364 T. As a result of the applied magnetic field B, the measured thermal flux Q decreases. The separation between the heat fluxes transferred by radiation Q _r, by atoms Q _a, and by electrons Q _e can be accomplished analyzing the decrement Q. A procedure to analyze the measured data in the presence and in the absence of the magnetic field in order to define the different mechanisms of the heat transfer has been introduced. The electron thermal conductivity can be obtained in the Frost approximation by means of the well-known transport phenomena theory using available electron–potassium atom cross sections in the range of electron energies =0.06 to 2 eV.     

Measurement of Optical Transfer Function with Polarization Interferometer

A method is described to determine the Fourier analysis of the image of a slit of finite width using polarization interferometers. Sinusoidal fringes of variable spatial frequency and of contrast one are projected on the slit image and the output flux is recorded. The modulation of the flux when the fringe system is displaced with respect to the slit image yields the spatial spectrum of the slit image. The spatial spectrum of the slit object being known, the transfer function (both amplitude and phase) of the optical system can be determined.     

Modulation Transfer Function Measurement Using Three- and Four-bar Targets

Modulation-transfer-function (MTF) measurement often involves the use of three- and four-bar resolution targets. In the conversion of three- and four-bar image data to MTF, biased results can occur when we use series-expansion techniques appropriate for square-wave targets of infinite extent. For systems where the image data are digitally recorded, a convenient and accurate conversion of bar-target data to MTF can be performed using a Fourier-domain method.     

Thermal Conductivity Measurement of Semitransparent Solids by Hot-Wire Technique1

A new simple analytic model applicable to the measurement system of a hot wire and a semitransparent solid material is developed. An experimental study is carried out on a special glass sample, glass K9, in the temperature range of 297 to 1230 K, and the radiation-free thermal conductivity is reported.     

Application of the Transient Hot-Wire Technique to the Measurement of the Thermal Conductivity of Solids

A novel application of the transient hot-wire technique for thermal conductivity measurements is described. The new application is intended to provide an accurate means of implementation of the method to the determination of the thermal conductivity of solids exemplified by a standard reference ceramic material. The methodology makes use of a soft-solid material between the hot wires of the technique and the solid of interest. Measurements of the transient temperature rise of the wires in response to an electrical heating step in the wires over a period of 20 s to 10 s allows an absolute determination of the thermal conductivity of the solid. The method is based on a full theoretical model with equations solved by finite-element method applied to the exact geometry. The uncertainty achieved for the thermal conductivity is better than ±1%, and for the product (C _p) about ±3%. The whole measurement involves a temperature rise less than 4 K.     

Correction of Systematic Errors of Ratiometric Measurement Transducers

New methods are considered for correcting additive and multiplicative systematic errors of ratiometric measurement transducers utilizing sensors whose output signal u(x) is proportional to their power supply voltage or current. It is shown that synthesized algorithms for processing the intermediate results of measurements provide a reduction in the additive errors by several orders of magnitude and almost completely eliminate multiplicative errors.     

Measurement of the Equivalent Electrical Parameters of Dissipative Quartz Transducers

We consider the theory and schematic diagram of a device for checking the electric parameters of quartz resonators used to study the mechanical (rheological) properties of thin films.     

Measurement of Instantaneous Fluid Temperature and Two Fluid Velocity Components Using Hot-Wire Anemometers

Hot-wire anemometers, when used in a nonisothermal flow field, respond to both fluid temperature and fluid velocity fluctuations, even when operating conditions are selected to minimize the response to one of the stimuli. Use of a two-or three-wire array for the simultaneous measurement of temperature and velocity fluctuations and their mutual statistics has been shown to lead to significant errors, if, as is general practice, the approximate sensor responses are assumed to be ideal responses. An extension of the traditional techniques is described which eliminates this major source of error but still retains the simplicity of signal processing of the earlier methods.     

双刀口扫描法测量可见光CCD调制传递函数

介绍了一种新型的刀口扫描法测量可见光CCD的调制传递函数(MTF),首次采用1∶1的无像差光学系统,消除了测量光学系统MTF所带来的较大不确定度分量;采用双刀口方法和动态定焦扫描法,提高了测量效率和精度.