Set Of Time Constants Research Articles

Prediction of Dynamic Characteristics of Thermocouples with Thin-Wire Sensing Elements

Thermocouples dynamic characteristicsʼ prediction is one of the relevant directions in the field of dynamic measurements of non-stationary temperatures of liquid and gaseous media. Thermocouples dynamic characteristicsʼ prediction makes it possible to provide effective continuous correction in automatic control systems for non-stationary temperatures. The purpose of this paper was to develop a theoretically justified relation linking the current or expected time constant of fine-wire thermocouples with the known time constant established at known parameters of liquid and gaseous media.A formula linking the time constant of fine-wire thermocouples with the conditions of heat exchange with the measured medium and the thermophysical characteristics of the thermocouple sensing elements has been deducted. An approximate formula is also given for calculating the internal resistance of wire sensing elements of thermocouples, which must be considered when calculating the time constant of a thermocouple. In consideration of the obtained formulas, a multi-parameter relation linking the current or expected time constant of fine-wire thermocouples with the known time constant set at the known parameters of the measured media has been formed.It is suggested to simplify the formed multi-parameter relation and make it dependent, for example, on the “expected velocity of the measured medium × expected density of the measured medium” complex (Vm2 ρm2 ). Simplified relations in the form of hyperbolic functions with constant parameters and argument in the form of Vm2 ρm2 complex were obtained for airflowat different temperatures, pressures, and velocities.On the example of airflow, it is shown that the complex multi-parametric relation linking the expectedand known time constants of thermocouples can be simplified to a hyperbolic dependence, where the argument can be the Vm2 ρm2 complex. Moreover, the degree of approximation of hyperbolic dependencies to the exact values of the multi-parametric relation can reach the R-square = 0.9592 criterion.A multi-parametric relation has been proposed. That relates the known time constant of a thermocouple to the expected or current time constant of the same thermocouple at other parameters of the measured medium from the point of view of the heat exchange and thermal conduction theory. The proposed relation can be used in automatic control systems of non-stationary temperature of various liquid or gaseous media to provide continuous correction of thermocouples dynamic characteristics. Depending on the number of measured medium parameters, the suggested multi-parameter relation can be replaced by simplified relations with other complexes containing, for example, density, velocity, flow rate and pressure of the measured medium.

Activation energies for two steps in the S2→ S3 transition of photosynthetic water oxidation from time-resolved single-frequency infrared spectroscopy.

The mechanism of water oxidation by the Photosystem II (PSII) protein-cofactor complex is of high interest, but specifically, the crucial coupling of protonation dynamics to electron transfer (ET) and dioxygen chemistry remains insufficiently understood. We drove spinach-PSII membranes by nanosecond-laser flashes synchronously through the water-oxidation cycle and traced the PSII processes by time-resolved single-frequency infrared (IR) spectroscopy in the spectral range of symmetric carboxylate vibrations of protein side chains. After the collection of IR-transients from 100 ns to 1 s, we analyzed the proton-removal step in the S2 ⇒ S3 transition, which precedes the ET that oxidizes the Mn4CaOx-cluster. Around 1400 cm-1, pronounced changes in the IR-transients reflect this pre-ET process (∼40 µs at 20 °C) and the ET step (∼300 µs at 20 °C). For transients collected at various temperatures, unconstrained multi-exponential simulations did not provide a coherent set of time constants, but constraining the ET time constants to previously determined values solved the parameter correlation problem and resulted in an exceptionally high activation energy of 540 ± 30 meV for the pre-ET step. We assign the pre-ET step to deprotonation of a group that is re-protonated by accepting a proton from the substrate-water, which binds concurrently with the ET step. The analyzed IR-transients disfavor carboxylic-acid deprotonation in the pre-ET step. Temperature-dependent amplitudes suggest thermal equilibria that determine how strongly the proton-removal step is reflected in the IR-transients. Unexpectedly, the proton-removal step is only weakly reflected in the 1400 cm-1 transients of PSII core complexes of a thermophilic cyanobacterium (T. elongatus).

In-Depth Analysis of Pole-Zero Compensations in CMOS Operational Transconductance Amplifiers

In this paper we explore the effects of pole-zero compensation in the settling performance of operational transconductance amplifiers (OTAs). We carry out the analysis by exploiting a proficient technique that provides an in-depth comprehension of the time domain behavior from the contour plots of the Normalized Settling Time. Starting from the case of a single-pole amplifier, we show the conditions upon which the settling time is degraded by the slow time constant set by the pole-zero doublet. Then, we extend these results to two-pole amplifiers and provide a useful design equation. Design examples of a two-stage and a single-Miller three-stage OTAs confirm the validity of the proposed theoretical models.

Dynamic of Gas Bubbles Surrounded by a Dullaert-Mewis Thixotropic Fluid

In the present work, the dynamics of a single spherical gas bubble surrounded by an elastic thixotropic liquid is addressed at the presence of an acoustic pressure field. The well-known Dullaert and Mewis' rheological model is used to represent different aspects of the fluid's thixotropic and elastic behavior. A numerical method based on Gauss-Laguerre quadrature is adopted to integrate the integro-differential equation governing bubble dynamics. The numerical results suggest that bubble response is significantly affected by the thixotropic properties of the surrounding fluid. A competition between the time constant set forth by the fluid's elasticity and the time constant related to the fluid's thixotropicity is predicted to give rise to the generation of second harmonics in the bubble's response for certain range of model parameters.

Analytical characterization of SOA-based optical pulse delay discriminator

Semiconductor optical amplifier (SOA)-based optical timing extraction and clock-recovery schemes offer compact size, low operating power, and added possibility for integration into an all-optical circuitry. In this paper, we analyze a device that could measure the relative delay between counterpropagating pulses incident on an SOA. Unlike previous designs based on differential photodiodes, our optical pulse delay discriminator (OPDD) uses the voltage difference between two contacts on the SOA. We therefore eliminate the two photodiodes and two optical couplers, making integration far easier. After giving a qualitative description of the operation of the proposed design, we carry out a comprehensive analytical analysis of the operation of the device performance. At each stage, we demonstrate the accuracy of the derived approximate formulas. An analytical expression for the transient response of OPDD shows it to be exponential with a time constant set by the carrier-recovery lifetime. We show that it is possible to reliably measure the incident delay between counterpropagating, periodic pulse trains by measuring the mean value (or low-pass-filtered value) of the induced voltage difference. Our analysis shows the OPDD has excellent linearity.

Response dynamics of the frequency comb output from a femtosecond fiber laser

The frequency comb from a mode-locked fiber laser can be stabilized through feedback to the pump power. An understanding of the mechanisms and bandwidth governing this feedback is of practical importance for frequency comb design and of basic interest since it provides insight into the rich nonlinear laser dynamics. We compare experimental measurements of the response of a fiber-laser frequency comb to theory. The laser response to a pump-power change follows that of a simple low-pass filter with a time constant set by the gain relaxation time and the system-dependent nonlinear loss. Five different effects contribute to the magnitude of the response of the frequency comb spacing and offset frequency but the dominant effects are from the resonant contribution to the group velocity and intensity-dependent spectral shifts. The origins of the intensity-dependent spectral shifts are explained in terms of the laser parameters.

Specific set of the time constants for characterisation of organic volatile compounds in the output of metal oxide sensors

The time dependence of the resistance response to a steep change of gas composition in the atmosphere is investigated for the gas sensors based on tin oxide and indium oxide thin films. The dependence is assumed to pertain to the exponential decrease with three time constants for the slope. The leading edge of the response is analysed for the sensors with the aim of characterising the target smell using a set of time constants instead of the equilibrium response signal. The sets are applied for the characterisation of the volatile substances emitted from the model solutions based on glucose and glycine in which Maillard's browning reaction took place. In the sets, the collection of the time constants is shown being characteristic of the odour produced by the target solutions. Based on the sets, volatile compounds could be recognised in the aroma.

A systematic method for the determination of the parameters of synchronous machines from the results of frequency response tests

This paper deals with the analysis of the frequency responses of the d and q axis impedances of synchronous machines. Numerical curve-fitting techniques have normally been used to find the best set of time constants to fit the frequency response data, but limitations or constraints are introduced with these techniques. The process to be described here is based on characteristic features of the equivalent circuits which overcome the need to make the assumptions inherent in a numerical approach. The extraction process is demonstrated using an equivalent circuit chosen to produce a frequency response similar to that for the direct axis of a production machine. This enables the intrinsic advantages of the proposed process for extraction of the time constants to be demonstrated which then leads directly to a unique set of equivalent circuit parameters.

Investigation of a solid-state detector for advanced computed tomography.

Utilization of solid-state detectors for computed tomography (CT) has been the focus of many studies. Previous phantom and clinical experiments have shown that one of the important performance parameters for the solid-state detector is the primary speed and afterglow. In this paper, we present a detailed investigation on the signal decay characteristics of the HiLight (GE Medical Systems, Milwaukee, WI) scintillating detector. The detector primary speed and afterglow are modeled by a multiexponential function and fully characterized by a set of time constants and relative strengths. The sensitivity of these parameters to X-ray photon energy, detector aging, and radiation exposure is then established and analyzed. No statistically significant variation is observed in these parameters due to changes in the above external variables. The impact of various decay time constants on CT image quality, such as spatial resolution, noise, and artifacts, is subsequently illustrated with computer simulations and phantom experiments. Finally, an algorithmic correction scheme is derived to compensate for detector afterglow. The correction scheme employs a recursive filter to remove adverse effects of the detector decay on image quality. Experimental results have shown that the correction scheme successfully restores system spatial resolution, produces a more homogeneous noise pattern, and eliminates ring-band image artifacts due to detector afterglow. The effectiveness and robustness of the correction scheme are demonstrated by extensive phantom and clinical experiments.

Noniterative synchronous machine parameter identification from frequency response tests

In this paper, a method to identify synchronous machine parameters from standstill frequency response tests is presented. It is common practice to use iterative techniques first to match a set of time constants with the measured response, and then to solve a set of nonlinear equations to obtain the equivalent circuit parameters. However, there is a difficulty of specifying an initial parameter estimate before any iterations can commence. This problem is overcome by the method presented here, which is able to approximate machine parameters straightforwardly and without the need of iterating. It was found that the transfer functions produced by the calculated parameters very closely resemble the measured frequency responses. Should refinements of the solution become necessary, the obtained parameters will still serve as an excellent initial estimate for standard curve fitting procedures.

Non-Differential Conduction Calorimeter, a Tool to Study the After Quench Behaviour in Shape Memory Alloys

After the development of differential conduction calorimeters realized by E. Calvet around 1946, the standard equipment always used a differential configuration. In home made systems for special purposes, the instrumentation available nowadays suggests that it is possible to use non-differential conduction calorimeters. In order to prove this, a simple and cheap design was constructed and tested. A sensitivity of 700 mV/W near 298 K (in agreement with the detecting semiconductors), a noise around 0.3 µW and a long time fluctuation of the base line lower than 1 µW were obtained. The reliability of the system was evaluated by analyzing the changes of single crystals of Cu-Zn-Al Shape Memory Alloys after different thermal treatments. The calorimeter allowed the determination of a reproducible set of time constants related to the heat treatments and to the mass (or shape) of the sample. It is concluded that the experimental configuration used is suitable for this isothermal analysis.

Characteristics of equivalent circuits of synchronous machines

Frequency response tests have now become accepted as a sound alternative to sudden short-circuit tests for the determination of parameters for synchronous machines for transient studies. The standard approach to the extraction of machine parameters from the results of frequency response tests generally concentrate on curve-fitting techniques to match the measured magnitude and phase with a set of time constants. These processes are fraught with difficulty in respect of needing to: first, define the order of the model before the analysis can commence; and secondly, initiate the curve fitting with initial estimates of the parameters. Unfortunately, there is not a unique set of time constants which produce a frequency response which fits the measured data, and a better method than a ‘blind’ numerical method is therefore needed. The author presents the application of standard linear systems theory to predict the positions of the poles and zeros in the frequency response and to determine the order of the equivalent circuit required to model the machine accurately. The process breaks quite naturally into two parts; the extraction of the time constants from the frequency response, and the determination of the parameters of the equivalent circuit from those time constants. The basis for the measurement technique is reviewed and the effects of different levels of complexity of the equivalent circuit are considered with respect to the increased difficulty normally experienced in extracting the parameters. The ease with which this method copes with the higher-order models and the sequential nature of the process, working from the lowest frequency to the highest frequency in the frequency response, justify accepting the procedure. Results obtained from tests on production machines are used to illustrate the procedures for both time constant extraction and equivalent circuit parameter determination to confirm the capabilities of the methods.

Absolute calibration of a ten-channel grating polychromator for electron temperature measurements on Princeton large torus

It has been possible to calibrate absolutely the ten-channel grating polychromator installed on PLT (Princeton large torus). Radiation from a blackbody source (eccosorb at liquid-nitrogen temperature) was chopped at 275 Hz and the signal detected using a lock-in amplifier with an integration time constant set at 125 s. A cascade of six grating filters was used to eliminate higher-order radiation from the input to the instrument. Each channel could be calibrated in approximately 2 h; under these conditions the rms calibration signal to noise for a typical channel is about 60.

Kinetics and saturation of light-induced near-infrared scattering changes in isolated bovine rod outer segments.

The axial and radial shrinkage of bovine rod outer segments, monitored by near-infrared scattering changes (P-signal), is investigated in dependence on the intensity of the activating flash. Suspensions of axially oriented and randomly oriented rod outer segments were measured. In the latter case, axial and radial effects are superimposed to another. The following results are obtained: 1. The axial signal (Pa, tau approximately 10 ms) and the radial signal (Pr, tau = 40-100 ms), simultaneously measured on axially oriented rod outer segments, are similarly saturated with a half-saturation at a rhodopsin turnover of 3.5%. 2. For the saturation of the signal amplitude, measured on randomly oriented rod outer segments, a good fit is obtained by: P(rho) approximately 1 - e-beta rho, rho: relative rhodopsin turnover by the flash; beta is found in the range 23 less than or equal to beta less than or equal to 27 in all measurements. 3. The kinetics of the signal, also measured on the isotropic sample, depends on the rhodopsin turnover, the apparent time constant becoming faster with increasing turnover, The distortion of the signal cannot be fitted by a sum of exponentials with a fixed set of time constants. The signals from the isotropic sample are fitted by a phenomenological model. It introduces three first order processes concatenated in series; the first step is assumed as a rhodopsin transition inducing the two further processes. The distortion of the signals with increasing rho is then described assuming a rho-dependent quenching of this induction, according to the measured amplitude saturation. The time constants remain thereby unchanged. The fit yields the values in 2/k = 4, 11, and 45 ms with mean square deviations of 20%.

Response of a Simple Photoconductor to a Square Light Pulse

The time dependent signal produced by a finite light pulse of constant intensity is calculated for a photo-conductor for which trapping effects are neglected. It is found that the signal is given by a sum of terms varying exponentially with time and involving an infinite set of time constants whose values are determined by the geometry and the rates of bulk and surface recombination. It is shown that the maximum signal occurs at the end of the pulse and that in order to maximize the ratio of the maximum signal to the noise it is desirable to have equal recombination rates on the two surfaces and to make the ratio of the thickness to the diffusion length as small as is possible without adversely affecting the steady-state detectivity.