Showing papers on "Time constant published in 2006"

Time-course of the human medial olivocochlear reflex.

Abstract: The time-course of the human medial olivocochlear reflex (MOCR) was measured via its suppression of stimulus-frequency otoacoustic emissions (SFOAEs) in nine ears. MOCR effects were elicited by contralateral, ipsilateral or bilateral wideband acoustic stimulation. As a first approximation, MOCR effects increased like a saturating exponential with a time constant of 277±62ms, and decayed exponentially with a time constant of 159±54ms. However, in ears with the highest signal-to-noise ratios (4∕9), onset time constants could be separated into “fast,” τ=∼70ms, “medium,” τ=∼330ms, and “slow,” τ=∼25s components, and there was an overshoot in the decay like an under-damped sinusoid. Both the buildup and decay could be modeled as a second order differential equation and the differences between the buildup and decay could be accounted for by decreasing one coefficient by a factor of 2. The reflex onset and offset delays were both ∼25ms. Although changing elicitor level over a 20dB SPL range produced a consistent ...

Integrated description of electrode/electrolyte interfaces based on equivalent circuits and its verification using impedance measurements.

Abstract: An integrated theory describing both faradaic and nonfaradaic currents obtained upon potential step at an electrified electrode/electrolyte interface has been developed based on equivalent circuits that had been used to explain electrochemical reactions and experimentally verified. The faradaic current is shown to consist of the mass transport-dependent and -independent parts, which is in general agreement with the expression previously derived from the diffusion equations. The decay of the capacitive current is determined by the time constant represented by the product of the resistance obtained from the parallel connection of the solution and polarization resistances and the double layer capacitance; this is not consistent with the current understanding of the capacitive current decay, which takes into account the double layer capacitance and the solution resistance only. Many insights into the electron-transfer reactions are discussed based on the interpretation of impedance representation of the system, which would not have been possible without the present theory.

Thermal and slip effects on rotor time constant in vector controlled induction motor drives

Abstract: In this paper, the fast variation of rotor resistance due to winding temperature is shown. Thus, the rotor time constant in the vector controlled induction motor drives, in contrary to common belief, changes fast via temperature. Moreover, it depends on the motor slip. The slip dependency of rotor time constant is due to motor loss that is usually ignored. The iron and stray loss is introduced in the induction machine dynamic and static models and a new expression of the rotor time constant is derived, that contains the motor slip. Thus, the rotor time constant rapidly varies at load torque changes. A novel slip frequency calculation procedure is proposed that ensures the accurate and fast estimation of the valid machine rotor time constant. The above aspects have been verified by extensive simulation and experimental tests in a wide speed-torque range.

Scintillation properties of pure CaF2

Abstract: The temperature dependence of the decay time and scintillation light yield of pure CaF 2 crystal was measured over the temperature range 8–305 K using the multiphoton coincidence counting technique. Pure CaF 2 exhibits emission of triplet self-trapped excitons at 280 nm with a slow decay, the time constant of which changes significantly with temperature. The main decay time constant increases by three orders of magnitude when cooled, from 0.96±0.06 μs at 295 K to 930±40 μs at 8 K. The results obtained demonstrate that the scintillation light yield of pure CaF 2 increases with decreasing temperature down to 20 K below which it is roughly constant. At low temperatures the light yield of CaF 2 is estimated to be 60% relative to that of pure CaWO 4 . It is concluded that undoped calcium fluoride is a very attractive target material for experimental searches for rare events based on the detection of phonon and scintillation signals.

Deep ultraviolet detection dynamics of AlGaN based devices

Abstract: The photoconductive response of AlGaN based UV detectors to 193nm excimer laser radiation is presented. Two devices have been tested: a metal-semiconductor-metal (MSM) planar structure and a Schottky diode. The transient response of the MSM device closely follows the laser pulses, with a photoconductive decay time constant shorter than 3ns. Conversely, the Schottky diode shows a slower photoconductive rise and decay kinetics due to the material series resistance coupled with the junction capacitance. Moreover, a longer time constant tail is also evident in this case with a characteristic time of about 40ns, due to the presence of trap states localized at 0.2–0.3eV from the band edge. The detection dynamics has been evaluated by changing the beam energy density between 2×10−5 and 0.2mJ∕mm2. The signal increases linearly in the case of the MSM device up to 0.001mJ∕mm2, whereas, for a further intensity rise, the response shows a sublinear behavior. On the contrary, the Schottky diode showed a linear trend in...

Nonequilibrium heating in LHCII complexes monitored by ultrafast absorbance transients.

Abstract: Evidence of nonequilibrium local heating in transient spectra of LHCII, the main light-harvesting complex of plants, was studied by using various excitation intensities over a wide temperature range, from 10 K to room temperature. No obvious manifestation of local heating was found at room temperature, whereas at 10 K, the local heating effect is discernible when more than 10 excitons per LHCII trimer per pulse are generated. Under these conditions, a major part of the excitation energy is converted into heat as a result of exciton-exciton annihilation. Initially, the heat energy is allocated on chlorophyll a molecules, reaching hundreds of degrees at the highest excitation intensities, which correspond to almost 100 excitons per trimer generated by a single excitation pulse. The decay of the nonequilibrium temperature is characterized well by two exponentials. The initial phase of cooling, which is most likely caused by the spreading of heat over the protein, corresponds to a characteristic time constant of approximately 20 ps. Later, the cooling rate decelerates to approximately 200 ps and is related to heat transfer to the solvent.

Modeling the calcium gate of cardiac gap junction channel.

Abstract: We addressed the question how Ca2+ transients affect gap junction conductance (Gj) during action potential (AP) propagation by constructing a dynamic gap junction model coupled with a cardiac cell model. The kinetics of the Ca2+ gate was determined based on published experimental findings that the Hill coefficient for the [Ca2+]i-Gj relationship ranges from 3 to 4, indicating multiple ion bindings. It is also suggested that the closure of the Ca2+ gate follows a single exponential time course. After adjusting the model parameters, a two-state (open-closed) model, assuming simultaneous ion bindings, well described both the single exponential decay and the [Ca2+]i-Gj relationship. Using this gap junction model, 30 cardiac cell models were electrically connected in a one-dimensional cable. However, Gj decreased in a cumulative manner by the repetitive Ca2+ transients, and a conduction block was observed. We found that a reopening of the Ca2+ gate is possible only by assuming a sequential ion binding with one rate limiting step in a multistate model. In this model, the gating time constant (T) has a bell-shaped dependence on [Ca2+]i, with a peak around the half-maximal concentration of [Ca2+]i. Here we propose a five-state model including four open states and one closed state, which allows normal AP propagation; namely, the Gj is decreased -15% by a single Ca2+ transient, but well recovers to the control level during diastole. Under the Ca(2+)-overload condition, however, the conduction velocity is indeed decreased as demonstrated experimentally. This new gap junction model may also be useful in simulations of the ventricular arrhythmia.

Method and apparatus for rapid temperature changes

Abstract: A method and apparatus for rapid temperature changes of thin samples is disclosed. The apparatus comprises of a thin-film resistive element embedded in a membrane, a narrow gap between the membrane and a heat sink, and a control circuit. The resistive element acts both as a heater and as a temperature sensor to reduce time constant of the control circuit. The gap between the membrane and the heat sink is filled with gas (e.g., N2 or He) acting as cooling medium with low thermal inertia. The temperature controller has a microsecond time constant, which allows adjusting rapidly the power applied to the membrane, depending on heat released/absorbed by a sample during an isotherm or during a given rate of temperature changes. The membrane has low thermal inertia and, coupled with high-speed temperature controller, allows controlled cooling and heating rates up to 100 000 K s−1 and higher. The method can be a core of any setup where controlled fast temperature-time profile of thin or small sample is desirable. The proposed control circuit can be readily applied to the variety of the existing setups with resistive heater.

Transient temperature measurements and characteristics for temperature sensors and energy wheels

Abstract: The transient responses of two types of temperature sensors-an RTD and a thermocouple-and of a stationary energy wheel exposed to a transient step change in temperature with no change in humidity are investigated. These responses are measured and correlated with exponential functions with two time constants. The first time constant of the RTD sensor in a humidity transmitter alone without the wheel is found to be about 70 s and the second time constant is about 6∼12 min, while the time constants of the thermocouple alone are found to be about 5 s and130 s. The response time (time for 90% of the change to occur) for the R TD sensor and thermocouple are 1200 s and 250 s, respectively. When these sensors are used downstream of an energy wheel to measure the transient temperature response of the energy wheel, the measured temperatures are also found to correlate with exponential functions with two time constants. The measured response of the sensors in this setup includes the combined effects of the wheel and sensor transient response characteristics. An analysis is presented to determine only the dynamic characteristics of the wheel matrix using only the measured responses of the sensor alone and sensor with a wheel upstream. It is found that the predicted response of the wheel alone gave time constants that were about 20 s and 170s, giving a response time of 450 s. Since the response time of the wheel is less than the response time of the RTD sensor, theR TD sensor cannot be used to measure the transient characteristics of the wheel.

Dynamic Thermal Analysis of a Power Amplifier

Abstract: This paper presents dynamic thermal analyses of a p ower amplifier. All the investigations are based on the transient junction temperature measurements performed during the circuit cooling process. The presented results incl ude the cooling curves, the structure functions, the therma l time constant distribution and the Nyquist plot of the t hermal impedance. The experiments carried out demonstrated the influence of the contact resistance and the positio n of the entire cooling assembly on the obtained results.

Constrained evolution of nanocrystallites

Abstract: Deviations from the universal predictions of shape-preserving structure evolution have been investigated in the context of realistic physical boundary conditions for supported nanoscale crystallites. Structural evolution was simulated using the continuum step model with volume conservation, variable interface free energy, and incorporating analytical solutions for equilibrium and metastable crystallite shapes. Early stages of evolution following a simulated temperature drop are consistent with the kinetics of shape-preserving evolution, e.g., not limited by the constant volume constraint. Later stages of decay show a distinct slow down, with an empirically-determined exponential form. The time constant of the slow final evolution increases linearly with the length scale of the crystallite, and also increases monotonically with interface adhesion strength. Under normal evolution, where the interface area between the crystallite and substrate is constant or increasing, the evolution progresses through the metastable states accessible to the volume. If a decreasing interface area can be induced, an alternative progression ending much closer to equilibrium is possible. The late-stage slow down provides additional kinetic information that allows the nonuniqueness of early-stage modeling to be resolved. The slow down observed in the late stages of relaxation of Pb crystallites has been fit, with a unique determination of the relative values of the terrace diffusion constant and step attachment constant.

Thermal effects in InGaAs/AlAsSb quantum-cascade lasers

Abstract: A quantum-cascade laser (QCL) thermal model is presented. On the basis of a finite-difference approach, the model is used in conjunction with a self-consistent carrier transport model to calculate the temperature distribution in a near-infrared InGaAs/AlAsSb QCL. The presented model is used to investigate the effects of driving conditions and device geometries on the active-region temperature, which has a major influence on the device performance. A buried heterostructure combined with epilayer-down mounting is found to offer the best performance compared with alternative structures and has thermal time constants up to eight times smaller. The presented model provides a valuable tool for understanding the thermal dynamics inside a QCL and will help to improve operating temperatures.

Dynamic behaviour of fuel cells

Abstract: This thesis addresses the dynamic behaviour of proton exchange membrane fuel cells (PEMFCs) and alkaline fuel cells (AFCs). For successful implementation in automotive vehicles and other applications with rapidly varying power demands, the dynamic behaviour of the fuel cell is critical. Knowledge of the load variation requirements as well as the response time of the cell at load change is essential for identifying the need for and design of a buffer system.The transient response of a PEMFC supplied with pure hydrogen and oxygen was investigated by load step measurements assisted by electrochemical impedance spectroscopy and chronoamperometry. Using an in-house designed resistance board, the uncontrolled response in both cell voltage and current upon step changes in a resistive load was observed. The PEMFC was found to respond quickly and reproducibly to load changes. Two transient processes limiting the fuel cell response were identified: i) A cathodic charge transfer process with a potential dependent response time and ii) a diffusion process with a constant response time. The diffusion transient only appeared at high current densities and was offset from the charge transfer transient by a temporarily stable plateau. Transient paths were plotted in the V-i diagram, matching a predicted pattern with overshooting cell voltage and current during a load step.The transient response of a PEMFC was measured for various cathode gas compositions and gas utilisations (fraction of supplied reactant gas which is consumed in the fuel cell reaction). For a PEMFC operated on pure hydrogen and oxygen, the cell voltage response to current steps was fast, with response times in the range 0.01-1 s, depending on the applied current. For a PEMFC supplied with air as cathode gas, an additional relaxation process related to oxygen transport caused a slower response (appr. 0.1-2 s depending on the applied current). Response curves up to appr. 0.01 s were apparently unaffected by gas composition and utilisation and were most likely dominated by capacitive discharge of the double layer and reaction with surplus oxygen residing in the cathode. The utilisation of hydrogen had only a minor effect on the response curves, while the utilisation of air severely influenced the transient PEMFC response. Results suggested that air flow rates should be high to obtain rapid PEMFC response.The load-following capability of a single PEMFC was studied by measuring the cell voltage response to a sinusoidal current load with large amplitudes. Effects on the cell voltage response when varying the DC value, amplitude and frequency of the current load were recorded. The load-following capability of the PEMFC was excellent in the operating range where changes in cell voltage were dominated by ohmic losses. No hysteresis in the cell voltage response was observed in this range for frequencies up to 1-10 Hz. In the operating range where changes in cell voltage were dominated by activation losses, hysteresis appeared at lower frequencies (>0.1 Hz) due to sluggish response in the voltage range near open circuit voltage. The increased mass transport limitation imposed when supplying the PEMFC with air caused hysteresis to appear at lower frequencies than for oxygen (above 0.1 Hz, compared to 1-10 Hz for oxygen).The dynamic behaviour of an AFC supplied with pure oxygen and hydrogen was investigated by load step measurements assisted by electrochemical impedance spectroscopy (EIS). Load step measurements were carried out using an in-house designed resistance board which gave step changes in a purely resistive load. Resistive load steps between various operating points along the polarisation curve were carried out and the corresponding transient response in cell voltage and current was measured. The transient cell response consisted of an initial ohmic drop followed by a relaxation towards the new steady state. The observed response was slower at higher cell voltages. Measured response times varied on a time scale of appr. 10 ms to 10 s, depending on the initial and final voltages. Results from EIS measurements suggested that the potential dependent response time stemmed from the charge transfer reaction at the cathode. Transient response curves were plotted in the V-i diagram and shown to follow a pattern determined by the load resistance and ohmic resistance of the AFC. Results showed that when supplied with pure oxygen and hydrogen, the AFC responded sufficiently fast for automotive applications.An iso-thermal, one-dimensional, transient model of an AFC cathode was developed, based on mass balances for oxygen and ionic species and floodedagglomerate theory. Model results show the coupled effects of oxygen diffusion, ion transport and propagation of local electrode potential on the response in current density to a cathodic step in electrode potential. For a set of base case parameters, oxygen diffusion and potential propagation, with characteristic time constants of 0.30 and 0.11 ms, respectively, dominated the current response up to appr. 1 ms, while the slower ion diffusion with time constant 5.0 s controlled the final relaxation towards steady state at appr. 60 s. A smaller agglomerate radius and electrode thickness and a smaller double layer capacitance gave faster electrode response. For a cathodic step in electrode potential, an overshoot in faradaic current appeared around 0.5 ms. This overshoot was related to an initially higher oxygen concentration in the agglomerates, but was masked by capacitive current for base case parameters. Simulated response in oxygen concentration profiles suggested that the potential dependent response time found in previous studies can be related to consumption of surplus oxygen in the catalyst layer.

Some studies on the pulse-height loss due to capacitive decay in the detector-circuit of parallel plate ionization chambers

Abstract: Pulse-type ionization chambers are invariably operated in the electron-sensitive mode where the capacitive decay in the detector-circuit during the electron collection produces loss in the pulse-height. In order to understand and appreciate the effect of this capacitive decay on the detector response, we have carried out Monte Carlo simulations of the response of two-electrode parallel plate ionization chambers with and without the capacitive decay keeping shaping time so large that the ballistic deficit is negligibly small. These simulations have been carried out incorporating the physical processes, namely, emission of charged particles from a point radioactive source, the generation of charge carriers in the active volume, separation and acceleration of the charge carriers, transport of the charge carriers, induction of charges on the electrodes, pulse processing by preamplifier-amplifier network, etc. These simulations have shown that the concerned capacitive decay produces appreciable loss in the pulse-height, if the detector-circuit time constant is of the order of maximum electron collection time. We have also carried out measurements on the pulse-height loss due to the capacitive decay in the detector-circuit during the electron collection for a two-electrode parallel plate ionization chamber. The experimental data on the pulse-height loss match reasonably well with the theoretical predictions.

Fast Extrapolation of a Thermal Sensor's Final Value and Discovery/Verification of a Thermal Sensor's Thermal Time Constant

Abstract: A power meter that uses a thermal mount whose response to changes in applied power is exponential, is equipped to digitally sample the conditions within the mount at a rate of many times per time thermal constant. Samples are monitored for an indication that a significant change in power level is occurring. When that condition is detected a forward extrapolation computational algorithm is performed upon several consecutive samples that may be taken over approximately the duration of one time constant. The extrapolation is a prediction the final value that would be obtained for the power sensor's indication of that same applied power after five time constants. The first of the several samples may occur immediately upon or shortly after the discovery that a significant change in power has occurred. An actual step in applied power need not last longer than the time during which the several samples for extrapolation are taken in order to be measured. Extrapolation may be performed continuously whenever significant change is detected. Extrapolation needs the time constant(s) for the mount in use, or some exponential rule that governs its behavior. Absent that information the power meter can find the thermal time constant of the mount, which it may then store in the power meter or in the mount itself. Similar extrapolation works for electronic thermometers having thermal probes having a thermal time constant.

Thermal Incremental And Time Constant Analysis On 20 Kv XLPE Cable With Current Vary

Abstract: In power cable, thermal factor must be considered where heat generated in power cable must be limited and lower than thermal rating of insulation materials. Overheating on cable insulation material will cause the electrical insulation aging is accelerated. This paper is present the result of thermal incremental test of the medium voltage XLPE cable type N2XEBY with three core and analysis when time constant come. From the test, temperature rise data is obtained transient condition to steady-state condition and time constant. A cable loaded with constant alternating current in one of its core, and measured the temperature of conductor (Tc), insulation material (Ti ) and the outer surface of the cable (Tp). Base on the test, Conductor is faster than insulation material and surface of cable to reach to thermal time constant, but They have same typical of graph. When current is raised from 90 A to 300 A, time constant is decrease and increase depend of current value and typical for all material. In this paper shown predict correlation of the steady-state temperature and time constant, then empiris equation are developed by step function

Photovoltage Decay in CDTE/CDS Solar Cells

Abstract: Photo-voltage decay (PVD) is a common technique used to characterize numerous semiconductor devices. However, the technique has not been widely applied to CdTe-based solar cells. We have applied PVD to CdTe solar cells made with various fabrication conditions using a red (620 nm) LED and digital oscilloscope. We find the decay to be described by the equation v(t)=V0+A1exp (-t/tau1)+A2exp (-t/tau2)+A3 exp (-t/tautau1) where v is the voltage, t is time, tau1, tau2 and tau3 are characteristic decay times, and A1, A2, A3 and V0 are constants. The three time constants have values of approximately 5-10 mus, 50-100 mus, and 800-1500 mus respectively. In general, cells with lower conversion efficiency have shorter decay times. The exponential nature of the decay indicates that in CdTe/CdS solar cells, the PVD is dominated by capacitance effects. The time constants decrease with increasing temperature

High sensitivity single or multi sensor interface circuit with constant voltage operation

Abstract: A sensor interface circuit is provided to interface many sensors simultaneously in a simple circuit arrangement consisting of two parts. Sensors in both parts operate under identical constant voltage. The circuit provides higher front end sensitivity than the Wheatstone bridge, with temperature compensation from all sensors. The circuit also can provide output zeroing to obtain high resolution measurements. The invention can be used as a unique constant voltage anemometer with auto zeroing, and with much higher sensitivity than related devices. Further, in the constant voltage anemometer embodiment, the time constant and the overheat of the hot-wire/hot-film can be measured in true in situ mode under actual test conditions. In another embodiment, the circuit can be used to measure dynamic capacitance from capacitance sensors, without any effect of associated cable capacitance.

Power converter controller

Abstract: Detecting and controlling the switching current of the power converter, the controller controls output current. The controller includes a first circuit, a second circuit, a third circuit and a switching circuit. Based on switching current of the power converter, the first power converter generates a first signal. The second circuit detects discharge time of transformer. Based on integral carried out by discharge time on the first signal, the third circuit generates a third signal. Time constant of the third circuit is changeable, and related to the switching period of the switching signal. Thus, the third signal is proportioned to the output current. Receiving the third signal and based on a reference voltage, the switching circuit controls the pulse wave width of the switching signal so as to adjust output current of the power converter.

Method for measuring wavelength of light with high accuracy

Abstract: PROBLEM TO BE SOLVED: To provide an absorption spectrum measuring method for a target analytical material, using a cavity ringdown spectrometer. SOLUTION: This method includes a step of adjusting a laser of the spectrometer so that light transmitted to an optical cavity of the spectrometer from the laser changes extending over a wavelength section, including both the absorption wavelength of spectrum characteristics of the target analysis material and free spectrum range of optical cavity; a step of recording the attenuation time constant and trigger time for intercepting the light to the cavity concerning each ring-down event; a step of systematizing the attenuating time constant, light wavelength and trigger time as a function of the trigger time; a step of calculating the average wavelength of each set of bin; and a step of calculating the average decay time concerning the respective decay time, and using the average of the decay time and the average wavelength of of parallel wavelength bins for calculating the optical loss of the target analysis material for the average wavelength. COPYRIGHT: (C)2006,JPO&NCIPI

KCNE2 modulates the function of Kv4.3 channel

Abstract: OBJECTIVE To understand the role of KCNE2 in functional regulation of Kv43, the major alpha subunit of transient outward current (I(to)) in human heart METHODS The cDNAs of Kv43 or Kv43 plus KCNE2 were transfected into COS-7 cells and 24-36 h after the transfection, the channel proteins were expressed in the surface membrane of the cells and the channel currents were recorded with patch-clamp technique in whole-cell mode RESULTS KCNE2 played an important role in modulating the channel function The recorded current density was decreased in cells co-expressing KCNE2 and Kv43 to 15296-/+3371 pA/pF (n=16) as compared with Kv43-expressing cells with a mean current density of 37513-/+11287 pA/pF (n=11) At the recording voltage of 60 mV, KCNE2 increased the time to peak (TTP) of the current TTP in only Kv43-expressing cells was 482-/+032 ms (n=11), significantly shorter than the TTP of 2041-/+213 ms (n=16) in cells co-expressing Kv43 and KCNE2 (P<005) In the presence of KCNE2, the voltage-dependent inactivation of Kv43 showed a positive shift The voltage of half maximum inactivation (V(05)) was decreased significantly from -5362-/+124 mV (n=8) in Kv43 group to -4658-/+16 mV (n=10) in KCNE2 co-expression group (P<005) KCNE2 accelerated the recovery of the channel from inactivation, reducing the recovery time constant (tau) from 19343-/+1798 ms to 13771-/+1829 ms CONCLUSION KCNE2 might serve as an important beta subunit and play a role in the regulation of I(to) function in human heart

Radiation detected value forecasting method and forecast responsive radiation detector

Abstract: In a radiation detector, a response is approximated as a primary delay system, and when a time constant T indicating the characteristic of the response is known, a final response value N 0 is forecasted from dose rates or counting rates N 1 and N 2 of two points in the initial or middle stage of response. When the time constant T is unknown, the final response value N 0 is forecasted from dose rates or counting rates N 1 , N 2 , and N 3 of three points in the initial or middle stage of response. Simultaneously, a time constant is obtained and the soundness of the radiation detector is also evaluated. Thereby, a dose rate in an existence field of radiation or a counting rate in an existence field of radioactive materials is quickly and accurately forecasted, whereby the measurement time is shortened.

Signal detection method and apparatus, and radiation image signal detection method and system

Abstract: A signal detection method including the steps of: initiating integration of charge signals by an integrating amplifier; holding a first electrical signal integrated by the integrating amplifier during a time period from the start of the integration to the end of a predetermined baseline sampling time, and passed through a first low-pass filter having a time constant τ 1 ; and performing signal detection by obtaining the difference between a second electrical signal and the first electrical signal, the second electrical signal being an electrical signal integrated by the integrating amplifier during a time period from the start of the integration to a predetermined time point which is a time point before the integrating amplifier is reset after the first electrical signal is obtained, and passed through a second low-pass filter having a time constant τ 2 which is greater than the time constant τ 1.

Discussion on parameters setting and loss of exciter time constant compensation in excitation system

Abstract: This paper develops a self-design model of automatic voltage regulator (AVR) with criteria of performance indices recommended in IEEE Std 421.5. During the control parameters design and model simulation phase, we can verify all performance indices to see if they meet the specification, such as the steady state error in time domain, phase margin, and the zero crossover frequency in frequency domain, etc. So it is easy to create a full design procedure step by step deterministically. In the voltage constant mode of the excitation control system of a synchronous generator, there is an exciter time constant compensation function to reduce the effective exciter field time constant and increase the small signal response bandwidth. The exciter time constant compensation consists essentially of a direct negative feedback around the exciter with signal coming from exciter field current (Ife). However, it is the main control loop in field constant mode of excitation system. In a traditional analog-based or in a modern digital-based excitation system, loss of exciter time constant compensation is a failure to cause generator terminal voltage unstable. The deteriorated phase margin will impact on power system stability maybe, or result in unit trip unexpectedly. From the point of operation risk assessment and management, we still have to evaluate stability margin in the design phase. This paper suggests that this failure mode should be taken into design consideration besides small signal performance indices. A simple way to resolve the stability margin is to restore the loop forward gain K2 properly to improve the phase margin. It is also necessary to offer a standard operation procedure (SOP) for operators to follow after loss of exciter time constant.