Thermistor Multivibrator Bridge with the Variable Balancing Point Position

This paper describes a thermistor multivibrator bridge and temperature-to-frequency converter for the case where the output characteristics have different balancing and inflexion points. The influence of the difference between balancing and inflexion temperatures (T0 - Ti) on sensitivity is analyzed.     

Linearized Thermistor Multivibrator Bridges for Temperature Measurement

Methods for output voltage linearization of a thermistor astable multivibrator bridge (AMB) and a monostable multivibrator bridge (MMB) are given. In addition to higher sensitivity in comparison with Wheatstone bridge, thermistor multivibrator bridges can have direct application in telemetering and digital recording of temperature. The linearity condition of thermistor AMB and MMB are independent of indicator resistance. Experimental multivibrator bridges with IC differential transistor pairs have shown excellent stability at ambient temperature variations.     

Conversion of Fluid Thermal Parameters into Frequency and Time by Means of Thermistors

A versatile direct converter of fluid thermal parameters into frequency and time is described. The circuit is based on a complementary multivibrator, the frequency of which is controlled by the temperature-sensitive current generator. Temperature-to-time (?-T) and temperature-to-frequency (?-f) conversion is obtained by simple rearranging of passive circuit elements. The linearizing conditions and sensitivity for various probe configurations are given. In battery telemetering systems, the circuit is economical in power supply consumption due to the very small mark-to-space ratio of output pulses. The sensitivity as well as the transducer Rmax/Rmin ratio are considerably increased in comparison with other direct thermistor converters. With the positive temperature coefficient (PTC) thermistor probe, the frequency change can be about three decades in the temperature range of 30°C, which represents the highest obtained sensitivity of ?-T/f converters. The circuit is also successfully applied with self-heated miniature bead thermistors as a sensor when it represents the linearized air speed-to-time converter within the range of 0-3.6 m/s.     

Monostable Multivibrator as the Bridge Circuit with Linear Characteristic

A monostable multivibrator, triggered by pulses of constant frequency, can be used as a bridge circuit either with capacitance or resistance transducers. The output voltage of the monostable multivibrator bridge is a linear function of transducer impedance. Sensitivity is four times higher compared with the Wheatstone bridge.     

A Linear Temperature-to-Frequency Converter

A new technique to linearize the temperature-frequency relationship of an astable multivibrator using one thermistor is proposed. The center frequency can be adjusted at any set frequency by an adjustable resistance. Furthermore, the oscillation frequency is not affected by the change of supply voltage.     

Precision RF Voltage Standard Using a Thermistor Bridge Covering the HF-UHF Range

This paper describes a thermistor mount designed so that residual inductances of leads in the thermistor are eliminated for use in the UHF range. The output voltage of the thermistor bridge is evaluated by the dc substitution method with an accuracy of 0.3 percent for 0.3-1 V over frequencies up to 1.5 GHz. The output voltage agrees with the voltage derived from power and impedance standards within the accuracy.     

Analysis of the operation of automatic thermistor bridges

Conclusions The results thus obtained can be used for designing thermistor bridge circuits according to the above-mentioned requirements. Different procedures can be used for computing a specific circuit. However, in every case it is necessary to aim at meeting the requirements of the auxiliary bridge operation under conditions of a small unbalance, and ensuring that the dc power which heats thermistor T should amount to 1/3 of the total power. In view of the dispersion of thermistor parameters it is advisable to make the initial selection of thermistors for the bridge so that when the thermistors are replaced the bridge can be reset solely by means of the adjustable bridge components.     

A new compensation scheme for thermistors and its implementationfor response linearization over a wide temperature range

A new four-constant curve fit is proposed for the R-T characteristic of a thermistor. That it provides a better fit than the two-constant law R=Ae^BT/ is demonstrated by taking the examples of two standard commercial thermistors. A simple numerical method is suggested for determining the constants of the new fit. Compared to other empirical relationships, the present equation lends itself to easy hardware linearization. A temperature-to-frequency converter that has been developed employing the proposed fit is described. The converter is free from any error due to thermistor lead resistances, and provides an accuracy better than 0.2 K over a temperature range from 300 K to 390 K     

Thermistor Bead Matching for Temperature Compensated RF Power Thermistor Mounts

The temperature compensated thermistor-power meter of the dual bridge design has for many years been the most widely used instrument for microwave power measurement. During these many years very little if anything has been written with regard to the manner or criteria for matching the thermistor beads. This paper attempts to fill that void. The procedure to match thermistor beads for less than 2 ?W/°C drift is to be accomplished by pairing the dR/dt characteristic of each bead and adjusting the dP/dR characteristic for a match. dR/dt of the beads may be determined from resistance data at 90°C and 110°C, and the expression dR/dt = 9.4497 [ln Ra-1.11648 ln Rb + 0.61749] which is derived for 200 ? operating resistance thermistors. The thermistor beads are then paired by selecting such that dR1/dt and dR2/dt are within 1 percent of each other. The conditions necessary for matched dP/dR of the thermistor beads are developed and procedures indicated. The paired beads are installed in the thermistor mount and the constant dP/dR of each bead adjusted for equality by moving the heat sink of one of the thermistors until a balance of the slave bridge and master bridge is obtained simultaneously.     

A Linear Temperature/Voltage Converter Using Thermistor in Logarithmic Network

A novel linearization technique comprising thermistor-resistor-log network is shown which exhibits a linear analog temperature/voltage relation over a wide temperature range (-25°C to +110°C) with reasonably good response linearity, reliability, and overall improved performance. A notable feature of the proposed network is that the power dissipation in the thermistor is quite low and it decreases with increasing temperature thus avoiding a self-heating problem in the thermistor.     

An Integrating Analog-to-Digital Converter for Differential Transducers

An improved dual-slope analog-to-digital converter for measurements made with a pair of resistive or capacitive differential transducers is described. The converter can be contrasted with the conventional method in which the transducers are placed in a bridge, the bridge output is amplified, and the conversion is made. In the new converter the transducers are part of the integrator. As a result, conversion of the signal to a time interval takes place at an earlier stage, eliminating the bridge and the amplifier. The method has the same advantages as the dual-slope method and several additional ones. The fractional change in the transducers is obtained as the ratio of the difference and sum of two time periods. As a result, the converter does not need an accurate voltage reference. In addition, errors due to offset in the integrating amplifier are eliminated.     

A Solid-State Converter for Measurement of Aircraft Noise and Sonic Boom

A solid-state converter, used in a system of instrumentation for measuring aircraft noise and sonic boom, features a dualgate FET mixer and an output stage designed for compatibility with a zero drive amplifier of MB Electronics, Inc. With a half-inch condenser microphone the converter itself has an operating frequency range from dc-28 kHz (-3 dB), dynamic range of 72 dB, and noise floor of 50 dB in the band 22.4 Hz-22.4 kHz; the system requires no impedance matching networks and is insensitive to cable length up to at least 3000 ft.     

The magnetic and semiconductor hybrid: Polyphase multivibrator with AC bias

An ac bias operated multivibrator for dc to polyphase conversion is presented. The multivibrator introduced here is of multicore construction, having the number of saturable cores equal to the number of phases. It has several common windings wound through all the cores and two or more separate windings wound on each of the cores. A multivibrator is constructed with the common windings and two transistors. Of the separate windings, one, acting as a bias winding, is connected to one of the common windings to receive ac bias mmf, and the others are used as output windings. By keeping the proper distribution of mmf's among the bias windings, the proper sequence is kept among the induced emf's in the output windings, and hence the polyphase voltages are produced. The same principle can be applied to a polyphase multivibrator with a multiaperture core.     

End-of-Line Waveguide Thermistor Power Meters in the Frequency Range 16.7–37.5 GHz

Measurement Techniques - In this study, a multiprobe end-of-line converter, which is a part of a waveguide thermistor wattmeter, was developed. This converter functions to improve the power...     

基于IMB-CNN的薄壁件超声铣削颤振辨识方法

针对薄壁件超声铣削加工时产生的颤振严重影响工件质量,加剧刀具磨损的问题,搭建了颤振图像监测系统,利用卷积神经网络(CNN)进行颤振图像辨识,综合运用趋磁细菌算法(MB)、爬山算法(HC)和禁忌算法(TS)的优点,改进MB算法进行超参数优化,提出了一种基于改进趋磁细菌卷积神经网络(IMB-CNN)的薄壁件超声铣削颤振辨识方法。首先,通过MB算法进行全局搜索,再以最优解为初始点,通过HC算法进行邻域搜索,避免了MB算法在最优解附近的振荡;同时,通过禁忌列表跳过已搜索的节点,减小计算规模,加快计算效率;最后,将获得的最优超参数用于CNN,实现颤振图像的精确辨识。与其他方法相比,该方法实现了97.69%的识别率,判断时间为363ms,能有效地进行颤振监测,且整体性能较优。     

An electronic integrating heat meter

The heat energy consumed by individual customers in a district heating system that uses hot water is found by integrating the flow rate (volume/second) and multiplying it by the temperature difference between the incoming and outgoing water. An electronic integrating heat meter is developed for this purpose using a programmable unijunction transistor (PUT) and linearized thermistor sensors. The temperatures of the incoming and outgoing radiator water are measured by means of the thermistor sensors mounted on the pipes connected to the radiator, and their temperature difference is converted to a current. The current is applied to a current-to-pulse frequency converter using the PUT that operates only during the time of the constant width of the pulses generated by a water-flow meter and correspond to the water-flow volume. Therefore, the number of counted output pulses of the current-to-pulse frequency converter shows the integrated multiplication of the flow rate and the temperature difference, which is the heat energy. The electronic circuit is simple and therefore not expensive. The accuracy of the heat meter is within ±2% for a temperature difference up to 40°C     

Mercury/homocysteine ligation-induced ON/OFF-switching of a T-T mismatch-based oligonucleotide molecular beacon

A molecular beacon (MB) with stem-loop (hairpin) DNA structure and with attached fluorophore-quencher pair at the ends of the strand has been applied to study the interactions of Hg(2+) ions with a thymine-thymine (T-T) mismatch in Watson-Crick base-pairs and the ligative disassembly of MB·Hg(2+) complex by Hg(2+) sequestration with small biomolecule ligands. In this work, a five base-pair stem with configuration 5'-GGTGG...CCTCC-3' for self-hybridization of MB has been utilized. In this configuration, the four GC base-pair binding energy is not sufficient to hybridize fully at intermediate temperatures and to form a hairpin MB conformation. The T-T mismatch built-in into the stem area can effectively bind Hg(2+) ions creating a bridge, T-Hg-T. We have found that the T-Hg-T bridge strongly enhances the ability of MB to hybridize, as evidenced by an unusually large MB melting temperature shift observed on bridge formation, ΔT(m) = +15.1 ± 0.5 °C, for 100 nM MB in MOPS buffer. The observed ΔT(m) is the largest of the ΔT(m) found for other MBs and dsDNA structures. By fitting the parameters of the proposed model of reversible MB interactions to the experimental data, we have determined the T-Hg-T bridge formation constant at 25 °C, K(1) = 8.92 ± 0.42 × 10(17) M(-1) from mercury(II) titration data and K(1) = 1.04 ± 0.51 × 10(18) M(-1) from the bridge disassembly data; ΔG° = -24.53 ± 0.13 kcal/mol. We have found that the biomarker of oxidative stress and cardiovascular disease, homocysteine (Hcys), can sequester Hg(2+) ions from the T-Hg-T complex and withdraw Hg(2+) ions from MB in the form of stable Hg(Hcys)(2)H(2) complexes. Both the model fitting and independent (1)H NMR results on the thymidine-Hg-Hcys system indicate also the high importance of 1:1 complexes. The high value of K(1) for T-Hg-T bridge formation enables analytical determinations of low concentrations of Hg(2+) (limit of detection LOD = 19 nM or 3.8 ppb, based on 3σ method) and Hcys (LOD = 23 nM, 3σ method). The conditional stability constants for Hg(Hcys)H(2)(2+) and Hg(Hcys)(2)H(2) at 52 °C have been determined, β(112) = 5.37 ± 0.3 × 10(46) M(-3), β(122) = 3.80 ± 0.6 × 10(68) M(-4), respectively.     

Dynamics analysis of LFR model for a single‐stage high power factor correction diagonal half‐bridge flyback ac/dc converter

Abstract

By means of a graft scheme, a buck‐boost cell and a wide range diagonal half‐bridge flyback cell are combined to create a novel single‐stage high power factor correction (HPFC) diagonal half‐bridge flyback ac/dc converter in this paper. When both of the two cells operate in discontinuous conduction mode, the proposed converter exhibits high power factor and low bulk capacitor voltage stress independent of the load variations. Based on the Loss‐Free Resistor (LFR) model, a new technique, referred to as ac‐dc balancing method, is also proposed. It is useful to determine the dc values, voltage ripples, and phase angle shifts of the bulk capacitor and output voltage of the converter. Moreover, the component values are well designed according to the operation conditions and design specifications of the converter. Finally, a prototype of the proposed converter with output voltage 48 V and power 100 W is built to test the theoretical analysis. It is successfully validated by IsSpice simulations and experimental results.     

The On-Mode Transistor Multivibrator

A mode of operation of astable and monostable multivibrators which has received little attention is discussed. The timing of the quasi-stable states in this mode is determined by an RC network as for the conventional two-transistor astable or monostable multivibrator. However, the timing is determined by the network associated with the "on" transistor, rather than the "off" transistor. The analysis of the basic symmetrical on-mode circuit considers design requirements and period stability. Comparison is made with the conventional off-mode multivibrator.     

Design and analysis of a full bridge LLC DC-DC converter for auxiliary power supplies in traction

This paper focuses on an 8 kW LLC resonant full bridge DC-DC converter topology using a high frequency transformer for auxiliary power supply systems in traction. The full bridge DC-DC converter with the LLC resonant network has been tested under hard switching and zero current switching conditions with 100 kHz switching frequency. In addition to this, an observation made for the effect of dead time variation of the power switches to improve the overall system efficiency. This paper describes the efficiency of the ZCS full bridge converter by considering different input power levels and also compared with hard switched topology. This paper presents the operating principles, simulation analysis, and experimental verification for 3 kW to 8 kW LLC resonant full bridge converter with 1200 V/40 A IGBTs, and its efficiency comparison.