Frequency-to-Time Converter for Measuring Sound Velocity in Liquids

The measuring converter is based on the principle of tracking the balancing of the separated informative value of the interval probed by an acoustic pulse in the studied medium at a given basic distance by a pulse period divisible by the period of pulses of a frequency-controlled generator. A high accuracy is reached by excluding an inconclusive (spurious) time delay of the acoustic and electric signals in the acoustic converter and electronic operational units. The acoustic base-line distance of the measuring converter is 0.1 m, the measurement range is 1400–1600 m/s, the output signal has a frequency of 140–160 kHz, the absolute basic error is ±0.015 m/s, and the time to reach a steady-state output signal is 0.6 s.     

An Extension of the Conductance-to-Electrical Signal Conversion Range of Capacitance Transducers by Using Self-Excited Oscillators with a Thermistor Bridge

A circuit for the compensation of unbalance is proposed, which allows one to decrease essentially the temperature stability effect on the error and conductance conversion range of a capacitance transducer in self-excited oscillators with a thermistor bridge. The device that converts simultaneously and independently the conductance of the transducer in a range of 10^–6–5 × 10^–3 S with an error of 5% and capacitance in a range of 10^–2–100 pF with an error of 1% into an electric signal is described.     

Laser-Induced Acoustic Imaging of Buried Objects

A 100 mJ, 100 ns pulsed CO₂ laser incident on the surface of soil is used as a localized acoustic source for the detection and imaging of underground objects. The acoustic pulse produced by the impulsive heating of the soil surface due to the absorbed 10.6 m radiation is detected with an acoustic transducer suspended over the surface. Application of a Fourier domain filter enables the separation of the direct acoustic return from the faint echo from an object buried 3–25 mm below the surface. Scanning of the laser pulses across the position of a buried object allows the resolution of the shape and the depth of the buried object. The application of this technique to image buried landmines is demonstrated in trials at an outdoor test track.     

A Temperature Controller with Film Elements

A temperature controller in the range from –20 to +150°C with an error of ±1°C is described. A sensor with a sensitivity of 1 mV/K and a time constant of 5–10 s, based on a Bi–Sb film thermal transducer and a correcting transducer (a wire thermoresistor), is used.     

An Acoustic Transceiver for Monitoring Dynamic Processes in the Ocean

An acoustic transceiver for the monitoring of dynamic processes in the ocean by acoustic tomography methods is described, and the results of its tests are presented. At an acoustic pressure of 2–6 kPa/m produced by the transceiver in the emission mode at frequencies of 250 Hz and an rms error in determining time intervals no larger than 2 ms, the flow velocity component can be measured to an accuracy of 10 cm/s by using the countersounding scheme.     

A Magnetometer Based on a Hall-Effect Transducer

An induction meter based on a Hall-effect transducer with in-phase signal suppression and thermostabilization circuits is described. It is powered by a 10³-Hz ac line. The maximum relative error in temperature measurements from 0 to 70°C does not exceed 0.7 % for magnetic fields of 50–100 T, 0.4% for 0.1–1 mT, and 0.1% for 1–625 mT. In the range of 50–500 T, the error is determined by an in-phase signal. The contribution of the total temperature error is 0.01% per 50°C. Depending on the induction of the measured magnetic field, the resolution changes from 0.12 to 19 T.     

A Differential Stroboscopic Integrator for Recording Small Signals

The instrument was designed for the separation of a periodic pulse signal from noise and interference. The desired-signal measurement range is 5 to 40 mV. Measurements can be performed at a signal-to-noise ratio of 10^–3. The measurement accuracy is better than 7%. The instrument has an analog input and an analog output and can be connected to any high-resistance recording device (ADC, plotter, or voltmeter).     

A Noisy Hollow-Cathode Tube in Pulsed and Continuous Excitation Regimes

The noise characteristics of the optoelectronic channel in an atomic-absorption spectrometer were studied. The spectrometer may be used with spiral and graphite electrothermal atomizers. The noise was measured during the development of a glow discharge in a hollow-cathode tube (HCT) at current-pulse lengths of 50 and 500 s and a filling factor of 2–20. It was found that the rms noise level in the optoelectronic channel decreased with increasing duration of the current pulses in the HCT. The results are compared to the rms noise level in the optoelectronic channel under conditions of continuous HCT feeding. The noise component of the relative measurement error is shown to be 5–10%, depending on the material of the HCT cathode and the measurement time (with reference to the beginning of the current pulse). It is demonstrated that the HCT is suitable for atomic-absorption spectrometers with the pulsed and continuous excitation.     

Generation of High-Voltage Subnanosecond Pulses with a Peak Power of 700 MW and Repetition Frequency of Up to 3.5 kHz

Test results of a combined subnanosecond modulator with an output impedance of 45 , which incorporates an all-solid-state high-voltage nanosecond charging device (with an inductive energy storage and a semiconductor opening switch) and a pulse sharpener with gas-filled gaps, are presented. The sharpening and cutting spark gaps filled with hydrogen at a pressure of 100 atm ensured the formation of stable pulses with amplitudes of –(180–200) kV and durations of (400–700) ps at a repetition frequency of up to 3.5 kHz. An average output power of 1.4 kW was achieved for the modulator's burst-mode operation with a number of pulses in a packet of 10⁴at a maximum pulse repetition rate.     

Some Aspect of Using a Magnetoresistive Transducer

The results of investigating the lower sensitivity threshold of a magnetoresistive transducer converting the magnetic field induction into an electric signal are presented. The voltage fluctuation amplitude measured in terms of the magnetic field induction units amounts to 25 × 10^–9 T at the transducer output. It is found that after termination of the action of the magnetic field the output transducer voltage returns to the zero level with a delay. The duration of this return may amount to tens of minutes (depending on the induction and duration of the field action). A digital magnetometer with the scale of ±200 T graduated to 0.1 T is fabricated on the basis of the magnetoresistive transducer.     

Computer-Aided Coulometric Control System

Several versions of a multifunctional computer-aided system for experimental high-temperature electrochemistry, each differing in platform (type of operational system—Windows, Real-time Linux; input–output cards; the availability of digital signal processors on these cards; etc.), are described. For each version, the comparative accuracy and time characteristics of the operation of the system's coulometric channel are given and ways to attain them are described. Advantages of the system include the possibility of real-time operation in a wide range of parameters (the interval between measurements runs from 4 × 10^–7 to 1 s, while the response time to external events runs from 0.8 to 60 s), the possibility of high-precision measurements of the amount of electricity passed through an electrochemical object (the minimum limit for measuring the amount of electricity is 1 C with a basic error of 0.1%), the automatic generation of control commands; and its applications for research, industrial, and experimental purposes.     

Analysis of acousto-ultrasonic characteristics for contact-type transducers coupled to composite laminated plates

The acousto-ultrasonic (AU) input–output characteristics for contact-type transmitting and receiving transducers coupled to composite laminated plates are considered in this paper. Combining a multiple integral transform method, an ordinary discrete layer theory for the laminates and some simplifying assumptions for the electro-mechanical transduction behaviour of the transducers, an analytical solution is developed which can deal with all the wave processes involved in the AU measurement system, i.e. wave generation, wave propagation and wave reception. The spectral response of the normal contact pressure sensed by the receiving transducer due to an arbitrary input pulse excited by the transmitting transducer is obtained. To validate the new analytical–numerical spectral technique in the low-frequency regime, the results are compared with Mindlin plate theory solutions. Based on the analytical results, numerical calculations are carried out to investigate the influence of various external parameters such as frequency content of the input pulse, transmitter/receiver spacing and transducer aperture on the output of the measurement system. The results show that the presented analytical–numerical procedure is an effective tool for understanding the input–output characteristics of the AU technique for laminated plates.     

Six-Port Receiver and Frequency Measurement for Radar Applications at 35GHz

The application of a six-port technology in the receiving part of a radar front-end is described in this paper. This receiver allows measuring magnitude and phase of the radar signal without the need of down-conversion. According to the applications and the availability of the devices needed for assembling the prototype sensor, the frequency of operation was set to 35GHz. The structure of this six-port as well as the calibration and measurement algorithms are described in detail. The accuracy of the phase measurement is 2–10° depending on the power level of the signal. Another key element of the proposed radar sensor is a direct frequency counter. Using this circuit it is possible to measure the frequency of operation with a resolution of 20 bits within 120s. The accuracy of the distance reading of the radar is directly related to the accuracy of the frequency measurement and has reached 0.1mm.     

A Video Pyrometer

A pyrometric device based on a consumer color digital video camera and a personal computer is described. A procedure for the study of thermodynamic processes is offered. The measured temperature range is 800–2500°C, and the measurement error is 50°C.     

A Device for Detecting the Location of a Gas Leak in a Spacecraft Module

Experiments with a multiparametric air-leakage transducer in a vacuum chamber with a volume of 180 m³ have been performed in the leakage range of 30–300 mTorr/s. The manufactured laboratory prototype of the device has the following characteristics: the dynamic detection range covers the diameters of holes of 0.1–0.5 mm at distances R 0.1–1.5 m from the leakage source at a through breakdown of casing with electric vacuum thermal insulation. Its power consumption is 3.0 W and its mass is 0.35 kg.     

A Dosimeter for On-line Dose Rate Monitoring Based on a Natural Diamond Detector

The structure and principle of operation of a dosimeter for on-line dose rate monitoring (DOM) are considered. The DOM provides real-time measurements of the absorbed -ray and electron dose rates, monitors relative distributions of radiation fields in radiotherapy facilities, and controls the radiation characteristics of radiotherapeutic equipment during its adjustment, certification, and service. The dosimeter can measure the dose absorbed in a certain period of time. Compared to conventional dosimeters based on air ionization chambers and silicon semiconductor detectors, the DOM has a number of advantages: dose-rate measurement linearity, energy independence of radiation detection in the range of 0.8–20 MeV for -rays and 8–20 MeV for electrons, high sensitivity compared to air ionization chambers, high radiation and thermal stability, and the small size of the device. The detecting element of the dosimeter is manufactured from a tissue equivalent to a biological material. The operating ranges of dose rate measurements are 10^–3–10 Gy/min and 10^–2–10² Gy/min. The DOM measurement error is <2%. Radiation therapy is the dosimeter field of application.     

A Transistor-Based Modulator for a Microwave Magnetron

A modulator designed as a power supply for a microwave magnetron with an output peak power of 3 MW and mean power of 10 kW is described. The 100 transistors used in the modulator are connected in parallel, and their capacitors are switched to the primary winding of a pulse transformer. Across the secondary winding, pulses are generated with a peak voltage of 50 kV, a current of 100 A, a duration of 0.6–6 s, and a repetition frequency of up to 2 kHz.     

A facility for metal surface treatment with an electron beam

A design for a facility for the surface treatment of metal samples is described, and the results from investigating the source of a high-current low-energy electron beam are presented. The electron beam, which has a current as high as 300 A, a pulse duration of 30 µs, and a pulse repetition rate of up to 10 Hz, is formed in a plasma-cathode gas-filled diode at an accelerating voltage of 20 kV. The space-charge compensated electron beam is transported a distance of 20 cm in a longitudinal magnetic field to the region of its interaction with a solid body. At a current density as high as 100 A/cm², the power density produced by the beam is sufficient for the metal surface to be melted in the duration of one or several pulses. Samples can be replaced in the facility without breaking the vacuum.Translated from Pribory i Tekhnika Eksperimenta, No. 1, 2005, pp. 135–140.Original Russian Text Copyright © 2004 by Koval, Shchanin, Devyatkov, Tolkachev, Vintizenko.     

A Facility with Resonant Pulse Compression for Generating High-Power Ku-Band Microwave Pulses

A generator of high-power Ku-band microwave pulses with resonant pulse compression is described. It allows thestepped control of output-pulse durations from 1 ns to 1.5 s at a pulse repetition rate of 0.2–1.5 kHz and a peak power of 58 kW to 10 MW. This source can be used for investigating the interaction of electromagnetic radiation with various objects.     

Eddy-current inspection of tubes in a nonuniform field

The problem of inspecting tubes and tubular articles from the inside in a nonuniform field of a through-type eddy-current transducer is considered. Based on an analysis of the transducers signal, sensitivities to the inspected tubes wall thickness and to changes in the electric conductivity are calculated. The inspection is optimized and the appropriate plots are presented.Translated from Defektoskopiya, Vol. 40, No. 8, 2004, pp. 38–49. Original Russian Text Copyright © 2004 by Dyakin, Sandovskii, Dudarev.