Phase-sensitive Rectifier Research Articles

Novel microprocessor based negative phase sequence relay and meter

Microprocessor application in relaying and condition monitoring technology is becoming increasingly popular. In this paper, a novel microprocessor based negative phase sequence (NPS) current detector for motor condition monitoring and relaying for motor/generator protection is developed. The proposed meter eliminates the need of a negative phase sequence filter and does not require complicated digital signal processing techniques. Instead it uses a phase sensitive rectifier. A prototype based on Intel's 8085 A microprocessor was built and tested. Complete circuitry, main and interrupt software flowcharts are provided. Results show the proposed NPS relay and meter can provide a high degree of accuracy and satisfactory results.

Phase-sensitive rectifier with a small dynamic error

Phase-sensitive rectifier with a small dynamic error

Use of the Castle Mask in Teaching Synchronous Detection and Waveform Analysis

A castellated mask, used to obscure alternate sections of a waveform, is useful in teaching the properties of the phase-sensitive rectifier, the process of Fourier analysis of a square wave, and the method of detection of a radio signal — especially one that is suppressed-carrier amplitude modulated.

A device for stationary and non-stationary measurement of heat production in the contracting muscle

An experimental arrangement is described to measure the heat production in the contracting muscle after a single stimulation (non-stationary) as well as after periodic stimulation (stationary). The variation of temperature is registered by a thermistor, a. c. bridge, and phase-sensitive rectifier, and is stored digitally. For fresh M. gastrocnemius at 0°C,one finds a heat production per cm 3 of about 3.3 mcal/contraction. In order to explain the systematic difference in the results of both methods, the heat conduction equation is solved for a model system in the non-stationary case. This allows one to estimate the tickness d of the necrotic zone which, during the measurement, arises around the thermistor stuck in the muscle. The calculated values are in the range of d = 0.1–0.6 mm. Finally, the possibility of measuring non-stationary heat production in situ is critically discussed.

New phase-sensitive rectifier circuit

The principle of operation of a recent phase-sensitive rectifier demodulator circuit is discussed. The incorporation of this in a commercial lock-in amplifier has allowed the recovery of signals 70 dB below the noise level, while giving an output stability of better than 0·02% full scale per degree kelvin.

Phase-sensitive rectifier which suppresses odd-harmonic groups

Phase-sensitive rectifier which suppresses odd-harmonic groups

Infrasonic relay phase-sensitive rectifier having third-harmonic suppression

Infrasonic relay phase-sensitive rectifier having third-harmonic suppression

A Complete Result Magnetometer for Measuring the Remanent Magnetization of Rocks

The cost of small digital computers has fallen to a level at which a slow spinner magnetometer using such a machine for data capture and processing is competitive in cost with existing high performance magnetometers. The advantages of using a computer to replace the phase sensitive rectifier and digital read-out of existing machines are many and include: drift free integration over extended time scales, Fourier analysis of the waveform from the sensors, storing of the intermediate results of the various orientations and combining these to produce a complete result in terms of total intensity, declination, and dip, while at the same time eliminating any consent magnetic moment of the rotating mechanism. The results are printed and the measuring system allows a very simple method of estimating the errors for any particular integration period. The overall effect is of an instrument which is quick and convenient to use yet which gives results which are at least as good as those from existing machines.

The rhometer: a continuous impurity monitor for liquid metal circuits

The rhometer uses the change in resistivity with impurity content of liquid metals, mainly sodium and sodium-potassium alloy, to measure the amount of impurities, such as oxide and hydride, etc., down to a few parts per million. It is a 'non-contact' or electrodeless instrument, in that the liquid metal through a toroidal pipe which forms one turn of a 50-c/s transformer. The output from this transformer is fed to a phase-sensitive rectifier, and changes in resistivity are then indicated on a standard chart recorder. A special circuit compensates for changes in resistivity caused by changes in temperature of the liquid metal. Operating experience with the rhometer in the primary coolant circuits of the Dounreay Fast Reactor is described in detail, and some possible future trends in the further development of the instrument are briefly discussed.

An Optical Null Double-Beam Double-Pass Infrared Spectrophotometer

A novel signal treatment for an optical null double-beam double-pass system is developed and used in a vacuum-type prism infrared spectrophotometer. A feature of this instrument is the arrangement of the specially-shaped beam switch and the second chopper working in conjunction with the phase-sensitive rectifier. The beam switch is made so that the lower half of the reference beam and the upper half of the sample beam are sent to the monochromator optics during one half of the cycle; the other parts of reference and sample beams reach the monochromator optics during the other half of the cycle. The second chopper alternately blocks the upper and lower halves of the image formed at the focal point of single-pass beam in proper synchronism with the beam switch. Fairly good cancellation of the scattered radiation was achieved through adjustment of the phase relation between the beam choppers and the phase-sensitive rectification system. In addition to reporting the general design and construction, detailed descriptions of the control and recording systems which provide the unique features are also included.

Investigation of a phase-sensitive rectifier circuit

Investigation of a phase-sensitive rectifier circuit

Precise automatic control by proton resonance of a continuously variable magnetic field

An improved form of a highly accurate continuously variable automatic frequency control system previously described is used to adjust the frequency of the marginal oscillator in a proton resonance magnetometer. The oscillator output is amplified, rectified and further amplified as a video signal. The proton resonance signal thus obtained is applied to a phase-sensitive rectifier which uses the mains supply voltage as reference, as mains current is used to provide the sweep field for the probe. The output of the phase-sensitive rectifier controls a servomechanism which adjusts the magnet current and thus holds its field at the value demanded, to a fraction of an oersted. The present range of the equipment is 1000 to 10000 oersted.

Impedanzmessungen an Ranvierschen Schn�rringen unter Einwirkung von Nickelchlorid

1. Impedance changes accompanying the markedly prolonged action currents of single Ranvier nodes in cold Ringer's solution containing 10−4–10−3 M N1Cl2 have been measured by means of a Wheatstone bridge followed by a phase-sensitive rectifier. 2. Maximum impedance decrease coincides with the peak of the action current. Impedance increases continously during the plateau, but remains far below the resting impedance; it rises most rapidly at the end of the plateau. Complete recovery of the resting impedance is reached 7–43 msec after the end of the action current. 3. Similar results are obtained by recording the action potential of the node and measuring the potential changes produced by alternating currents of constant strength. 4. The impedance changes are referred to changes of the ionic slope conductances G Na and G K.

A simple phase sensitive rectifier for use with radiation detectors

The ratio of light to dark resistance of a cadmium selenide photocell is sufficiently great for the cell to be used effectively as a light controlled switch. Where radiation incident on a detector is chopped at a frequency of less than 20 c/s, two such photocells can be used in a very simple arrangement to make a coherent demodulator which has the advantages of a mechanical rectifier without the usual disadvantages.

A Solar Magnetograph

THE first test observations for the detection and measurement of both small magnetic fields and small Doppler effects on the Sun's surface have been carried out during recent months at the Cambridge Observatories with a photoelectric magnetometer newly built under a grant from the Department of Scientific and Industrial Research. This instrument is a modified version of one constructed by H. W. Babcock some time ago at the Mount Wilson and Palomar Observatories1. It is used in conjunction with the Cambridge solar spectrograph which has a large diffraction grating of excellent quality, ruled by H. W. Babcock2 and working in the 5th order, where it reaches a measured resolving power of 600,000. The Zeeman effect in a suitable Fraunhofer line is analysed with the aid of an electro-optical retardation plate of ammonium di-hydrogen phosphate and a fixed ‘Polaroid’. The retardation of the plate oscillates in sign at 400 c./s. due to the applied potential of 3.5 kV. r.m.s. A selected portion of each wing of the Fraunhofer line is imaged on the cathode of a corresponding photomultiplier (E.M.I type 6094). The outputs from the two photomultipliers are fed into a difference amplifier, and the resulting signal after amplification by a selective frequency amplifier is applied to a phase-sensitive rectifier. Time constants up to 10 sec. are provided. The difference amplifier rejects elliptical polarization from the cœlostat mirrors, and, provided the examining slits are correctly placed, small Doppler shifts of the line are relatively unimportant.

A photoelectric microscope for the measurement of linear scales

A description is given of a photoelectric microscope which is suitable for the accurate measurement of linear scales of high precision. A real image of a graduation line, formed by means of an ordinary microscope objective, is caused to oscillate across a fixed slit in front of a photoelectric cell. A phase-sensitive rectifier determines when the mean position of the line image coincides with the centre line of the slit. When this is so, the d c. output of the rectifier is zero and for small displacements of the mean position of the line image, the d.c. output - which is measured on a microammeter - is proportional to the displacement. The standard deviation of a single setting of the microscope is about 0.03 μ and by associating the microscope with an interferometer, short linear scales have been measured directly in wavelengths with a standard deviation of about 0.1 μ. It is thought that, with a properly designed interferometer to measure the displacement of a scale with respect to a fixed photoelectric microscope, a standard deviation of 0.05 μ would be achieved.

Measurements on high-speed magnetic servo amplifiers with 2-phase motor load

Measurement of steady-state characteristics and transient-response time of high-speed magnetic servo amplifiers with 2-phase motor load offers two special problems: 1. The output current of a magnetic amplifier with rectangular-hysteresis-loop core material represents a peculiarly truncated sine wave which consists of a fundamental (60- or 400-cycle) component and an array of harmonics having relatively large tnagnitudes. The 2-phase motor. however, responds only to the fundamental component of this output current multiplied by the sine of the actual. phase angle between it and the substantially sinusoidal line-field current of the motor. Thus, in this case, conventional methods for measuring output-input characteristics by means of a separately excited wattmeter are not always applicable. 2. The transient-response time of modern forms of magnetic amplifiers is in the order of 1 to 4 half-cycles of the power-supply frequency. Therefore, for studying the dynamic properties of such high-speed amplifiers it will be advisable to employ a transient analyzer which produces a synchronous square-wave signal voltage and permits, also with higher power-supply frequencies, direct visual observation of a stationary pattern on a dual-beam oscilloscope. This paper is concerned with the solution of these two problems. At first it describes the basic principle and the advantages of the ���torque-balance method��� which permits direct measurement of magnetic-amplifier output in terms of the ���equivalent sinusoidal output voltage��� for stalled-motor operating conditions. Then, it illustrates the use of a novel form of square-wave signal-voltage transient analyzer with a ���magnetic switch��� which consists essentially of a special saturablereactor circuit producing a synchronous unidirectional current with nearly rectangular waveshape. When applying this analyzer, a dual-beam oscilloscope displays the wave forms of input and output voltages of the magnetic amplifier under test simultaneously on a common time base in such a way that these wave forms are exhibited on a long-persistence screen as a stationary pattern. Thus, it is possible to study the effect of various circuit-parameter changes on actual speed of response and to determine optimum design. Finally, this paper gives results of additional measurements on the circuit under test. Measurement of bandwidth on a 400-cycle position servomechanism illustrate the dynamic performance of the circuit when operated in connection with a phase-sensitive rectifier in a closed-loop servo system. Measurements concerning reduction of asymmetry zero-drift errors make it evident that such errors are reduced to about 1/40 of their original values as a result of the application of a large amount of electric negative feedback resistance-coupled into the controlcircuit loop.

The ring modulator as a polarized rectifier

The performance of the ring modulator as a phase-sensitive rectifier is described qualitatively. Under the assumption of idealized conditions, and with the use of the analytical approach originally developed for the ring modulator, the polarized rectifier is described quantitatively, both for steady state and transient state. The analytical findings are checked experimentally. A differential polarized rectifier functioning as a true null detector is also discussed.

Precision measurement of phasors in electric networks as a function of frequency

Measurement of phasor relationships in networks is considered in general, and a system is described which accomplishes this task. Numerical examples for purposes of orientation are given. Detection is based on the performance of a phase-sensitive rectifier of the ring modulator type. A system is described, using a pair of such detectors being polarized by two auxiliary voltages, of the frequency under consideration, the voltages being in time quadrature to each other. In this manner true null detection is accomplished unambiguously. The differential polarized rectifier, the polarizing supply circuit, and the required auxiliary amplifiers, containing means of amplitude-and-phase adjustment, are discussed briefly. Operation in the frequency range of 1 to 1,000 cycles for input signals of the order of 100 microvolts and for extremely adverse signal-to-noise ratios is accomplished with an over-all accuracy of 1 per cent.

Two electrostatic field-meters

Two electrostatic field-meters are described, one operating from a.c. mains and the other from dry batteries. An alternating potential proportional to the field is generated by the measuring head, amplified, and fed to a phase-sensitive rectifier. The mains-operated instrument gives, at full sensitivity, an output current of 1 mA for a field of about 400 V/ft, the direction of the current depending upon the sign of the field. Its sensitivity can be adjusted over a range of 900: 1; at maximum sensitivity the zero drifts by no more than 2% of the full-scale reading in 15 h. The battery-operated instrument, which is truly portable, has two fixed ranges giving full output current for fields of 5 and 50 kV/ft; its sensitivity is hardly affected by normal changes in battery voltages.