Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/003
A. Edgar
The limitation on the performance of a lock-in amplifier imposed by noise and drift in the DC amplifier is discussed. Measurements on a commercial instrument show that if the time constant tau is increased whilst holding the ratio of tau to the scan time T fixed, the output noise first falls as tau -0.5, as expected for white noise, but then rises as tau 0.09. This shows that there is an optimal setting for the time constant beyond which the signal-to-noise ratio deteriorates, and suggests that the power density of the drift and noise from the DC amplifier in this instrument has an f-1.18 spectrum. The effect of both drift and noise may be reduced by signal averaging; if the number of scans n is varied while holding both the total measurement time nT and tau /T constant, the averaged RMS noise at first decreases as roughly 1/n, but not 1/n12/, before reaching a limiting value set by white noise. Replacing the first stage DC amplifier with an equivalent circuit based on a low-drift commutating auto-zero instrumentation amplifier reduces the drift and noise by up to a factor of four, and thus extends the useful range of time constants for single-scan measurements.
{"title":"Drift in low-cost lock-in amplifiers","authors":"A. Edgar","doi":"10.1088/0022-3735/22/8/003","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/003","url":null,"abstract":"The limitation on the performance of a lock-in amplifier imposed by noise and drift in the DC amplifier is discussed. Measurements on a commercial instrument show that if the time constant tau is increased whilst holding the ratio of tau to the scan time T fixed, the output noise first falls as tau -0.5, as expected for white noise, but then rises as tau 0.09. This shows that there is an optimal setting for the time constant beyond which the signal-to-noise ratio deteriorates, and suggests that the power density of the drift and noise from the DC amplifier in this instrument has an f-1.18 spectrum. The effect of both drift and noise may be reduced by signal averaging; if the number of scans n is varied while holding both the total measurement time nT and tau /T constant, the averaged RMS noise at first decreases as roughly 1/n, but not 1/n12/, before reaching a limiting value set by white noise. Replacing the first stage DC amplifier with an equivalent circuit based on a low-drift commutating auto-zero instrumentation amplifier reduces the drift and noise by up to a factor of four, and thus extends the useful range of time constants for single-scan measurements.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"64 1","pages":"551-553"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84483022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/021
A. Abdel-Rahman, G. Hitchman, P. Slawson, A. B. Strong
A calibration and signal analysis technique has been developed for a multiple-sensor probe, comprising an X-array hot wire and a cold wire, to account for the effects of both yaw angle and temperature on the instantaneous output signals of the X-wire. The technique assumes the response equation first proposed by Collis and Williams (1959) and involves a series of velocity calibrations at different flow angles producing independent sets of the calibration coefficients which thus describe the yaw angle dependence. The complexity of the calibration is comparable to variable angle methods which use a look-up table approach, but the present technique offers complete separation of the temperature and velocity effects on the X-wire signals over a large range of temperature without requiring additional calibration. The instantaneous velocity vector is unambiguously resolved within the full 90 degrees included angle between the sensors of a standard gold-plated X-wire, and in addition, the technique identifies the occurrence of rectification errors. The signal analysis technique is verified in the calibration apparatus and has been applied successfully in an inclined heated plane jet of low mean velocity.
{"title":"An X-array hot-wire technique for heated turbulent flows of low velocity","authors":"A. Abdel-Rahman, G. Hitchman, P. Slawson, A. B. Strong","doi":"10.1088/0022-3735/22/8/021","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/021","url":null,"abstract":"A calibration and signal analysis technique has been developed for a multiple-sensor probe, comprising an X-array hot wire and a cold wire, to account for the effects of both yaw angle and temperature on the instantaneous output signals of the X-wire. The technique assumes the response equation first proposed by Collis and Williams (1959) and involves a series of velocity calibrations at different flow angles producing independent sets of the calibration coefficients which thus describe the yaw angle dependence. The complexity of the calibration is comparable to variable angle methods which use a look-up table approach, but the present technique offers complete separation of the temperature and velocity effects on the X-wire signals over a large range of temperature without requiring additional calibration. The instantaneous velocity vector is unambiguously resolved within the full 90 degrees included angle between the sensors of a standard gold-plated X-wire, and in addition, the technique identifies the occurrence of rectification errors. The signal analysis technique is verified in the calibration apparatus and has been applied successfully in an inclined heated plane jet of low mean velocity.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"10 1","pages":"638-644"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79523481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/025
M. Colclough
A low-power circuit that provides a constant-voltage output pulse is described. The stability of the pulse voltage is better than 1 part in 104 and the on/off power ratio is about 1010. The duration of the pulse is controlled by an optically isolated timing signal. The circuit has been used to drive the specimen heater in heat capacity measurements at dilution refrigerator temperatures.
{"title":"A pulse generator output stage suitable for very low-temperature heat capacity measurements","authors":"M. Colclough","doi":"10.1088/0022-3735/22/8/025","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/025","url":null,"abstract":"A low-power circuit that provides a constant-voltage output pulse is described. The stability of the pulse voltage is better than 1 part in 104 and the on/off power ratio is about 1010. The duration of the pulse is controlled by an optically isolated timing signal. The circuit has been used to drive the specimen heater in heat capacity measurements at dilution refrigerator temperatures.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"6 1","pages":"663-663"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75800890","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/018
J. Hlína
A simple system for the investigation of space and time changes of non-stationary arcs in the spectral range 400-1100 nm is described. The system consists of a monochromator, an array-photodetector, amplifiers, a multiplexer, a transient recorder and a computer with peripherals. The arrangement and evaluating procedure was tested on a decaying high-pressure mercury arc and during observations of a switching arc in SF6.
{"title":"Optoelectronic system for investigations of non-stationary arcs","authors":"J. Hlína","doi":"10.1088/0022-3735/22/8/018","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/018","url":null,"abstract":"A simple system for the investigation of space and time changes of non-stationary arcs in the spectral range 400-1100 nm is described. The system consists of a monochromator, an array-photodetector, amplifiers, a multiplexer, a transient recorder and a computer with peripherals. The arrangement and evaluating procedure was tested on a decaying high-pressure mercury arc and during observations of a switching arc in SF6.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"13 1","pages":"623-626"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80160271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/010
C. Tran, M. Franko
A novel dual-wavelength thermal-lens spectrometer with pump/probe configuration that is capable of simultaneously measuring thermal-lens signals at two different wavelengths has been developed. In this instrument, the two excitation beams are derived from the same argon-ion laser operating in a multiline mode. The sample is excited by these two wavelengths alternately and the corresponding thermal-lens signals are monitored by a He-Ne probe laser. Advantages of this dual-wavelength apparatus include its inherent sensitivity and enhanced selectivity. The selectivity is improved because the ratio of the thermal-lens signals at the two different wavelengths provides fingerprints and allows identification of the sample. Therefore, it can be used not only to detect and identify trace chemical species at very low concentration but also to analyse two-component mixtures. Using this apparatus, the detection limit for NO2 using 30 mW excitation beams modulated at 4.6 Hz is estimated to be 300 PPB.
{"title":"Dual-wavelength thermal-lens spectrometry as a sensitive and selective method for trace gas analysis","authors":"C. Tran, M. Franko","doi":"10.1088/0022-3735/22/8/010","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/010","url":null,"abstract":"A novel dual-wavelength thermal-lens spectrometer with pump/probe configuration that is capable of simultaneously measuring thermal-lens signals at two different wavelengths has been developed. In this instrument, the two excitation beams are derived from the same argon-ion laser operating in a multiline mode. The sample is excited by these two wavelengths alternately and the corresponding thermal-lens signals are monitored by a He-Ne probe laser. Advantages of this dual-wavelength apparatus include its inherent sensitivity and enhanced selectivity. The selectivity is improved because the ratio of the thermal-lens signals at the two different wavelengths provides fingerprints and allows identification of the sample. Therefore, it can be used not only to detect and identify trace chemical species at very low concentration but also to analyse two-component mixtures. Using this apparatus, the detection limit for NO2 using 30 mW excitation beams modulated at 4.6 Hz is estimated to be 300 PPB.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"11 1","pages":"586-589"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77762694","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/014
A. Delong, V. Kolarik
An electron gun has been designed for a TFE W 100 ZrO cathode with a magnetic lens for voltages up to 15 kV. The main fields of application are assumed to be electron beam lithography, electron beam diagnosis and analysis of microstructures.
{"title":"Field emission gun for microengineering application","authors":"A. Delong, V. Kolarik","doi":"10.1088/0022-3735/22/8/014","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/014","url":null,"abstract":"An electron gun has been designed for a TFE W 100 ZrO cathode with a magnetic lens for voltages up to 15 kV. The main fields of application are assumed to be electron beam lithography, electron beam diagnosis and analysis of microstructures.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"132 1","pages":"612-614"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79657273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/026
M. Slifkin, J. Ely
A cheap, simple device has been built which enables short-lived capacitance transients to be measured. The device uses phase modulation. This device is particularly suitable for deep-level transient spectroscopy (DLTS).
{"title":"A cheap capacitance meter for the measurement of fast transients and suitable for deep-level transient spectroscopy","authors":"M. Slifkin, J. Ely","doi":"10.1088/0022-3735/22/8/026","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/026","url":null,"abstract":"A cheap, simple device has been built which enables short-lived capacitance transients to be measured. The device uses phase modulation. This device is particularly suitable for deep-level transient spectroscopy (DLTS).","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"27 1","pages":"664-666"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75736407","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/027
B. Krishnarajulu, G. Muralidhar, S. Mohan, A. Menon
Ion implantation systems, used for producing high-current ion beams, employ wide-beam ion sources which are rotated through 90 degrees . These sources need mass analyser optics which are different from the conventional design. The authors present results of calculation of the image distance as a function of entrance and exit angles of a sector magnet mass analyser having such a source. These computations have been performed for the magnetic deflection angles 45 degrees , 60 degrees and 90 degrees . The details of the computations carried out using the computer program MODBEAM, developed for this purpose, are also discussed.
{"title":"DESIGN NOTE: Mass analyser optics for wide-beam ion sources in ion implantation systems","authors":"B. Krishnarajulu, G. Muralidhar, S. Mohan, A. Menon","doi":"10.1088/0022-3735/22/8/027","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/027","url":null,"abstract":"Ion implantation systems, used for producing high-current ion beams, employ wide-beam ion sources which are rotated through 90 degrees . These sources need mass analyser optics which are different from the conventional design. The authors present results of calculation of the image distance as a function of entrance and exit angles of a sector magnet mass analyser having such a source. These computations have been performed for the magnetic deflection angles 45 degrees , 60 degrees and 90 degrees . The details of the computations carried out using the computer program MODBEAM, developed for this purpose, are also discussed.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86482268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/015
C. A. Hamilton, K. Mclauchlan, S. Nattrass
A novel dual-beam fluorescence measurement technique is described which involves beam splitting of an excitation pulse so as to cause fluorescence from experimental and reference samples. The emissions are combined at a single detector, but separated in time. The technique is illustrated using measurements resulting from a free radical reaction performed in the absence and presence of an applied external magnetic field.
{"title":"A dual-beam flash-photolysis fluorescence technique for use with pulsed lasers","authors":"C. A. Hamilton, K. Mclauchlan, S. Nattrass","doi":"10.1088/0022-3735/22/8/015","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/015","url":null,"abstract":"A novel dual-beam fluorescence measurement technique is described which involves beam splitting of an excitation pulse so as to cause fluorescence from experimental and reference samples. The emissions are combined at a single detector, but separated in time. The technique is illustrated using measurements resulting from a free radical reaction performed in the absence and presence of an applied external magnetic field.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"1 1","pages":"615-616"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83530797","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1989-08-01DOI: 10.1088/0022-3735/22/8/016
G. R. Duffill, D. Dunstan
Conventionally, furnaces are controlled by measuring the temperature and processing the data by, for example, a three-term temperature controller. The authors report successful control of a furnace using non-thermal data taken directly from the heated object. The expansion of a sample tube, in a simulation of a horizontal Bridgmann system for growing GaAs in a quartz tube, provided the integral term of a three-term controller.
{"title":"Furnace control using non-thermal parameters (semiconductor growth)","authors":"G. R. Duffill, D. Dunstan","doi":"10.1088/0022-3735/22/8/016","DOIUrl":"https://doi.org/10.1088/0022-3735/22/8/016","url":null,"abstract":"Conventionally, furnaces are controlled by measuring the temperature and processing the data by, for example, a three-term temperature controller. The authors report successful control of a furnace using non-thermal data taken directly from the heated object. The expansion of a sample tube, in a simulation of a horizontal Bridgmann system for growing GaAs in a quartz tube, provided the integral term of a three-term controller.","PeriodicalId":16791,"journal":{"name":"Journal of Physics E: Scientific Instruments","volume":"10 1","pages":"617-618"},"PeriodicalIF":0.0,"publicationDate":"1989-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75055982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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