Microcomputer-based langmuir probe system
A simple microcomputer-basedd ata acquisition systemi s set up to obtain the I-V characteristic of the Langmuir probe. The system is ideal for extensive probe data collection in the study of steadystate plasmas. The Langmuir probe is a simple but effective tool for the diagnostic of fairly large vol...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
1985
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| Subjects: | |
| Online Access: | http://eprints.um.edu.my/7714/1/Microcomputer-Based_Langmuir_Probe_System.PDF |
| _version_ | 1825719416048844800 |
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| author | Wong, C.S. Saw, S.H. Chin, Oi Hoong |
| author_facet | Wong, C.S. Saw, S.H. Chin, Oi Hoong |
| author_sort | Wong, C.S. |
| collection | UM |
| description | A simple microcomputer-basedd ata acquisition systemi s set up to obtain the I-V characteristic of the Langmuir probe. The system is ideal for extensive probe data collection in the study of steadystate plasmas. The Langmuir probe is a simple but effective tool for the diagnostic of fairly large volume, relatively cold and low density plasmas.F rom the I-V .characteristico f the probe, plasmap arameters such ag the electron temperature, electron density, space potential and electron energy distribution can be deduced. For a time-varying plasma, the pulsed Langmuir probera must be used. In the case of a steady-state plasma, it is usually sufficient to use the point-by-point technique, although the pulsed method can also be employed. However, the process of obtaining the Langmuir probe characteristic by the point-by-point method and its analysis is tedious and time-consuming if it is done manually. This is particularly true in casesw here the Langmuir probe is employeda s a basicd iagnostic and extensived ata are required to be collectedc oncurrently with other diagnosticso f the plasma. In this note, a simple microcomputer-basedd ata acquisition systemf or the Langmuir probe is described. The system employs an Apple-II microcomputer to control the variation of the probe's bias potential as well as to monitor the probe curent automatically. The data acquisition system consists of a 64k RAM Apple-II micrommputer which is supported by a high-resolution CRT display unit; two mini floppy diskdrives and a dot matrix printer with highresolution graphic capability (Fig. l). Data acquisition is done via a multi-channel A/D + D/A interface card (Mountain Computer Inc.) which can be plugged directly into the expansion slot of the Apple-II. This interface card provides 16 cannelse ach of analog-todigital and digital-to-analogc onverters.T he rangeo f its analogi nput/output level is -5V to +5V, with a digital equivalenceo f 0 to 255. The experimentasl et-upo f the miqocomputer-basedo uble Langmuirp robe measuremenotf a plasma is as shown in Fig. 2. A I kO resistor is connected in place of the usual microammeter for measuringth e probe curent, Ip. The potentiald rop acrosst he I kS2r esisteri s expectedt o be of the order of mV only and hence it must be amplified before it is fed into an A/D channel of the computer. This is done by using a HP2470A data amplifier. The probe potential Vp is supplied by using the HP457A power amplifier acting as a variable power supply. The output of the power amplifier can be varied within the range of -3OV to +30V by applying a voltage of -3V to +3V to its input. Thus when used in conjunction with a digitaltoanalog converter, the HP467A power amplifier functions as a low voltage digitally controlled power supply. This iurangementis good enoughf or the presentp urpose.I f -higherv oltagesa re required, the digitally controlled power supply described by Fanelli and Merangelli" may be employed. |
| first_indexed | 2024-03-06T05:19:24Z |
| format | Article |
| id | um.eprints-7714 |
| institution | Universiti Malaya |
| language | English |
| last_indexed | 2024-03-06T05:19:24Z |
| publishDate | 1985 |
| record_format | dspace |
| spelling | um.eprints-77142019-12-06T06:11:53Z http://eprints.um.edu.my/7714/ Microcomputer-based langmuir probe system Wong, C.S. Saw, S.H. Chin, Oi Hoong QC Physics A simple microcomputer-basedd ata acquisition systemi s set up to obtain the I-V characteristic of the Langmuir probe. The system is ideal for extensive probe data collection in the study of steadystate plasmas. The Langmuir probe is a simple but effective tool for the diagnostic of fairly large volume, relatively cold and low density plasmas.F rom the I-V .characteristico f the probe, plasmap arameters such ag the electron temperature, electron density, space potential and electron energy distribution can be deduced. For a time-varying plasma, the pulsed Langmuir probera must be used. In the case of a steady-state plasma, it is usually sufficient to use the point-by-point technique, although the pulsed method can also be employed. However, the process of obtaining the Langmuir probe characteristic by the point-by-point method and its analysis is tedious and time-consuming if it is done manually. This is particularly true in casesw here the Langmuir probe is employeda s a basicd iagnostic and extensived ata are required to be collectedc oncurrently with other diagnosticso f the plasma. In this note, a simple microcomputer-basedd ata acquisition systemf or the Langmuir probe is described. The system employs an Apple-II microcomputer to control the variation of the probe's bias potential as well as to monitor the probe curent automatically. The data acquisition system consists of a 64k RAM Apple-II micrommputer which is supported by a high-resolution CRT display unit; two mini floppy diskdrives and a dot matrix printer with highresolution graphic capability (Fig. l). Data acquisition is done via a multi-channel A/D + D/A interface card (Mountain Computer Inc.) which can be plugged directly into the expansion slot of the Apple-II. This interface card provides 16 cannelse ach of analog-todigital and digital-to-analogc onverters.T he rangeo f its analogi nput/output level is -5V to +5V, with a digital equivalenceo f 0 to 255. The experimentasl et-upo f the miqocomputer-basedo uble Langmuirp robe measuremenotf a plasma is as shown in Fig. 2. A I kO resistor is connected in place of the usual microammeter for measuringth e probe curent, Ip. The potentiald rop acrosst he I kS2r esisteri s expectedt o be of the order of mV only and hence it must be amplified before it is fed into an A/D channel of the computer. This is done by using a HP2470A data amplifier. The probe potential Vp is supplied by using the HP457A power amplifier acting as a variable power supply. The output of the power amplifier can be varied within the range of -3OV to +30V by applying a voltage of -3V to +3V to its input. Thus when used in conjunction with a digitaltoanalog converter, the HP467A power amplifier functions as a low voltage digitally controlled power supply. This iurangementis good enoughf or the presentp urpose.I f -higherv oltagesa re required, the digitally controlled power supply described by Fanelli and Merangelli" may be employed. 1985 Article PeerReviewed application/pdf en http://eprints.um.edu.my/7714/1/Microcomputer-Based_Langmuir_Probe_System.PDF Wong, C.S. and Saw, S.H. and Chin, Oi Hoong (1985) Microcomputer-based langmuir probe system. Jurnal Fizik Malaysia, 6. ISSN 0128-0333, |
| spellingShingle | QC Physics Wong, C.S. Saw, S.H. Chin, Oi Hoong Microcomputer-based langmuir probe system |
| title | Microcomputer-based langmuir probe system |
| title_full | Microcomputer-based langmuir probe system |
| title_fullStr | Microcomputer-based langmuir probe system |
| title_full_unstemmed | Microcomputer-based langmuir probe system |
| title_short | Microcomputer-based langmuir probe system |
| title_sort | microcomputer based langmuir probe system |
| topic | QC Physics |
| url | http://eprints.um.edu.my/7714/1/Microcomputer-Based_Langmuir_Probe_System.PDF |
| work_keys_str_mv | AT wongcs microcomputerbasedlangmuirprobesystem AT sawsh microcomputerbasedlangmuirprobesystem AT chinoihoong microcomputerbasedlangmuirprobesystem |