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Digital optically coupled transient recorder

Olyabek, Z. (1993). Digital optically coupled transient recorder. (Unpublished Doctoral thesis, City, University of London)


This work is concerned with the investigation and development of a random-impulse acquisition system which combines a number of important features. These include fast acquisition, high speed digital transmission and recording. The design approach has been to divide the system into two sections; one operating in the harsh environment of the measurement point and the other in a relatively interference-free area. The two sections communicate through a high speed digital fibre optic link. The system is also designed to allow random 'single-shot' recording without the provision for an external trigger.

In the proposed system of this work, the high-speed digitisation of the signal being monitored is carried out at the point of measurement and the digital data is transmitted to the recording unit of the instrument via the digital fibre optic link. Such a system is far less susceptible to distortion than one which uses an analogue optical link where the digitisation of the signal is carried out at the receiving end of the link. The superior linearity provided by the proposed measurement system enables accurate traceable measurements to be achieved readily, whereas such measurements are difficult to accomplish with existing systems.

In this work a survey was made of the conductor-connected as well as optically coupled transient recording systems. The optically-coupled systems either used wide bandwidth analogue links or very low speed digital links. The suitability of a high speed digital system is studied. This involved a thorough investigation of the various parts of the system down to component level. The electronic circuits for the different sub-units of the digital fibre optic link were investigated using discrete components. Model parameter extraction for the transistors used was carried out using the s- parameter measurement technique. The results of this characterisation were used in the computer simulation programme, SPICE, to obtain reliable simulation results. The fibre optic link unit was implemented and tested successfully. The designs of the various sub-units of the high speed recording unit were investigated and the simulations of these were carried out using the digital simulation programme System- HILO. The simulation of the transient recorder unit circuits revealed that this unit would be capable of data recording at a rate of more than 100 Mega Samples/sec. Both simulation programmes used during this work for circuit analysis (SPICE and System HILO) were found to contain significant faults, the sources of which were identified and eliminated.

Subsequent testing of the complete system and the more detailed study of the recorder unit have shown that the system is capable of recording at the rate of 100 Mega Samples/sec. In these tests sinusoidal and chopped-impulse input signals were used. The chopped-impulse had a rise time of 1 ps and a chop time of 0.1 ps. The multi-wire technology of the circuit board of the recorder unit has been shown to be capable of high speed operation, but minor faults in the ADC driver and the RAM device have detracted from the completely successful operation of the system.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Science & Technology > Engineering > Electrical & Electronic Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
[thumbnail of Olyabek thesis 1994 PDF-A.pdf]
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