optical pyrometer. The optical pyrometer output was then converted to emitter temperature and transmitted to the computer. The Output Load Instrumentation System. Figure 3 is a simplified schematic of the converter output load circuit. The converter output voltage was measured across the emitter and collector and fed directly to the HP-3852A acquisition system along with the converter output current, which was measured across a shunt (0.0033 ohm) resistance. Biasing the diode was accomplished initially by using a variable resistance box but as this method does not allow negative output voltages, it was changed to a 50 V, 6 A DC power supply, which was connected across a water cooled load resistance through a bipolar switch. The bipolar switch was introduced to bias the diode with both positive and negative voltages. Manual biasing resulted in a sudden change in electrode temperatures which had to be brought back to its original level by manipulating the heaters and the cooling mechanism before further biasing. This way it takes a very long time to complete a sweep and it would be impossible to complete performance mapping for a pair of electrodes in a reasonable period of time. Efforts are currently being made to develop a pulsing mechanism in the form of a low duty voltage pulse to reduce the sweeping period to less than 20 ms. At this speed, the time taken is much lower than the time constant of the electrode material and so there is virtually no change in temperature. The Data Acquisition/Processing System. Because of the large amount of data involved in the study of electrical output characteristics of the diminiode, a computer system was required to control, collect and correlate converter output data. The computer system design for data acquisition and processing is shown in Fig. 4. The system consists of: (i) The test apparatus made up of the converter, DC power supply, load circuit, thermocouples, and optical pyrometer. (ii) The data acquisition system, which is the HP-3852A model. This system included a multiplexer, A/D converter and an integrating high speed voltmeter. (iii) The desk top PC, a Zenith-248 and the applicable software.
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