1、 本科生毕业设计（论文）外文翻译 题目： A new Semiconductor Thermometer for Geothermal Measurements 学 院： 信息科学与工程学院 专业班级： 电信 1002 班 学生姓名： 指导教师： 2014 年 3 月 16 日 A new Semiconductor Thermometer for Geothermal Measurements By SATYABRATA DATTA1 ) Summary :A portable solid state device designed and constructed for the measu
2、rement of temperature variation with depth inside a borehole is described. Saturation current (which is highly dependent on ambient temperature) in a reverse biased PN junction has been utilised for the purpose of measurement. The equipment is inexpensive and possesses several advantages over other
3、types of instruments for geothermal measurement regarding simplicity in construction and operation. 1. Introduction Usually, thermistors are utilised as temperature pick-up element in borehole geothermal measurements 12 ) . This is chiefly because thermistors have high negative temperature coefficie
4、nt of resistance. In the method of measurement with thermistor, a resistance bridge is used in association with an oscillator 2 or a D.C. 3 voltage source. A thermistor with the cable forms one arm of the bridge. Out-of-balance volt- age due to change in thermistor resistance caused by temperature v
5、ariations is noted after amplification when the thermistor with the cable is lowered in the borehole. The temperature under measurement is then found from a calibration chart or curve showing unbalance voltage versus temperature previously constructed in the laboratory under controlled conditions. S
6、ources of error in this method of measurement are largely due to drift in the thermistor and amplifier characteristics, and also due to undesirable changes in cable and other bridge arm resistances. The design and construction of the equipment described in this paper was under- taken for the use of
7、a glacier expedition party of the Geological Survey of India to study temperature variations with depth inside boreholes in glacier. Obviously, the equipment to suit the purpose should be light and simple in construction, and its performance should not be susceptible to adverse surface climatic vari
8、ations likely to be encountered. 2. Description The working principle of the instrument is as follows: The current (I) flowing through a PN junction is given by the relation I i0 (e V/VT -1), (1) 1) Geophysics Division, Geological Survey of India, Calcutta-16 (India). - This paper is published by th
9、e kind permission of the Director General, Geological Survey of India. 2) Numbers in brackets refer to References, page 126. Where io = junction saturation current, V = applied junction voltage which is + ve in the forward direction, VT = Junction barrier voltage = (K T)/q, K = Boltzman constant, T
10、= Junction temperature in 0 K q = electronic charge. When the junction applied voltage is in the forward direction (+ ve), the exponential term in equation (1) predominates and as a result the current increases exponent- tally with applied voltage. For applied voltage several times larger than VT (V
11、T is about 26 mV at 25 0 C )in the reverse direction, the current becomes independent of the applied voltage and practically remains constant at the saturation current level i0 so long as breakdown or avalanche voltage is not exceeded. This saturation current is actually caused by the flow of therma
12、lly generated minority carriers in the P and N regions. Therefore, its value is highly dependent on temperature and in actual practice increases exponentially with it. In the instrument designed this highly temperature dependent nature of the saturation current which is practically unaffected by the
13、 magnitude of supply voltage has been utilised for the purpose of measurement. The electronic circuit diagram of the instrument is shown in figure 1. Two reverse biased base-collector PN junctions of Germanium transistors are connected in parallel so that individual saturation currents of the two junctions add up. These two transistors in parallel form temperature sensing head and are in thermal contact with the borehole fluid. Resultant saturation current is then amplified by a third transistor which acts as a D. C. current amplifier. The
