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单片机温度计英文文献和翻译(2)

时间:2016-12-28 12:46来源:毕业论文
by a nominal temperature coefficient a = (385k2)10-5 C. With an excitation current of 373 pA and a total differential subtraction gain of 68.2 V/V, a sensitivity of +)(cc 10 pV/mK has been obtained at


by  a nominal  temperature coefficient a = (385k2)10-5  "C'.
With  an excitation current  of 373 pA  and a total
differential subtraction gain of  68.2 V/V, a  sensitivity of
+)(cc
10 pV/mK has been  obtained at  the measurement circuit
output  (voltage  Vhem  in  Figg.  1  and  2).  The  output
voltage from the measurement circuit of Fig. 2 is sent to
an A/D converter (Harris,  ICL7129) which then drives a
liquid  crystal display  (Varitronix, BD503DP) with  4%
digits.  An  analog  voltage is also available  at  a  BNC
output  connector on  the  back  of  the  thermometer case.
Due  to  the kinds of A/D  converter and display that have
been  adopted,  the theoretical  resolution  of  the  digital
measurements  turns  out  to be 1 mK  or 10 mK  in  the
temperature intervals of 320 "C or +200 "C,  respectively.
The  desired measurement range can  be  selected  by  a
manual switch  acting on  the  A/D  converter  and on  the
dynamic of  the display (SO0 mV or +2 V,  respectively).
Calibration  of  the instrument offset  and gain is  made
possible by  means  of  the Rwl and  Rw2 potentiometers,
respectively.  The  power  supply  consists  of  two  9-V
batteries which are connected in series. Owing to  the low-
power consumption of  the adopted electronic circuit, the
power supply  allows for  a  continuous  operation of  the
thermometer for a period longer than 100 hours.
A picture of the entire instrument and sensor is shown
in Fig. 3.  This  thermometer has been  developed mostly
for near-room-temperature operation and it is specifically
designed for thermoelectronic control loops aimed at the
temperature  stabilization of  small  optical or mechanical
parts  even  out side  of  the laboratory  environment.
Henceforth, the device is portable and battery operated.
loop topology  is  now  becoming  widely used  for
temperature measurements using  resistive sensors. When
compared  to  a  standard bridge circuit, the Anderson's
loop  also presents the clear advantage  of  generating an
output voltage  which varies;  linearly with the sensor
resistance. If  a perfectly linear and calibrated electronic
circuit  is  developed, the remaining measurement errors
then arise from the sensor non-linearity and from the
aging of both the sensor and the electronic circuit.
In this paper the design and performance of a compact
and accurate digital thermometer, with a 4%  digit display,
is  described. The  thermometer  uses  a four-lead  Pt-100
commercial temperature transducer sensed  by  a  doubly
differential subtraction  circlcit  in  an  Anderson's  loop
configuration. The combination of a low-noise electronics
and a careful instrument calibration  allows  for  accurate
temperature measurements  in  a  e00  OC  interval withm
the operating range of the sensor.
2. Digital Thermometer Design
The  thermometer design  is based  on  a  current  loop
excitation acting on  a  resistive  thermal  sensor whereas
active doubly differential  subtraction is used  to  read  the 单片机温度计英文文献和翻译(2):http://www.youerw.com/fanyi/lunwen_1615.html
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