菜单
  
    AbstractA  simple and practical digital thermometer with  an
    accuracy better than 0.1 T  over a near-rooin-temperature
    (from  -10 "C  to  50 "C)  measurement range has been
    developed.  The instrument is compact and battery
    operated and provides for both digital and analog outputs.
    A four-lead platinum thermal sensor, driven by a constant
    current  loop,  allows  for  accurate temperature readings
    with high immunity to the contact resistances and to their
    variations. A low-noise electronics allows for temperature
    measurements with a 1-nK  resolution. By experimentally
    characterizing the non-linearity of  the  adopted Pt-100
    sensor, a suitable readout correction table  has  been
    calculated in order  tal  compensate  for  the sensor
    non-linearity. This compensating procedure allows for  a
    wider (from  -50 "C  to  +200 "C)  and  higher accuracy
    (-0.05  "C) measurement range. The accuracy, up to now,
    IS  essentially limited by the  accuracy of  the  temperature
    standard  used for calibration.4827
    1. Initroduction
    Temperature measurements characterized by  the best
    accuracy  levels use platinum sensors  to  transduce the
    thermal  signal into an electric one  [l].  The low  thermal
    coefficient  (a  = l/R-dR/dT  z  0.385 Yd"C  for  standard
    commercial  probes  121)  and  the relatively  low  ohmic
    value  of  these sensors push toward the  need  for  high-
    resolution measurements of  the variation in the sensor
    resistance.  Such  measurements require a careful
    consideration of  the additional resistances  arising  from
    the lead wires  and  contact  weldings  arid  from the
    associated thermal  mi;.  For  this  reason, the  most
    accurate resistance measurements need four-wires
    probes [3].  With  a  four-wire resistor the voltage
    difference between the high-impedance voltmetric
    terminals can be read, essentially without spurious
    resistance effects, when a constant current is flowing
    trough the other  mperometric wires and terminals.  A
    particular and quite recent application of  this concept is
    exploited in the Anderson's loop circuit [4]. This current- 4-lead thermistor  Analog ovtput
    Km
    Measurement
    electronic  circuR
    Figure 1. Block diagram of the digital thermometer.
    sensor, the main electronic sections, and both outputs,  is
    depicted  in Fig. 1, while  the details of  the measurement
    electronic circuit are indicated in Fig. 2. The excitation
    current is  obtained by  means  of  a precise 5-V voltage
    reference (Linear Technology,  LT1236), an  ultra  low
    noise  operational amplifier (Analog Device, OP177), and
    a  reference  resistor  R2=100S.1 R  (3 ppm/"C).  The
    doubly  differential subtraction section is  made  of  two
    instrumentation amplifiers (Burr Brown, INAl18) and of
    another OP177  operational amplifier. As  a temperature
    sensor,  a four-wire  Pt-100 commercial  and cheap
    thermistor (RS, 237-1657) has been used. This sensor, in
    compliance with  BS1904:1984 class  B  quality,  is
    characterized  by  a  nominal-resistance  value  of
    Ro  = 10033.1  R  at  a  reference  temperature T,=O  "C  and
  1. 上一篇:甲基叔丁基醚MTBE英文文献和翻译
  2. 下一篇:LabVIEW外文文献和翻译
  1. 汽车乘员舱的声振耦合英文文献和中文翻译

  2. 立体光照成型的注塑模具...

  3. 数控机床英文文献和中文翻译

  4. 工业机械手英文文献和中文翻译

  5. 低频振动的铁路车轴的状...

  6. 接头的形状对沥青塞接头...

  7. 数控加工技术英文文献和中文翻译

  8. 杂拟谷盗体内共生菌沃尔...

  9. java+mysql车辆管理系统的设计+源代码

  10. 十二层带中心支撑钢结构...

  11. 电站锅炉暖风器设计任务书

  12. 酸性水汽提装置总汽提塔设计+CAD图纸

  13. 大众媒体对公共政策制定的影响

  14. 当代大学生慈善意识研究+文献综述

  15. 河岸冲刷和泥沙淤积的监测国内外研究现状

  16. 乳业同业并购式全产业链...

  17. 中考体育项目与体育教学合理结合的研究

  

About

751论文网手机版...

主页:http://www.751com.cn

关闭返回