DIFFERENTIAL TEMPERATURE SENSOR ON THE INTEGRATING SIGNAL CONVERTER BASIS

2018;
: pp. 25-36
1
Danylo Halytsky Lviv National Medical University
2
Lviv Polytechnic National University
3
Lviv Polytechnic National University

The work is devoted to the problem of signal transducers of high-sensitivity differential temperature sensors. The conducted  studies  have  shown  that  the  scheme  of  the  signal  converter with  the  stabilization  of  the  total  emitter  currents  of  a transistors pair is characterized by a combination of high sensitivity and stability of the steepness of a transformation function. In particular,  as  compared  to  the  circuit with  the  stabilization  of  the  collector  current  of  a  reference  transistor,  the  instability  of steepness is reduced 20-fold. The research of the developed signal converters and their parametric analysis was carried out on the basis of transistors SPICE models.

For the number of modern sensors problems, in particular in micro and nanocalorimetry, a combination of high resolution of measurement of differential  temperature and  the speed of such measurement  is necessary. Obviously,  these  requirements are inherent  in  the  contradiction,  i.e.  increasing  the  speed  leads  to  an  inevitable  loss  of measurement  accuracy.  To  eliminate  this contradiction,  the  scheme  of  the  signal  converter  on  the  basis  of  an  integrator,  which  allows  increase  the  resolution  of  the temperature difference measurement, is proposed.

In  the  schemes  of  the  signal  converter  of  differential  temperature  and  the  integrator,  the  high-precision  operational amplifier  of  series  AD8551  /  AD8552  /  AD8554  have  been  used.  They  operate  on  principle  of  the  signal  modulation-demodulation, which allows  reach the minimum values of  the bias voltage and its  instability of 0.005 mV/°C. The characteristic relationship between accuracy and measurement time on the basis of the high-precision micro converter ADuC834 based on 24-bit sigma-delta (S-D) ADC used in the developed sensor of differential temperature is considered. 

Experimental  results of  the developed  sensor  investigation have underlined  the  significant exactness:  depending on  the ADC range, the non-reproducibility of the voltage measurement is within ± 1 (10) μV, which corresponds to the resolution of the temperature measurement ±(10-4…10-3)°C.

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