Study On Multi-channel Platinum Resistance Thermometry Readout Based On Cross Polling Structure

The high precision and fast multi-channel platinum resistance thermometry readout is widely used in the development of research instruments such as calorimeter and quality comparator.Existing multi-channel platinum resistance thermometry readout generally adopts the AD converter or transformer time-sharing multiplexing extension the channel number,there are problem with increasing channel number but the accuracy decreased,unable to meet the requirements of the above instrument measurement accuracy.In this paper,we propose to a multi-channel high precision temperature measurement method based on cross polling structure,and carry out the main error analysis and correction research.The details are as follows.First of all,according to the principle of resistance ratio method and the analysis of classic multi-channel resistance temperature limitations,this paper put forward temperature measurement structure based on cross polling mode of multi-channel system,and carry out related theoretical formula derivation and error source analysis.Secondly,we design a multi-channel temperature measurement system based on cross-polling structure.Using multi-channel analog switch array and develop the corresponding firmware implementation of any polling of all resistance of ADC sampling,any resistance by all polling of ADC sampling,and according to the theory of cross polling for resistance calculation formula.The multi-channel test results show that the system overcomes the shortage of the measurement precision decreasing with the increase of channel number.Thirdly,in view of the cross structure of polling temperature measurement system error sources,in this paper we carry out the linearity evaluation of system based on RBC,put forward the error model(operational amplifier and the ADC)and system nonlinear error correction method.The experimental results show that this method has a significant effect on the linearity of the multi-channel temperature measurement system.Finally,we carry out measurement noise and uncertainty evaluation of multichannel temperature measurement system.Test results show that the design of multi-channel temperature measuring system in-50?~250? temperature range precision is better than the 0.1 millikelvin,the temperature drift in 2 hours is better than that of ±0.1 millikelvin.The temperature uncertainty is 1 millikelvin,the system linearity up to 10 ppm after error correction,superior to classical multi-channel thermometer Fluke1529.It is of great significance for the development and development of instruments with multi-point high precision temperature measurement.