第30卷第7期 2017年7月
传感技术学报
CHINESE JOURNAL OF SENSORS AND ACTUATORS
Vol. 30No.7 July 2017
EstimatingTransferFunctionModelsforSheathedThermocouple
LIWenjun,SUNHongjian,ZHENGYongjun
( College of Merological Technofogy and Engineering , China Jiliang U/ninersity,Hangahou 310018, Ching)
Abstract : This paper presents a method for evaluating the dynamic characteristics of sheathed thermocouple. Com-posite lumped heat capacitance model of the sheathed thermocouple is derived based on the method of lumped heat capacitance analysis. Sheathed thermocouple heat transfer process includes protecting tube heat transfer, insulating layer heat transfer and hot junction heat transfer. The process is described as a series of three inertial element with lag. Thermal contact resistance is significant between protecting tube and insulating layer. A temperature drop is ob-served at the interface between the two surfaces in contact. Similar situations occur between insulating layer and hot junction. When the constant time of protection tube and the constant time of insulation are small,the transfer func-tion of a sheathed thermocouple is simplified to be a first order process with delay. Based on the double thermostatic bath device , a bidirectional step temperature experiment system is established. The arrangement,in response to the changes in the temperature of the two thermostatic bath, provides input and output signals of the sheathed thermo-couple. Two cases for the response of a thermocouple are reported, the first case concerns the response to a step per-turbation , while the second deals with the response to a step perturbation with disturbance. Parameters are estimated by using computation algorithms to arrive at coefficients that best fit the selected auto regressive moving average model. Experiments are carried out and results prove that auto regressive moving average model is feasible for off line identification of sheathed thermocouple.
Key words : sheathed thermocouple ; lumped capacitance ;transform function; auto regressive moving average
EEACC:7230
doi:10.3969/j.issn.10041699.2017.07.013
铠装热电偶传递函数参数估计*
李文军*，孙宏健，郑永军
（中国计量大学计量测试工程学院，杭州310018）
摘要：为了评价铠装热电偶动态特性，针对铠装热电偶测量动态温度过程用集总热容法和复合集总热容法建立了铠装热电偶的传热模型。从所建立模型分析，铠装式热电偶传热过程是保护管、绝缘层和测量接点这3个小时间常数惯性环节的串联，且保护管与绝缘层、绝缘层与测量接点存在接触热阻，产生了两个耦合作用。当保护管时间常数和绝缘层时间常数都比较小时，传递函数可近似为带时滞的惯性环节。建立了基于双槽法的正负温度阶跃实验系统，测量热电偶在正负温度阶跃激励下的输出响应。接照预估延退时间和预估延退时间加扰动两种情形，用输出误差自回归滑动平均方法估计了传递函数的
参数。结果表明，输出误差自回归滑动平均方法适用于铠装热电偶实验建模和模型的离线辨识。关键词：铠装热电偶；集总热容法；传递函数；自回归滑动平均
中图分类号：TP212.11
文献标识码：A
工业测量中存在着测量动态温度的需求[1-2]，以及对温度传感器动态特性做测试的需求(3-5)。作为温度传感器，热电偶和铠装热电偶得到了广泛应用。为了用热电偶测量动态温度，工业测量中常通过组合方式比如利用双偶或三偶组合实现动态测
项目来源：国家科技重大专项项目（2015ZX02101）
收稿日期：2016-12-30
修改日期：2017-02-17
文章编号：10041699(2017)07-1044-06
温[6-8]。同时为了提高铠装热电偶测量动态温度的精度，还利用系统辨识技术进行实验建模以近似得到系统模型进行补偿[9-11]
由于铠装热电偶测量端存在接触热阻以及多重换热[12]，其测温过程物理上构成一个延迟系统，采用