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在室温12℃、湿度30%、大气压强101.325kPa的环境下对4支OMEGA公司的热电偶进行时间常数的测试,热电偶的详细参量如表 1所示。表中K表示镍铬-镍硅热电偶,J表示铁-康铜热电偶,E表示镍铬-铜镍热电偶。热电偶的实物图如图 5所示。
Table 1. Basic parameters of thermocouple
serial number thermocouple model indexing number range 1 KQXL-18U-6 K 0℃~1149℃ 2 TJ36-ICSS-18U-6 J 0℃~521℃ 3 TJ36-CASS-18U-6 K 0℃~899℃ 4 TJ36-CXSS-18U-6 E 0℃~521℃ 经过透镜聚焦后的半导体激光器在全量程(500W)输出时,聚焦后的激光可使热电偶温度接近2000℃,鉴于4支热电偶的测温范围,设置激光器输出功率100W,在同等条件下对KQXL-18U-6型、TJ36-ICSS-18U-6型、TJ36-CASS-18U-6型及TJ36-CXSS-18U-6型4支热电偶进行时间常数测量。热电偶测试波形如图 6所示。
在同等条件下,采用ADLINK公司的PCI8554数据采集卡,采集热电偶电压输出曲线,对测试结果进行小波降噪处理,得到热电偶时间常数曲线如图 6所示。根据以上时间常数曲线,可以得到4支热电偶的时间常数如表 2所示。
Table 2. Thermocouple test results
serial number thermocouple model laser power/W time constant/s 1 KQXL-18U-6 100 2.806 2 TJ36-ICSS-18U-6 100 3.094 3 TJ36-CASS-18U-6 100 2.229 4 TJ36-CXSS-18U-6 100 2.457
热电偶时间常数测试中阶跃温升信号的研究
Study on step temperature rise signal in thermocouple time constant test
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摘要: 为了对热电偶时间常数进行准确测试,采用上升时间5μs、功率500W的大功率半导体激光器作为系统激励源对热电偶进行加热的方法,对时间常数进行了理论分析和实验验证。利用半导体激光器输出连续且光斑能量均匀稳定的优点,解决了原测试系统中传统激励源作用机理的限制。结果表明,由于半导体激光器输出功率恒定,利用闭环反馈控制激光功率的方法,产生激光阶跃温升信号,保证了热电偶的均匀加热,得到了期望的平衡温度;4支不同热电偶时间常数分别测得为2.806s,3.094s,2.229s和2.457s。该反馈控制器具有较强的鲁棒性,测试系统可激发较理想的阶跃温升信号,为热电偶时间常数测试提供高质量的激励源。Abstract: In order to accurately test the thermocouple time constant, a high power semiconductor laser with rise time of 5μs and power of 500W was used as excitation source to heat the thermocouple. Theoretical analysis and experimental verification were carries out about time constant. Because of continuous output of semiconductor laser and stable uniformity of spot energy, the restriction of traditional excitation source mechanism of the formal test system was solved. The results show that, as the output power of semiconductor laser is constant, by closed-loop feedback control of laser power, laser step temperature rise signal is generated to ensure the uniform heating of thermocouple and obtain expected equilibrium temperature. Time constants of four different thermocouples were 2.806s, 3.094s, 2.229s and 2.457s. The feedback controller has strong robustness. The test system can stimulate the ideal step temperature rise signal to provide high quality excitation source for thermocouple time constant test.
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Table 1. Basic parameters of thermocouple
serial number thermocouple model indexing number range 1 KQXL-18U-6 K 0℃~1149℃ 2 TJ36-ICSS-18U-6 J 0℃~521℃ 3 TJ36-CASS-18U-6 K 0℃~899℃ 4 TJ36-CXSS-18U-6 E 0℃~521℃ Table 2. Thermocouple test results
serial number thermocouple model laser power/W time constant/s 1 KQXL-18U-6 100 2.806 2 TJ36-ICSS-18U-6 100 3.094 3 TJ36-CASS-18U-6 100 2.229 4 TJ36-CXSS-18U-6 100 2.457 -