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(1)反射率测量实验结果
如图7所示,对低温辐射计吸收腔的反射率进行了测量,测量过程中激光功率的稳定性在0.5 h内优于5×10−5。根据中国计量科学研究院出具的校准证书,标准板在632.8 nm波长下的反射率为0.990,吸收腔反射率测量结果如表1所示。
Number of measurements $\dfrac{ { {V_c} } }{ { {V_s} } }$ $\dfrac{ {V_s'} }{ {V_c'} }$ $ \;{\rho _c} $ $ \;{\rho _c} $ average $ \;{\rho _c} $ experimental standard deviation $ 1 - \;{\rho _c} $ 1 0.0002375 0.99992 0.0002351 0.000 2417 5.3×10−6 0.99976 2 0.0002418 0.99994 0.0002394 3 0.0002502 0.99991 0.0002477 4 0.0002392 0.99992 0.0002368 5 0.0002408 0.99995 0.0002384 6 0.0002415 0.99993 0.0002391 7 0.0002398 0.99994 0.0002374 8 0.0002518 0.99992 0.0002493 9 0.0002483 0.99996 0.0002458 10 0.0002502 0.99995 0.0002477 Table 1. Summary of measurement results of the reflectivity of the absorbing cavity
(2)吸收率测量实验结果
如图8所示,通过调节低温辐射计工作温度从室温到4 K,分别测量反射监测组件输出的信号值,得到吸收腔吸收率测量结果如表2所示。测量时,四象限探测器测量的背景平均值为0.002616 mV,室温条件下四象限探测器测量的信号平均值为0.033568 mV,4 K条件下四象限探测器测量的信号平均值为0.027561 mV,信噪比优于10。实验结果表明:所研制的低温辐射计吸收腔吸收率在4 K温度条件较室温条件发生了微小变化,与吸收腔涂层吸收特性的分析结果一致,实际使用时需要对低温辐射计的功率测量结果进行进一步修正。
Figure 8. Physical diagram of the absorbing cavity absorptivity measurement device under variable temperature conditions
Number of measurements $\dfrac{ { { {{V} }_{\text{T} } } }}{ { { {{V} }_{} } } }$ $ {\rho _c}\left( {632.8} \right) $ ${\rho _{_{\rm{ T}}} }\left( {632.8} \right)$ 1−${\rho _{_{\rm {T} } } }\left( {632.8} \right)$ 1−${\rho _{_{\rm {T}}} }\left( {632.8} \right)$ average 1−${\rho _{_{\rm {T}}} }\left( {632.8} \right)$ experimental
standard deviation1 1.208611 0.0002417 0.0002921 0.9997079 0.99971 2.2×10−5 2 1.213973 0.0002934 0.9997066 3 1.223985 0.0002958 0.9997042 4 1.213982 0.0002934 0.9997066 5 1.209048 0.0002922 0.9997078 6 1.223989 0.0002958 0.9997042 7 1.234034 0.0002983 0.9997017 8 1.213992 0.0002934 0.9997066 9 1.228026 0.0002968 0.9997032 10 1.209935 0.0002924 0.9997076 Table 2. Summary of the measurement results of the absorbing cavity absorptivity
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4 K条件下吸收腔吸收率的测量不确定度可用4 K条件下吸收腔反射率的测量不确定度表征。4 K条件下吸收腔反射率测量的模型如公式(3)所示,通过分析,4 K条件下吸收腔吸收率的测量不确定度分量主要有:
(1) 室温条件下反射率测量对4 K条件下吸收腔吸收率测量引入的测量不确定度分量u1;
(2) 室温条件下四象限探测器V测量对4 K条件下吸收腔吸收率测量引入的测量不确定度分量u2;
(3) 4 K条件下四象限探测器VT测量对4 K条件下吸收腔吸收率测量引入的测量不确定度分量u3;
(4) 测量重复性引入的测量不确定度分量u4。
(1) u1
反射率测量数学模型如公式(2)所示,通过分析,
$\; {\rho _c} $ 的测量不确定度主要受$ \;{\rho _s} $ 、$ {V_c} $ 、$ {V_s} $ 、$V_s'$ 、$V_c'$ 的影响。根据校准证书,标准板反射率为0.990时,$ {\rho _s} $ 引入的测量不确定度$ \Delta {\rho _s} $ 为5×10−3,标准板反射率对吸收腔反射率测量引入的测量不确定度为:$ {V_s} $ 、$V_s'$ 、$V_c'$ 对吸收腔反射率测量引入的测量不确定度主要受数字电压表电压测量的影响。根据校准证书,数字电压表的相对测量不确定度$ \Delta {V_s} $ 为0.005%(k=2),经过分析,Vs、Vs'、Vc' 对吸收腔反射率测量引入的测量不确定度均为6.0×10−9。由于 $ {V_c} $ 较$ {V_s} $ 、$V_s'$ 、$V_c'$ 的大小低了四个数量级,因此$ {V_c} $ 对吸收腔反射率测量引入的测量不确定度除了受数字电压表的影响,还受前置放大器换挡误差以及探测器非线性的影响。经过分析,$ {V_c} $ 对吸收腔反射率测量引入的测量不确定度为1.3×10−5。根据表1反射率测量重复性为5.3×10−6,则测量重复性引入的测量不确定度为1.7×10−6。通过对以上不确定度来源进行合成,并且灵敏系数VT/V为1.22,得到室温条件下反射率测量对4 K条件下吸收腔吸收率测量引入的测量不确定度u1为2×10−5。(2) u2
根据校准证书,数字电压表的测量不确定度为0.005% (k=2),吸收腔的反射率为0.0002417,灵敏系数VT/V为1.22,因此 V测量引入的测量不确定度u2为8×10−9。
(3) u3
根据校准证书,数字电压表的测量不确定度为0.005% (k=2),吸收腔的反射率为0.0002417,灵敏系数VT/V为1.22,因此 VT测量引入的测量不确定度u2为8×10−9。
(4) u4
根据重复性实验,测量重复性引入的测量不确定度u4为7×10−6。
通过对以上各测量不确定度来源进行分析,其不确定度分析详见表3,4 K条件下吸收腔吸收率的测量不确定度为0.005% (k=2)。
Uncertainty component Standard uncertainty Evaluation method Uncertainty component introduced by absorptivity measurement u1 0.2×10−4 Type B Uncertainty component introduced by the output V of the detector u2 8×10−9 Type B Uncertainty component introduced by the output VT of the detector u3 8×10−9 Type B Uncertainty component introduced by measurement repeatability u4 0.07×10−4 Type A Combined standard uncertainty 0.22×10−4 Relative combined standard uncertainty 0.0022% Relative expanded uncertainty(k=2) 0.005% Table 3. Analysis of measurement uncertainty
Measurement technique research for the absorptivity of cryogenic radiometer absorbing cavity at the 4 K temperature
doi: 10.3788/IRLA20210984
- Received Date: 2021-12-17
- Rev Recd Date: 2022-01-10
- Accepted Date: 2022-01-13
- Publish Date: 2022-09-28
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Key words:
- cryogenic radiometer /
- absorbing cavity /
- reflectivity /
- absorptivity
Abstract: In order to realize measuring the absorptivity of cryogenic radiometer absorbing cavity at the 4 K temperature, a method of measuring the absorptivity with variable temperature is researched. By designing reflection monitoring components in front of the Brewster window of the cryogenic radiometer, and controlling the cryogenic radiometer to work in a vacuum environment of 10−6 Pa, then adjusting the refrigeration temperature of the cryogenic radiometer, the reflection signals of the cryogenic radiometer absorbing cavity are measured at 632.8 nm under room temperature and different temperature conditions. Combined with the measurement results of the reflectance at 632.8 nm of the cryogenic radiometer absorbing cavity at room temperature using the traditional integrating sphere method, the absorptivity of the cryogenic radiometer absorption cavity can accurately obtain under different temperature conditions through calculations. The experimental measuring the absorptivity of the absorbing cavity at room temperature and 4 K temperature, the absorptivity is 0.99976 and 0.999 71, respectively. The measurement uncertainty of the absorptivity of the cryogenic radiometer absorption cavity at the 4 K condition is evaluated, and the results obtained show that the relative expanded uncertainty is 0.005%(k=2).