Walker James H, Thompson Ambler
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
J Res Natl Inst Stand Technol. 1994 May-Jun;99(3):255-261. doi: 10.6028/jres.099.021.
As radiometric lamp standards improve, the need to set lamp current to specific values becomes more important. Commercially available power supplies typically provide 12 bit internal digital-to-analog logic which permits current control with a relative expanded uncertainty of about 1 part in 4096, corresponding to an expanded uncertainty of the current of about 2 mA at 8 A (in this paper, expanded uncertainties arc given as 2 standard deviations). For an FEL-type standard spectral irradiance lamp, this corresponds to a spectral irradiance difference of 0.12% at 655 nm. We have developed a technique using 16 bit digital-to-analog conversion which permits current control with a relative expanded uncertainty of about 1 part in 65536, corresponding to an expanded uncertainty of the current of about 0.1 mA at 8 A. This corresponds to a spectral irradiance difference of approximately 0.006% for an FEL lamp at 655 nm. We describe the technique used to achieve this improvement and we show data from a lamp demonstrating the effect of the improvement. We also describe the limitation provided by the uncertainty of the resistance of the current measuring shunt.
随着辐射测量灯标准的提高，将灯电流设置为特定值的需求变得更加重要。市售电源通常提供12位内部数模逻辑，这使得电流控制的相对扩展不确定度约为4096分之一，相当于在8 A时电流的扩展不确定度约为2 mA（在本文中，扩展不确定度以2倍标准差给出）。对于FEL型标准光谱辐照灯，这对应于655 nm处光谱辐照度差为0.12%。我们开发了一种使用16位数模转换的技术，该技术允许电流控制的相对扩展不确定度约为65536分之一，相当于在8 A时电流的扩展不确定度约为0.1 mA。这对应于FEL灯在655 nm处光谱辐照度差约为0.006%。我们描述了用于实现这一改进的技术，并展示了来自一盏灯的数据，证明了改进的效果。我们还描述了电流测量分流器电阻不确定度所带来的限制。
