American NBS provisions of test material may be solid standard filter, such as 930, 203 standard piece etc, also can be in standard solution is: compounds, such as: potassium chromate, dichromate solution of P, the user can choose. China's national standards can be used neutral filters can also be used as a standard compound material standard solution. But in the various national standards are pointed out the advantages and disadvantages of both solid and liquid. The researchers through long-term practice and repeated comparisons that: solid standard filter is better than that of standard solution. The reasons are as follows:
The solid standard filter has the advantages of simple operation, convenient carrying.
The solid standard filter can be used as reference for air, avoid the ideal reference picture based trouble.
The solid standard filter can obtain a plurality of need, the ideal peak or valley.
Standard plate basic body the solid standard filter can absorb a part of stray light, in the absorption (or transmission) peak intensity is very small (or large), can improve the accuracy of measurement.