ISO 16526-2:2011规定了X射线系统的恒定性检查，主要检查X射线电压，以及管电流和靶材的结构，这些都可能因管的老化而发生变化。 厚滤光片法基于使用X射线管、滤光片和测量装置之间的定义距离测量定义厚滤光片后面的剂量率。 该方法对电压变化非常敏感，但不能提供X射线管电压的绝对值。因此，需要一个参考值，建议在系统验收测试中找到该参考值。 厚滤光片法是一种相当简单的技术，可由X射线系统的操作员应用，以定期对系统进行稳定性检查。 该方法也可用于更换可能影响X射线管电压的部件后的一致性检查。 该方法适用于所有类型的X射线系统，即管电流大于1mA的恒电位、半波和脉冲波发生器。

ISO 16526-2:2011 specifies a constancy check of a X-ray system where mainly the X-ray voltage is checked and also the tube current and the constitution of the target which can be changing due to ageing of the tube. The thick filter method is based on a measurement of the dose rate behind a defined thick filter using defined distances between the X-ray tube, the filter and the measuring device. This method is very sensitive to changes of the voltage, but it does not provide an absolute value for the X-ray tube voltage. Therefore, a reference value is needed and, it is recommended to find this reference, for example, within the acceptance test of the system. The thick filter method is a rather simple technique and may be applied by the operator of an X-ray system to perform regularly a constancy check of the system. The method can also be applied for consistency checks after changing components which may affect the X-ray tube voltage. This method can be applied for all types of X-ray systems, i. e. for constant potential, half wave and impulse wave generators with a tube current larger than 1 mA.