The most general form of linear time-invariant time-delay systems described by delay-differential-algebraic equations is considered. Necessary and sufficient conditions for a mode of such a system to be delay-independent are derived. Then, such a system under centralised control is considered, and some necessary and sufficient conditions for a mode of such a system to be spectrally uncontrollable and/or spectrally unobservable independent of any time-delays are derived. Finally, such a system under a decentralised control structure is considered, and some necessary and sufficient conditions for a decentralised fixed mode to be independent of any time-delays are derived. An example to illustrate the use of the results is also presented.

考虑了由延迟-微分-代数方程描述的线性时不变时滞系统的最一般形式。推导了这种系统的模态与时延无关的充分必要条件。然后，考虑这样一个集中控制下的系统，并导出了这样一个系统的模式在光谱上不可控和/或光谱上不可观测的一些必要和充分条件，而与任何时延无关。最后，考虑了这种分散控制结构下的系统，导出了分散固定模态独立于任何时滞的充要条件。还提供了一个示例来说明结果的使用。