Untersignal

Untersignal is a term used in German-language discussions of signaling systems to denote a signal of a lower rank within a hierarchical set of signals. The phrase literally means subsignal. It is not a universally standardized term, but is employed in various domains to describe an indicator that conveys supplementary or conditional information derived from higher-level signals rather than deciding the primary action itself.

In railway signaling, a subsignal would usually be something that informs the operator about auxiliary conditions affecting route safety but does not by itself require an action such as proceed or stop. In control and process automation, an under-signal may indicate a status such as valve position, sensor fault, or degraded connection, while the main control signal governs the primary operation.

In digital communications or network monitoring, subsignals can be used to carry status flags or quality metrics that are subordinate to an overarching alarm or control signal.

Etymology: from German unter- meaning under and Signal meaning signal. Usage varies by system architecture; in some texts the term may be replaced by subsignal, auxiliary signal, or cascading signal.

See also: Hauptsignal, Vorsignal, signaling hierarchy, indicator, status signal.