usually; ordinarily; at all times
Adverbial use meaning that something is normally or consistently the case. It is somewhat more formal or written than everyday いつも.
The machinery in this factory operates around the clock.
This shop usually stocks more than twenty kinds of bread.
警備員が常時巡回している。
Security guards patrol at all times.
noun which may take the genitive case particle 'no'
continuous; 24-hour; always on
Used before another noun or in compounds for systems, operation, care, connection, monitoring, and similar states that continue without interruption.
常時接続のインターネット環境が必要です。
An always-on internet connection is required.
その患者には常時介護が必要だ。
That patient needs constant care.
A staff member is always stationed at the reception desk.
The security guard carries a radio with him at all times.
常に is a general literary adverb for 'always/constantly', whereas 常時 more specifically emphasizes a maintained state, availability, or continuous operation.
随時 in its 'at any time' sense implies continuous availability similar to 常時, but 常時 more strongly emphasizes an unbroken, constant state rather than on-demand access.
常時 is a stiff, technical word for 'at all times' (e.g. in manuals or notices), while いつでも is the everyday spoken equivalent.
随時 means 'as needed' or 'from time to time', the opposite of 常時, which describes something continuous or always available.
臨時 describes something temporary or ad-hoc (e.g. 臨時雇用), directly contrasting with 常時's sense of ongoing, permanent operation.
非常時 (an emergency) is easily confused with 常時 (all the time) because of the shared kanji, but they mean nearly opposite things.
emergency; time of emergency
always-on connection
full-time employment; regular employment
A Sino-Japanese compound of 常, associated with regularity or constancy, and 時, 'time'; literally, roughly 'constant times' or 'ordinary times.'