The 651 series is manufactured by Marsh Bellofram, and is a panel mounted, microprocessor-based digital timer that has the capacity of operating four varying timing modes over three varying timing ranges.
The timing modes are on-delay, off-delay, on-delay with momentary start, and on-delay with store time. The timing ranges enable delays ranging from 1 m up to 199 h 59 min.
By utilizing an internally integrated 7 switch DIP, the timing modes and ranges are selected. The time setting is entered via a keyboard placed at the face plate of the timer, and it can be disabled to prevent unintended time changes. The unit is enclosed in a 15-terminal plug-in round case, and it features a sealed face plate which makes it suitable to use in harsh environments.