Series Operation: The Shawnee 355 operates on a digital logic circuit with three main elements: a clock which uses utility line frequency of 50 or 60 Hz as its time base; a read-only-memory (ROM) whose output is set by the timer's digital setting number wheels; and a comparator that continuously examines the outputs of the clock and ROM.
When power is applied (start signal on), two things happen simultaneously; the instantaneous DPDT relay is energized transferring both sets of contact, and the clock circuit begins to count each cycle of the utility line frequency. Translating this count into hundredths of a second, the clock accumulates it and feeds it continuously to the comparator. When clock output exactly equals the output of the ROM, the comparator causes the 355C to time out.
At this point, (1) the DPDT delay relay is energized, immediately transferring both sets of contacts and (2) the clock turns itself off automatically. Since the clock stops counting even if the start signal remains on, it is not necessary to tie up one of the 355C's delayed contacts to do this job.
To reset the Shawnee 355, power must be removed from terminal 1 (L1) for 75 milliseconds or more. The 355 operates in the On-Delay mode only, always resetting whenever there is a power outage and starting a new cycle when power is restored.
CYCLE PROGRESS INDICATION: When the timer is in the reset condition, the LED display is blank. During the timing cycle, the display counts up from zero, thus always indicating the amount of time that has elapsed since the start of cycle. At time-out, the display shows total elapsed time and exactly equals the numbers on the digital setting wheels. |
