103

Automatic Timing & Controls

800.727.5646

atcdiversified.com

OPERATION

TYPICAL INSTALLATION

DELAYED MODE —

Sustained* start

INTERVAL MODE —

Sustained* or

momentary** start

INTERVAL MODE —

Sustained* start

REPEAT CYCLE PULSE

GENERATOR —

Uninterrupted start

signal

The Shawnee 353 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), the clock 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 353 times out.

At that instant, the clock turns itself off automatically.

At the same instant, the 353 generates one type of control action or another,

depending on how it is wired.

When the 353 is wired for interval operation, the timer’s output device (either

the standard SPDT relay or the optional SPST switch module) is energized

from the start to the end of the time cycle; so is the -24 VDC output at

terminal 16.

When the 353 is wired for delayed control, the output device is energized at

the end of the cycle and remains on until the timer is reset; so is the -24 VDC

output.

When the 353 is wired as a repeat cycle pulse generator, the output device

and the DC signal are both off until the end of the cycle, at which time they

are both on for about 80 mSEC. The length of the pulse is included in the time

cycle: the cycle runs from the start of one pulse to the start of the next. The

353 automatically starts a new cycle immediately after reset.

The duration of the standard output pulse generated by the 353 is 80

mSEC (±20 mSEC), but it can be easily lengthened or shortened by using a

capacitor or resistor across terminals 4 and 11. To shorten the output pulse,

the size of the resistor (fixed or variable) is calculated as follows:

Where:

t = time in milliseconds (± 25%)

2.2t - 2.64

_________ = R

80-t

R = resistance in megohms

(must be at least 0.2 megohm.)

To lengthen the output pulse, the size of the capacitor is calculated as follows:

Where:

T = time in seconds (± 25%)

T - 0.08

_________ = C

1.6

C = capacitance in microfarads.

NOTE Observe Polarity: (+) Terminal of the capacitor goes to 11, (–)

Terminal to 4. To start from AC voltage, jumper terminals 8-9 and 4-11 and

start with AC power at terminals 1 and 2.

*Start switch must be closed — or DC start signal must be on —

for entire cycle. Timer resets when start switch opens or DC start

signal turns off. To start from DC voltage, apply external ground on

11 and start signal on 9.

**Start switch may be closed — or DC start signal may be on —

for less that the entire cycle. Timer resets at end of cycle.

Automatic Timing & Controls

800.727.5646

atcdiversified.com