Figure 2-30 Ltch Function Block Example - Honeywell UMC800 Reference Manual

Function Blocks
2.33 LTCH Function Block,
Example
Figure 2-30 shows a Function Block Diagram using an LTCH function block
PLC Ladder Logic
An ON Delay timer is added to a basic Start/Stop circuit
which activates the ON Lamp. In ladder logic, the DO1
contact status is used to activate the timer and latch in the
start pushbutton action. After 20 sec., SOL4 (DO2) is turned
ON which is held as long as DO1 is ON.
UMC 800 Logic
The Start/Stop latch circuit is used since no
external confirmation is needed. In this
example, the Operator Panel pushbutton
switches (F1 and F2) are used to substitute
for panel switches. The Push Button function
block is used to assign Start to F1 and Stop
to F2. The latch output turns on the ON
Lamp and starts the timer. After 20 sec.,
Solenoid 4 is activated. Note: the ON and
OFF Delay timers are reset after timeout or if
the logic state to the input goes to logic 0 (or
low).
5 Function Blocks
94
continued

Figure 2-30 LTCH Function Block Example

Function Block Reference Guide
Stop
Start
Start/Stop Circuit
DO 1
On Timer
1
20 SEC
DO1
On Lamp
DO 1
SOL 4
PUMP 1
DO 2
3/99