D-22
D.3.4 The Example for Designing Basic Program
Start, Stop and Latching
In the same occasions, it needs transient close button and transient open button to be start
and stop switch. Therefore, if you want to keep the action, you should design latching
circuit. There are several latching circuits in the following:
Example 1: the latching circuit for priority of stop
When start normally open contact X1=On, stop
normally contact X2
＝
Off, and Y1=On are set at
the same time, if X2=On, the coil Y1 will stop
acting. Therefore, it calls priority of stop.
X2
Y1
X1
Y1
Example 2: the latching circuit for priority of start
When start normally open contact X1=On, stop
normally contact X2
＝
Off and Y1=On (coil Y1 will
be active and latching) are valid at the same time, if
X2=On, coil Y1 will be active due to latched
contact. Therefore, it calls priority of start.
X2
Y1
X1
Y1
Example 3: the latching circuit of SET and RST commands
The figure at the right side is latching circuit that made
up of RST and SET command.
It is top priority of stop when RST command is set
behind SET command. When executing PLC from up
to down, The coil Y1 is ON and coil Y1 will be OFF
when X1 and X2 act at the same time, therefore it calls
priority of stop.
It is top priority of start when SET command is set after
RST command. When X1 and X2 act at the same
time, Y1 is ON so it calls top priority of start.
SET
Y1
RST
Y1
X1
X2
Top priority of stop
SET
Y1
RST
Y1
X2
X1
Top priority of start
