User`s guide

Appendix A - Logic Application Examples
Basic PLC Ladder Logic
226 UMC800 Control Builder User’s Guide Release E
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Example 2 - Basic PLC ladder logic
LS 1 LS 2
SOL 1
Coil
This is a basic series-parallel circuit. If Limit Switch 1
(LS1) is ON and Limit Switch 2 (LS2) is ON, or
if pushbutton PB1 is ON, then Solenoid 1 is turned ON,
otherwise it is OFF. Note “power flow” can be delivered
in either of two paths to the solenoid.
PB1
Equivalent Boolean Logic Expression
UMC 800 Logic
A = LS1,
B = LS2
D = Output
(A * B) + C = D
AND Symbol
A
B
C
C = PB1,
OR Symbol
D
OR
This uses a basic 2 Input AND block
and a 2 Input OR block.
6 Function blocks are used.
AND
Example 3 - Basic PLC ladder logic
LS 1
LS 2
SOL 1
Coil
PB1
Example 2 is expanded by adding a Normally Closed (NC)
Contact in series with the series-parallel circuit. In PLC
logic, if Pump B is OFF (the logic true state for an NC
contact), then “power flow” will be allowed through to
SOL 1. This is equivalent to a Boolean NOT.
PumpB
(NC
Contact)
Equivalent Boolean Logic and Expression
A = LS1,
B = LS2
E = Output
((A * B) + C)*D = E
A
B
C
C = PB1,
D
OR
AND
D = Pump B
AND
NOT Symbol
Boolean
NOT Symbol
Another discrete input is added plus a
2-In AND block. Note that the DI6 block
(PUMP B) is inverted (DI dialog box
selection) without adding an Inverter
block.
8 Function blocks are used.
UMC 800 Logic