Eaton ELC-PB - 1.2 Current Flow; 1.3 NO Contact, NC Contact

1. ELC Concepts
MN05003003E For more information visit: www.eaton.com
1-3
Scan time exception
The ELC can process certain items faster than the scan time. Program interrupts halt the scan
time to process the interrupt subroutine program. A direct I/O refresh instruction REF allows the
ELC to access I/O immediately during user program evaluation instead of waiting until the next
scan cycle.
1.2 Current Flow
Ladder logic follows a left to right principle. In the example below, the current flows through paths
started from either X0 or X3.
X0
Y0
X1 X2
Y0
X3
X4
Reverse Current
When a current flows from right to left, which makes a reverse current logic, an error will be
detected when compiling the program. The example below shows the reverse current flow.
X6
X0
Y0
X1
X2
Y0
X3
X4 X5
a
b
1.3 NO Contact, NC Contact
NO contact
Normally Open Contact, A contact
NC Contact
Normally Closed Contact, B contact