Delta DVP-ES2/EX2/SS2/SA2/SX2/SE manual Current Flow, No Contact, NC Contact, Scan time exception

1. PLC Concepts

Scan time exception

PLC can process certain items faster than the scan time. Some of these items interrupts and halt the scan time to process the interrupt subroutine program. A direct I/O refresh instruction REF allows the PLC to access I/O immediately during user program evaluation instead of waiting until the next scan cycle.

1.2Current 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 X1

X3 X4

Reverse Current

X2 Y0

Y0

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.

X0			X1		X2		Y0
							Y0
	X3 a			X4	b	X5
		X6

1.3NO Contact, NC Contact

NO contact

Normally Open Contact, A contact

NC Contact

Normally Closed Contact, B contact

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