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4-2 Series 90-30/20/Micro Programmable Controllers Reference Manual – September 1998 GFK-0467K
4
Section 1: Relay Functions
This section explains the use of contacts, coils, and links in ladder logic rungs.
Function Page
Coils and negated coils. 4-3
Normally open and normal closed contacts. 4-2
Retentive and negated retentive coils. 4-4
Positive and negative transition coils. 4-5
SET and RESET coils. 4-6
Retentive SET and RESET coils. 4-7
Horizontal and vertical links. 4-7
Continuation coils and contacts. 4-8
Using Contacts
A contact is used to monitor the state of a reference. Whether the contact passes power flow
depends on the state or status of the reference being monitored and on the contact type. A reference
is ON if its state is 1; it is OFF if its state is 0.
Table 4-1. Types of Contacts
Type of Contact Display Contact Passes Power to Right:
Normally Open —| |— When reference is ON.
Normally Closed —|/|— When reference is OFF.
Continuation Contact <+>——— If the preceding continuation coil is set ON.