System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin
13
See High Input Signal Selection
on page 23 and Differential Control on page 24 for more information about these
functional sensors and system control features.
Relay Outputs
Relay outputs provide low and line-voltage on/off control for devices and equipment in your controlled systems.
Each relay output is a Single-Pole, Double-Throw (SPDT) set of dry contacts. See Figure 18 on page 37.
Note: System 450 output relays are SPDT dry contact relays only and they do not provide any power source for
your controlled equipment.
Selecting an ON value that is less than the OFF value (ON < OFF) turns the relay on when the sensed condition
value decreases, which is the typical heating mode in temperature applications and referred to as reverse-acting
on/off control.
Selecting an ON value that is greater than the OFF value (ON > OFF) turns the relay on when the sensed condition
value increases, which is the typical cooling mode in temperature applications and referred to as direct-acting
on/off control.
You can set up multiple relay outputs to create a variety of equipment staging control systems. See Wiring
System 450 Components on page 36 for information on wiring output relays. See Related Documentation on page
61 for the relay output electrical ratings.
A green LED on the relay control and relay expansion module housings (Figure 1) indicates the relay output status.
When a relay output is On:
• the corresponding green LED on the module housing is lit
• the LC to LNO (Line Normally Open) relay contact is closed
• the LC to LNC (Line Normally Closed) relay contact is open
• the corresponding Output Status screen in the UI displays On
When a relay output is Off:
• the corresponding green LED on the module housing is not lit
• the LC to LNO relay contact is open
• the LC to LNC relay contact is closed
• the corresponding Output Status screen in the UI displays OFF
System 450 control and expansion modules are available with one or two relay outputs. See Table 12 on page 55
and Related Documentation
on page 61 for more information about the System 450 series modules.
A relay output’s control action is determined by the values that you select in the ON and OFF relay output setup
screens:
• Relay ON values (ON) are the values at which the relay turns On.
• Relay Off values (OFF) are the values at which the relay turns Off.
Table 3 illustrates direct and reverse relay actions. When you select On/Off condition values where OFF is less
than On, the output relay is a direct-acting relay. When you select condition values where On is less than Off, the
output relay is a reverse-acting relay.
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