System 450™ Series Control Module with Ethernet Communications Installation Instructions
15
Binary Input Control for Relay Outputs
You can connect a binary input (dry contacts) to any of the three System 450 communications control module
inputs (Sn1, Sn2, or Sn3), and control the output relays in your control system based on the binary input’s state
(open or closed).
A sensor (Sn-1, Sn-2, or Sn-3) set up as a binary input can only be referenced by a relay output. Sensors set up as
binary inputs are not available for selection on analog outputs.
When a relay output references a sensor that is set up as a binary input, the On and OFF parameter screens are
not available as you set up the output. The relay output’s On/Off state is controlled by the binary input’s Closed/
Open state and any of the timer parameters (ONT, OFFT, ONd, or OFFd) that you set up for the relay output. Refer
to the Binary Input Control for Relay Outputs section on page 15 of the System 450 Series Modular Control
Systems with Communications Control Modules Technical Bulletin (LIT-12011826) for more information.
High Input-Signal Selection
System 450 control modules with communications include the High Input-Signal Selection control feature.
The High Input-Signal Selection feature enables a System 450 control system to monitor a condition (temperature,
pressure, or humidity) with two or three sensors (of the same type) and control relay and/or analog outputs based
on the highest condition value sensed by the two or three referenced sensors.
In two sensor applications (HI-2), Sn-1 and Sn-2 must be the same Sensor Type. In three sensor applications
(HI-3), Sn-1, Sn-2, and Sn-3 must be the same Sensor Type.
A System 450 control system, using High Input-Signal Selection, can monitor the outlet pressures of two
condenser coils in a multi-circuit condensing unit using two pressure sensors of the same type; one connected to
each coil outlet.
Differential Control
System 450 control modules with communications include the Differential Control feature. Differential control is
used to monitor and maintain a given difference in a condition (temperature, pressure, or humidity) between two
sensor points within a system, process, or space.
The Differential Control feature enables a System 450 control system to monitor the temperature, pressure, or
humidity differential between two sensors of the same type (Sn-1 and Sn-2) and control relay and/or analog
outputs based on the sensed differential value relative to user-selected differential values (dON, dOFF, dSP, and
dEP).
When a Differential Control sensor (Sn-d) is set up, the displayed differential sensor value is a calculated variable
value: (Sn-d) = (Sn-1) – (Sn-2).
The Sn-d value appears in the System Status screens as either a temperature differential value (dIFT), pressure
differential value (dIFP), or humidity differential value (dIFH). The unit of measurement associated with the
displayed differential value is determined by the Sn-1 and Sn-2 Sensor Type. See Table 4 on page 11 for Sensor
Types and their units of measurement.
The relay output setup values dON and dOFF are condition differential values. When a relay output is set up for
differential control, System 450 controls the relay state (On or Off) based on the difference between Sn-1 and Sn-2
(Sn-d) relative to the user-selected differential On (dON) and differential Off (dOFF) values.
When an analog output is set up for differential control, System 450 controls the analog signal strength based on
the difference between Sn-1 and Sn-2 (Sn-d) relative to the user-selected differential setpoint (dSP) and differential
endpoint (dEP) values.
Differential Sensor Range of Usable Values
The System 450 Differential Control sensor (Sn-d) value is always equal to Sn-1 minus Sn-2. Depending on the
intended control action of the output, the differential value may be either a positive or negative value. Therefore, the
range of usable values is twice as large as a single sensor, and each Sensor Type has an equal number of positive
and negative values. See Table 7 for the range of usable values when an output references Sn-d.
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