Differential Control - Johnson Controls Penn System 450 Series Technical Bulletin

• fan motor speed control on multi-circuit condensing units
The Hybrid Analog and High Input Signal Selection Control System Example on
page 32 provides module assembly, wiring, and UI setup information for a
System 450 hybrid analog output control system that uses the High Input Signal
Selection feature.

Differential Control

Standard System 450 control modules include the Differential Control feature.
The Differential Control feature enables a System 450 control system to monitor
and maintain a temperature, pressure, or humidity differential between two sensors
of the same type and control relay and/or analog outputs based on the sensed
differential value relative to user-selected differential values.
Note: Differential Control is available on standard System 450 control modules
beginning with firmware Version 2.00. Differential Control is not available
on the hybrid analog control module (C450CPW-100).
Differential Control application examples include:
• solar heating systems
• pump pressure-drop monitoring and control
• fluid filter pressure-drop monitoring
• air filter pressure-drop monitoring
Setting up an output (relay or analog) for Differential Control requires connecting
two identical sensors to input terminals Sn1 and Sn2 and selecting the same Sensor
Type in the System 450 UI for Sensor 1 (Sn-1) and Sensor 2 (Sn-2). The
System 450 control system recognizes the same Sensor Types and makes the
functional Differential Control sensor (Sn-d) available for selection when you set
up each of the control system outputs.
Note: Setting up Sn-1 and Sn-2 as the same Sensor Types also enables the
functional High Input Signal Selection sensor (HI-2). See High Input
Signal Selection on page 24 for more information.
When a Differential Control sensor (Sn-d) is set up, the differential sensor value is
a calculated value; (Sn-d) = (Sn-1) minus (Sn-2). The Differential Control sensor
(Sn-d) value is always equal to Sn-1 minus Sn-2. Therefore, depending on the
intended control action of the output, the differential value may be either a positive
or negative value.
The sensed differential value (Sn-d) between Sn-1 and Sn-2 is displayed 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 2 on page 16 for Sensor Types and their
units of measurement.
System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin 25