High Input Signal Selection - Johnson Controls Penn System 450 Series Technical Bulletin

The integration constant establishes the rate at which the control readjusts the
analog output signal. The faster the integration constant, the faster the control
readjusts the output signal and the faster the recovery rate of a properly sized and
setup control loop.
Note: PI control is not suitable for all controlled systems. Improperly applied PI
control loops are unstable and can overshoot setpoint, resulting in control
loop oscillation. Also, with PI control, the proportional band (throttling
range) and the integration constant are interdependent and you must
properly set up these values in relation to each other. You must also
properly size the system equipment to handle the maximum load. Close
observation over several cycles and under different load conditions is
required to properly set up a PI control loop. On a properly sized system, a
PI control loop can drive the system condition much closer to setpoint than
proportional-only control.
In addition to a proportional-only setting, System 450 provides six time-integral
settings in the Integration Constant Setup screen for matching the analog
signal's response rate to the controlled system's recovery rate. The seven
integration constant settings are shown in Table 8 on page 60.
See Determining the Integration Constant for an Analog Output on page 56 for
more information and the procedures for determining an integration constant and
testing a PI control loop in your controlled system.

High Input Signal Selection

Standard System 450 control modules, including the C450CPW-100 hybrid analog
control module, 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 analog outputs based on the highest
condition value sensed by the two or three referenced sensors.
When Sn-1 and Sn-2 are set up with the same Sensor Type, the functional High
Input Signal Selection sensor (HI-2) is available for selection when you set up the
outputs in the control system. When Sn-1, Sn-2, and Sn-3 are set up with the same
Sensor Type, the functional sensor (HI-3) is also available for selection.
Note: High Input Signal Selection is available on standard System 450 control
modules beginning with firmware Version 2.00 and on the hybrid analog
control module (C450CPW-100). On the hybrid analog control module,
High Input Signal Selection is only available for the hybrid analog output
(OUTA1).
Note: Setting up Sn-1 and Sn-2 as the same Sensor Types also enables the
functional Differential Control sensor (Sn-d). See Differential Control on
page 25 for more information.
High Input Signal Selection control application examples include:
• fan-staging control on multi-circuit condensing units
24 System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin