Sensor Failure Mode - Johnson Controls Penn System 450 Series Technical Bulletin

When a relay output is set up for Differential Control, System 450 compares the
sensed differential value, Sn-d (Sn-d = Sn-1 minus Sn-2), to the user-selected
differential values (dON and dOFF) to control the relay's On/Off state.
When an analog output is set up for Differential Control, System 450 compares the
sensed differential value, Sn-d (Sn-d = Sn-1 minus Sn-2), to the user-selected
differential values (dSP and dEP) to control the analog output signal strength.
The Solar Heating Control System Example Using Differential Control on page 28
provides module assembly, wiring, and UI setup information for a standard
System 450 control system that uses the Differential Control feature.
Note: Because of the way that the System 450 Differential Sensor (Sn-d) is set up
and calculated using two sensors with identical Sensor Types, the Range of
Usable Values for each Sensor Type is twice as large as a single sensor.
(Each Sensor Type has an equal number of positive and negative values on
outputs that reference Sn-d.) See Table 5 for a Sensor Type's Range of
Usable Values when an output references Sn-d.
Table 5: Range of Usable Values for Sensor Types in Differential Control
Applications
Sensor Type Sn-d Range of Usable
Values
F -290 to 290
C -161.0 to 161.0
rH -95 to 95
P 0.5 -0.500 to 0.500
P 2.5 -2.50 to 2.50
P 5 -5.00 to 5.00
P 8
-9.00 to 9.00
P 10 -10.00 to 10.00
P 15
-16.0 to 16.0

Sensor Failure Mode

System 450 allows you to select the mode of operation for your control system
outputs in the event of a sensor (or sensor wiring) failure of the sensor or sensors
that the outputs reference. When you set up an output in the System 450 UI, you
must select a sensor failure mode of operation in the Sensor Failure Mode (SNF)
screen. Your selection determines how an output responds if a referenced sensor or
sensor wiring fails.
System 450 outputs can be set up to directly reference a single compatible sensor
hardwired to the control system (Sn-1, Sn-2, or Sn-3). Outputs in control systems
with System 450 standard control modules can also be set up to reference several
functional sensors (Sn-d, HI-2, or HI-3). The functional sensors reference input
from one or more of the hard-wired sensors; thus one or more of the hard-wired
sensors can influence the outputs that reference functional sensors.
26 System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin
Sensor Type Sn-d Range of Usable
Values
P 30 -30.0 to 30.0
P 50 -50.0 to 50.0
P 100 -100.0 to 100.0
P 110 -110.0 to 110.0
P 200 -200 to 200
P 500 -500 to 500
P 750
-750 to 750
HIF -380 to 380
HIC
-210.0 to 210.0