Johnson Controls Penn System 450 Series Technical Bulletin page 76

Term
Functional Sensor
Hg
HI-2
76
Definition
In addition to the wide variety of System 450 compatible hard-wired
temperature, pressure, and humidity sensors available, the System 450
firmware also enables several functional sensors based on the input from
one or more of the hard-wired sensors in your control system. Functional
sensors include the Reset Setpoint sensor (rES), which enables reset
control, setback control, and load balancing; the Differential Control
sensor (Sn-d), which enables the Differential Control feature; and the High
Input Signal Selection functional sensors (HI-2 and HI-3), which enable
the High Input Signal Selection feature. When you select a functional
sensor for an output, the output is controlled according to values sensed at
multiple sensors and the control logic/calculation designed into the
functional sensor. See System 450 Functional Sensors on page 18 for more
information.
Hg appears in the Main (sensor status) screens along with the current
sensed pressure value, when your control system uses one or more
pressure transducers with P 110 Sensor Types. Hg is an abbreviation of the
unit of measurement inHg, which is used to measure negative pressure
values (below 0 psi). P 110 Sensor Type is capable of monitoring and
displaying negative pressure values. Outputs that reference P 110 sensors
requires a unique setup calculation and the negative pressure values are
displayed differently in the P 110 setup and status screens. See System 450
Sensors and Transducers for Standard Control Modules on page 16 and
Sensor Failure Mode on page 26 for more information.
A functional High Input Signal Selection Sensor that references two
hard-wired sensors of the same Sensor Type. When you set up the
hard-wired sensors Sn-1 and Sn-2 as the same Sensor Type, functional
sensor HI-2 is available for selection when you set up the control system
outputs. Outputs that are set up to reference HI-2 use the higher of the two
condition values (sensed at Sn-1 and Sn-2) to control the output. High
Input Signal selection is available on standard control modules with
firmware Version 2.00 or later, hybrid analog output control modules, and
communication control modules, but is not available on reset control
modules. See High Input Signal Selection on page 24 for more
information.