Active And Passive Sensors - Johnson Controls Penn System 450 Series Technical Bulletin

Active and Passive Sensors

Each sensor/transducer hardwired to a System 450 control system is either an
active or passive sensor. Passive System 450 sensors are two-wire temperature
sensors that connect to one of the sensor input terminals and a common terminal
(C) only. Active sensors are three-wire humidity sensors and pressure transducers
that connect to one of the sensor input terminals, a common terminal, and a voltage
supply terminal (24V or 5V). The sensors and transducers have the following
requirements:
• Temperature sensors do not require a power source.
• Humidity sensors and differential air pressure transducers require 24 VAC
supply power and must be connected to the 24V terminal on the input terminal
block.
• P499 pressure transducers require a 5 VDC power source and must be
connected to the 5V terminal on the input terminal block.
On control modules with analog outputs, set the active/passive switches to ON for
passive temperature sensors and off for active humidity sensors.
Figure 6: Example Showing the Active/Passive Slide Switch Settings
on a Control Module with Analog Outputs
On control modules with relay outputs, position the active/passive jumpers across
both pin terminals for passive temperature sensors and on one terminal for active
humidity and pressure sensors.
Figure 7: Example Showing the Active/Passive Jumper Positions
See System 450 Standard Control System Examples on page 27 for System 450
control system examples showing active/passive sensor jumper or switch settings.
System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin
on a Control Module with Relay Outputs
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