Analog Outputs; Direct And Reverse Control Actions For Analog Outputs - Johnson Controls Penn System 450 Series Technical Bulletin

In pressure applications, directing acting relays are often used for condenser fan
cycling control or pump-down control, while reverse acting relay may be used for
high pressure cut-out.
In humidity applications, direct acting relays often control dehumidification
equipment, and reverse acting relay often control humidification equipment.

Analog Outputs

Analog outputs provide proportional analog signals for devices and equipment in
your controlled systems. Each analog output can generate either a 4 to 20 mA or
0 to 10 VDC signal. The output signal type is self-selecting; after you connect the
analog output to the controlled equipment, the output detects the analog input on
the controlled equipment and generates the appropriate analog signal for the
connected input.
You can set up an analog output to generate a direct acting or reverse acting
proportional output signal. You can also set up the output signal strength to
increase or decrease in either the direct acting or reverse acting mode. See Direct
and Reverse Control Actions for Analog Outputs on page 20 for more information.
System 450 also provides six integration constants that allow you to set up a
proportional plus integral control signal, which can provide more precise setpoint
control. See Proportional Plus Integral Control and Integration Constants on page
23 for information on determining the integration constant for an analog output.
For procedures on setting up analog outputs on standard control modules, see
Setting up an Analog Output on page 50.
System 450 control and expansion modules are available with one or two analog
outputs. See Table 11 on page 62 and Technical Specifications on page 67 for more
information about the System 450 Series module models that are used to build
standard control systems.

Direct and Reverse Control Actions for Analog Outputs

An analog output can be set up to provide one of four different control actions,
which allow you to match the output signal to the requirements of your control
system and the controlled equipment. The proportional output signal can provide
direct acting or reverse acting control. In addition, the output signal can be set up
to generate either the minimum or the maximum output signal strength at Setpoint.
A control ramp icon is displayed on the status screens for all analog outputs in your
control system. See Figure 2 on page 10. The displayed control ramp icon
represents the control action of the analog output signal. See Table 4 on page 22
for more information on analog output control actions and control ramp icons.
An analog output's control action and the corresponding control ramp are
automatically determined by the values that you select in four analog output setup
screens:
• Setpoint value (SP) is the target value that the control system drives toward,
and along with the End Point, defines the output's proportional band.
20 System 450™ Series Modular Control Systems with Standard Control Modules Technical Bulletin