Watlow EZ-ZONE ST - Manual (Page 6)

Watlow EZ-ZONE ® ST • 4 • Chapter 1 Overview
A Conceptual View of the ST
The flexibility of the ST software and hardware allows
a large range of configurations. Acquiring a better
understanding of the controller's overall functionality
and capabilities while at the same time planning out
how the controller can be used will deliver maximum
effectiveness in your application.
It is useful to think of the controller in terms of
functions; there are internal and external functions.
An input and an output would be considered exter-
nal functions where the PID calculation would be an
internal function. Information flows from an input
function to an internal function to an output function
when the controller is properly configured. A single
ST control can carry out several functions at the same
time. For instance, closed-loop control monitoring for
several different alarm situations, while at the same
time operating switched devices, such as lights and
motors. Each process needs to be thought out carefully
and the controller’s various functions set up properly.
Inputs Functions
The inputs provide the information that any given
programmed procedure can act upon. In a simple form,
this information may come from an operator pushing
a button or as part of a more complex procedure it
may represent a remote set point being received from
another controller.
Each analog input typically uses a thermocouple
or RTD to read the temperature of something. It can
also read volts, current or resistance, allowing it to
use various devices to read humidity, air pressure,
operator inputs and others values. The settings in the
Analog Input Menu (Setup Page) for each analog input
must be configured to match the device connected to
that input.
Each digital input reads whether a device is ac-
tive or inactive. A controller with digital input-output
(DIO) hardware includes two sets of terminals each.
Each DIO must be configured to function as either an
input or output with the Direction parameter in the
Digital Input/Output Menu (Setup Page).
The EZ-ZONE Remote User Interface (RUI) has a
function, or EZ Key on the front panel, this too can be
configured as a digital input by toggling the function
assigned to it in the Digital Input Function parameter
in the Function Key Menu (Setup Page). If interested
in learning more about the RUI and how it is used
with the ST retrieve the RUI user manual from the
Watlow web site. Point your browser to:
http://www.watlow.com/literature/pti_search.cfm?dltype=5
Once there, type in EZ-ZONE for a keyword at the
bottom of the page and then click on the search button
to find the user manual.
Internal Functions
Functions use input signals to calculate a value. A
function may be as simple as reading a digital input to
set a state to true or false, or reading a temperature to
set an alarm state to on or off. Or, it could compare the
temperature of a process to the set point and calculate
the optimal power for a heater.
To set up a function, it’s important to tell it what
source, or instance, to use. For example, an alarm may
be set to respond to either analog input 1 or 2 (in-
stance 1 or 2, respectively).
Outputs Functions
Outputs can perform various functions or actions in
response to information provided by a function, such
as operating a heater, driving a compressor, turning a
light on or off, unlocking a door, turning on a buzzer
etc...
Assign an output to a Function in the Output
Menu or DIO Menu. Then select which instance of
that function will drive the selected output. For exam-
ple, you might assign an output to respond to alarm 2
(instance 2).
You can assign more than one output to respond to
a single instance of a function. For example, alarm 2
could be used to trigger a light connected to output 1
and a siren connected to digital output 5.
Input Events and Output Events
Input and output events are internal states that are
used exclusively by profiles. The source of an event
input can come from a real-world digital input or an
output from another function. Likewise, event outputs
may control a physical output such as an output func-
tion block or be used as an input to another function.