Watlow EZ-ZONE PM - Manual (Page 7)

Watlow EZ-ZONE ® PM Limit Controller • 4 • Chapter 1 Overview
A Conceptual View of the PM
The flexibility of the PM’s software and hardware allows a large range of configurations. Acquiring a better
understanding of the EZ-ZONE ® family controller’s and their overall functionality and capabilities while at
the same time planning out how the controller can be used will deliver maximum effectiveness in your appli-
cation.
It is useful to think of the controller in three parts: inputs, procedures and outputs. Information flows
from an input to a procedure to an output when the controller is properly configured. A PM limit controller
can carry out several procedures at the same tim, for instance, monitoring for several different alarm situ-
ations, monitoring and acting upon digital inputs and driving output devices such as lights and contactors.
Each process needs to be thought out carefully and the controller’s inputs, procedures and outputs set up
properly.
Inputs
The inputs provide the information that any given programmed procedure can act upon. Simply stated, this
information may come from an operator pushing a button or from a sensor monitoring the temperature of a
part being heated or cooled.
Each analog input typically uses a thermocouple or RTD to read the process temperature. 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 config-
ured to match the device connected to that input.
Each digital input reads whether a device is active or inactive. A PM with digital input/output hardware
includes two sets of terminals where each of which can be used as either an input or an output. Each pair of
terminals must be configured to function as either an input or output with the direction parameter in the
Digital Input/Output Menu (Setup Page).
The Function or EZ Key/s (PM4/6/8/9 only) on the front panel of the PM also operates as a digital input by
toggling the function assigned to it in the Digital Input Function parameter in the Function Key Menu (Set-
up Page).
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, if a failure with the
primary sensing device should occur the limit could trip a contactor removing power from the heating ele-
ment to avoid damaging the load.
To set up a function, it’s important to tell it what source, or instance, to use. For example, if the control is
equipped with digital inputs they can be configured as an alarm. If configured as such the next step would
be to define which of the four available alarm instances this digital input would be tied to. So, in this exam-
ple the source would be Digital Input 5 or 6 where the instance would be selected as 1, 2, 3, or 4 correspond-
ing to the alarm instances.
Keep in mind that a function is a user-programmed internal process that does not execute any action outside
of the controller. To have any effect outside of the controller, an output must be configured to respond to a
function.
Outputs
Outputs can perform various functions or actions in response to information provided by a function, such as
removal of the control voltage to a contactor; turning a light on or off; unlocking a door; or turning on a buzz-
er.
Assign an output to a Function in the Output Menu or Digital Input/Output Menu. Then select which in-
stance of that function will drive the selected output. For example, in using a Limit Control an output can be
configured to respond to an alarm, i.e., (instance 4) or to a limit condition.
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.