Watlow D4T Data Logger
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6
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Chapter 1 Overview
Note:
In this configuration, the heat output of the control function would be uninterrupted if an
alarm were to occur.
You will find more detailed information regarding the function blocks and how they work fur-
ther on in this document.
Inputs
The inputs provide the information that any given programmed function can act upon. In a
simple form, this information may come from an operator pushing a button, or as part of
a more complex function it may represent a remote set point being received from another
zone.
Each universal input can be configured for thermistors, thermocouples, or RTDs to read the
process variable. They can also read mV/volts, current or resistance, enabling usage of various
devices to read humidity, air pressure, operator inputs and other values. The settings associ-
ated to each analog input must be configured to match the device connected to that input.
Each digital input reads whether a device is on or off (voltage or resistance) and each system
can be equipped with multiple digital I/O modules. Each I/O point must be configured to func-
tion as either an input or output.
Functions
Functions use input signals to calculate a value and or performs an action. A function may be
as simple as reading a digital input as on or off, or reading an analog value (temperature) to
set an alarm state to on or off. As an example, a user could use sensor backup to avoid an un-
wanted shutdown if a failure with the primary sensing device should occur.
Keep in mind that a FB can be a purely internal function (i.e., control loop, alarm, logic,
etc...), while they can also serve as a connection point between real-world devices (i.e., ther-
mocouple, heater etc...) and internal functions like a Universal Input connected to the Control
Loop PV input. To have an effect outside of the data logger, an output FB must be configured
to respond to some other function. Functions and all associated dependencies would be con-
figured using Composer software. To learn more about setting up function blocks see Chapter
2 of this document in the section titled "
Configuring the Application with the Function Block
".
