Applications Guide Tracer Graphical Programming - Trane

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Chapter 4 Cooling tower with two-speed fan example
Writing the sump heater module
Take another look at the part of the sequence of operation dealing with
control of the sump heater.
Cycle the sump heater if the sump temperature falls below 40°F (this
value is adjustable at the operator display). If the outdoor air temperature
falls below 32°F, turn on the sump heater continuously.
The programming elements required to accomplish this task, including
the following:
• Use a deadband to cycle the sump heater under normal operating conditions.
A deadband prevents excessive heater cycling.
• Use a comparison to keep the sump heater on continuously when the
outdoor air temperature is below the freezing point.
Adding the input blocks
Begin by adding blocks to represent the inputs to this part of the program.
Adding wireless connections
YouusedSumpTempandOutdoorAirTempinthealarmsmodule.
Instead of adding these blocks again or trying to connect to them from
another module, use wireless connections.
➤ Connecting blocks using wireless connections
Use wireless connections to pass data from block to block when wired
connections are impractical. In general, it is good programming practice
to use an input in a program only once. By doing so, you will have
an easier time debugging your program. By using the wireless connection,
you can also prevent long and overlapping wired connections
that are difficult to follow.
First create a wireless connection for the Sump Temp input.
To add a wireless connection:
1. From the Blocks menu, choose Wireless. The cursor changes to a
cross-hair (✛) inthedesignspace.
2. Click in the design space to place a Wireless block. The Wireless Connection
Properties dialog box appears (Figure 68 on page 67).
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