Applications Guide Tracer Graphical Programming - Trane

®
Chapter 3 Modifying the exhaust fan program
5. Add a comment below the Deadband block indicating its mode for documentation
purposes (Figure 34).
Figure 34: Program with Deadband block
Deadband block
Adding a variable
In the first version of the Exhaust Fan program, you used a constant
value as the temperature setpoint. In this scenario the operator must be
able to adjust the setpoint using the operator display. Use an analog variable
to incorporate this functionality. For more information on using constants
and variables, see “Constants and variables” on page 19.
➤ Reading from and writing to a variable using the variable
block
Read and write privileges depend on the selected variable and its
source. Read refers to the ability of a program to know the value of
the variable. On the other hand, write refers to the ability of a program
to change the value of a variable. Table 4 summarizes the rules
regarding reading from and writing to variables in graphical programming.
See the Tracer MP580/581 Programmable Controller Programming
guide (CNT-SVP01A-EN) for more information about
variables and control sources.
Table 4: Variable block read or write rules for each control source
Source
Read
Write
Program X X
Tracer Summit
X
Operator display/service tool
X
Operator display/service tool
and program
X
X
To add a variable:
1. Move the 85.0 constant block and the Equip Rm Temp Setpoint comment
down to make space for a variable block.
2. From the Blocks menu, choose Input/Output. From the Input/Output
menu, choose Variable.
34 CNT-APG001-EN