Applications Guide Tracer Graphical Programming - Trane
Applications Guide Tracer Graphical Programming - Trane Applications Guide Tracer Graphical Programming - Trane
® Chapter 5 Cooling tower with variable-speed fan example sured variable increases. In this program, the fan speed increases when the cooling tower supply water temperature increases. 6. In the Error Deadband field, type: 0.5 Error deadband prevents the PID from changing when the measured value is within plus or minus this value of the setpoint. 7. Click to clear the Proportional Only check box. The Proportional Bias field remains unavailable. 8. Under PID Frequency, verify the value is 30 seconds. The PID Frequency defaults to the same frequency as the program. For this program, do not change the default frequency. But note that you may run a PID loop at the same rate as its parent program or at a slower rate. The time interval must be an integer multiple of the program run frequency. 9. In the Maximum field, type: 100 This field sets the maximum output of the PID loop to 100%. 10. In the Minimum field, type: 25 This field sets the minimum output of the PID loop to 25%. 11. In the Disable Position field, type: 0 When the Output Enable/Disable port of the PID block receives a value of false, the PID loop outputs the disable-position value. Otherwise, the PID loop outputs its calculated value. 12. In the Fail Safe Position field, type: 0 When the Fail port of the PID block receives a value of true, the PID loop outputs the fail-safe-position value. Otherwise, the PID loop outputs its calculated value. 13. Click OK. 92 CNT-APG001-EN
® Writing the cooling tower fan module Incorporating the PID block Add the necessary intermediate blocks and then make the PID block connections. To incorporate the PID block: 1. Place a Fail block in the design space and connect it so that it checks the measured variable, the supply temperature, for failure. Note: Wireless connections with input blocks do not pass the fail flag to the Fail block, so add an Input (Hardware) block for the supply temperature. 2. Place three constant blocks to serve as the proportional, integral, and derivative gains for the PID block. 3. Set the constant values to 4.0, 1.0, and 0.0, respectively. These values are place holders for the proportional, integral, and derivative gains. When you are writing a program for a specific job, determine the best values for that job. You could also use Variable blocks here so that you can tune the PID loop from the operator display. 4. Create a Wireless write block, name it FanStart, and connect it to the And block. Remember that Wireless blocks can be used to pass any type of analog or binary data. Use a Wireless block to pass a hardware input value or to pass the result of some arbitration. 5. Place a FanStart wireless read block in the design space and connect it to the Output Enable/Disable port of the PID block. When the PID block receives a true value here, it outputs its calculated result. When the PID block receives a false value here, it outputs its disable-position value. 6. Connect the Fail block to the Fail port of the PID block. When the PID block receives a false value here, it outputs its calculated result. When the PID block receives a true value here, it outputs its fail-safe-position value. 7. Connect the Supply Temperature input block to the Measured Variable port of the PID block. 8. Connect the Limit block to the Setpoint port of the PID block. 9. Connect the Constant blocks to the appropriate ports of the PID block. 10. Connect the PID block to the NO port of the Switch block. 11. Placecommentsinthedesignspacetoexplainthelogicofthemodule (Figure 95 on page 94). 12. Compile and save your program to check for errors and to preserve your work. CNT-APG001-EN 93
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®<br />
Writing the cooling tower fan module<br />
Incorporating the PID block<br />
Add the necessary intermediate blocks and then make the PID block connections.<br />
To incorporate the PID block:<br />
1. Place a Fail block in the design space and connect it so that it checks<br />
the measured variable, the supply temperature, for failure.<br />
Note:<br />
Wireless connections with input blocks do not pass the fail flag<br />
to the Fail block, so add an Input (Hardware) block for the supply<br />
temperature.<br />
2. Place three constant blocks to serve as the proportional, integral, and<br />
derivative gains for the PID block.<br />
3. Set the constant values to 4.0, 1.0, and 0.0, respectively.<br />
These values are place holders for the proportional, integral, and<br />
derivative gains. When you are writing a program for a specific job,<br />
determine the best values for that job. You could also use Variable<br />
blocks here so that you can tune the PID loop from the operator display.<br />
4. Create a Wireless write block, name it FanStart, and connect it to the<br />
And block.<br />
Remember that Wireless blocks can be used to pass any type of analog<br />
or binary data. Use a Wireless block to pass a hardware input value<br />
or to pass the result of some arbitration.<br />
5. Place a FanStart wireless read block in the design space and connect<br />
it to the Output Enable/Disable port of the PID block.<br />
When the PID block receives a true value here, it outputs its calculated<br />
result. When the PID block receives a false value here, it outputs<br />
its disable-position value.<br />
6. Connect the Fail block to the Fail port of the PID block.<br />
When the PID block receives a false value here, it outputs its calculated<br />
result. When the PID block receives a true value here, it outputs<br />
its fail-safe-position value.<br />
7. Connect the Supply Temperature input block to the Measured Variable<br />
port of the PID block.<br />
8. Connect the Limit block to the Setpoint port of the PID block.<br />
9. Connect the Constant blocks to the appropriate ports of the PID<br />
block.<br />
10. Connect the PID block to the NO port of the Switch block.<br />
11. Placecommentsinthedesignspacetoexplainthelogicofthemodule<br />
(Figure 95 on page 94).<br />
12. Compile and save your program to check for errors and to preserve<br />
your work.<br />
CNT-APG001-EN 93
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