Applications Guide Tracer Graphical Programming - Trane

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® Chapter 4 Cooling tower with two-speed fan example Figure 63: Latch Properties dialog box Figure 64: Alarm reset implemented 4. Under Mode, click the Manual option. 5. Click OK. The Latch block changes to include only Trigger and Cancel ports. 6. Connect the Or block to the Trigger port of the Latch block. 7. Connect the Alarm Reset variable block to the Cancel port of the Latch block. 8. Connect the Latch block to the Alarm output block (Figure 64). 62 CNT-APG001-EN
® Writing the alarms module Turning the alarm reset off automatically The source for the Alarm Reset binary variable is both the operator display/service tool and the program. The ability to apply both control sources to a variable makes what you are about to do possible. To reset an alarm condition, the operator changes the value of the Alarm Reset variable from off to on. In the current form of the program, after the alarm resets, the operator is required to change the Alarm Reset variable from on to off. If the operator neglects this last step, subsequent alarms will reset automatically without being addressed. But you can eliminate this extra step with a little additional programming. See Figure 65. To turn the alarm reset off automatically: 1. Place a Constant block in the design space and assign the binary value OFF to it. 2. Place a Switch block in the design space and set it as binary. 3. Place a Variable block in the design space and assign the binary variable Alarm Reset to it. 4. Set the Alarm Reset variable block to be a write variable. 5. Connect the first Alarm Reset variable block to the Relay Control port of the Switch block. 6. Connect the OFF constant block to the NO port of the Switch block. 7. Connect the output port of the Alarm Reset variable block to the NC port of the Switch block. 8. Connect the Switch block to the second Alarm Reset variable block (Figure 65). 9. Compile and save your program to check for errors and to preserve your work. Figure 65: Alarm reset module As you go through the logic, make the initial assumptions that no alarm conditions exist and that the Alarm Reset variable is off. Upon the detection of an alarm condition, such as a temperature sensor failure, the Trigger input of the Latch block becomes true. This turns on the Alarm binary output. Because the Alarm Reset remains off at this point, the Switch block passes the value of the Alarm Reset variable itself, essentially its own value. The operator may observe the alarm at this point and, after correcting the situation that caused the alarm, changes the Alarm Reset to on. First, the Cancel port of the Latch block becomes true, turning the Alarm output CNT-APG001-EN 63
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Applications Guide Tracer Graphical
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CNT-APG001-EN ®
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® Special notifications and format
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® Contents Arrangingblocks........
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® Contents Chapter 5 Cooling tower
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® Contents Chapter7 Constant-volum
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® Contents Summary-question answer
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® Figures Chapter3 Modifyingtheexh
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® Figures Figure 96: Input blocks
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® Figures Chapter 8 Constant-volum
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® Tables Chapter7 Constant-volumeA
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® Chapter 1 Using the Tracer Graph
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® Summary-question answers PROGRAM
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® Index dehumidification, 166-169,
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Applications Guide Tracer Graphical Programming - Trane

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