Applications Guide Tracer Graphical Programming - Trane

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Chapter 5 Cooling tower with variable-speed fan example
Figure 97: Output blocks for the condenser water pump module
2. Place a Variable block in the design space and assign the binary variable,
Pump Fail (sourced from the program and a write variable), to it
(Figure 97).
Determiningwhentostartandstopthepump
To simply start the pump based on the request, you could connect the
Condenser Water Request directly to the Pump Start/Stop output. However,
control of the pump is also dependent on the flow status. If flow is
not confirmed in 30 seconds following the request for flow, the pump must
be controlled to off. Furthermore, an alarm indication is required. A block
exists specifically for this purpose—the Feedback Alarm block.
Adding a Feedback Alarm block
The Feedback Alarm block compares the status of a binary input, output,
variable, or other binary value to a requested state. The binary output of
the Feedback Alarm block is determined by the selected relationship
between the status and the request. Using the properties dialog box for
the Feedback Alarm, configure the block with one of the following three
relationships:
• Request XOR Status
• Request AND NOT(Status)
• NOT(Request) AND Status
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