Applications Guide Tracer Graphical Programming - Trane
Applications Guide Tracer Graphical Programming - Trane Applications Guide Tracer Graphical Programming - Trane
® Chapter 4 Cooling tower with two-speed fan example Implementing the alarm reset function The alarm reset function requires the introduction of a new block known as the Latch block. The Latch block, a member of the Time Delay blocks group, maintains a binary-output on signal for a specified amount of time or until it is cancelled. It may be configured as timed (Figure 59) or manual (Figure 60). Figure 59: Latch block in timed mode Figure 60: Latch block in manual mode For example, the Latch block in timed mode is often used to implement a timed override. You could use the Latch block in timed mode to control a binary signal for a specified amount of time. A trigger causes the countdown clock to begin and the signal to change. The trigger is a change in state (from off to on) of the controlling binary-input signal. Using the properties dialog box for the Latch block, select the units of time as seconds, minutes, or hours. In the timed configuration, the latch function may be resettable or non-resettable (Figure 63 on page 62). If the Latch block is set as resettable, it resets its countdown clock every time the input signal changes state (from off to on). If it is set as non-resettable, the Latch block maintains its countdown clock despite repeated input signal changes in state. Or you could use the Latch block in manual mode to output a binary signal indefinitely based on a change in state (from off to on) of a controlling binary-input signal. In either mode, the Cancel input turns the output of the Latch block off. See Figure 61 on page 60 and Figure 62 on page 61 for sample timing diagrams using the Latch block. The letter “t” represents the time interval. Figure 61: Latch block timing diagram, relationship between trigger and output 60 CNT-APG001-EN
® Writing the alarms module Figure 62: Latch block timing diagram, relationship between trigger, cancel, and output Adding a Latch block to control the alarm In this program, the Alarm output is to be turned on if any of the alarm conditions is true. And it is to be turned off by the user using the binary variable, Alarm Reset. The Latch block in manual mode provides this functionality. Placing it between the Or block and the Alarm output block results in the following logic: Whenever the output of the Or block is true, the Latch will turn on and subsequently turn on the alarm output. Then when Alarm Reset is turned on, the Latch will turn off and subsequently turn off the Alarm output. To add a Latch block to reset the alarm: 1. Delete the connection between the Or block and the Alarm output block. 2. Place a Latch block in the design space. 3. Double-click the Latch block. The Latch Properties dialog box appears (Figure 63 on page 62). CNT-APG001-EN 61
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®<br />
Writing the alarms module<br />
Figure 62: Latch block timing diagram, relationship between trigger,<br />
cancel, and output<br />
Adding a Latch block to control the alarm<br />
In this program, the Alarm output is to be turned on if any of the alarm<br />
conditions is true. And it is to be turned off by the user using the binary<br />
variable, Alarm Reset. The Latch block in manual mode provides this<br />
functionality. Placing it between the Or block and the Alarm output block<br />
results in the following logic: Whenever the output of the Or block is true,<br />
the Latch will turn on and subsequently turn on the alarm output. Then<br />
when Alarm Reset is turned on, the Latch will turn off and subsequently<br />
turn off the Alarm output.<br />
To add a Latch block to reset the alarm:<br />
1. Delete the connection between the Or block and the Alarm output<br />
block.<br />
2. Place a Latch block in the design space.<br />
3. Double-click the Latch block. The Latch Properties dialog box appears<br />
(Figure 63 on page 62).<br />
CNT-APG001-EN 61
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