Applications Guide Tracer Graphical Programming - Trane

®
Chapter 4 Cooling tower with two-speed fan example
3. Connect the Sump Temp input block and the 32.0 constant block to
the Less Than or Equal block.
4. Connect the Sump Temp input block and the Sump Alarm Setpoint
variable block to the Less Than block (Figure 52).
Figure 52: Comparing the sump temperature to the alarm setpoint and
the freezing point
Timing the sump temperature alarm
From the sequence of operation, you know that the sump temperature
must be less than the Sump Alarm Setpoint for 15 minutes before indicating
an alarm. For applications involving time-based control, take advantage
of the Time Delay blocks.
Time Delay blocks provide time-based control functions using program
cycles to measure time. These blocks require a program run frequency to
operate correctly. For further definitions of the time delay blocks behavior,
see the online Help.
For example, you could use the Delay on Start block to delay a binary on
signal for a specified amount of time based on a binary-input on signal.
The delay timer starts when a change in state (from off to on) occurs in
the controlling binary-input signal. After the delay time passes, the output
signal follows the input signal. In the Delay on Start block properties
dialog box, set the delay time units as seconds, minutes, or hours and use
another Constant or Variable block to represent the amount of time.
Figure 53 illustrates how the Delay on Start block works. The letter “t”
represents the delay time.
Figure 53: Delay on start timing diagram
Add a Delay on Start block and connect its On/Off Control port to the output
of the Less Than block. Use a Constant block to supply the time interval
value. Remember to use the Delay on Start block properties dialog box
to set the delay time interval units to minutes.
56 CNT-APG001-EN