Applications Guide Tracer Graphical Programming - Trane

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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