The following examples are similar, in that they all use a Schedule component to invoke a latch. Other components may be used to invoke a latch, however, any latch that is invoked using the Clock property must include a method for setting the Clock property status back to False before the Clock is available for latching again. Example 3 illustrates the use of a latch component's latch action instead of using the Clock property.
Example 1. Example 1: BooleanLatch Component
In this example, a building manager wants a record of days when the building has occupants that arrive before scheduled opening time of 6:00AM. This involves collecting the occupancy status from a building security system at the scheduled opening time once a day. The following illustration shows a BooleanLatch component (OccupancyState) being used to capture the occupancy status value at a 6:00AM (scheduled occupancy time) every day.
Note the following about this example:
-
A Boolean Schedule (OccupancySchedule) Out value is linked to the BooleanLatch Clock property and a Boolean Out value from the "Occupied" boolean point is linked to the BooleanLatch In property.
-
At 6:00AM, the OccupancySchedule Out value changes to True and sets the Clock property to True, causing the BooleanLatch component to "latch" the 6:00AM In value into the Out property.
-
The BooleanLatch component Out property is linked to the BooleanWritable (OccRecord) component which can record the value using a history extension.
-
At 6:00PM the Schedule Out value changes to False and sets the Clock property to False from True. No latch occurs here since the Clock property only latches on the "rising edge" (False to True). No change is made in the Out value until the Clock property status changes again from False to True - scheduled for 6:00AM the next day.
Example 2. Example 2: NumericLatch Component
This example involves collecting the return air temperature value once a day according to a scheduled building opening time. The following illustration shows a NumericLatch component (StartTempLatch) being used to capture the return air temperature value at a specific time (scheduled occupancy time) every day.
Note the following about this example:
-
A Boolean Schedule Out value is linked to the NumericLatch Clock property and a Numeric Out value from the ReturnTemp numeric point is linked to the NumericLatch In property.
-
At 6:00AM, the Schedule Out value changes to True and sets the Clock property to True, causing the NumericLatch component to "latch" the 6:00AM In value into the Out property.
-
The NumericLatch component Out property is linked to the NumericWritable (StartTemp) component which can record the value using a history extension.
-
At 6:00PM the Schedule Out value changes to False and sets the Clock property to False from True. No latch occurs at this time and no change is made in the Out value until the Clock property status changes again from False to True (scheduled for 6:00AM).
Example 3. Example 3: NumericLatch Component Latch Action
This example involves collecting the return air temperature value twice a day according to scheduled building opening and closing times. The following illustration shows a NumericLatch component (StartTempLatch) being used to capture the return air temperature value at two specific times (scheduled occupancy time and scheduled un-occupancy) Monday through Friday. This example is similar to Example 1 except that the Schedule Out value is linked to the NumericLatch "Latch" action.
Note the following about this example:
-
A Boolean Schedule Out value is linked to the NumericLatch Clock property and a Numeric Out value from the ReturnTemp numeric point is linked to the NumericLatch In property.
-
At 6:00AM and at 6:00PM, the Schedule Out value changes to True or to False, respectively. In each case this status change invokes the latch action, causing the NumericLatch component to "latch" the In value into the Out property.
-
The NumericLatch component Out property is linked to the NumericWritable (StartTemp) component which can record the values using a history extension.
-
A Trigger Schedule may be simpler to use in this example. Using a Trigger Schedule, you can simply define the two time in the day that you want trigger the latch. The Boolean Schedule requires start and stop times for each event.