If you add a trigger setting, the point you are configuring is updated only when the trigger condition evaluates to TRUE.

Example

You configure a point that requires an update for logging purposes.

If the update needs to be hourly, but the device is being scanned every quarter hour for other purposes:

Use a device Trigger Point that is configured with a one-hour scan rate .

If the update needs to occur when a particular condition changes:

Use a Device point that represents the condition and is configured to be updated On Change

Settings for the trigger point are as follows:

1	Trigger point.
2	Relation
3	Value

 

1	Trigger point

A Trigger Point is another device point that serves as the trigger for the point being configured.

The point being configured is updated only when the trigger is updated.

Trigger points can be used to:

Coordinate or direct the sampling frequency of device points, (or the calculation frequency of virtual points).

Example

Data needs to be collected from point PLC1 at an interval signaled by a ready bit on the PLC.

Trigger Settings and Scan Rate for PLC1 are as follows:

At runtime, PLC1 will only be updated while the point PLC1_READY is equal to 1.

Make the system more efficient by reducing the amount of data that needs to be managed by the data collection functions.

Example

For every contiguous sixteen bits of inputs or outputs on a Series 90-70 PLC, a single analog point that overlaps them uses On Scan as the Update Criteria.

The trigger settings and scan rate for each of the digital points has the following configuration.

Update Criteria	On Change
Trigger point	ANALOG1 (with On Scan update criteria)

If the trigger point ANALOG1 does not change frequently there is a performance benefit because the digital points will only be updated when the analog point changes.

The trigger point's Update Criteria determines when triggered reads take place.

The criteria can be either when:

The trigger point value changes or

When the trigger point is scanned.

You make this selection when the trigger point is configured.

Example

You are configuring a point that requires an update for logging purposes.

If the update needs to:	Use a:
Be hourly	Device Trigger Point that is configured with a one-hour scan rate.
Occur when a particular condition changes	Device point that represents the condition and is configured to be updated On Change

Important: (For device points) triggers must be:

A configured device point.

On the same port as the points it is triggering. The points may be on different devices, but the devices must be on the same port.

2

Relation

The Relation field specifies how the trigger point will be evaluated.

Options are:

Option	Trigger is active when the trigger point's value:
None	Triggering will not occur.
Equal	Equals Value.
Greater Than	Is greater than Value.
Greater Than Equal	Is greater than or equal to Value.
Less Than Equal	Is less than or equal to Value.
Less Than	Is less than Value.
On Change	Whenever the Trigger Point is changed.

 

3

Value

The value the trigger point will be compared with the entered Value to determine if the trigger condition has been met.

Result: The trigger condition is evaluated each time the trigger point is polled, so effectively, this point is polled at the trigger point's scan rate while the trigger condition is true.

More information

Step 3.2. Enter device point advanced device properties.

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