### To collect trend data for a point Before you can see a point's trend graph, you must enable trending for that point and then define how you want the controller to collect the point's data. This can be done in the EIKON® application or you can do it in the WebCTRL® interface using the instructions below. NOTE I/O microblocks have trending capability built-in, and you enable trend logging in the I/O microblock. Any other microblock value must have a trend microblock attached in the control program, and you enable trend logging of the value in the trend microblock. To set up a point's trending in the WebCTRL® interface: On the Geographic tree, select the equipment that has the point you want to trend. Click the Trends button drop-down arrow, select Disabled Points, then select the point. On the Enable/Disable tab, check Enable Trend Log. Enter information in the appropriate fields. See table below. Click Accept. TIP You can set up all trends for a piece of equipment at once on the Trend Sources tab of the equipment's Properties page.
Field | Notes
--- | ---
Sample every _:_:_ (hh:mm:ss) | Records the point’s value at this interval. NOTE Set trend intervals for U line controllers to one minute or greater. U line controllers are designed to meet low end, high volume terminal control applications and are not suited to very short trend intervals.
Sample on COV (change of value) | Records the point’s value only when the value changes by at least the amount of the COV Increment. NOTE Use this method for a binary point or for an analog point that has infrequent changes in value.
Max samples | The maximum number of samples that you want the controller to store. CAUTION Changing the value in Max samples will delete all of the point's trend samples currently stored in the controller. Click the Store Trends Now button before changing the value to transfer the trend data from the controller to the system database. NOTES Trending consumes memory in the controller. The amount of memory available depends on the type of controller. Each trended point consumes 48 bytes of memory plus 10 bytes for each trend sample. Each trend microblock consumes 416 bytes of memory plus 10 bytes for each trend sample. Click Reset to delete all samples currently stored in the controller.
The above sample and memory allocation fields together define trend data storage in the controller in terms of hours. EXAMPLE If you set these fields so that samples are collected every 5 minutes for a maximum of 120 samples, the controller will store 600 minutes (5 x 120) or 10 hours of trend data.
Stop When Full | Check this field to stop trend sampling when the maximum number of samples is reached.
Enable trend log at specific times only | Collects trend data for the specific period of time you define in the time and date fields.
Enable Trend Historian | Archives trend data to the system database.
Store Trends Now | Writes all trend data in the controller to the system database without having to enable trend historian.
Write to historian every __ trend samples | Writes all trend data in the controller to the system database each time the controller collects the number of samples that you enter in this field. This number must be greater than zero and less than the number entered in the field Max samples. The number of trends specified must be accumulated at least once before the historical trends can be viewed.
Trend samples accumulated since last notification | Shows the number of samples stored in the controller since data was last written to the database.
Last Record Written to Historian | Shows the number of trend samples that were last written to the database.
Keep historical trends for __ days | This is based on the date that the sample was read. Select the first option to use the system default that is defined on the System Settings > General tab. Select the second option to set a value for this trend only.
Delete | Deletes all trend samples stored in the database for the item selected on the Geographic tree.
BACnet Configuration | The Object Name is a unique alphanumeric string that defines the BACnet object. Although the Object Name field can be edited, it is not recommended. The Notification Class is set to 1 to receive alarms generated by Automated Logic® controllers.
NOTES You can use Global Copy to copy trend properties to other pieces of equipment that use the same control program. Run a Trend Usage report to view trend configurations.