Data in the trend acquisition function block is sampled with the cycle time of the task the function block is running in. Additionally, in the parameters of the function block, you can set a Scan-Down Factor, which results in multiples of the task cycle time to be used for data sampling. Let's say the function block runs in a 500ms task. With a Scan-Down Factor of 10, the sample time would be 10 x 500ms = 5 seconds. To set it to 30 seconds you would need to set the Scan-Down factor to 60 to get a sample time of 30 seconds.