How to raise the trigger if the data for the period are the same?

I have an item, where stored an information of the form "Thu Apr 05 14:22:09 2018". Interval 30 minutes. I need to raise zabbix trigger if this item not change information for the day.

Solution

Zabbix cannot compare textual values in a reasonable way. I'd suggest changing the item to store Unix timestamp instead of the human readable string and then using the delta() trigger function.