Automatic update of exported calendar

Hi, I am new in this forum, I did a search but apparently I did not find a solution to my problem. At my institute we use a all-in-one evnt calendar and now we want to export it in a public google calendar and invite people to events, in order to allow people to integrate, if they like, the public google calendar into their private ones. Every thing seems to work finely, but when we modify the all-in-one calendar there is apparently no update in the exported data.
Could anyoone help us?
Thank you very much!