To get automatic updates when the gate opens or closes, you need to configure the input in alarm mode (normally open or closed) and wire a simple on/off contact sensor between the input wire and ground. Also, the only child device giving an open/closed status is the digital input child device.
See this post
Configuring the input as analog is not really meant to do what you want although you might be able to do it if you configure the " minimal change to report" parameter to get a report when the analog voltage changes and create a OPEN/CLOSE variable based on those reports...
