PLECS uses the FlexNet Publisher (previously FLEXlm) license server program for concurrent licenses, which is provided by Flexera Software. There is quite a bit of information online about different management options.
I use now a batch file and lmutil.exe
With the command “lmutil lmstat -a -c 27000@[ServerAdress]” you can get the users with use the license at the moment. Put you servername or IP-adress in [ServerAdress].
or with the GUI lmtools.exe as described in the Link of Bryan. But I need administrator rights for this.