Add Rating to sharepoint list on site collecion using power shell

ShellScript:

[void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint") 
 $site = New-Object Microsoft.SharePoint.SPSite("http://sitecollection URL") 
 $web=$site.OpenWeb() 
 if ($web -ne $Null) 
 { 
       $AverageRating=$web.Fields[[System.Guid]"5a14d1ab-1513-48c7-97b3-657a5ba6c742"] 
       $RatingCount=$web.Fields[[System.Guid]"b1996002-9167-45e5-a4df-b2c41c6723c7"] 
       $PagesList=$web.lists["Pages"] 
       if ($PagesList -ne $Null) 
       { 
             Write-Host " Processing List : " $PagesList.Title 
             $ct=$PagesList.ContentTypes["Page"] 
             If ($ct -ne $null) 
             { 
                   Write-Host " Adding Rating columns to content type : " $ct.name 
                   $AverageRatinglink = new-object Microsoft.SharePoint.SPFieldLink $AverageRating 
                   $RatingCountLink = new-object Microsoft.SharePoint.SPFieldLink $RatingCount 
                   $ct.FieldLinks.Add($AverageRatinglink) 
                   $ct.FieldLinks.Add($RatingCountLink) 
                   $ct.update()               
             } 
       } 
 } 
 $web.Dispose()