In order to ensure that at least some of the tools to 12 4) in a string of tools that is permanently installed in an oil well are kept in operation even in {HEAD ~ the event} of a localized fault, the link interconnecting the tools and a surface installation is subdivided into segments by {TAIL ~ switch members}  
In order to ensure that at least some of the tools to 12 4 ) in a string of tools that is permanently installed in an oil well are kept in operation even in { HEAD ~ the event } of a localized fault , the link interconnecting the tools and a surface installation is subdivided into segments by { TAIL ~ switch members }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH