When {HEAD ~ the preconcentrator} has {TAIL ~ such a resistor}, a proportional integral differential controller may be used to control the preconcentrator temperature 
has
When { HEAD ~ the preconcentrator } has { TAIL ~ such a resistor } , a proportional integral differential controller may be used to control the preconcentrator temperature
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH