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