sensing the temperature of {TAIL ~ reaction products} at {HEAD ~ said outlet side} of said tube bundle; and 
sensing the temperature of { TAIL ~ reaction products } at { HEAD ~ said outlet side } of said tube bundle ; and
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH