The transducer produces an output electrical signal proportional to {HEAD ~ the extent} to which {TAIL ~ the third laser beam energy} is absorbed by the propane gas 
The transducer produces an output electrical signal proportional to { HEAD ~ the extent } to which { TAIL ~ the third laser beam energy } is absorbed by the propane gas
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH