Photoacoustic detection system with differential amplifier for determing target species presence and triggering fault

A photoacoustic detection system comprising:

• a detector including,
• a chamber having an inlet and an outlet for flow of an analyte,
• a pulsed light source adjacent the chamber, the pulsed light source, when operated, emitting a light beam along a path through the chamber,
• a plurality of piezoelectric tuning forks arranged along the path, each of the piezoelectric tuning forks operable to emit first sensor signals,
• a photosensor arranged along the path and operable to emit second sensor signals;
• and
• a controller connected to receive the first and second sensor signals, the controller configured to:
• (a) determine whether a target species is present in the analyte based on the first sensor signals, and
• (b) determine whether the target species is present in the analyte based on the second sensor signals,
• the controller including a differential amplifier connected to receive the first sensor signals of each of the first and second piezoelectric tuning forks, the differential amplifier subtracting the first sensor signals of the second piezoelectric tuning fork from the first sensor signals of the first piezoelectric tuning fork, wherein the first sensor signals of the second piezoelectric tuning fork are out of phase with the first sensor signals of the first piezoelectric tuning fork, to produce differentiated sensor signals, wherein the controller makes the determination in (a) based on the differentiated sensor signals, and the controller is further configured to trigger a fault based on comparison of the determinations in (a) and (b), wherein the fault is triggered if there is a negative presence determination in (a) and a positive presence determination from (b) and the fault is triggered if there is a positive presence determination in (a) and a negative presence determination from (b).