Photoacoustic measurement system
The photoacoustic measuring system consists simply of the aforementioned piezoelectric transducer (CM) connected first to an ultrasonic pre-amplifier (CP) and then to a digitizing oscilloscope (O). The oscilloscope, together with the remaining main measuring devices of the calorimeter (see below), is interfaced with a personal computer (PC) running a home-made program which controls the data acquisition during the photoacoustic experiments. The transducer (Panametrics V101-RB) has a characteristic frequency of 0.5 MHz. The photoacoustic signals detected by the transducer are first amplified (Panametrics 5662) with a gain of 34 dB and then digitized and stored in the oscilloscope (Tektronix 2430A), with 8 bits resolution. All the connections are made with shielded coaxial cables (BNC50, Tektronix 012-0057-01). The optical trigger sets off the acquisition by the oscilloscope, which communicates with the computer through a GPIB interface (Keithley KPC-488.2AT). A home-made program then syncs all the remaining devices acquisitions with the oscilloscope.
 |
|
 |
 |
Figure 1. Details of the calorimeter cell (CC) and photoacoustic measurement system, showing the oscilloscope (top), the calorimeter microphone (CM), the calorimeter preamplifier (CP), the pyroelectric probe (P), and the probe preamplifier (PP).