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MONITORING 
duce the time when the voltage is applied. This 
can be done by applying voltage pulses of short 
duration compared to the period between them. 
The power input will then be greatly reduced. 
Using this method, the transducer output can 
be sampled only during the excitation period of 
the pulses, and the pulse rate will determine the 
frequency response of the system. Because the 
highest frequency in physiological pressure sig- 
nals is 25 hz, a pulse rate of 200 pulses/sec was 
decided upon. The pulses had a duration of 200 
(microsec.) and were 5 volts in amplitude. 
The average power input to the transducer 
was reduced by a factor of 25 below that of a 5- 
volt D-C excitation. A diagram of the system 
used is shown in Figure 4. From the pulse gen- 
erator, the pulse is fed into a pulse filter and 
amplifier. The amplifier is used to provide suffi- 
cient power to drive the transducer bridge, and 
the pulse filter was found necessary in order to 
round off the sharp edges of the pulse by filter- 
ing the pulse at frequencies lower than 10 kilo- 
cycles. This was necessary because slight differ- 
ences in pulse shape detected by the differential 
amplifier from each side of the transducer 
bridge could drive the amplifier into saturation. 
The pulse was also delayed and narrowed and 
used as the trigger for the track and hold cir- 
cuit which samples the output voltage during 
the excitation period. This method also allowed 
PRESSURE 
SIGNAL 
PULSE 
GENERATOR 
PULSE 
DELAY 
AND 
NARROWER 
SIGNAL 
SMOOTHER 
AND 
AMPLIFIER 
PULSE FILTER 
AND 
AMPLIFIER 
FiGTOE 4. — Functional block diagram for a pulse-driven catheter tip pressure transducer. 
