Ultrasound Technologies Fetatrack 310, Руководство по обслуживанию

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Circuit Description
Fetatrack310 Service Manual Issue3
©Ultrasound Technologies Ltd, Lodge Way, Portskewett, Caldicot, South Wales NP26 5PS, United Kingdom.
T +44 (0) 1291 425425 F: +44 (0) 1291 427093 E: ultratec@doppler.co.uk W:
www.doppler.co.uk
Ultrasound Technologies Ltd
Signal Pre-processing
The detected audio complex is fed to U5 a bandpass amplifier where the filter
characteristics are arranged to reject signals below 150Hz and above 330Hz ,
and the output is taken do a digital AGC U3. The amplitude stabilised signal is
then amplified and full wave rectified by U2 . This full wave rectified signal is then
buffered and smoothed by an active filter. The smoothing is achieved by the low
pass active filter having a 3db at 5Hz hence giving the average value, or “power
envelope”, of the audio complex. This signal is then passed to the A/D converter
stage of the cpu U8 for further digital signal processing .
Ultrasound Channel 2
Ultrasound 2 is identical in operation to Ultrasound Channel 1 with only a change in
component references.
Toco Circuit
A stabilised 5V is fed to the toco transducer along with 0V which form the
excitation of a Whetstone bridge in the transducer. The Differential output of the
transducer is fed via a high gain differential amplifier U26 to a low pass filter U32
for signal smoothing into the A/D converter U11 further digital signal processing
U8.
Toco Zero is automatically adjusted by D/A converter U31 providing an offset
voltage into the input of U32 . Overall gain is adjusted by VR2.
Event Marker
The fetatrack 310 is supplied with a hand held event marker. This is a switch wich
when pressed connects an input on the microprocessor U8 to 0V via resistors
R110 and R106..