Ultrasound Technologies PD1 series, Руководство по обслуживанию

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Ultrasound Technologies Ltd
With the exception of the 2MHz Fetal transducer, the electronics are housed in the main
audio unit.
The oscillator and detector are built up of four discrete sections. These are the master
oscillator, transmitter amplifier, receiver amplifier and detector.
These operate to produce a pulse wave ultrasound signal that is passed to the transmitting
crystal in the transducer.
The signal is then reflected from moving interfaces within the body to the receiver crystal in
the transducer, amplified and then detected so the audio Doppler shift of that moving interface
can be heard audibly and / or converted into a velocity signal.
3.5
6 5
Oscillator and Transmitter Amplifier
Field effect transistor Q2, with L1, C16, C17 and associated components form a Colpitts
oscillator. This oscillator runs at a nominal frequency of 2, 5 or 8MHz producing a pulse wave
of amplitude of approximately 5V Pk.
The signal is then fed to output transistor Q3 that drives the transmitter crystal in the
transducer. The output power is set by VR1. The signal is fed to the transducer via a tuned
transformer L2 (C23), the output impedance of which is set correctly to match the transducer
crystal impedance. The output drive signal is nominally 1.5V Pk.
3.6
6 6
Receiver and Detector
The reflected Doppler signal is fed via a resonant transformer L4 (C25) to the gate of Q5, the
drain of this FET connects to the source of Q4 to form a cascode amplifier the drain of which
contains the resonant circuit L3,(C21).
From the drain of Q4 the amplitude complex of the received signal is detected by passing the
signal through diode D2 with the high frequency signals being filtered by R12 and C15.
The raw low frequency complex is then amplified and filtered by U1 where its associated
components form a band pass filter amplifier with a bandwidth of 150Hz to 1KHz for the
obstetrics or 300Hz to 4KHz in the vascular transducer.
This signal is passed to the audio unit via the retractile cable.
3.7
6 7
Audio Amplifier
The audio signal is routed via the retractile cable to J4 pin 4 on the audio circuit board. The
signal passes through the potentiometer VR1 to the audio amplifier U2, where it is amplified
and output to the loudspeaker connected to J3.
3.8
6 8
Velocity Processor (PD1V Model Only)
The audio signal is fed from the band pass amplifier (U5) through the threshold control VR3 to
the V to F converter (U3).
The conversion factor is 0.5V/ KHz with fine adjustment provided by VR2.
The output of this circuit is then scaled by R4, 6 to a suitable voltage level for most ECG
machines and recorders.
©Ultrasound Technologies Ltd Page 12 of 32
PD1 / FT120 service manual Issue 3 January 2007