Valleylab CUSA EXcel-8 - Fundamentals of Operation; Interface Connectors; Ultrasonics Board-Ultrasonic Generator

Ultrasonics Board-Ultrasonic Generator
Voltage Regulators
There are voltage regulators for the isolated supplies. LM317 adjustable
regulators provide op amps with supply voltages with enough overhead
margin to output voltages in the required range. A switching regulator
boosts and regulates the 5V supply for the machine control and display
driver boards. This is necessary because the 5Vin signal is expected to dip
momentarily due to the voltage drop when the displays are lit up. A diode
placed around the regulator eliminates start up delay in the 5V supply for
the PLD. This sheet shows bypass capacitors as well as the independent
power shutdown driver circuits. The open collector output signals drive
an opto-isolator LED inside the power modules in order to shut off the
supplies.
Interface Connectors
J2 and J3 are the ultrasonics interface connectors. J1 is the 5V input power
supply connector. J5 is the power shutdown control connector. J4 is the
display board interface connector.
Ultrasonics Board-Ultrasonic Generator
Fundamentals of Operation
The CUSA EXcel ultrasonic generator is based on the principle of the
Wien Bridge Oscillator. The system has a non-inverting feedback loop to
establish the fundamental frequency of oscillation and an additional
negative feedback loop, which controls the amplitude of oscillation. The
fundamental oscillation component is a function of the resonant
frequency of the magnetostrictive handpiece.
Oscillation criteria for a Wien Bridge are that the gain around the loop
must add up to unity and the phase must add up to 360° or 0°. Only if the
gain is initially greater than unity and some perturbation (noise) in the
initial conditions of the system exists can startup occur.
The handpiece design uses the magnetostrictive and inverse
magnetostrictive effects. A magnetic field produces a small change in the
physical dimensions of ferromagnetic materials—on the order of several
parts per million in steel—-and, conversely, a physical deformation or
strain (or stress which causes strain) produces a change of the
magnetization in the material.
Much like a tuning fork excited by a “ping” or deformation, the handpiece
transducer—excited by these small deformations caused by the
magnetostrictive effect—resonates at an ultrasonic frequency. Linear
operation within this framework relies on biasing the magnetic field at 4
roughly linear point along the main B-H curve. The feedback signal,
sensing the change in the magnetic field produced by the inverse
magnetostrictive effect, is proportional to the deformation.
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CUSA
EXcel-8
System
Service
Man