THEORY OF OPERATION
4-2
Versapulse Select Service Manual
0621-499-01 01/94
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Once the system operating parameters are selected, the user selects the READY mode, positions the fiber
output at the treatment site, then depresses the footswitch to deliver treatment pulses at the rate and energy
selected. The treatment delivery will continue until the footswitch is released. Note that the Versapulse Select
does not require any ramp up firings before delivering treatment pulses - the shutter opens and treatment
delivery begins without delay.
Fault monitoring continues for as long as the system is turned on, and any detected fault is reported on the
touch screen.
An emergency off button is located on the console next to the key switch. Depressing it will turn the system
off.
4.1.2 Functional Overview
There are several models of Versapulse Select in (or planned for) production. The primary difference be-
tween the models is the maximum average power available. The Versapulse Select can hold up to four
Ho:YAG rods. The maximum average power the system provides is determined by the number of rods used.
The lower power systems do not have all four rods installed. The remainder of this subtopic will describe the
Versapulse Select with four rods installed. Lower power systems operate in the same manner, but with fewer
rods.
Refer to the Versapulse Select Simplified Block Diagram. The Versapulse Select has four identical Ho:YAG
cavities arranged in a 2x2 matrix. Each cavity includes its own rod, flash lamp, high reflector, output coupler
and set of two relay mirrors. The rods are operated sequentially - never together - thus each rod is capable of
producing the maximum selectable pulse energy (2.8 Joules). Each rod delivers every fourth pulse. This
sequential firing allows the Versapulse Select to provide four times the pulse rate as could be provided by a
single rod, increasing the maximum average power available by the same factor (four).
For example, at the 40 Hz pulse rate, each rod is operating at 10 Hz, and is producing 1/4th of the average
power. As a result, the Versapulse Select provides higher selectable pulse rates and higher average powers
without requiring the extreme rod cooling as would be required in a single rod system at the same operating
point.
The use of multiple heads results in a number of advantages over previous surgical Ho:YAGs: Versapulse
Select is smaller and lighter; it has a much simpler and more reliable cooling system; and it can operate at
much higher pulse rates, resulting in higher average powers.
While the use of multiple heads provides all the above mentioned user advantages, it also results in several
design challenges:
Flash lamp supply switching - The Versapulse Select uses a capacitor discharge to supply the current
required to flash the lamps. The voltage level of the charge on the capacitor determines the amount
of light energy out of the lamp, and therefore the pulse energy out of the rod. A vendor supplied high
voltage power supply charges the capacitor between pulses. Using four heads requires a method of
switching the charging supply current between the four flash lamps. The Versapulse Select uses
SCR's to switch the charging supply current between the four heads.
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