6-15
tions. This component has an output proportion-
al to the differential pressure across the calibrated
restriction and the output is referred to as dP
(TP3 - delta pressure). With the unit in standby
only, dP is to be 0V. The PABS & dP signals are
processed by an analog multiplier (U6), which
results in a product term called “Q” (measured
flow) at the cathode of D5 that is linearly propor
-
tional to the mass flow rate.
With flow regulation, the voltage at D5 cathode
or Q will be approximately the same as VGAS. A
differential amplifier compares the difference in
VGAS and Q at U8D. Should Q be greater than
VGAS, U8-14 will be positive and when Q is less
than V
GAS, then U8-14 is negative. The integra-
tor, U8B has an output of opposite polarity of the
input (U8-6), and as an integrator, it controls the
time at which the flow response can occur. The
output of the integrator (U8-7) is always posi
-
tive with a range of approximately 1V (minimum
flow) to 12V (maximum flow). The transistor
Q2 is the driver for the proportioning control
valve.
The output signal labeled F
MEA is monitored by
the controlling microcontroller on the display
assembly. This signal is one-half of the PABS volt
-
age and is a means of allowing the system to mon
-
itor the argon back pressure. F
MEA has a range of
2V to 3.5V.
The output signal labeled FMON is watched by
the monitoring microcontroller on the display
assembly as a means of verifying the proportion
-
ing valve current is within specified limits for each
flow setting. FMON is calibrated at 4 lpm to be
2V. A loop failure that can cause flow to deviate
from the requested flow or a shorted driver will be
detected by FMON and the flow is inhibited by
shutting off the proportioning valve.
6.6.3 Smart Sense
The System 7500™ utilizes “Smart Sense” to
control the mass flow rate in different manners
for each of the flow modes when a partial or total
occlusion is detected. This discussion will be lim
-
ited to only Smart Sense response for each mode
and what causes actions to occur.
• Automatic Mode: When a partial occlusion is
detected in this mode, the flow rate is reduced
by 1 lpm increments; or until the maximum
back pressure occurs which will set an alarm.
Flow reduction only occurs for flow settings
greater than 4 lpm; and for all dial settings
that meet this criteria, the flow rate may
be reduced down to 4 slpm. If the partial
occlusion is removed, the flow will return to
the original setting. Any change in the flow
rate is displayed. A partial occlusion may be
caused when the tip of the handpiece is in
contact with the tissue, or by an accessory
that has a small exit orifice; or a reduced exit
orifice with a long nozzle. (NOTE: Some
accessories cannot be used in the Automatic
mode because the back pressure exceeds speci
-
fied limits - use manual mode instead.)
• Manual Mode: Smart Sense only tests for total
occlusions in Manual mode. An occlusion
alarm occurs with a back pressure greater than
7 psi within the argon flow tubes. This mode
will not override user settings.
• Endo Mode: This mode will reduce flow rates
when partial occlusions are detected, however
at a different rate and for a different reason.
With a flow setting greater than 2 lpm, a par
-
tial occlusion will reduce the flow rate down
to 2 lpm. When the dial for flow is set for 2
or less, then the flow will only be reduced by
.5 lpm. The purpose of the flow reductions
is to allow a GI probe to be connected, auto
-
matically sensed, and the flow rate adjusted to
optimize arc initiation.
6.7 Full Bridge Amplifier [A8]
Refer to Figure C-14 for this section. The Full
Bridge Amplifier assembly houses the power
switching devices (MOSFETS) that amplify
respective drive waveforms for Cut, Blend,
Bipolar, and Pinpoint modes of operation. The
power FETS are arranged in an “H-bridge” con-
figuration where two separate drive signals are
alternately switched on to develop a push-pull
action on the output transformer primary. The
drive signals are referred to as 01 and 02 (phase 1
and phase 2) and each drive signal has a reset that
is referred to as /01 and /02 (not phase 1 and not
phase 2).
Phase 1 (01) and Phase 2 (02) drive signals are
developed on the Power Control Assembly and
they are 180° out of phase. The /01 is turned on
immediately after 01 is turned off and the same
applies to /02. The /01 and /02 signals reset the
magnetics of T1 & T2 allowing a faster turn off of
the power devices. The drivers U1 & U2 step up
the drive voltage from 5V to 12V.
To Next Page
Loading...