Utah Medical Products Finesse ESU-110, Service Manual

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switching circuit be electrically isolated from ground. To achieve this
result, optical isolators are driven by op amp comparators between
the hand switch wires and the generator logic elements. Between
periods of surgical activity the comparator outputs are low and the
optical isolators stay in the "off" condition. When one of the two
handswitches is activated, the corresponding comparator toggles high
and the optical isolator switches "on". When current flows through
either of these optical isolators, the various gates that activate the
450 kHz oscillator, select the appropriate output control voltage, pro-
duce the correct cut/blend or coag waveforms, and activate the vac-
uum motor, are enabled.
The footswitch operates an isolated circuit that is identical to the
handswitching circuit.
Downstream of the first level cut/blend and coag gates, another pair
of gates are used which are disabled in case of cross key activation.
This blocks output from the generator when both cut/blend and coag
switches are simultaneously activated and generates a high pitch tone
on the speaker.
Besides their functional purposes, the signals generated by the
switching logic circuits also trigger the visual and audible indications
of their operation. The logic board contains a group of switching
transistors that control the indicator lamps, amber for cut/blend, and
blue for coag. They also select the appropriate tone outputs from a
frequency divider driven by an audio frequency oscillator which,
together, constitute the audio frequency generator block. These tone
signals are routed to a FET which drives a speaker mounted on the
front panel. The lowest pitch tone denotes cut or blend. The next
higher pitch tone denotes coag, and the highest tones are reserved
for cross key, patient alarm, and output alarm functions.
Vacuum Motor Control Circuit
The vacuum motor circuit is activated by either the cut/blend or coag
switches. A voltage representing either cut/blend or coag operation
is applied to the trigger input of a timer chip connected in a mono-
stable mode. The output of the timer turns on a solid-state relay
which controls the current to the vacuum motor. At an adjustable
interval after cessation of output activation, the timer output goes
low and the vacuum motor is shut off. The nominal delay for turn-
off is five seconds which is adjusted by R102 on the logic board.
Patient Alarm Circuit
The patient alarm circuit monitors the continuity between the two
parallel leads that are used to connect the dispersive pads to the gen-
erator. If either lead breaks or is otherwise compromised such that
the impedance between the two leads becomes greater than about
300 ohms, the generator shuts down and both visual and audible
alarms are produced.
Detection of the patient safety alarm condition is accomplished by a
transistor with a transformer in its collector circuit whose secondary is
connected between the two dispersive pad leads. The base of the
transistor is driven with a square wave at approximately 44 kHz.
When the dispersive leads are intact, the secondary of the trans-
former in the collector circuit is shorted. If this circuit opens or
develops a high impedance, an AC potential is produced on the sec-
ondary. This is rectified and applied to an optical isolator which,
when turned on, activates a number of gates that shut down the RF
waveform generator, turn on the red alarm indicator lamp on the
front panel, and generate a high-pitch interrupted beep signal in the
audio frequency generator.
Output Alarm Circuit
An output alarm circuit is included to prevent excessive output
power in the event of a generator malfunction. This circuit is a
direct copy of the controlled output feedback circuit described previ-
ously. The circuit monitors the generator output and sends a signal
directly to the microprocessor, where it is compared to pre-pro-
grammed values in a table. Should the output exceed conditions
that are considered normal with respect to the output setting, the
microprocessor will disable all unit functions and enable the audio
alarm circuit. The Finesse
®
system must be shut off to clear this
problem.
Finesse Service Manual
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