Utah Medical Products FINESSE +, Руководство по обслуживанию

Страница: 32 / 54

28
Service Manual
width on this PWM is also determined by lookup tables in the microprocessor, and is also used to
control the output power and provide the appropriate output wave shape. A second FET drives
the output of this circuit.
The RF output is coupled to the active and dispersive output terminals through series capacitors
in both leads. In combination with the output transformer, this results in an electrosurgical
output which is RF isolated from ground and which is incapable of conducting low frequency
currents which may cause serious neuromuscular stimulation in the patient.
Controlled Output Circuitry
+
Monitoring and Error Detection
Controlled Output Ci (COC+) is a three-tier output monitoring curcuit, and is an important
element in the 's performance.
The first tier of COC+ attempts to minimize variation in the peak output voltage so that a
consistent tissue effect is realized, for example, when using a loop electrode. A high voltage high
frequency rectifier across the output transformer terminals on the RF Power Amplifier Board
produces a signal that corresponds to the peak output voltage. The signal is optically isolated and
read by the microprocessor. The microprocessor compares the signal to a lookup table value
based on the output and mode settings and implements an algorithm that adjusts the Buck PWM
in order to maintain the output peak voltage under low output load resistances. This prevents
suppressed peak output voltages that cause desiccation and significant thermal effects on tissue.
A high voltage shunt monitor exists on the Buck PWM supply. This provides the microprocessor
with output voltage and current data for monitoring the output power. The microprocessor
continuously monitors these two signals and compares their product to values in a lookup table
(which have been calculated according to the requirements of electromedical safety standard IEC
60601-2-2:2009 sec 12.4) for protection against hazardous output. COC+'s second tier provides
protection against excessive output by use of both firmware and hardware. The
firmware complares the output power and current level to an absolute limit defined in lookup
tables that are based on the output setting. When this limit is reached, the microprocessor will
first attempt to correct the output via the COC+'s first tier circuit. The second protection is
provided by current limiting hardware that will shut off pulses in the Buck PWM circuit in an
attempt to lower the power available for modulation. If neither of these methods corrects the
situation, COC+'s third tier circuit will enable an output error indication. In this mode, the
system enters a 'lockdown mode' that is only corrected by toggling off the main power
switch.
COC+ circuits are instrumental in both protecting against high outputs and minimizing stress on
the output amplification components.
Handswitch and Footswitch Logic
The commonly available hand switching pencils for electrosurgery have three-wire connections to
the generator with independent single pole switches for cut/blend and coag. The active lead to
the electrosurgical implement is the common wire for both switching functions. To maintain RF
isolation of the generator output, it is necessary that the handswitch pencil circuit be electrically
isolated from ground. To achieve this result, optical isolators are driven by op amp comparators