25/08/2004 ©
Söring
Service-Manual Arco- and RF-units
1
not valid for A-3000/ -2000
2
not valid for Arco-2000
-33-
3
not valid for MBC600
4
not valid for Arco-1000
6. Description of Cut-module
4
6.1. General description
The cut-module delivers the RF-signal for the cutting process. Furthermore the signals
for contact coagulation (desiccation, respectively force coagulation) are generated. For
pure cutting a sinusoidal signal of approx. 350kHz with low distortion is used. The
maximum output voltage is 70V. By means of an output transformer on the RF-output
module it is transformed to 420V (monopolar) respectively 280V (bipolar). The maximum
output current is 1.2A, the maximum output power is 350W. In order to enhance
coagulation during cutting (Blend), the signal can be pulsed. The pulse repetition
frequency is variable within the range 20 to 400Hz. The duty cycle can be adjusted from
0 to 100%. Thereby a variation between pure coagulation, coagulating cut and pure cut is
possible. In order to enhance the quality of cutting different types of tissue the module
possesses an arc detection and regulation. Due to an internal power- and current limiter
the CPU is relieved from these control tasks. If the module is used for coagulation, the
arc detector switches off for a short time (programmable from approx. 0.5 to 100ms) in
case an arc occurs, so that an arc would extinguish immediately, thereby preventing
unwanted cutting into the tissue. With this function coagulation with a pure sine is
possible.
The module consists of:
-Final stage (MOS-bridge)
-Output filter (distortion suppresser)
-Power detection (broadband multiplier)
-Effective current detection (indirectly by the current through the final stage)
-Arc detection (detection of harmonics by the arc)
-Control circuits for current, power and arc regulation
-Spark suppression (by immediate short timed disconnection of final stage, sparks
in connection with short circuits at the generator output are avoided)
-Control logic for pulse generation etc.
-Communication with microprocessor (function modes, parameters and returned
values) as well as with high-power supply (signal DOWN module status bus for
down regulation of supply voltage) is done by the interface board, which is
mounted on the cut module as an additional board.
6.2. Final stage and output filter
The final stage consists of the MOS-power transistors T3 to T6. These four transistors
are bridge-connected. From the driver transformer TR2 the transistors T3/T6 and T4/T7
are periodically switched on. This results in a periodic switching of the supply voltage
(+U_SUP, -U_SUP). Thereby the output voltage is a rectangular signal with an amplitude
proportional to the supply voltage. With TR1, a transformer with air gap and defined
inductance, the capacitors C119 to C121 (serial resonant circuit) and L2, C122 and C123
(parallel resonant circuit) the rectangular signal is filtered to a sinusoidal signal with low-
distortion. The resonance frequency is approx. 350kHz. The rectangular signal is tuned
to this frequency. As the capacitance of the connection cable is different for monopolar
and bipolar operation, correctional capacitors can be switched in by a relay. This reduces
the reactive current and thereby the losses in the final stage. The signal is then routed
via the current transformer TR3 to the output socket. TR4 acquires the actual output
voltage for power registration.
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