Erbe ICC 200, Service Manual

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3 CIRCUIT DESCRIPTION
In this way there is another DC voltage, proportional to the spark intensity, which is reduced via the resistor
divider R32, R33 and then fed to the isolation amplifier IC9. The output signal U_FUNKE moves from
there via the control board to control the processor.
The electronic components of this isolation amplifier within the patient circuit require an isolated voltage
supply to function. For this, a DC/DC converter is used which consists of a Colpitts oscillator (circuit
around Transistor T6), the alternating signal of which is transferred from the transformer UE6 to the secondary
side and rectified by diodes D4 and D6. The DC voltages thus resulting are limited to 9.1 volts by the Z-
diodes D3 and D5 respectively.
In this way, voltages of +9.1 volts and –9,1 volts are available to the electronic circuit within the patient
circuit which is identified with I+9 and I–9.
Safety system for the neutral electrode (NESSY)
Problem description: The line for the neutral electrode must be monitored for wire break according to the
standard since there is risk of topical burns for the patient with an incorrect supply line.
In the ICC, correct application of the neutral electrode on the patient is also checked, as well as the uniform
distribution of the HF current to the two electrode surfaces (symmetry).
To monitor the connecting line, the cable is designed as a two-wire connection, the loop resistance of which
is measured. If the resistance value determined in this way is below a specific limit value, one can assume
that the neutral electrode line has no wire break. With conventional single-surface neutral electrodes,
monitoring is performed in this way.
However, such monitoring cannot determine whether the neutral electrode is actually applied to the patient
or whether it is lying around somewhere else.
To also check the correct application to the patient, the contacts of the neutral electrode must be divided,
whereby a control current must flow over the electrode halves and the patient. This control current permits
resistance measurement of the tissue impedance of the patient and thus information as to whether
• the electrode is not connected or has a wire break (impedance > 120 ohms),
• is lying directly on the operating table (impedance < 5 ohms),
• or, most probably, is correctly applied to the patient (impedance between 5 and 120 ohms).
If the high-frequency current is not flowing regularly over both surfaces of a divided neutral electrode, this
can lead to burns due to current concentration under the electrode. It is therefore also necessary to check the
symmetrical current distribution on both halves of the electrode.
The NESSY system, a neutral electrode safety system patented by ERBE, takes care of all the tasks
mentioned.
Principle of the NESSY measurement system
The electric resistance of the neutral electrode is measured via an oscillator, the amplitude of which is
dampened by the resistance from the patient and measured by the system. With a correct circuit design, a
sufficiently precise resistance measurement is possible in this way.
Senso-board
Slot J7