Monopolar Applied Part

The monopolar applied part is located on the corresponding monopolar module at the left edge of the main board. The following functional groups can be distinguished:

• Finger switch interface

• Monopolar regulators

• Neutral electrode monitoring

• Microcontroller with optocoupler interface

7.3.3.1 Finger Switch Interface

The monopolar outputs M1 and M2 allow connection of electrode handles with finger switches (pushbuttons) for activating the cutting and coagulation functions. These switches relate to the conductor leading to the active electrode.

In the KLS Martin handles featuring a circular coaxial plug, two diodes polarized for different conducting directions are connected in series with the switches, so one additional lead suffices for both switches. Differentiation between which of the two switches has been selected is poss-ible by decoding the current flow direction once alternating current has been applied. In con-trast, US handles with 3-pin flat connectors have a separate conductor for each switch. There-fore, the monopolar socket module board features two diodes for each of the two connectors.

These diodes re-code these 3-pin connectors to adapt them to the Martin format to ensure that both types of handle can be used in the same way.

monopolar board X13

T12

T11

L6

X3.9 X3.10 X3.2 X3.1

X9.1 X9.2

X9.10

output M2X9.9

NE connector

X5.1 X5.2

X4.2 X4.1

PIN2

PIN1 CG2

CG1

+12V

+12V

PIN2

CG2

PIN1

CG1

main board

output M1

Through optocouplers, the finger-switch activation signals CT1 and CG1, or CT2 and CG2, are transmitted to the NE-side microcontroller. LEDs connected in series with the optocouplers in-dicate the presence of an activation signal – yellow for cutting and green for coagulation.

When using instrument cables with a plain 4-mm connector, misconnection may occur because this plug – which should be inserted into the inner conductor of the coaxial socket – technically fits the adjacent 4-mm sockets for the finger switch signals as well. Such misconnection could damage the finger switch because when the HF current is activated with the footswitch (which is the usual source of activation when using instruments with such cables), the current would be rerouted through the finger-switch control circuit. To prevent damage, HF current flow through the finger switch circuit is monitored. As soon as a critical limit is exceeded, the signal PIN1 or PIN2 is generated and indicated by a red LED. While presence of such a signal is nor-mal in connection with one of the finger switch activation signals, the generator is switched off and an error message displayed if the signal PIN1 or PIN2 occurs alone or in conjunction with a footswitch activation signal.

7.3.3.2 Monopolar Regulators

In electrosurgical cutting, tissue dissection is achieved by a very high power density at the point of contact between the active electrode and the tissue. In this process, water vapor is released from the tissue in the cutting canal, separating the tissue from the electrode (the so-called Leidenfrost effect) so that the current cannot pass unhindered from the electrode to the tissue. Therefore, a correspondingly high electric current is needed to overcome (break down) the insulating vapor layer. In this process, gas discharge occurs inside the vapor layer, where-by the vapor must be ionized to make it electrically conductive. As the energy necessary for this is taken from the electric circuit, this leads to a voltage drop above the vapor layer.

Ionization takes place above the surface of the cathode. However, since high-frequency alter-nating current is used here, the electrode and the tissue alteralter-natingly function as the cathode.

This is a highly asymmetrical pair of electrodes, though, leading to varying energetic conditions for the ionization process. For example, it can be observed that the breakdown of the negative half-wave takes place at an apparently lower resistance than that of the positive half-wave.

Therefore, the current of the negative half-wave would be greater than that of the positive half-wave, which means that a direct current would be superimposed on the high-frequency alternating current – which must definitely be prevented because it would cause nerve irrita-tion. For this purpose, capacitors C19 and C20 have been included. They build up direct cur-rent that is used to shift the HF alternating voltage symmetrical to the zero line (as present at the secondary side of T11) into the positive range to such an extent that negative and positive current half-waves carry the same amount of electric charge.

X13 T11

L6

X3.9 X3.10 X3.2 X3.1

+12V

main board

demodulatorPWM

+12V

PWM

monopolar board from HW 00 to HW 02 (C40-1929 and C40-2224)

X6.16c X6.15c

X9.1 X9.2

X9.10 X9.9

output M1

output M2 NE connector

The same direct voltage builds up between the neutral and active electrodes and is again supe-rimposed on the HF voltage. By capturing the voltage between the output sockets and filtering

The monopolar patient circuit incorporates a measuring circuit for the direct-current content and a regulator that receives its setpoint value from the microcontroller that is also part of the circuit. The regulator’s deviation signal controls an LED that serves as the sender side in an optocoupler consisting of a separate sender and receiver and connected to the receiver of the power manager module via an plastic optical fiber. There, the signal acts upon a busbar via an amplifier (the voltage and power regulators acting upon it as well).

When using a capacitive neutral electrode on the patient, it is not possible to capture the di-rect-voltage component, so arc regulation is not possible in this case.

X13 T11

L6

X3.9 X3.10 X3.2 X3.1

X9.1 X9.2

X9.10

output M2X9.9

NE connector

+12V

main board

output M1

demodulatorPWM demodulatorPWM

+12V

PWM

monopolar board from HW 03

X6.16c X6.15c

From HW03, the monopolar board features a second HF output voltage regulator at outputs M1 and M2, designed for HF output voltage limitation in no-load condition to reduce the load on connected instruments and minimize HF leakage currents.

Apart from measurements for the DC component, there is also an HF voltage measuring path.

The PWM output of the microcontroller in the monopolar applied part must be multiplexed in order to obtain separate setpoints for the AC regulator and the DC regulator, formed by down-stream PWM demodulators. Both regulators act upon the same LED which, via a plastic optical fiber, transmits the control signal to the power controller located on the power manager board, as described in section 10.3.2. If the HF voltage regulator is active, this is indicated by the red LED “ACR” lighting up brightly (while glowing darkly if the regulator is non-active). The same applies to the “DCR” LED indicating DC regulator action or non-action.

The microcontroller of the applied part can bypass these regulators by using the CRB signal to control the LED at the optical link directly. This allows it to switch off the HF output power very quickly.

7.3.3.3 Neutral Electrode Monitoring

The ME402 allows connection of both single-plate and split neutral electrodes. The NE-side HF current path is split on the main board by capacitors C20 and C21, and both paths are then conducted to the NE. The impedance between the two lines is monitored by a monitor consist-ing of a free-runnconsist-ing oscillator whose amplitude is attenuated by the parallel resistance at the NE.

In the case of single-plate NEs, the two lines are connected to each other directly at the elec-trode, so the monitor recognizes a short if such an NE is used (and the cable connection is O.K.), interpreting this correctly as connection of a plate NE. Consequently, the single-plate NE symbol appears in green on the unit’s display. It is possible, however, to exclude the use of single-plate NEs via the “Setup” item of the control menu. In this case, a message will inform the user that single-plate NEs are not permitted (disabled by user). As from software version 1.328, the use of small-surfaced baby NEs can be enabled through the setup as well.

This limits the output power of appropriate currents to values that allow only smaller NE cur-rents.

X13 T11

L6

X3.9 X3.10 X3.2 X3.1

X9.1 X9.2

X9.10

output M2X9.9

NE connector

+12V

main board

output M1 monopolar board

X6.16c X6.15c

If split NEs are used, impedance measurement is possible only on the patient’s skin because the patient closes the monitoring circuit. The alarm is switched off as soon as impedance drops below a limit of approx. 250 ohms and a green split-NE symbol is shown on the screen. Usual-ly, however, impedance is much lower, but the minimum is reached only after a few minutes.

The monitor stores this minimum and uses it as a reference value for the alarm decision. Ex-ceeding this minimum by a predefined value triggers NE alarm with the consequence that no monopolar HF current can be generated or power output is interrupted. This ensures NE alarm

yellow (transition range; no HF output if the sliding indicator is moving up from the red field, HF output possible if it comes from the green section) and green (HF output possible). The indicator is useful for recognizing tendencies in the NE’s contact with the patient’s skin over time. It is also very useful for troubleshooting when the NE alarm persists. This graphical indi-cator can be deselected through the Setup menu item.

7.3.3.4 Microcontroller with Optocoupler Interface

The monopolar patient circuit has its own microcontroller that coordinates the signals within the monopolar part and communicates them to the main controller. This includes the following signals:

+12V

PWM CG1 PIN1 CG2 PIN2

+12V NE contact

monitor (3)

MOSI MISO

CSM-CSM X6.2a +CSM X6.1a -CLK X6.6a +CLK X6.5a

NE2 X6.16c NE1 X6.15c

monopolar board

X7.7a CSM- X7.8a CSM+ X7.5a CLK- X7.6a CLK+

X5.5a X5.5c X5.4c X5.4a

X7.29c X7.30c X7.31c X7.28c CSMO

bipolar board

DCI

FAIL

+15V

SPI bus multiplexer

MOSIMISO

main controller board main board

+5V

ID

• Input signals CT1, CG1 and PIN1 of the finger-switch interface circuit of the monopolar output M1;

• input signals CT2, CG2 and PIN2 of the finger-switch interface circuit of the monopolar out-put M2;

• output signals K1 and K2 for controlling the high-voltage relays in the output paths leading to sockets M1 and M2;

• up to HW02: PWM output signal DCS, which is used for generating the analog setpoint for the arc regulator.

• from HW03: PWM output signal “PWM” multiplexed with signal “PWU”, which are used to generate the analog setpoints “DCS” and “ACS” for the two regulators;

• analog input signal DCI, which corresponds to the DC actual-value signal;

• from HW03: analog input signal “ACI”, which corresponds to the analog actual value of the HF voltage;

• analog input signal NEI, output signal of the NE monitor;

• signals of the synchronous serial interface: MOSM, MISM, CLKM and CSM.

The controller features a flash EPROM that can be programmed in-circuit on the board with a programming plug. Provided a bootloader has been installed (available from program version V8.0, implemented with HW02), this program can be updated automatically by the main con-troller after updating the unit’s software.

The transmission format of the synchronous serial interface, which serves for communication with the main controller, is equivalent to an SPI bus. Due to the insulation required between the patient circuit and the intermediate circuit, the optocouplers U1…U4 are used to deliver the signals MOSI, MISO, CLK and CSM to the main board. While the sender and receiver circuit of the high-voltage side is found on the monopolar module, the associated circuit of the interme-diate circuit side is located on the bipolar module.

In normal operation, a yellow LED flashes on the monopolar module at a frequency of approx.

1 Hz. A red LED lights up if communication between the main controller and the patient circuit controller – via the SPI bus – is interrupted. This is also the case during to the main control-ler’s self-test. A green LED lights up when the main controller is sending an activation com-mand.

In document maxium (Page 149-155)