Bipolar Applied Part

The bipolar applied part is located in the upper half of the bipolar module, next to the monopo-lar module. The following functional groups can be differentiated:

• impedance monitors

• finger switch interface and instrument recognition

7.3.4.1 Impedance Monitors

Parallel to each of the two bipolar outputs B1 and B2, the unit features an impedance monitor that delivers the signal IMP1 or IMP2, respectively. This signal represents the tissue resistance measured between the conductors and serves for controlling the automatic and half-automatic activation of the bipolar coagulation currents having such an auto-function. If a half-automatic type of current (Auto Stop) is activated (by the surgeon), the monitor connected to the acti-vated channel superimposes on the HF current a low medium-frequency voltage that generates a current which in turn serves as a measure of tissue impedance. When starting the coagula-tion process, tissue impedance typically begins to drop to a minimum, then increases again. If a certain level is reached relative to the minimum, the HF current is switched off. This limit or rise can be set by the user for the various types of current via a submenu. Following cut-off, renewed activation is possible only after releasing the switch and operating it again.

In fully automatic operation (Auto Start + Auto Stop), the impedance monitor of the channel for which a bipolar coagulation current with auto-start/auto-stop function has been selected controls the switching-on process as well. The HF current is activated if the resistance between the output poles of the electrode leads drops below a defined value. Switching off follows the same rules as described above for semi-automatic currents with Auto Stop. Activation can be delayed by a certain time factor that can be set via the same submenu as the switch-off level.

IEN2

The signals IEN1 and IEN2 are used to activate or deactivate the impedance monitors of the outputs B1 or B2, respectively. In these two identical monitors, a multivibrator generates a periodic signal that is fed to the poles of the corresponding bipolar output socket via a filter network. Tissue contact of the active electrode creates a shunt that attenuates the signal. The resulting decrease in the signal’s amplitude (due to attenuation) is then used as a tissue resis-tance measure. The signal amplitude is determined by rectification; the trimmers IMP1 and IMP2 are used to set the output voltages for operation without tissue contact, with the output signals IMP1 and IMP2 transmitted to the main controller in analog form.

To ensure that the impedance measurement works also with activated bipolar HF current, it is necessary to eliminate the influence of the HF voltage that is simultaneously present to the monitor. To this end, a selective filter is used that lets pass through only the monitor signal. At the same time, the transformers T2 and T3 provide the required electrical isolation between the bipolar applied part and the intermediate circuit in this network. The frequency of the mul-tivibrators must be adjusted to the parallel resonance of the respective filter networks. This is done with the trimmers F1 and F2.

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bipolar applied part X3.2 X7.26a

When the Auto Start type of current was implemented with HW02, a monitor with higher sensi-tivity was required. The monitor signal is now a periodic sequence of groups of individual pulses (bursts) whose instantaneous values are registered via sample-and-hold elements to restore analog DC signals IMP1 and IMP2. Adjustment to the resonance frequency of the filter network is done with the switches S1, S2 and S3 by setting a division ratio by which the moni-tor frequency is derived from the fixed frequency of a quartz.

When activating HF current, the circuit of the HF output transformer T13 (on main board) is connected in parallel to the filter network via C1 and C2 on the bipolar board. This not only changes the resonance frequency of the filter network, but the output signal IMP1 or IMP2 as well. Therefore, the amplification of these signals is switched depending on the position of the output relays – which also explains why the basic setting of the signals IMP1 and IMP2 must be done separately for the open source circuit (OC) and for the closed source circuit (CC). The yellow and green LEDs next to the trimmers indicate the current state of the circuit. With the HF output socket shorted, the trimmers SC1 and SC2 are used to adjust the output signal to a

a fully automatic type of current. The same applies if the unit starts up with a program that includes such a current.

In fully automatic operation, it is not possible to use a cutting current at the same output be-cause the ME402 cannot differentiate whether the decrease in resistance at the leads has been caused by tissue contact of a coagulation or a cutting instrument. So if a current with Auto Start/Auto Stop is selected, the cutting channel belonging to the same output is switched off.

Conversely, the current with Auto Start/Auto Stop is switched off if the cutting channel is rese-lected with the yellow channel selector button.

7.3.4.2 Finger Switch Interface and Instrument Coding

The B2 bipolar output socket also allows users to connect instruments with finger switches that can activate the cutting and coagulation functions, just as with monopolar handles. In the case of the circular Martin socket, the auxiliary contacts required are located on the rim of the sock-et – which means that the small coaxial plug of the forceps connecting cable does not support this function. The international (“i”) socket module, in contrast, provides an additional 2-mm socket for this purpose, but this requires a corresponding plug with a 2-mm pin, of course. The multifunction socket of the Erbe (“e”) version also allows connection of this plug. An optocoup-ler transmits the corresponding signals to the intermediate circuit, and from there they are passed on to the main controller as signals BCT and BCG.

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X7.24a X7.24c

bipolar board

T13

X2.5

X4.1 X4.2 X4.4 X4.5 X4.6 IC2

bipolar applied part

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X2.1

output B2

X5.12c

X5.9c

main controller board

main board

BCG +12V

X7.21a IC

IC

X5.9c

X7.16c X7.17c

from aux.

supply

X24.1

In addition, the B2 socket offers a resistance-coded instrument recognition function. If an in-strument coded in this way is connected, the system automatically assigns a specific program to this output that optimally serves the instrument. As this function is also controlled through the additional contacts of the B2 socket, instruments with special connecting plugs are re-quired. The pulse width-modulated signal is passed on to the intermediate circuit via an opto-coupler, where it is demodulated by a low pass and then transferred to the main controller as the analog signal IC.