Patent Description:
A typical configuration for a medical-grade ECG measurement system makes use of a measurement unit (e.g. a mobile unit or an ECG monitor), a trunk cable, a trunk unit, a lead set with grabbers or snappers, and ECG electrodes. The electrodes are placed on the body. The lead set connects to the electrodes using snappers or grabbers. Each electrode is connected to the trunk unit via a lead, typically a shielded cable. Inside the grabber or snapper, an inductor is sometimes used to provide enhanced protection and filtering for electrosurgery (ESU) signals. This is important for lead sets used in the operating theatre. Inside the trunk, safety resistors are often placed to protect the measurement unit against high voltages that can occur during defibrillation treatments. Additional safety elements such as sidactors are used inside the measurement unit to limit the maximum voltage on the input of the ECG measurement unit.

Snappers and grabbers are both commonly used as ECG electrode connector. They are electrically equivalent, and the choice between grabber or snapper depends on the preference of the user. Herein, reference is generally made to ECG electrode connector, and all technical details apply to all embodiments, including snappers, grabbers or clamping means, if not specified otherwise.

Conventional ECG electrode connectors have a single electrical connection to the lead wire (also called lead), which connects to the trunk unit. The lead wire is a shielded cable. The shield of this cable ends (unconnected) at the attach point from the cable to the ECG electrode connector. Inside the ECG electrode connector, an inductor can be used for ECG electrode connectors that are part of a so-called orange lead set, intended for use in the operating theatre. This inductor provides additional filtering between electrode and ECG measurement unit when the patient is undergoing electrosurgery treatments.

The conventional hardware between the measurement unit and the ECG electrode is rather bulky and heavy, making it uncomfortable, in particular for mobile applications, e.g. when the patient can freely move outside the bed. Hence, there is a need for reducing the size and weight of this hardware.

<CIT> discloses a medical coupling unit for electrical signal transmission between the medical coupling unit and a medical sensor coupled to the medical coupling unit. The medical coupling unit comprises a coupling-side connector comprising a plurality of first electrical contacts in or on a first surface and a plurality of second electrical contacts in or on a second surface opposite the first surface, and a connector interface for analyzing electrical signals available at one or more of the plurality of first and second electrical contacts to detect one or more of presence of a medical sensor coupled to the medical coupling unit, the type of medical sensor coupled to the medical coupling unit, and the orientation of a sensor-side connector of a medical sensor coupled to the medical coupling unit. Further, a sensor-side connector is disclosed.

<CIT> discloses an amplifying electrode for an electrocardiograph device. It consists of an integrated impedance converter amplifier circuit having a high input impedance and a low output impedance, potted in a metal shell for electrostatic and electromagnetic shielding. The amplifier circuit is driven by a nanoamp current signal sensed by a small conductive plate which caps, but is insulated from, the conetic metal shell. The high input impedance of the integrated circuit minimizes the effect of skin contact resistance, while the low output impedance minimizes noise pickup in the signal line to the remainder of the EKG electronics. Most importantly, the integrated impedance converter amplifier circuit requires only about a <NUM>-nanoamp biasing current for operation. Hence, signal traces of up to <NUM> separate electrodes can be simultaneously recorded without exceeding the maximum permissible current through the human body. <CIT> discloses an ECG lead set assembly.

It is an object of the present invention to provide an ECG electrode connector and an ECG cable comprising said connector, by which the size and weight of the hardware between the measurement unit and the ECG electrode are reduced.

In a first aspect of the present invention an ECG electrode connector for mechanically and electrically connecting an external ECG electrode with a lead wire is presented, as defined by claim <NUM>.

The present invention is based on the idea to incorporate the safety network comprising at least one or more resistors and voltage clamping elements (preferably sidactors; alternatively neons or trigards), and optionally one or more inductors, into the ECG electrode connector. The trunk unit can thus be eliminated completely, leading to a substantial reduction in size and weight of the complete hardware required between measurement unit and ECG electrode. The ECG electrode connector is connected to the measurement unit via a lead wire. From an electrical perspective, the measurement system using conventional ECG electrode connectors and a trunk unit on the one hand and a measurement system using ECG electrode connectors as disclosed herein on the other hand are substantially equal and their performance is substantially identical.

In an embodiment the ECG electrode connector further comprises an inductor coupled between the lead wire terminal and the electrode contact, in particular between the resistor and the electrode contact. This inductor provides enhanced protection and filtering for ESU signals.

In another embodiment the resistor comprises two or more resistor elements coupled in series. For instance, multiple lower-value resistor elements can be used in series to allow for an attractive low-cost connector design. The resistor elements can then also be reduced in size compared to a single resistor.

The ECG electrode connector may further comprise a ground plane coupled to the shield terminal and arranged between the resistor and the voltage clamping element on the one side and the ECG electrode on the other side, when the connector and the ECG electrode are connected. This ground plane then acts as a ground shield, which reduces overall sensitivity to interference.

The connection arrangement of the ECG electrode connector may comprise a clamping arrangement or a snapping arrangement or a grabbing arrangement. A conventional mechanical design may thus be used. Other designs are possible.

In one embodiment the ECG electrode connector comprises a single lead wire terminal, a single shield terminal, a single voltage clamping element and a single resistor. This embodiment is particularly used for ECG electrodes which shall not be used for respiration measurement.

A medical-grade ECG measurement system shall generally provide the capability to measure respiration, i.e. at least some ECG electrodes (usually RA, LA and LL) shall be used for respiration measurement. The bio-impedance from the human body seen between electrodes is modulated by respiration. Thus, respiration can be measured via an impedance measurement system in the ECG measurement unit.

In an ECG measurement system using a classical trunk cable and lead set there exist different types of lead set that are intended for various use cases. In particular, an orange lead set exists that is intended for use in the operating theatre. In the orange lead set, extra protection and filtering by means of a series inductor in each lead is used in the lead set. When the orange lead set is used, the respiration measurement function of the ECG measurement unit is not reliable and must not be used. This is because of the presence of inductors in series with the electrodes, which attenuate the modulation and demodulation signals used in the respiration detection system.

Hence, in an embodiment the ECG electrode connector further comprises a second lead wire terminal for connection with a second signal line of the lead wire, a second voltage clamping element coupled between the second lead wire terminal and the shield terminal, and a second resistor coupled between the second lead wire terminal and the electrode contact. Thus, a duplicate safety network is provided to support improved respiration detection accuracy.

In this embodiment it may be preferred that one end of the inductor is coupled to the electrode contact and the other end of the inductor is coupled to the resistor and the second resistor, i.e. both resistors connect at one end to the same inductor.

In another embodiment a second inductor is provided that is coupled between the second lead wire terminal and the electrode contact, in particular between the second resistor and the electrode contact. In this way the connection point where the two paths merge is moved closer to the ECG electrode which further improves the accuracy of the respiration measurement system.

In the latter embodiment a second electrode contact may be provided for contacting a second electrical contact of the ECG electrode, wherein the inductor is coupled to the electrode contact and the second inductor is coupled to the second electrode contact. By means of these separated contacts to the ECG electrode, a simple detection method is supported to detect if the ECG electrode connector is connected to an ECG electrode.

The ECG electrode connector may further comprise a second shield terminal for connection with the shield of the lead wire, wherein the second voltage clamping element is coupled between the second lead wire terminal and the second shield terminal. This further improves the safety.

In a practical implementation the resistor may have a resistance of at least 2kΩ, in particular in the range of 2kΩ to 50kΩ or in the range of 5kΩ to 20kΩ, e.g. 10kΩ.

The proposed ECG cable comprises one or more lead wires and one or more of the proposed ECG electrode connectors. It may further comprise at least two respiration type lead wires, each having two signal lines, and at least two ECG electrode connectors including a duplicate safety network as described above, each of said at least two ECG electrode connectors being connected to a respective respiration type lead wire.

The ECG cable may further comprise at least one non-respiration type lead wire, each having a single signal lines and at least one ECG electrode connector having a single safety network as described above, said at least one ECG electrode connector being connected to a respective non-respiration type lead wire.

<FIG> shows a perspective view of an embodiment of an ECG electrode <NUM> and an ECG cable <NUM> comprising an ECG electrode connector <NUM> and <FIG> shows a cross-sectional view of the ECG cable <NUM> according to the present invention. The ECG cable <NUM> comprises one (or more) lead wire(s) <NUM> and one (or more) ECG electrode connector(s) <NUM>. Generally, one lead wire <NUM> is provided per ECG electrode <NUM> and each ECG connector <NUM> is connected to a respective lead wire <NUM>. The one (or more) lead wire(s) may be combined into a common cable connecting the one (or more) ECG electrode(s) with an ECG measurement unit (not shown), e.g. a mobile unit or an ECG monitor. A lead wire <NUM> generally comprises a signal line <NUM> carrying the measured signal and a shield <NUM> for shielding the signal line <NUM> from disturbing radiation.

The ECG electrode connector <NUM> comprises a connection arrangement <NUM> for mechanically connecting the ECG electrode connector <NUM> with the ECG electrode <NUM>. The connection arrangement <NUM> may generally comprise any kind of connection means that allow a fixed mechanical connection of the ECG electrode connector <NUM> to the ECG electrode <NUM> during use. For instance, it may comprises a clamping arrangement or a snapping arrangement or a grabbing arrangement. In the embodiment shown in <FIG> the connection arrangement <NUM> of the ECG electrode connector <NUM> comprises a female connection portion <NUM> that engages with a corresponding male portion <NUM> the ECG electrode <NUM>, said male portion representing an electrical contact of the ECG electrode. For instance, the housing <NUM> of the ECG electrode connector <NUM> may be designed accordingly.

The ECG electrode connector <NUM> further comprises safety elements (also called protection elements), in particular a voltage clamping element <NUM> (in this embodiment a sidactor) that is coupled between a lead wire terminal <NUM> and a shield terminal <NUM> and a resistor <NUM> that is coupled between the lead wire terminal <NUM> and an electrode contact <NUM>. The voltage clamping element <NUM> and the resistor <NUM> may e.g. be arranged on a PCB <NUM> that is mounted inside the ECG electrode connector <NUM> or may be coupled between respective wires (not shown).

Generally, it may be distinguished between ECG electrodes (and corresponding ECG electrode connectors) that can take part in a <NUM>-wire respiration detection system (usually the ECG electrodes RA, LA and LL) and all other ECG electrodes (and corresponding ECG electrode connectors) that need not to take part in a <NUM>-wire respiration detection system (usually the ECG electrodes RL and V1-V6). The ECG electrodes (and corresponding ECG electrode connectors) that are not used to measure respiration do not require dual protection circuitry.

<FIG> shows a circuit diagram of a first embodiment of an ECG electrode connector 1a according to the present invention that may not be used for respiration measurement. The ECG electrode connector la comprises, besides the electrode contact <NUM>, a single lead wire terminal <NUM>, a single shield terminal <NUM>, a single voltage clamping element <NUM> and a single resistor <NUM> (Rs). The voltage clamping element <NUM> is coupled between the lead wire terminal <NUM> and the shield terminal <NUM>. The resistor <NUM> is coupled between the lead wire terminal <NUM> and the electrode contact <NUM>.

<FIG> shows a circuit diagram of a second embodiment of an ECG electrode connector 1b according to the present invention that may be used for respiration measurement in a <NUM>-wire respiration detection system (using two ECG electrodes, each connected to e.g. one such ECG electrode connector 1b). In addition to the elements of the first embodiment of an ECG electrode connector 1a shown in <FIG>, the ECG electrode connector 1b further comprises a second voltage clamping element <NUM>, a second resistor <NUM> (Rsv) and a second lead wire terminal <NUM> for connection with a second signal line (not shown) of the lead wire <NUM>. The second voltage clamping element <NUM> is coupled between the second lead wire terminal <NUM> and the shield terminal <NUM>. The second resistor <NUM> is coupled between the second lead wire terminal <NUM> and the electrode contact <NUM>.

<FIG> shows a circuit diagram of a third embodiment of an ECG electrode connector 1c according to the present invention that may not be used for respiration measurement. In addition to the elements of the first embodiment of the ECG electrode connector 1a shown in <FIG>, the ECG electrode connector 1c further comprises an inductor <NUM> (Ls) coupled between the lead wire terminal <NUM> and the electrode contact <NUM>, in particular between the resistor <NUM> and the electrode contact <NUM>. The inductor provides enhanced protection and filtering between the ECG electrode and the ECG measurement unit when the patient is undergoing electrosurgery (ESU) treatments, which is particularly important for lead sets used in the operating theatre.

<FIG> shows a circuit diagram of a fourth embodiment of an ECG electrode connector 1d according to the present invention that may be used for respiration measurement (using two ECG electrodes, each connected to e.g. one such ECG electrode connector 1d). In addition to the elements of the second embodiment of the ECG electrode connector 1b shown in <FIG>, the ECG electrode connector 1d further comprises an inductor <NUM> (Ls) coupled between the second lead wire terminal <NUM> and the electrode contact <NUM>, in particular between the second resistor <NUM> and the electrode contact <NUM>. One end of the inductor <NUM> is coupled to the electrode contact <NUM> and the other end of the inductor <NUM> is coupled to the resistor <NUM> and the second resistor <NUM>.

The accuracy of the respiration impedance measurement can be further improved by duplicating the inductor inside the ECG electrode connector. <FIG> shows a circuit diagram of a fifth embodiment of an ECG electrode connector 1e according to the present invention making use of this option. In addition to the fourth embodiment of the ECG electrode connector 1d shown in <FIG>, the ECG electrode connector 1e further comprises a second inductor <NUM> (Lsv) coupled between the second lead wire terminal <NUM> and the electrode contact <NUM>, in particular between the second resistor <NUM> and the electrode contact <NUM>. The measured impedance for the ECG electrode connector 1e equals Rbody (resistance of the body) + <NUM> Z_electrode (impedance of the ECG electrode), which is an improvement over the ECG electrode connector with a single inductor, e.g. the ECG electrode connector 1d shown in <FIG>, since the impedance of the inductor Ls plays no role in the measured impedance.

<FIG> shows a circuit diagram of a sixth embodiment of an ECG electrode connector 1f according to the present invention. In addition to the fifth embodiment of the ECG electrode connector 1e shown in <FIG>, the ECG electrode connector 1f further comprises a second electrode contact <NUM>. In this embodiment the electrical contact of the ECG electrode may be split into two electrical contacts <NUM>, <NUM>, wherein a first electrical contact <NUM> is connected with the first electrode contact <NUM> and the second electrical contact <NUM> is connected with the second electrode contact <NUM>. The two electrical contacts <NUM>, <NUM> are, however, preferably connected electrically (i.e. short-circuited) within the ECG electrode <NUM>. The dual connection of the ECG electrode connector 1f to the ECG electrode <NUM> provides the advantage that it enables reliable detection of the ECG electrode connector 1f being connected to the ECG electrode <NUM> (if the two electrode contacts <NUM> and <NUM> being short-circuited) or not (if the two electrode contacts <NUM> and <NUM> being open-circuited).

In a <NUM>-wire respiration configuration, as e.g. shown in <FIG>, <FIG>, the safety resistors <NUM> (Rs) and <NUM> (Rsv) do not dissipate much energy during defibrillation, e.g. typically <1J each at Rs = Rsv = 10kΩ for a single defibrillation pulse. Relatively small resistors (in size) are sufficient to dissipate this energy reliably. However, next to the energy rating, the resistors should also be capable of handling the defibrillation voltage of up to 5kV. This usually requires large resistors (in size). Smaller resistors are possible by using potting techniques. A further alternative is to split the resistors Rs and Rsv into multiple resistors in series as shown in <FIG>.

<FIG> shows a circuit diagram of a seventh embodiment of an ECG electrode connector <NUM> according to the present invention. Different from the sixth embodiment of the ECG electrode connector 1f shown in <FIG>, in the ECG electrode connector <NUM> the resistor <NUM> comprises two or more resistor elements 16a-16c coupled in series and the second resistor <NUM> comprises two or more resistor elements 20a-20c coupled in series. For instance, in the embodiment shown in <FIG> the resistor <NUM> is split into three resistor elements of equal resistance value and the resistor <NUM> is split into three resistor elements of equal resistance value. In other embodiment only the resistor <NUM> or the second resistor <NUM> comprises two or more resistor elements. In embodiments of the ECG electrode connectors having a single resistor <NUM> only, the same idea may be used as well, i.e. the resistor <NUM> may comprise two or more resistor elements 16a-16c as well.

In the embodiment shown in <FIG>, n resistor elements (n=<NUM> in the exemplary embodiment shown in <FIG>) are used in series, each of value Rs/n and Rsv/n. The energy dissipation per resistor element and voltage across each resistor element reduces proportionally with n, and therefore each resistor element can be much smaller and cheaper, leading to a more compact and cheaper overall solution for the ECG electrode connector. Moreover, the series connection can be constructed in an arbitrary physical configuration (e.g. straight, circular, etc.) which allows for a more attractive design of the ECG electrode connector.

In further embodiments of the ECG electrode connector, the inductor(s) <NUM>, <NUM> can be split and implemented from a series network in a similar fashion as the resistors <NUM>, <NUM> in the embodiment shown in <FIG>.

A top view of a practical implementation of an ECG cable 200a including the ECG electrode connector <NUM> shown in <FIG> is depicted in <FIG>. The lead wire 300a comprises a first signal line <NUM> connected with the first lead wire terminal <NUM>, a second signal line <NUM> connected with the second lead wire terminal <NUM> and a shield <NUM> connected with the shield terminal <NUM>. This ECG cable 200a thus provides <NUM>-wire respiration support by means of duplicate safety networks and two signal connections to a <NUM>-wire shielded lead wire 300a. Split resistors (in this case each resistor being split into three resistor elements) enable resistor elements of small physical size and flexible positioning and layout of the resistor networks. Further, two separate contacts <NUM>, <NUM> to the ECG electrode <NUM> support inside the ECG measurement unit simple detection of the ECG electrode <NUM> being attached or not. Still further, embedded voltage clamping elements <NUM>, <NUM> limit the highest voltage in the lead wire and thus relax the voltage handling requirement for the lead wire.

Generally, the inductor is only needed if the ECG electrode connector is intended for use in the operating theatre. If usage in the operating theatre is excluded, ECG electrode connector versions without inductor can be envisaged as e.g. shown in <FIG> in a top view. These designs can be smaller in physical size for increased patient comfort.

<FIG> shows a top view of an ECG cable 200b including an embodiment of an ECG electrode connector <NUM> that supports <NUM>-wire respiration measurement using dual protection networks and is intended for leads that can be used for respiration measurements (e.g. RA, LA and LL). It does not comprise an inductor. Split resistors are used that allow the use of resistor elements with reduced voltage rating for small physical size. Further, split electrical contacts of the ECG electrode are used that support simple detection if the ECG electrode is connected or not.

<FIG> shows a top view of an ECG cable 200c including an embodiment of an ECG electrode connector 1i that is intended for all other leads (e.g. RL and V1-V6). It does not comprise an inductor. The lead wire <NUM> in this embodiment comprises a single signal line <NUM>. The ECG electrode connector 1i comprises a single safety network.

One or multiple small PCBs may be embedded inside the ECG electrode connector to hold the safety elements. Such a PCB may have multiple conducting layers. One layer can be used as shield. This would reduce the sensitivity of the ECG measurement system to interference. <FIG> shows a top view of an ECG cable 200c including an embodiment of an ECG electrode connector 1j with shield. A ground plane <NUM> covers the largest part of the ECG electrode <NUM>, in particular near the safety elements, and is electrically connected to the shield <NUM> of the lead wire 300a.

In a conventional ECG measurement system, the partitioning of elements from the ECG measurement unit to the ECG electrodes is shown <FIG> depicting an embodiment of a known respiration measurement system <NUM>. It comprises an impedance measurement unit <NUM>, a connector <NUM>, a trunk cable <NUM>, ECG electrode connectors <NUM>, <NUM> and ECG electrodes <NUM>, <NUM>. The respiration impedance measurement system (inside the impedance measurement unit) drives an AC-current i_ac to the patient's body and measures the resulting voltage V across nodes A, B. The actual measured impedance is the series impedance of Rbody + <NUM>·Z_electrode + <NUM>·Z_Ls + <NUM> Rs. The voltage clamping elements are conventionally placed inside the impedance measurement unit <NUM>. ESU protection inductors Ls are embedded in the ECG electrode connectors <NUM>, <NUM>. The trunk cable <NUM> includes the safety series resistors Rs.

In a <NUM>-wire respiration measurement system, the resistors Rs have a typical value of Rs=1kΩ. The value of Rs is limited because a higher Rs results in reduced accuracy of the measurement of Rbody. Lower-ohmic resistors Rs are preferred for accurate Rbody measurement, but dissipate more energy when a patient is undergoing defibrillation treatments and thus need to be large in physical size.

<FIG> shows a circuit diagram of a first embodiment of a respiration measurement system <NUM> according to the present invention. It comprises an impedance measurement unit <NUM> and, per ECG electrode <NUM>, a lead wire <NUM> and an ECG electrode connector 1a. Compared to the conventional respiration measurement system <NUM> shown in <FIG>, the trunk cable is completely omitted and the safety elements are all placed in the ECG electrode connectors 1c as shown in <FIG>.

The measurement of Rbody can be done more accurate using a <NUM>-wire impedance measurement system. <FIG> shows a circuit diagram of a second embodiment of an ECG measurement system <NUM> according to the present invention using such a <NUM>-wire impedance measurement system <NUM>. The ECG measurement system <NUM> comprises, besides the <NUM>-wire impedance measurement unit <NUM>, per ECG electrode <NUM>, a lead wire 300a (comprising two signal wires and a shield, as e.g. shown in <FIG>) and an ECG electrode connector 1d as shown in <FIG>.

In the <NUM>-wire respiration measurement, the measured impedance equals Rbody + <NUM>·Z_electrode + <NUM>·Z_Ls. The value of Rsv does not play a role in the measured impedance because the voltage is measured behind the series resistance Rs in the modulator path, at the side of the inductor. The series resistances Rsv in the voltage measurement path are required for protection but are not seen in the measured impedance because there is no current i_ac in Rsv. As a result, the <NUM>-wire respiration measurement method provides an improved and more reliable approach for Rbody measurements. The impedance from the inductors Ls is still seen in series with Rbody.

Since, in the <NUM>-wire impedance measurement method, resistors Rs and Rsv are both not seen in the impedance measurement, their values can be increased with respect to the original <NUM>-wire configuration shown in <FIG>. For example, Rs = Rsv = 10kΩ can be used. The increased resistance results in a reduced energy dissipation during defibrillation treatments. Therefore, resistors of smaller physical size can be used for the <NUM>-wire respiration measurement system compared to the <NUM>-wire configuration shown in <FIG>.

Contrary to a conventional ECG measurement system, in which there is still a trunk unit present in which the voltage clamping elements are placed, according to the ECG measurement system depicted in <FIG> the trunk unit is eliminated. Safety and protection components (resistor, voltage clamping element and inductor) are placed inside each ECG electrode connector 1d. Each ECG electrode connector 1d is connected to the impedance measurement system 601via a lead wire <NUM>. The ECG electrodes <NUM> that can take part in the respiration measurement system have duplicate safety networks (voltage clamping element and resistor).

From an electrical perspective, the measurement system <NUM> according to the present invention and a comparable conventional measurement system using a trunk cable are substantially equal and their performance is identical. The proposed partitioning with safety elements inside the ECG electrode connectors is possible and advantageous in combination with <NUM>-wire respiration detection, since the <NUM>-wire method allows for increased resistance values Rs and Rsv, as explained above, which dissipate less energy from a defibrillation pulse and thus can be smaller in size.

<FIG> shows a diagram of an exemplary realization of an ECG cable <NUM> (also called ECG lead set) interfacing to three ECG electrodes by use of three lead wires 300a. The protection network is embedded in the ECG electrode connectors 1d, supporting <NUM>-wire respiration measurement.

<FIG> shows a diagram of another exemplary realization of an ECG cable <NUM> using different ECG electrode connectors supporting five ECG electrodes via five lead wires. Three ECG electrode connectors 1d and the corresponding respiration-type lead wires 300a are configured for <NUM>-wire respiration measurement and two ECG electrode connectors 1c and the corresponding non-respiration type lead wires <NUM> are not configured for <NUM>-wire respiration measurement.

Claim 1:
ECG electrode connector (<NUM>) for mechanically and electrically connecting an external ECG electrode (<NUM>) with a lead wire, the ECG electrode connector (<NUM>) comprising:
- a connection arrangement (<NUM>) for mechanically connecting the ECG electrode connector (<NUM>) with the external ECG electrode (<NUM>),
- a lead wire terminal (<NUM>) for connection with a signal line (<NUM>) of a lead wire (<NUM>),
- a shield terminal (<NUM>) for connection with a shield (<NUM>) of the lead wire (<NUM>),
- an electrode contact (<NUM>) for contacting an electrical contact (<NUM>) of the ECG electrode (<NUM>),
- a voltage clamping element (<NUM>) electrically coupled between the lead wire terminal (<NUM>) and the shield terminal (<NUM>), and
- a resistor (<NUM>) electrically coupled between the lead wire terminal (<NUM>) and the electrode contact (<NUM>).