Patent Description:
Embodiments of the present disclosure relate generally to sensors and methods of measuring material properties, such as of harvested crops. In particular, embodiments relate to methods and apparatus for generating electric fields that interact with materials.

When harvesting crops, information about the properties of the crop material (e.g., mass flow, moisture content, crop density, etc.) can be used to make decisions about how and when to operate machinery for improved yield. To increase the speed and efficiency of machines, it would be beneficial to have sensors that can quickly detect properties of crop material without interfering with operation of the machines.

Such sensors could also be used in other situations in which a non-destructive test (and potentially a non-contact test) is desirable, such as in detecting material in packages, in buildings (e.g., within wall structures), in manufacturing processes, mining, etc..

<CIT> relates to a capacitive measuring device.

A method includes broadcasting a first electric field from a sensing electrode into a volume containing crop material, broadcasting a second electric field from at least one guard electrode of a plurality of guard electrodes adjacent the sensing electrode, measuring an attribute related to the first electric field, and correlating the measured attribute related to the first electric field to an amount or distribution of the crop material in the volume. At least some field lines of the first electric field emanate from the sensing electrode through the volume. The presence of the second electric field changes a shape of the field lines of the first electric field.

While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the present disclosure, various features and advantages of embodiments of the disclosure may be more readily ascertained from the following description of example embodiments when read in conjunction with the accompanying drawings, in which:.

The illustrations presented herein are not actual views of any machine, sensor, or portion thereof, but are merely idealized representations that are employed to describe example embodiments of the present disclosure. Additionally, elements common between figures may retain the same numerical designation.

The drawings accompanying the application are for illustrative purposes only, and are thus not drawn to scale.

<FIG> is a simplified diagram illustrating a capacitive sensor <NUM>. The sensor <NUM> includes a transmitter assembly <NUM>, at least one sensing electrode <NUM>, and at least one guard electrode <NUM>. The sensor <NUM> may also include one or more ground electrode(s) <NUM>. The sensor <NUM> may be considered a "guarded" capacitive sensor because it can generate two electric fields <NUM>, <NUM>, which can interact with one another and shape one another (i.e., one can "guard" the other). In particular, the field <NUM> associated with the sensing electrode(s) <NUM> may be considered the sensing field, and the field <NUM> associated with the guard electrode(s) <NUM> may be considered the guard field. The guard field <NUM> may be used to shape the sensing field <NUM>, as described in further detail below.

The transmitter assembly <NUM> shown in <FIG> includes a signal driver <NUM>, a guard driver <NUM>, and a sensing circuit <NUM>. A power source <NUM> may provide power to the components of the transmitter assembly <NUM>, and may be within or external to the transmitter assembly <NUM>. As illustrated, the signal driver <NUM> may be configured to provide a selected voltage to the sensing electrode <NUM> (which may be a constant or time-variable voltage). The sensing circuit <NUM> may measure the output of the signal driver <NUM>, such as the current or power levels required to provide the selected voltage. The guard driver <NUM> may be configured to provide a selected voltage to the guard electrode <NUM>, and may optionally receive its power from the power source <NUM> via the signal driver <NUM>. In other embodiments, the guard driver <NUM> receives its power directly from the power source <NUM>.

The sensing electrode <NUM> may have a major front surface <NUM> and a major rear surface <NUM> on an opposite side of the sensing electrode <NUM>, each of which may be generally planar. In other embodiments, the major front surface <NUM> and the major rear surface <NUM> may be curved or of another shape. For example, if the sensor <NUM> is designed to measure material in a tube, the major front surface <NUM> and the major rear surface <NUM> may have curvature matching the curvature of the tube. The major rear surface <NUM> may be generally aligned with the major front surface <NUM>. For example, if both are generally planar, the major front surface <NUM> may be parallel to the major rear surface <NUM> and separated by a distance smaller than either dimension (e.g., length or width) of the major front surface <NUM>. The sensing electrode <NUM> is powered by the signal driver <NUM> of the transmitter assembly <NUM>.

The guard electrode <NUM> may have similar geometry, with a major front surface <NUM> and a major rear surface <NUM>. The guard electrode <NUM> is powered by the guard driver <NUM> of the transmitter assembly <NUM>. The major front surface <NUM> of the guard electrode <NUM> may be located adjacent the major rear surface <NUM> of the sensing electrode <NUM>, such as separated by a distance smaller than the shortest of the lateral length or width of the sensing electrode <NUM>.

<FIG> depicts a few field lines of the electric field <NUM> of the sensing electrode <NUM> and the electric field <NUM> of the guard electrode <NUM>. The major front surface <NUM> of the guard electrode <NUM> may be oriented such that the field <NUM> of the sensing electrode <NUM> is shaped at least in part by the field <NUM> of the guard electrode <NUM>. As shown in <FIG>, the electrodes may be positioned such that the distance from the major rear surface <NUM> of the sensing electrode <NUM> to the major front surface <NUM> of the guard electrode <NUM> is smaller than the distance from the major rear surface <NUM> of the sensing electrode <NUM> to the ground electrode <NUM> (or to any other electrode, if any, or any other object). The shortest path from any point on the major rear surface <NUM> of the sensing electrode <NUM> outward (i.e., in a direction generally downward in the view of <FIG>) may intersect the major front surface <NUM> of the guard electrode <NUM> before reaching any other object. In this way, the guard electrode <NUM> may prevent other objects from interfering with the portion of the field <NUM> emanating from the major rear surface <NUM> of the sensing electrode <NUM>. Thus, the guard electrode <NUM> may "guard" the major rear surface <NUM> of the sensing electrode <NUM> from interacting with other electrodes, and may cause the sensing electrode <NUM> to function similar to a theoretical one-sided electrode (i.e., with no field lines emanating from the major rear surface <NUM> of the sensing electrode <NUM> past the guard electrode <NUM>). In such an arrangement, the field lines of the field <NUM> emanating from the maj or rear surface <NUM> of the sensing electrode <NUM> are spaced more densely than field lines emanating from the major front surface <NUM>. Thus, the field lines of the field <NUM> of the sensing electrode <NUM> do not pass or intersect the guard electrode <NUM>.

The ground electrode <NUM>, if present, may be separated from and coplanar with the sensing electrode <NUM>. In such embodiments, some field lines of the field <NUM> of the sensing electrode <NUM> may have an arcuate shape extending outward from the major front surface <NUM> of the sensing electrode <NUM> to the ground electrode <NUM>. Some field lines of the field <NUM> of the guard electrode <NUM> may have an arcuate shape extending outward from the major rear surface <NUM> of the guard electrode <NUM> to the ground electrode <NUM> (which may be the same ground electrode <NUM> or a different ground electrode <NUM>). The ground electrode(s) <NUM> may laterally surround the sensing electrode <NUM> and/or the guard electrode <NUM>. In some embodiments, the ground electrode <NUM> may include a shield <NUM> protecting the transmitter assembly <NUM>, such that the fields <NUM>, <NUM> do not interfere with the operation of the transmitter assembly <NUM>. Field lines emanating from the sensing electrode <NUM> and the guard electrode <NUM> may intersect the ground electrode <NUM>.

In some embodiments, a cable <NUM> may connect the transmitter assembly <NUM> to the electrodes <NUM>, <NUM>, <NUM>. The cable <NUM> may be a coaxial cable having two or more conductors sharing a common axis. For example, the cable <NUM> may have a first conductor, shown as an inner core conductor (e.g., a wire) of a triaxial cable, connecting the sensing circuit <NUM> to the sensing electrode <NUM>. The cable <NUM> may have a second conductor, shown as an intermediate cylindrical conductor of a triaxial cable, connecting the guard driver <NUM> to the guard electrode <NUM>. The cable <NUM> may have a third conductor, shown as an outer cylindrical conductor of a triaxial cable, connecting the ground electrode <NUM> to a physical ground. In some embodiments, the ground electrode <NUM> may be omitted, and thus, the cable <NUM> may be a biaxial cable, having only two conductors.

The transmitter assembly <NUM> is configured to provide a first signal to the sensing electrode <NUM> and a second signal to the guard electrode <NUM>. For example, and as discussed above, the transmitter assembly <NUM> may send preselected voltage signals to the electrodes <NUM>, <NUM>. In some embodiments, the voltage provided to each electrode <NUM>, <NUM> may be identical in magnitude but electrically isolated. Isolated outputs may enable the transmitter assembly <NUM> to distinguish material sensed in the volume encompassed by field <NUM> from <NUM>, and that the interference between them may be insignificant. That is, the magnitude of the difference between the two fields <NUM>, <NUM> as they extend outward, and/or the field established between the major rear surface <NUM> of the sensing electrode <NUM> and the major front surface <NUM> of the guard electrode <NUM> may be significantly smaller (e.g., at least one order of magnitude, at least two orders of magnitude, etc.) than the magnitude of the fields <NUM>, <NUM> themselves.

The transmitter assembly <NUM> may provide the selected signals to the electrodes <NUM>, <NUM> using the signal driver <NUM> and the guard driver <NUM>. The power source <NUM> may provide power to the signal driver <NUM> and the guard driver <NUM>.

In some embodiments, the transmitter assembly <NUM> may be configured to provide a first voltage to the sensing electrode <NUM> and a second, different voltage to the guard electrode <NUM>. The second voltage may be offset from the first voltage by a preselected amount. The offset may be in the magnitude of the voltages, in the phase, or a combination of both the magnitude and phase. These different voltages may be useful for active sensing of material, using changing field parameters (e.g., detection area size or shape, direction of view, calibration, etc.).

The sensing circuit <NUM> may measure the output of the signal driver <NUM>, such as the current or power levels required to provide the selected voltage. The guard driver <NUM> may be configured to provide a selected voltage to the guard electrode <NUM>, and may optionally receive its power from the power source <NUM> via the signal driver <NUM>. Though the transmitter assembly <NUM> is described as providing a known voltage and measuring known power or current, other attributes of the field may be measured, such as current, power, voltage, reactance, impedance, resonance, capacitance, frequency, permittivity, time, etc..

The sensing field <NUM> may have a response curve, meaning that its attributes vary in a particular way in response to different conditions. For example, the sensing field <NUM> may have a field strength that decreases in proportion to <NUM>/r<NUM> or <NUM>/r<NUM>, where r is the distance from the major front surface <NUM> of the sensing electrode <NUM>. If the field <NUM> is formed by electromagnetic radiation having a frequency that excites water molecules, moisture in the field <NUM> can affect the field lines of the field <NUM>. The material in the field <NUM> may cause a change in the electrical load provided by the signal driver <NUM> to generate the field <NUM>, and may be measured by the sensing circuit <NUM>. The use of electromagnetic sensors for characterizing crop material is described in more detail in <CIT>.

<FIG> is a simplified diagram illustrating another capacitive sensor <NUM>. The sensor <NUM> includes a transmitter assembly <NUM>, at least one sensing electrode <NUM>, and at least one guard electrode <NUM>. The sensor <NUM> is depicted as lacking a ground electrode, and with the guard electrode <NUM> also serving as the shield <NUM> to protect the transmitter assembly <NUM> from interference by the fields <NUM>, <NUM> emanating from the electrodes <NUM>, <NUM>. As depicted, the fields <NUM>, <NUM> may extend generally outward to another physical ground. The electrodes <NUM>, <NUM> may be arranged such that the guard field <NUM> shapes the sensing field <NUM>. In the embodiment shown, the field lines of the sensing field <NUM> extend generally upward and outward.

<FIG> is a simplified diagram illustrating another capacitive sensor <NUM>. The sensor <NUM> includes a transmitter assembly <NUM>, a sensing electrode <NUM>, a guard electrode <NUM>, switchable electrodes 307a-307e, and a ground electrode <NUM> (which may operate as a shield <NUM> to protect the transmitter assembly <NUM> from interference, either alone or in combination with the guard electrode <NUM>). The major front surfaces of the electrodes <NUM>, <NUM>, 307a-307e may be generally coplanar. In embodiments in which the major front surfaces are curved or another shape, the curvature of the major front surfaces of the electrodes <NUM>, <NUM>, 307a-307e may be generally continuous.

The transmitter assembly <NUM> may include a signal driver <NUM>, a guard driver <NUM>, a sensing circuit <NUM>, and a power source <NUM>, as discussed above. Furthermore, the transmitter assembly <NUM> includes a multiplexor <NUM> and a controller <NUM>. The multiplexor <NUM> is configured to selectively provide power from the guard driver <NUM> to individual switchable electrodes 307a-307e. The controller <NUM> can drive the multiplexor <NUM> to change which of the switchable electrodes 307a-307e are powered and which are grounded. Thus, the switchable electrodes 307a-307e may, when so powered, operate as guard electrodes, similar to the guard electrode <NUM>. The multiplexor <NUM> may also ground one of the switchable electrodes 307a-307e. As depicted in <FIG>, the electrode 307b is grounded by the multiplexor <NUM>, while the electrodes 307a, 307c, 307d, and 307e are powered by the guard driver <NUM>. Thus, field lines of the guard field <NUM> connect the guard electrodes <NUM>, 307a, 307c, 307d, and 307e to the grounded switchable electrode 307b and/or to the ground electrode <NUM>. The field lines of the sensing field <NUM> connect the sensing electrode <NUM> to the grounded switchable electrode 307b. The approximate shape of the sensing field <NUM> is shaded in <FIG>.

<FIG> is a simplified diagram illustrating how the shape of the fields changes when the multiplexor <NUM> changes which electrodes are powered. In particular, switchable electrode 307c is depicted as grounded in <FIG>, and the guard field <NUM> has field lines connecting the electrodes <NUM>, 307a, 307b, 307d, and 307e to the grounded switchable electrode 307c and/or to the ground electrode <NUM>. The field lines of the sensing field <NUM> connect the sensing electrode <NUM> to the grounded switchable electrode 307c. The approximate shape of the sensing field <NUM> is shaded in <FIG>. By changing which of the switchable electrodes 307a-307e are powered and which are grounded, the shape of the sensing field <NUM>, <NUM> can be changed without changing the physical location of the electrodes <NUM>, <NUM>, <NUM>, 307a-307e. The multiplexor <NUM> may likewise ground any of the switchable electrodes 307a-307e to cause different sensing fields. Thus, the multiplexor <NUM> may enable rapid switching between sensing fields of different size and/or shape without physical movement of the sensor <NUM> or components thereof.

<FIG> is a simplified diagram illustrating another capacitive sensor <NUM>. The sensor <NUM> may be generally configured similar to the sensor <NUM> shown in <FIG> and <FIG>, including a transmitter assembly <NUM>, a sensing electrode <NUM>, a guard electrode <NUM>, switchable electrodes 307a-307e, and a ground electrode <NUM> (which also operates as a shield <NUM> to protect the transmitter assembly <NUM> from interference). The transmitter assembly <NUM> differs from the transmitter assembly <NUM> shown in <FIG> in that it includes switched guard drivers 513a-513e, instead of the multiplexor <NUM>. One switched guard driver 513a-513e is configured to power each of the switchable electrodes 307a-307e. The switched guard drivers 513a-513e may be independently driven by the controller <NUM>, such that the transmitter assembly <NUM> can generate different sensing and guard fields in a similar manner as the sensor <NUM>.

In some embodiments, different sensing electrodes may form different sensing fields concurrently. For example, <FIG> is a simplified diagram illustrating another capacitive sensor <NUM>. The sensor <NUM> includes a transmitter assembly <NUM>, sensing electrodes 604a-604e, a guard electrode <NUM>, and a ground electrode <NUM> (which also operates as a shield <NUM> to protect the transmitter assembly <NUM> from interference).

The transmitter assembly <NUM> includes a signal driver <NUM> configured to provide selected voltage(s) to the guard electrode <NUM> and the sensing electrodes 604a-604e. Sensing circuits 615a-615e may selectivity detect the output of the signal driver <NUM> to each corresponding sensing electrode 604a-604e. An output driver <NUM> may control voltages applied to each of the sensing electrodes 604a-604e. Sensing fields <NUM> may form between each sensing electrode 604a-604e and the ground electrode <NUM>. Each sensing electrode 604a-604e may generate a separate sensing field, and the size and shape of each is dependent on the distance from each sensing electrode 604a-604e to the ground electrode <NUM>, the position of the other sensing electrodes 604a-604e, the power levels of each sensing electrode 604a-604e, the size and shape of each sensing electrode 604a-604e, etc. The different sensing fields <NUM> may shape one another, and may together be used to measure properties of material in different volumes or in different ways.

Each of the sensors <NUM>, <NUM>, <NUM> shown in <FIG> include a guard electrode <NUM> depicted on the left of the sensing electrode(s) <NUM> or 604a-604e. However, in some embodiments, the guard electrode <NUM> may be omitted and replaced by additional switchable electrodes or sensing electrodes. In such embodiments, the additional switchable electrodes or sensing electrodes may serve to shape the sensing fields and/or limit the influence of external electric fields on the sensing fields. Furthermore, the sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM> shown in <FIG> are depicted as unitary structures (either combined with or separate from the transmitter assemblies), but the various electrodes may also be configured to be separately mounted on a body or on separate bodies in such a manner that fields generated affect one another.

The sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM> described herein may carried by an agricultural vehicle frame and may be used to measure crop material in crop-harvesting operations, such as in combines, windrowers, balers, etc. The sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and methods herein may also be used to measure properties of any other type of material, and may be used in various industries, such as mining, chemical processing, food processing and packaging, shipping, security (e.g., nondestructively detecting properties of unopened parcels), construction (e.g., detecting materials inside walls), manufacturing (e.g., nondestructive parts inspection), etc..

<FIG> is a simplified side view of a baling system <NUM> including a tractor <NUM> towing a baler <NUM>, each of which include vehicle frames. The baling system <NUM> is operable to receive loose crop material <NUM>, form it into individual charges, and compress the charges to form a bale <NUM>. The baler <NUM> may include a stuffing component <NUM>, a forming chamber <NUM>, and a plunger <NUM>. The stuffing component <NUM> picks up the loose crop material <NUM>, and transfers it to the forming chamber <NUM>. The plunger <NUM> compresses the loose crop material <NUM> to form the bale <NUM> or a portion thereof. Baling systems are described in more detail in International Patent Application Publication <CIT>. As depicted in <FIG>, the baler <NUM> may include one or more sensors <NUM>, <NUM>, <NUM>. For example, the sensor <NUM> is depicted adjacent to the stuffing component <NUM> to detect properties of the loose crop material <NUM> entering the baler <NUM>. The sensor <NUM> is depicted on or in the plunger <NUM> to detect properties of the crop material before or during compression The sensor <NUM> is depicted adjacent the bale <NUM> to detect properties of the crop material in the bale <NUM> as the bale <NUM> is ejected from the baler <NUM>. The sensors <NUM>, <NUM>, <NUM> may be a sensor <NUM>, <NUM>, <NUM>, <NUM>, <NUM> as shown in <FIG> and described above. Additional sensors may be in other locations within the baling system <NUM>, such as carried by the tractor <NUM>. Multiple sensors may be used to characterize whether operating parameters of the baling system <NUM> are effective, and may enable a control system to adjust the operating parameters (e.g., ground speed, compaction force, etc.) to improve the properties of the bale <NUM>. For example, the sensor(s) <NUM>, <NUM>, <NUM> may be used to measure the moisture content and/or density of crop material in the bales <NUM>.

<FIG> is a simplified side view of a self-propelled windrower <NUM>. In some embodiments, pull-type or other types of harvesting machines may be used. The windrower <NUM> broadly includes a self-propelled tractor <NUM> having a vehicle frame and a harvesting header <NUM> attached to and carried by the front of the tractor <NUM>. An operator drives the windrower <NUM> from a cab <NUM>, which includes an operator station having a tractor seat and one or more user interfaces (e.g., FNR joystick, display monitor, switches, buttons, etc.) that enable the operator to control various functions of the tractor <NUM> and header <NUM>. In one embodiment, a controller <NUM> or computing system is disposed in the cab <NUM>, though in some embodiments, the controller <NUM> may be located elsewhere or include a distributed architecture having plural computing devices, coupled to one another in a network, throughout various locations within the tractor <NUM> (or in some embodiments, located in part externally and in remote communication with one or more local computing devices).

The header <NUM> includes a cutter <NUM>, a conditioning system, a swathboard <NUM>, and a forming shield assembly <NUM>. The cutter <NUM> is configured for severing standing crops as the windrower <NUM> moves through the field. The conditioning system, in the depicted embodiment, includes one or more pairs of conditioner rolls <NUM>. The forming shield assembly <NUM> may include a pair of rearwardly converging windrow forming shields located behind the conditioner rolls <NUM>. The swathboard <NUM> is located between the conditioner rolls <NUM> and the forming shield assembly <NUM>. In some embodiments, the conditioning system may be of a different design, such as a flail-type conditioning system. The swathboard <NUM> and/or the forming shield assembly <NUM> may be adjusted by one or more actuators <NUM>.

A sensor <NUM>, which may be any of the sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM> described above and shown in <FIG>, may be carried by the windrower <NUM> or the header <NUM> such that it can measure the crop material being cut by the header <NUM> and formed into a windrow. The measuring device <NUM> may communicate with the controller <NUM> such that the controller <NUM> can change operating parameters of the windrower <NUM> and/or the header <NUM> (e.g., a position of one or more of the actuators <NUM>). In some embodiments, the measuring device <NUM> may report information to the operator, and the operator may make changes to the operating parameters of the windrower <NUM> and/or the header <NUM>. Changing operating parameters of a windrower <NUM> or header <NUM> based on information about the crop is described in more detail in <CIT>.

<FIG> is a simplified flow chart illustrating a method <NUM> of measuring electric fields associated with crop material. In block <NUM>, a first electric field is broadcast from a sensing electrode into a volume containing crop material. At least some field lines of the first electric field emanate from the sensing electrode through the volume. The first electric field may be broadcast by applying a first voltage to the sensing electrode, which may be a constant voltage or a variable voltage. In block <NUM>, a second electric field is broadcast from at least one guard electrode adjacent the sensing electrode. The presence of the second electric field changes a shape of the field lines of the first electric field. The second electric field may be broadcast by applying a second voltage to the sensing electrode, which may be the same as or different from the first voltage. In some embodiments, the sensing electrode may be electrically isolated from the guard electrode.

In block <NUM>, an attribute of the first electric field is measured. For example, the attribute measured may be current, power, voltage, reactance, impedance, resonance, capacitance, frequency, permittivity, time, etc. In block <NUM>, the measured attribute is correlated to the first electric field to an amount or distribution of the crop material in the volume, such as total crop volume, crop density, crop distribution (e.g., lateral distribution of crop material, crop depth on the sensor, or distance from the sensor to the crop), etc..

In block <NUM>, an operating parameter of an agricultural machine is modified based on the amount or distribution of crop material in the volume.

Still other embodiments involve a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) having processor-executable instructions configured to implement one or more of the techniques presented herein. An example computer-readable medium that may be devised is illustrated in <FIG>, wherein an implementation <NUM> includes a computer-readable storage medium <NUM> (e.g., a flash drive, CD-R, DVD-R, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), a platter of a hard disk drive, etc.), on which is computer-readable data <NUM>. This computer-readable data <NUM> in turn includes a set of processor-executable instructions <NUM> configured to operate according to one or more of the principles set forth herein. In some embodiments, the processor-executable instructions <NUM> may be configured to cause a computer associated with an agricultural machine, such as the baling system <NUM> (<FIG>) or the windrower <NUM> (<FIG>) to perform operations <NUM> when executed via a processing unit, such as at least some of the example method <NUM> depicted in <FIG>. In other embodiments, the processor-executable instructions <NUM> may be configured to implement a system, such as at least some of the example baling system <NUM> (<FIG>) or windrower <NUM> (<FIG>). Many such computer-readable media may be devised by those of ordinary skill in the art that are configured to operate in accordance with one or more of the techniques presented herein.

Claim 1:
An agricultural machine, comprising:
a vehicle frame; and
a capacitive sensor (<NUM>) carried by the vehicle frame, the capacitive sensor comprising:
a transmitter assembly (<NUM>) comprising a signal driver (<NUM>), at least one guard driver (<NUM>), and at least one sensing circuit (<NUM>) configured to detect an output of the signal driver;
at least one sensing electrode (<NUM>) powered by the signal driver; and
a plurality of guard electrodes (<NUM>) powered by the at least one guard driver (<NUM>);
wherein the guard electrodes are oriented such that a first electric field emanating from the at least one sensing electrode is shaped at least in part by a second electric field emanating from at least one guard electrode of the plurality of guard electrodes;
wherein the transmitter further comprises a multiplexor (<NUM>) configured to selectively provide power from the at least one guard driver to individual guard electrodes of the plurality of guard electrodes; and wherein the sensor further comprises a controller (<NUM>) configured to drive the multiplexor.