Simplified jaw assembly for a clamp meter

A current clamp meter includes a current meter body and a jaw assembly. The jaw assembly is configured so that the current clamp meter may be used to reach and readily single-out a desired wire from amongst adjacent wires.

TECHNICAL FIELD

This invention generally relates to electronic test tools, and more specifically, to a current clamp meter including a jaw assembly that has a reduced cross-section to aid a user in selecting a wire for measuring current through the wire.

BACKGROUND OF THE INVENTION

Electrical current can be measured by connecting a current meter in series with the wire. In many cases, however, disconnecting the wire to connect the current meter can be inconvenient. For example, the wire can be tightly grouped in a bundle with several other wires making it difficult to individually disconnect the wire of interest. Another example of the inconvenience is where a terminal to which the wire is connected is not conveniently located or is inaccessible, requiring the wire to be cut for the current meter to be connected in series. It is time consuming to reconnect the two ends of the cut wire after a measurement is taken, and can be dangerous in situations where relatively high current is carried by the wire. Additionally, the integrity of the wire is compromised by cutting and reconnecting, thus, potentially raising reliability problems.

A clamp probe connected to a conventional multimeter can be used to measure electrical current without the need for disconnecting a wire. The clamp probe is opened, the wire is inserted into the clamp, and the clamp is closed to take a current measurement. The closed clamp includes a core of ferromagnetic material, which when closed, represents the core of a transformer. The wire passing through the clamp represents the primary winding. As known, a current flowing in the wire induces a magnetic flux in the core of the transformer, which in turn, induces a current in a secondary winding of the transformer. Using these physical phenomena, the magnitude and polarity of the current in the clamped wire can be determined based on the current induced in the secondary winding and the characteristics of the transformer formed by the clamped wire.

A known clamp meter is designed with the clamp integrated into the body of the meter, which can provide the convenience of taking a measurement using one hand. That is, only one hand is used to open and close the clamp for clamping a wire and to take a current reading. “One-handed” clamp meters are generally acceptable for applications where the display can be easily viewed by the technician with the meter clamped to the wire for measurement. However, problems with reading the measurement can arise where the wire is difficult to reach or cannot be readily singled-out from amongst adjacent wires.

FIG. 6illustrates an exploded view of a known jaw assembly. The known jaw assembly includes housings that are split in two approximately equal pieces. In particular, neither housing piece of the known jaw assembly has a volume approximately sufficient to individually contain a current sensing core. Additionally, the known jaw assembly includes separate end caps that are not integrally formed with either piece of the housing. It is therefore more difficult to use the known jaw assembly to select an individual wire from a group of wires because the cross-section of the known jaw assembly is enlarged due to the location of the joints between the housing pieces and the separate end caps.

DETAILED DESCRIPTION

The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description.

Without intent to further limit the scope of the disclosure, examples of instruments, apparatus, methods and their related results according to the embodiments of the present disclosure are given below. Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.

The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Certain terms that are used to describe the disclosure are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the disclosure. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and is not intended to further limit the scope and meaning of the disclosure or of any exemplified term. Likewise, the disclosure is not limited to various embodiments given in this specification.

Certain details are set forth below to provide a sufficient understanding of the invention. However, it will be clear to one skilled in the art that the invention may be practiced without these particular details. Moreover, the particular embodiments of the present invention described herein are provided by way of example and should not be used to limit the scope of the invention to these particular embodiments. In other instances, well-known circuits, controls, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the invention.

FIG. 1illustrates a clamp meter according to an embodiment of the present invention. As will be described in more detail below, the clamp meter100includes a current clamp jaw assembly110that is integrated into a housing112in which circuitry for the clamp meter100is encased. The jaw assembly110includes a current sensor for detecting current in a wire (not shown) positioned in an opening111. Examples of current sensors include Hall-effect devices and coils such as a current transformer, as known in the art. As shown inFIG. 1, the jaw assembly110is positioned in a recess120in a body114. The jaw assembly110includes a lever portion130that is exposed in the recess120. When depressed, the lever portion130configures the jaw assembly110in an open arrangement (FIG. 3A) to receive a wire in the opening111for measurement. The jaw assembly110is a spring loaded device whereupon release of the lever portion130, the jaw assembly110is biased to a closed arrangement (FIG. 3B). Consequently, when the wire is positioned in the opening111, the lever portion130can be released to capture the wire for measurement. The wire can be released from the opening111by depressing the lever portion130and withdrawing the clamp meter100.

On a front-side of the meter100there is a user interface for receiving input from and providing information to a user. The user interface shown inFIG. 1includes a display132for displaying information, such as a measured value, mode of operation, and device and battery status. The user interface further includes a thumb wheel134that can be used to receive input from the user and carry out functions in the meter, for example, turning the meter on and off, selecting a mode of operation, selecting a measurement range, and taking a measurement. Although the present embodiment includes thumb wheel134, additional or alternative user input devices can be used in other embodiments, such as dials, buttons, and switches. Additionally, the user input devices can be located at different positions than shown inFIG. 1.

The jaw assembly110is electrically coupled to circuitry enclosed by the housing112.FIG. 2illustrates a simplified block diagram of electrical circuits that can be included in the clamp meter100. The electrical circuits shown inFIG. 2are provided by way of example. The circuits included in the clamp meter100can be implemented in the meter100using conventional designs and operation.

The jaw assembly110may be electrically coupled to a connector310through a wire116. Electrical signals generated by the current sensor in the jaw assembly110in response to detecting current in a wire positioned in the opening111may be provided through the connector310to a signal conditioning circuit320. The signal conditioning circuit320can condition the electrical signals, for example, by buffering, filtering, and amplifying the signal. A processor330can receive the conditioned signal and compute a current measurement. The processor330generates signals to drive a liquid crystal display (“LCD”)132to display information, including the computed current value. Although not shown inFIG. 2, the current sensor in the jaw assembly110may form an electrical connection with circuitry enclosed by the housing without a distinct connector310or signal conditioning circuit320. A processor or controller may include either or both of a connector and signal processing circuit. Additionally, an analog-to-digital converter (“ADC”) may be used in addition to, instead or, or part of a signal processing circuit to quantize the conditioned signal into digital information representing the conditioned signal prior to processing by the processor330. The electrical circuitry in housing112may be an application specific integrated circuit (ASIC). Thumb wheel134is provided for user input to the processor330. A power supply340provides power to various circuitry of the meter100, such as the signal conditioning circuit320, the processor330, and the LCD132. The power supply340typically includes a battery and power circuits for regulating the provision of power to the circuits in the meter100. Alternatively, the power supply could be adapted to receive power from an AC source.

In other embodiments of the present invention, the processor330is operable to compute measurements for other electrical characteristics, as detected by test probes coupled to electrical terminals122further included in the connector310. For example, multimeter functionality can be integrated into the meter100, such as measuring voltage and resistance.

FIGS. 3A and 3Billustrate the jaw assembly110separated from the housing112. The open arrangement of the jaw assembly110is shown inFIG. 3Aand the closed arrangement of the jaw assembly110is shown inFIG. 3B. The jaw assembly110includes a generally fixed jaw140with respect to the housing112and a relatively pivotable jaw150. The pivotable jaw150includes the lever portion130and is pivotally supported relative to the housing112via a pivot132, e.g., aligned pivot holes.

FIG. 4illustrates a cross-section of the jaw assembly110taken along the chain line IV-IV shown inFIG. 3A. A first portion142of the current sensor is disposed in the fixed jaw140and a second portion152of the current sensor is disposed in the pivotable jaw150. In the closed arrangement of the jaw assembly110shown inFIG. 4, the first and second portion142together with the second portion152surround the opening111and form the current sensor. The output of the current sensor is conducted via the wire116.

FIG. 5illustrates an exploded view of the jaw assembly110. The fixed jaw140includes shield having a base144, a cover146, a first end cap148aand a second end cap148b. Preferably, the cover146defines a channel having a volume approximately as large as the first portion142of the current sensor. The first portion142of the current sensor is therefore received within the cover146and the base144occludes the channel. Accordingly, the first portion142of the current sensor is disposed in a pocket140a(FIG. 4) defined by the base144and the cover146. The first and second end caps148and the base144are preferably integrally formed as a monolithic structure and the cover146is coupled, e.g., adhered, welded, bonded, etc., to the base144to form the pocket140a. The pivotal jaw150similarly includes a shield having a base154, a cover156, a first end cap158aand a second end cap158b. Preferably, the cover156defines a channel having a volume approximately as large as the second portion152of the current sensor. The second portion152of the current sensor is therefore received within the cover156and the base154occludes the channel. Accordingly, the second portion152of the current sensor is disposed in a pocket150a(FIG. 4) defined by the base154and the cover156. The first and second end caps158are preferably integrally formed as a monolithic structure with the base154and the cover156is coupled, e.g., adhered, welded, bonded, etc., to the base154to form the pocket150a.

FIG. 7Ashows a schematic cross-section of the known clamp meter shown inFIG. 6. In particular, the joint or seam coupling the two housing pieces is centered along a side of the current sensor. In contrast,FIG. 7Bshows a schematic cross-section of the clamp meter shown inFIG. 1. Embodiments according to the present disclosure relocate the coupling between the base144,154and the cover146,156proximate to a corner of the current sensor.

An advantage of embodiments according to the present invention is reducing the cross-sectional size of the fixed jaw140and the pivotable jaw150. The thickness “T” (FIG. 4) of the jaw assembly110is reduced by approximately 30% or more as compared to the known jaw assembly (FIG. 6) because the end caps148and158are integrally formed with the bases144and154. For example, the thickness T of the known jaw assembly is approximately 18.5 millimeters whereas the thickness T of the jaw assembly110is approximately 13 millimeters. The reduced cross-sectional size of the jaw assembly110therefore enables a user to reach and readily single-out a desired wire from amongst adjacent wires.

Another advantage of embodiments according to the present invention is simplifying the jaw assembly110as compared to the known jaw assembly (FIG. 6). The assembly is simplified by reducing the number of steps needed for assembly because the end caps148and158are integrally formed with the bases144and154rather than being separately attached.