Hot plug detection at the meter

Abstract

Techniques for hot socket detection are disclosed. In an example, an instrument includes a current transformer having a secondary bifilar winding. The instrument is proximate to a current coil. The secondary bifilar winding includes a first bifilar winding and a second bifilar winding. A start leg of the first bifilar winding is connected to a start leg of the second bifilar winding. The instrument also includes a voltage source configured to generate a DC (DC) voltage signal. The DC voltage signal is provided to an end leg of the first bifilar winding. A first sense resistor is connected between an end leg of the second bifilar winding and ground. Processing circuitry receives a signal indicative of a voltage across the first sense resistor and determines a temperature associated with the current coil. The processing circuitry is also configured to detect a hot socket condition based on the temperature.

Description

Technical Field

[0001] This invention generally relates to electric meters and more specifically to systems and methods for detecting hot sockets in electric meters. Background Technology

[0002] An electricity meter measures the energy or power consumed between a utility power line and a load. For example, a residential customer's electricity meter is often connected at the point where the home's electrical system connects to the utility line. Utility meters include one or more electrical contacts through which a large current flows. For example, the meter may have blades that connect to the power line and the load to enable the measurement of load current and load voltage from within the meter. The blades are received by jaws in meter mounting equipment used in buildings.

[0003] To replace or repair an instrument, it is removed from the mounting equipment, thus pulling the blade out of the jaws. Although blades and jaws are generally mechanically robust, they are still susceptible to wear and potential corrosion. This is especially true if the instrument has been removed or replaced several times. If the wear on the jaws is significant, or if the jaws are corroded, there is a possibility of introducing non-trivial resistance at the jaw-blade connection, which is undesirable.

[0004] A "hot-swap" condition can occur when the connection between the jaws of the instrument mounting equipment and the blades of the instrument becomes unreliable due to increased resistance, bulging, or other conditions. When a hot-swap condition exists, the temperature of the instrument, and especially the temperature of the blades, increases.

[0005] Furthermore, meters may have one or more switches that take into account disconnecting the electrical service to the load. For example, many meters consider remote control of the switches. These switches must have substantial contacts because they carry the full current of the load when closed. If these switches are used at a certain frequency, then degradation is possible. Degradation of the switch contacts increases the resistance across the switch contacts. This resistance generates additional power losses within the meter, which is undesirable.

[0006] Because we do not want to introduce resistance, there is a need for ways to detect the potential degradation of this connection over time. Summary of the Invention

[0007] Certain aspects and features include techniques for detecting hot-swappable connectors. In an example, an instrument includes a current transformer comprising a primary winding, a secondary winding, and a secondary bifilar winding. The primary winding corresponds to a current coil, and the secondary bifilar winding comprises a first bifilar winding and a second bifilar winding connected in series. A start lead of the first bifilar winding is connected to a start lead of the second bifilar winding. The instrument also includes a voltage source configured to generate a direct current (DC) voltage signal. The DC voltage signal is provided to the finish lead of the first bifilar winding. A first sensing resistor is connected between the finish lead of the second bifilar winding and ground. The temperature coefficient of the first sensing resistor is less than the temperature coefficient of the resistivity of the materials of the first and second bifilar windings. The instrument also includes processing circuitry configured to receive an input corresponding to a voltage across the first sensing resistor. The processing circuitry is configured to use the voltage across the first sensing resistor to determine the temperature associated with the current coil. The processing circuit is also configured to detect hot-swap conditions when the temperature exceeds a temperature threshold.

[0008] In another example, the instrument includes a current transformer. The current transformer includes a primary winding, a secondary winding, and a secondary bi-wire winding. The primary winding corresponds to a current coil, and the secondary bi-wire winding includes a first bi-wire winding and a second bi-wire winding connected in parallel. The end lead of the first bi-wire winding is connected to the start lead of the second bi-wire winding. The instrument also includes a voltage source configured to generate a DC voltage signal. This DC voltage signal is provided to the end lead of the first bi-wire winding and the start lead of the second bi-wire winding, and a first sensing resistor is connected between the start lead of the first bi-wire winding, the end lead of the second bi-wire winding, and ground. The temperature coefficient of the first sensing resistor is less than the temperature coefficient of resistivity of the materials of the first and second bi-wire windings. The instrument also includes processing circuitry configured to receive an input corresponding to a voltage across the first sensing resistor. The processing circuitry is configured to use the voltage across the first sensing resistor to determine the temperature associated with the current coil. The processing circuitry is also configured to detect a hot-swap condition when the temperature exceeds a temperature threshold.

[0009] In another example, the instrument includes a current transformer. The current transformer includes a primary winding, a secondary winding, and a secondary bi-wire winding. The primary winding corresponds to a current coil. The secondary bi-wire winding includes a first bi-wire winding and a second bi-wire winding. The start lead of the first bi-wire winding is connected to the start lead of the second bi-wire winding. The instrument also includes a voltage source configured to generate a DC voltage signal. This DC voltage signal is provided to the end lead of the first bi-wire winding. The instrument also includes a first sensing resistor connected between the end lead of the second bi-wire winding and ground. The temperature coefficient of the first sensing resistor is less than the temperature coefficient of resistivity of the materials of the first and second bi-wire windings. The instrument also includes an A / D converter connected between the first sensing resistor and an input to processing circuitry. The processing circuitry is configured to receive a signal corresponding to the voltage across the first sensing resistor from the A / D converter, use the signal from the A / D converter to determine the temperature associated with the current coil, and detect a hot-swap condition when the temperature exceeds a temperature threshold.

[0010] These illustrative examples are cited not to limit or restrict this disclosure, but to provide examples to aid in understanding it. Additional examples and further descriptions are provided in the detailed description. Attached Figure Description

[0011] These and other features, aspects, and advantages of this disclosure will be better understood when the following detailed description is read with reference to the accompanying drawings, in which: Figure 1 This is a schematic block diagram of an exemplary metering system according to aspects of this disclosure.

[0012] Figure 2 This is a schematic diagram of an exemplary temperature sensor circuit having a bi-wire winding with a series connection, according to aspects of this disclosure.

[0013] Figure 3 It is a graph showing the relationship between voltage and temperature measured according to aspects of this disclosure.

[0014] Figure 4 This is a schematic diagram of an exemplary temperature sensor circuit having a bi-wire winding with windings connected in parallel, according to aspects of this disclosure.

[0015] Figure 5 It is a graph showing the relationship between voltage and temperature as measured according to aspects of this disclosure.

[0016] Figure 6 This is a flowchart illustrating an example of a process for deriving the temperature of a current coil according to aspects of this disclosure. Detailed Implementation

[0017] This disclosure relates to detecting hot-swappable terminals in an electricity meter. A hot-swappable terminal is defined as a condition in which a component of the meter, such as a current-carrying blade, or the jaws of the terminal are worn or damaged, causing a potentially hazardous increase in temperature within the meter. Hot-swappable terminals can occur when the jaws, blades, or current coil degrade over time.

[0018] Previous techniques for detecting hot-swappable connectors involved adding a temperature sensor to the instrument or using a modified current transformer with an additional secondary winding. This additional secondary winding was voltage-biased such that the current formed partially indicated the permeability of the transformer. The permeability of the transformer depends on temperature, thus deriving the temperature from it. However, in this technique, the bias voltage must be applied intermittently to minimize the net magnetization of the winding and maintain the accuracy of the current sensor. This results in less frequent temperature measurements and may affect the accuracy of the current measurement.

[0019] In contrast, this disclosure achieves temperature measurement by biasing an auxiliary bi-wire winding around the core of a current transformer located near the blades or current coil. The bi-wire winding comprises two closely spaced parallel windings. The current transformer can be an existing current transformer within a meter, for example, a current transformer configured to measure the current flowing through a current coil.

[0020] The two-wire windings can be interconnected in parallel or series. For example, in a series configuration, the start lead of the first winding is connected to the start lead of the second winding, the end lead of the first winding is connected to a voltage source, and the end lead of the second winding is connected to a sensing resistor. In contrast, in a parallel configuration, the two-wire windings are configured such that the start lead of the first winding and the end lead of the second winding are connected to a voltage source, and the end leads of both windings are connected to a sensing resistor.

[0021] The technical advantages of this disclosure include more frequent temperature measurements and more accurate current measurements without the need for a temperature sensor. For example, previous techniques could cause saturation and / or distortion in the measurement of the current flowing through the sensing resistor by applying a direct current (DC) voltage to the secondary winding, thereby reducing the accuracy of the temperature measurement derived therefrom. Additional advantages include the ability to apply a constant bias voltage due to the magnetic fields of the two-wire windings canceling each other out.

[0022] Now turn to the attached image. Figure 1 This is a schematic block diagram of an exemplary instrument measurement system according to aspects of this disclosure. Figure 1 The instrument measurement environment 100 is depicted, which includes power lines 50a-n, a load 60, an instrument 101, and a power source 104. Figure 1In the example depicted, power lines 50a-n transfer power from power source 104 to load 60 via instrument 101, which performs various instrumentation, including voltage and current measurement, current measurement, and temperature measurement.

[0023] Figure 1 Three power lines are depicted, corresponding to two lines for each phase: 50a and 50b, and a neutral line 50n. However, meter 101 can have any number of phases. For example, meter 101 can be adapted to connect to meters for various other standard power line configurations associated with standard electrical services, including but not limited to multiphase electrical services and single-phase residential services.

[0024] Power lines 50a and 50b are provided to instrument 101 for measurement. Power lines 50a and 50b are connected to a socket or instrument mounting device having jaws 52a, 52b, 54a, 54b, and 54n. Specifically, power lines 50a and 50b are electrically coupled to jaws 52a and 52b, and neutral line 50n is electrically coupled to jaw 54n. Jaws 54a and 54b are electrically coupled to the connections 60a and 60b of load 60. Neutral line 50n is also coupled to load 60. Jaws 52a, 52b, 54a, 54b, and 54n may be spring-loaded receptacles configured to receive instrument blades.

[0025] Instrument 101 includes one or more of the following: service switch 105, sensor circuit 110, metrology circuit 112, power supply 113, communication circuit 121, and display 130. Sensor circuit 110 is configured to measure voltage, current, and / or temperature. For example, as depicted, the sensor circuit includes voltage sensor circuit 140, current sensor circuits 160 and 180, and temperature sensor circuits 170 and 190. The measurement signal generated by sensor circuit 110 is an analog signal having corresponding waveforms representing the voltage and current supplied to the load. The measurement signal is transmitted to metrology circuit 112.

[0026] Service switch 105 is configured to enable or disable the connection of power lines 50a-n to meter 101. Service switch 105 is a relay controllable by processing circuitry 115. Processing circuitry 115 can enable or disable the connection of power lines 50a-n via service switch 105. In this way, utilities can be remotely enabled or disabled.

[0027] Meter 101 also includes current coils 122 and 124, which may be partially inside meter 101. Current coil 122 includes a body 122a of a conductive metal, such as a copper bar, which terminates at either end of blades 122b and 122c. When meter 101 is properly mounted in a meter mounting device, blade 122b is received by jaws 52a, and blade 122c is received by jaws 54a. Thus, power can flow from power line 50a to load 60 via jaws 52a, current coil 122, jaws 54a, and connection 60a. Blades 122b and 122c are typically located outside the housing, while the body 122a of current coil 122 extends through the interior of the housing.

[0028] Similarly, the current coil 124 includes a body 124a of a conductive metal, such as a copper strip, which terminates at either end of blades 124b and 124c. When the instrument 101 is properly installed, blade 124b is received by jaw 52b, and blade 124c is received by jaw 54b. Thus, power can flow from the power line 50b to the load 60 via jaw 52b, current coil 124, jaw 54b, and connection 60b. Blades 124b and 124c are typically outside the housing, while the body 124a of the current coil 124 extends through the interior of the housing. The neutral line 50n is coupled into the instrument via blade 125.

[0029] Temperature sensor circuits 170 and 190 are configured to identify phenomena indicating hot-swap conditions, including those where the temperature of instrument 101 exceeds a threshold temperature level. Temperature sensor circuit 170 is configured to measure the temperature of current coil 122 (the first phase supplied with power), and temperature sensor circuit 190 is configured to measure the temperature of current coil 124 (the second phase supplied with power). Therefore, in a multiphase system, more than one temperature sensor circuit can be used, for example, one temperature sensor circuit per phase.

[0030] More specifically, the temperature sensor circuit 170 is connected to a winding 172 surrounding a core 174. The core 174 is the same core discussed regarding the current sensor circuit 160, for example, a core configured in a current-sensing relationship with the current coil 122. The winding 172 is a two-wire winding, i.e., two parallel windings surrounding the core 174. Further details will be discussed regarding... Figure 2 and 4 This will be discussed further. Similarly, the temperature sensor circuit 190 is connected to the winding 192 surrounding the core 194. The core 194 can be the same as the core 184 discussed with respect to the current sensor circuit 180, for example, a core configured in a current-sensing relationship with the current coil 124. The winding 192 is a two-wire winding, i.e., two windings surrounding the core 194. Regarding... Figure 2 and4 This section discusses example implementations of temperature sensor circuits 170 and 190.

[0031] If temperature sensor circuits 170 and / or 190 detect a hot-swap condition, instrument 101 can be configured to send an alarm signal to a remote device, allowing mitigation steps to be taken to prevent or minimize damage to instrument 101 and to prevent or minimize service interruption to load 60. Mitigation steps may include remotely disconnecting service switch 105.

[0032] Current sensor circuit 160 is operable to detect current flowing in current coil 122. Current sensor circuit 160 includes a winding 162 disposed around a core 164. Core 164 may be part of a current transformer configured in a current-sensing relationship with current coil 122. Current sensor circuit 180 is operable to detect current flowing in current coil 124. Current sensor circuit 180 includes a winding 182 disposed around a core 184. Core 184 may be part of a current transformer configured in a current-sensing relationship with current coil 124.

[0033] The metering circuit 112 includes an analog-to-digital (A / D) converter 114 and a processing circuit 115. The processing circuit 115 may be part of a commercially available chip package including the A / D converter 114, memory 120, and / or other supporting devices. The A / D converter 114 may be any suitable analog-to-digital converter configured to sample the analog measurement signal generated by the sensor circuit 110. The A / D converter 114 is operatively coupled to provide the resulting digital measurement signal to the processing circuit 115.

[0034] Processing circuitry 115 includes a processing device configured to execute program instructions stored in a memory to perform various functions described herein, as well as other instrumentation measurement functions. Processing circuitry 115 is operatively coupled to receive digital measurement signals from A / D converter 114 and generate voltage, current, temperature, or energy consumption data therefrom. An example of the process for generating a temperature measurement is provided below. Figure 6 The processing circuit 115 may include digital processing circuitry that processes the digitized measurement signals to generate energy consumption data, power consumption data, voltage data, current data, or temperature data. The processing circuit 115 may also include the functions of a controller and / or a digital signal processor. The processing circuit 115 may also suitably include general-purpose control and monitoring processing circuitry, not shown in detail. The processing circuit 115 transmits information to external devices using serial input and output ports (not shown) or communication circuitry (also not shown).

[0035] Memory 120 includes one or more storage devices of different types. Memory 120 may include volatile or non-volatile random access memory, read-only memory, or other readable and / or writable memory devices. Memory 120 stores instructions and / or parameters used by processing circuitry 115 to perform the operations described herein, and may also store power consumption data. Memory 120 may include non-transitory computer-readable media.

[0036] Communication circuit 121 is operatively coupled to process circuit 115 and at least one external device to transmit information. For this purpose, communication circuit 121 may include an optical transceiver located at a semi-transparent or transparent optical port (not shown). Communication circuit 121 may also include remote communication circuitry, such as a power line modem, a radio frequency (RF) transceiver, for example, a paging radio, or other wireless devices capable of transmission over a wide area network (WAN) or another wireless communication network, or a cellular radio.

[0037] Display 130 is any display suitable for outputting information about instrument 100, such as a liquid crystal display (LCD), a light-emitting diode (LED) display, or a touch screen. For example, the information may include the operating status of instrument 100, such as instrument measurement or network status, or consumption information.

[0038] Figure 2 This is a schematic diagram of an exemplary temperature sensor circuit having a bi-wire winding with a series connection, according to aspects of this disclosure. Figure 2 An instrument environment 200 is depicted, which includes a temperature sensor circuit 201, a current coil 202, a current transformer 210, an A / D converter 114, a processing circuit 115, a DC voltage source 250, and a current sensor circuit 260. The DC voltage source 250 may be supplied by the instrument's power supply or from another component within the instrument. The temperature sensor circuit 201 is an example implementation of temperature sensor circuits 170 or 190.

[0039] The temperature sensor circuit 201 includes a first double-wire winding 220, a second double-wire winding 230, and a sensing resistor 240. The first double-wire winding 220 includes a start lead 222 and an end lead 224. The second double-wire winding 230 includes a start lead 232 and an end lead 234. The first double-wire winding 220 and the second double-wire winding 230 are of the same length and are wound around the core of the current transformer 210, such that the start leads 222 and 232 are at the first end of the current transformer and the end leads 224 and 234 are at the second end of the current transformer.

[0040] The current transformer 210 is configured in a current sensing relationship with the current coil 202, which serves as the primary winding. The current transformer 210 includes a first bi-wire winding 220 and a second bi-wire winding 230, which are secondary windings, as well as a current sensor winding 270, also serving as a secondary winding. The current sensor winding 270 is used by a current sensor circuit 260 to sense the current in the current coil 202. The current sensor circuit 260 includes a sensing resistor 261.

[0041] As depicted, the first two-wire winding 220 and the second two-wire winding 230 are configured in series. A start lead 222 is connected to the start lead 232. An end lead 224 is connected to the DC voltage source 250. An end lead 234 is connected to the first terminal of the sensing resistor 240 and to the input of the A / D converter 114. The second terminal of the sensing resistor 240 is connected to ground.

[0042] In an alternative configuration (not depicted), end lead 224 is connected to end lead 234. In this configuration, start lead 222 is connected to DC voltage source 250, start lead 232 is connected to the first terminal of sensing resistor 240, and the second terminal of sensing resistor 240 is connected to ground.

[0043] The first bi-wire winding 220 has an inherent resistance R1, the second bi-wire winding 220 has an inherent resistance R2, and the sensing resistor has a resistance R3. In some cases, the resistance of the sensing resistor R3 is greater than the inherent resistance of the bi-wire windings. In one example, the inherent resistance of each bi-wire winding is 100 Ohms, the resistance of the sensing resistor is 200 Ohms, the inherent impedance L1 of the first bi-wire winding 220 is 50 Henry, and the inherent impedance L2 of the second bi-wire winding L2 is 50 Henry.

[0044] As the temperature of the current coil (primary winding) changes, the measured voltage across the sensing resistor R3 changes because the temperature coefficients (or temperature coefficients of resistance) of the first and second bi-wire windings differ from the temperature coefficient of resistance of the sensing resistor. In one example, the temperature coefficient of the sensing resistor is smaller than the temperature coefficient of resistance of each of the bi-wire windings. Examples of temperature coefficients include 0.00393 for each bi-wire winding and 0.0001 for the sensing resistor.

[0045] When a voltage is applied by the DC voltage source 250, the A / D converter 114 receives a signal indicating the voltage across the sensing resistor 240. In one example, the DC voltage source provides approximately 3.3 volts to the end lead of the first two-wire winding. The A / D converter converts the signal into a digital output. The processing circuitry 115 receives the digital output signal from the A / D converter 114 and uses the digital signal to determine the temperature value. The voltage level provided by the DC voltage source and the size of the sensing resistor can be selected based on the requirements of the A / D converter. Some implementations select the voltage and resistance such that the input of the A / D converter is in the middle of the A / D converter's range when the current coil operates at the expected normal operating temperature. As the temperature of the current coil changes, the voltage measured at the sensing resistor changes. Therefore, as... Figure 3 As shown, the measured voltage indicates the temperature.

[0046] Figure 3 A graph showing the relationship between measured voltage and temperature is provided according to an aspect of this disclosure. Figure 3 A figure 300 is depicted, including plot 310. Plot 310 depicts the sensed voltage 302 against temperature 301. As can be seen, the sensed voltage decreases as the temperature increases.

[0047] Figure 4 This is a schematic diagram of an exemplary temperature sensor circuit having a bi-wire winding with windings connected in parallel, according to aspects of this disclosure. Figure 4 An instrument environment 400 is depicted, which includes a temperature sensor circuit 401, a current coil 402, a current transformer 410, an A / D converter 114, a processing circuit 115, a DC voltage source 450, and a current sensor circuit 460. The DC voltage source 450 may be supplied by the instrument's power supply or from another component within the instrument. The temperature sensor circuit 401 is an example implementation of temperature sensor circuits 170 or 190.

[0048] The temperature sensor circuit 401 includes a first double-wire winding 420, a second double-wire winding 430, and a sensing resistor 440. The first double-wire winding 420 includes a start lead 422 and an end lead 424. The second double-wire winding 430 includes a start lead 432 and an end lead 434. The first double-wire winding 420 and the second double-wire winding 430 are of the same length and are wound around the core of the current transformer 410, such that the start lead 422 and the start lead 432 are at the first end of the current transformer, and the end lead 424 and the end lead 434 are at the second end of the current transformer.

[0049] A current transformer 410 is configured in relation to the current sensing relationship of a current coil 402, which is a primary winding and includes a first bi-wire winding 420 and a second bi-wire winding 430 as secondary windings, as well as a current sensor winding 470, which is also a secondary winding. The current sensor winding 470 is used by a current sensor circuit 460 to sense the current flow in the current coil 402. The current sensor circuit 460 includes a sensing resistor 461.

[0050] The first bi-wire winding 420 and the second bi-wire winding 430 are connected in parallel. The start lead 422 and the end lead 434 are connected to each other and to a DC voltage source 450. The end lead 424 and the start lead 432 are connected to a sensing resistor 440, which in turn is connected to ground. The end lead 424 and the start lead 432 are also connected to the input of the A / D converter 114. Thus, the first bi-wire winding 420 and the second bi-wire winding 430 are oriented to produce opposite but equal magnetic fields. Therefore, the magnetic field caused by the current flowing in the first bi-wire winding 420 cancels out the magnetic field caused by the current flowing in the second bi-wire winding 430, resulting in zero net flux on the core and very little effect on the accuracy of the current measurement performed by the current sensor circuit 460.

[0051] The first bi-wire winding 430 has an inherent resistance R1, the second bi-wire winding 440 has an inherent resistance R2, and the sensing resistor has a resistance R3. In some cases, the resistance of the sensing resistor R3 is greater than the inherent resistance of the bi-wire windings. In one example, the inherent resistance of each bi-wire winding is 10,000 Ohms, the resistance of the sensing resistor is 5,000 Ohms, the inherent impedance L1 of the first bi-wire winding 420 is 100 Heng, and the inherent impedance L2 of the second bi-wire winding 430 is 100 Heng.

[0052] As the temperature of the current coil (primary winding) changes, the measured voltage across the sensing resistor R3 changes because the temperature coefficient (or temperature coefficient of resistance) of the first and second bi-wire windings differs from the temperature coefficient of resistance of the sensing resistor. In one example, the temperature coefficient of the sensing resistor is less than the temperature coefficient of resistance of each of the bi-wire windings. Examples of temperature coefficients include 0.00393 for each bi-wire winding and 0.001 for the sensing resistor.

[0053] When a voltage is applied by a DC voltage source 450, the A / D converter 114 receives a signal indicating the voltage across the sensing resistor 440. In one example, the DC voltage source provides approximately 3.3 volts to the start lead of the first two-wire winding. The A / D converter converts the signal into a digital output. The processing circuitry 115 receives the digital output signal from the A / D converter 114 and uses this digital signal to determine a temperature value. The voltage level provided by the DC voltage source and the size of the sensing resistor can be selected based on the requirements of the A / D converter. Some implementations select the voltage and resistance such that when the current coil operates at the expected normal operating temperature, the input of the A / D converter is in the middle of the A / D converter's range. As the temperature of the current coil changes, the voltage measured at the sensing resistor changes. Therefore, as... Figure 5 As shown, the measured voltage indicates the temperature.

[0054] Figure 5 A graph showing the relationship between the measured voltage across the sensing resistor and temperature is provided according to aspects of this disclosure. Figure 5 Figure 500, including plot 510, is depicted. Plot 510 depicts the sensed voltage 502 against temperature 501. As can be seen, the sensed voltage decreases as the temperature increases.

[0055] Figure 6 This is a flowchart illustrating an example of a process for deriving the temperature of a current coil according to aspects of this disclosure. For illustrative purposes, relative to... Figure 2 Circuit discussion shown Figure 6 However, it can also be used Figure 4 The circuit shown is used to perform Figure 6 .

[0056] At block 601, process 600 involves applying a direct current (DC) voltage signal to the secondary two-wire winding of the transformer. Figure 2 As an example, processing circuit 115 applies a DC voltage from DC voltage source 250 to the first two-wire winding 220 and the second two-wire winding 230. As long as instrument 101 is powered, processing circuit 115 can supply power to DC voltage source 250, which in turn supplies power to the two-wire windings.

[0057] At block 602, process 600 involves receiving an input corresponding to a voltage across a sensing resistor connected to a two-wire winding. A / D converter 114 receives a signal indicating the voltage across the sensing resistor 240.

[0058] At block 603, process 600 involves determining the temperature using the voltage across the sensing resistor. Processing circuitry 115 receives a digitized voltage representing the voltage across the sensing resistor from A / D converter 114 and converts the digitized voltage into a temperature. Processing circuitry 115 can use a predefined ratio or scale between the voltage and temperature (e.g., as shown in Figure 114). Figure 3 As shown in the image).

[0059] At block 604, process 600 involves responding to determining that the temperature exceeds a temperature threshold and detecting hot-swap conditions. When the temperature is greater than the temperature threshold, processing circuitry 115 can then identify the hot-swap conditions. In response, processing circuitry 115 can perform actions such as causing communication circuitry 121 to transmit a message to the headend system or disconnecting service switch 105.

[0060] Although this subject matter has been described in detail with respect to specific aspects, it will be understood that modifications, variations, and equivalents of such aspects can be readily made by those skilled in the art upon acquiring an understanding of the foregoing. Therefore, it should be understood that this disclosure has been presented for illustrative purposes and not for limitation, and does not exclude modifications, variations, and / or additions to the subject matter as will be apparent to those skilled in the art.

Claims

1. An instrument comprising: A current transformer includes a primary winding, a secondary winding, and a secondary double-wire winding. The primary winding corresponds to a current coil, and the secondary double-wire winding includes a first double-wire winding and a second double-wire winding connected in series. The starting lead of the first double-wire winding is connected to the starting lead of the second double-wire winding. A voltage source is configured to generate a DC voltage signal, wherein the DC voltage signal is provided to the end lead of the first two-wire winding; A first sensing resistor is connected between the end lead of the second double-wire winding and ground, wherein the temperature coefficient of the first sensing resistor is less than the temperature coefficient of resistivity of the materials of the first and second double-wire windings; and The processing circuit is configured as follows: Receive an input corresponding to the voltage across the first sensing resistor; The temperature associated with the current coil is determined using the voltage across the first sensing resistor; and When the temperature exceeds the temperature threshold, the hot-swap condition is detected.

2. The meter of claim 1, further comprising an A / D converter, wherein, The input of the A / D converter is connected to a first sensing resistor, and the output of the A / D converter is connected to the processing circuit and provides an input corresponding to the voltage across the first sensing resistor.

3. The instrument according to claim 1 further includes: The second sensing resistor is connected between the secondary winding and ground. The processing circuit is also configured as follows: Receives an input corresponding to the voltage across the second sensing resistor; and The voltage across the second sensing resistor is used to determine the current associated with the current coil.

4. The meter of claim 1, wherein, The resistance of the first sensing resistor is greater than the resistance of the first two-wire winding and the second two-wire winding.

5. The meter of claim 1, further comprising a communication circuit, wherein, The processing circuitry is also configured to transmit a message indicating hot-plug conditions to a remote system via a communication circuitry.

6. The meter of claim 5, further comprising a service switch that controls the connection of the meter to the power source, wherein, The processing circuitry is also configured to control the service switch to disconnect the instrument from the power supply in response to receiving a message, including a disconnect command, via the communication circuitry.

7. The instrument according to claim 1, wherein, The system also includes: a current coil corresponding to the first phase and a second current coil corresponding to the second phase, and further includes: A second current transformer includes a primary winding, a secondary winding, and a secondary two-wire winding, wherein the primary winding of the second current transformer corresponds to a second current coil, and the secondary two-wire winding of the second current transformer includes a first two-wire winding and a second two-wire winding; and The third sensing resistor is connected between the end lead of the second two-wire winding of the second current transformer and ground. The processing circuit is configured as follows: Receives an input corresponding to the voltage across the third sensing resistor; The temperature associated with the second current coil is determined using the voltage across the third sensing resistor; and When the temperature exceeds the temperature threshold, the hot-swap condition is detected.

8. An instrument comprising: A current transformer includes a primary winding, a secondary winding, and a secondary double-wire winding. The primary winding corresponds to a current coil, and the secondary double-wire winding includes a first double-wire winding and a second double-wire winding connected in parallel. The end lead of the first double-wire winding is connected to the start lead of the second double-wire winding. A voltage source is configured to generate a DC voltage signal, wherein the DC voltage signal is provided to the start lead of the first two-wire winding and the end lead of the second two-wire winding. The first sensing resistor is connected between the end lead of the first two-wire winding, the start lead of the second two-wire winding, and ground. Wherein, the temperature coefficient of the first sensing resistor is less than the temperature coefficient of resistivity of the materials of the first and second double-wire windings; and The processing circuit is configured as follows: Receive an input corresponding to the voltage across the first sensing resistor; The temperature associated with the current coil is determined using the voltage across the first sensing resistor; and When the temperature exceeds the temperature threshold, the hot-swap condition is detected.

9. The instrument according to claim 8 further includes an A / D converter, wherein, The input of the A / D converter is connected to a first sensing resistor, and the output of the A / D converter is connected to the processing circuit and provides an input corresponding to the voltage across the first sensing resistor.

10. The instrument according to claim 8, further comprising: The second sensing resistor is connected between the secondary winding and ground. The processing circuit is also configured as follows: Receives an input corresponding to the voltage across the second sensing resistor; and The voltage across the second sensing resistor is used to determine the current associated with the current coil.

11. The instrument according to claim 8, wherein, The resistance of the first sensing resistor is greater than the resistance of the first two-wire winding and the second two-wire winding.

12. The instrument according to claim 8 further includes a communication circuit, wherein, The processing circuitry is also configured to transmit a message indicating hot-plug conditions to a remote system via a communication circuitry.

13. The instrument of claim 12 further includes a service switch that controls the connection of the instrument to the power supply, wherein, The processing circuitry is also configured to control the service switch to disconnect the instrument from the power supply in response to receiving a message, including a disconnect command, via the communication circuitry.

14. The instrument according to claim 8, wherein, The system also includes: a current coil corresponding to the first phase and a second current coil corresponding to the second phase, and further includes: A second current transformer includes a primary winding, a secondary winding, and a secondary two-wire winding, wherein the primary winding of the second current transformer corresponds to a second current coil, and the secondary two-wire winding of the second current transformer includes a first two-wire winding and a second two-wire winding; and The third sensing resistor is connected between the end lead of the second two-wire winding of the second current transformer and ground. The processing circuit is configured as follows: Receives an input corresponding to the voltage across the third sensing resistor; The temperature associated with the second current coil is determined using the voltage across the third sensing resistor; and When the temperature exceeds the temperature threshold, the hot-swap condition is detected.

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