Automation system power over Ethernet redundancy system and method

There is provided a powered device configured to switch between a power over Ethernet (PoE) source and an auxiliary power source without restarting the device. A PoE circuit within the device includes a minimum load circuit which enables detection of the device by PoE power sourcing equipment (PSE) even when the device is powered by the auxiliary power source. The minimum load circuit may maintain a load of around 10 mA to simulate powered components, thereby enabling the PSE to reinitiate PoE even though the powered components of the device are at that time powered by the auxiliary power source. When the power supplied to the powered components by the PSE overcomes that of the auxiliary power source, the power scheme may automatically revert to PoE.

BACKGROUND

The present disclosure relates generally to automation systems, and to techniques for providing power over Ethernet for components of such systems. More specifically, the present techniques provide for supply of uninterrupted power for such components in the event of a failure.

Power over Ethernet (PoE) is used to supply power to a device through an Ethernet network. That is, devices such as, for example, telephones, local area network access points, webcams, Ethernet hubs, computers, etc. may be powered via an Ethernet cable. Power may be sent to a powered device (PD) via power sourcing equipment (PSE).

The Institute of Electrical and Electronics Engineers has promulgated a standard for PoE. IEEE 802.3 provides for 48 volts of DC power over two out of four available connector pairs on a standard “Category” cables. Data may also be transferred via the connector pairs used to carry power.

In implementing PoE, the PSE first conducts discovery, in which a voltage is applied across the connection and currents are measured to determine if an appropriate resistance is detected. If resistance is detected, the PSE may then classify the power level of the PD based on another detected resistance or may assume a default classification. Appropriate power is then supplied via the Ethernet network to the PD.

In the event of a failure, such as a disconnection of the Ethernet cables or a loss of power from the PSE, the PD may also be connected to an auxiliary power source. The PD may include a switch to determine when PoE is lost and convert to auxiliary power. In existing applications, the PD must generally be restarted after the failure has been corrected in order to return to PoE. That is, upon reconnection of the Ethernet cables or the PSE regaining power, the PD does not revert to PoE but rather continues to be powered by the auxiliary power source. This configuration may be problematic as the auxiliary power source may be a temporary device, such as a battery backup, which itself loses power after some time. In addition, it may be extremely inconvenient to restart the PD every time PoE is regained.

Such problems may be exacerbated by the environment in which powered devices are used. For example, in automation applications (e.g., factory automation) a high degree of reliability is required for system components, particularly components used to provide feedback, inputs, outputs, and information for operators and other personnel.

There is a need for solutions in PoE schemes to provide enhanced robustness in the event of failures, and particularly in automation systems.

BRIEF DESCRIPTION

In accordance with one aspect, the present disclosure presents an automation system comprising a monitoring and/or control component configured to control a machine or process, an Ethernet network coupled to the monitoring and/or control component for exchanging data during operation of the machine or process, and an input and/or output device coupled to the Ethernet network that, in operation, provides data to or receives data from the monitoring and/or control component via the Ethernet network and that is powered by a PoE scheme during operation. The input and/or output device comprises a minimum load circuit configured to maintain a minimum load in for the PoE scheme.

In accordance with another aspect, an automation system comprises an automation component configured to perform an automation operation on a monitored and/or controlled machine or process by exchanging data or signals with other automation components, and a PoE circuit. The PoE circuit comprises a detection circuit configured to enable detection of the automation component by power sourcing equipment, an isolation circuit configured to protect the automation component from current supplied by the power sourcing equipment during the detection of the automation component, and a minimum load circuit configured to maintain a minimum load on the PoE circuit to enable the detection of the automation component while the device is powered by an auxiliary power source.

The disclosure also relates to methods for implementing such technology. In accordance with one embodiment, a method comprises providing data and power to an automation component via a PoE connection, and switching a power source for the automation component from an auxiliary power source to a PoE source, wherein switching does not comprise restarting the powered device.

DETAILED DESCRIPTION

Turning now to the figures, and referring first toFIG. 1, an exemplary automation system10employing a novel PoE scheme is illustrated. The system10generally includes monitoring and/or control circuitry12that, in operation, receives sensed signals and data from a machine or process14, and provides output signals and data for the control of the machine or process. The monitoring and/or control circuitry12will comprise one or more processors P and associated memory M. The memory may store programming code executed by the processor in carrying out the monitoring and/or control functions, typically in real or near-real time, as well as configuration settings, routines, error logs, and any number of useful data for the operations regulated by the monitoring and/or control circuitry. Interface circuitry will also be provided that aids in communicating with external devices, including via powered Ethernet connections, as summarized below.

The parts and components of the machine or process14will typically be driven by motors M which are in turn, driven by power signals from motor drives D. Any of a variety of actuators may be used, including such rotary motors, linear motors, solenoid-actuated devices, and so forth. Instrumentation, such as sensors16are provide to sense operating parameters of the machine or process and to provide representative signals and/or data, such as through input/output interfaces18(sometimes referred to as “I/O”) to the monitoring and/or control circuitry. As discussed in greater detail below, such I/O may represent one form of PoE component with which data is exchanged and power provided by the PoE scheme disclosed. Other components of the system may include various types of human machine interface or HMI, as indicated by reference numeral20. Many other systems, devices, and components may also be provided, including remote monitoring and/or control systems, and these may be coupled to exchange data with the monitoring and/or control circuitry by a network22. Where HMIs20are provided, these may be powered by Ether net cabling24that may itself extend between the powered devices and the circuitry with which they exchange data. Such cabling is illustrated, by way of example, between the circuitry12an HMI20, between the I/O18and the circuitry12, and between the network22and another HMI20. In terms of the PoE scheme discussed here, the network or the circuitry12may serve as the PSE, and such PSEs may be local to the powered devices (e.g.,18,20) or may be located remotely and connected via the network.

FIG. 2is a diagrammatical illustration of a part of the system illustrated inFIG. 1. In the illustrated embodiment, a powered device or PD18,20is connected to the Ethernet network via the cable24. The cable may, for example, be a “Category” with twisted cable pairs terminating at each end in pins in a standard modular jack. The pairs may be connected to pairs of twisted cables in the Ethernet network. The Ethernet network may in turn be connected to one or more sources of power, as indicated by block PSE inFIG. 2, as well as to non-powered data sources. The PSE may be connected to only two of the available pairs to provide supply the power. The data source may be coupled to another available pair, as illustrated, or may be coupled to all available pairs, as in gigabit Ethernet connections. In addition, a two pair twisted Ethernet cable (not shown) may be utilized, and power and data may both be sent over the same two pairs in the cable. In addition to being connected to the Ethernet network, the PD12,20may be connected to the auxiliary power source or network22. For example, a standard power cable may be utilized to connect the PD1820to the power grid.

FIG. 3illustrates a block diagram of a PoE circuit30in a powered device32in accordance with the prior art. Specifically, an Ethernet connector34may be provided to enable connection of the PD32to the PSE12(FIG. 1) via the Ethernet network18(FIG. 1). In this example, four pairs of wires are utilized to transfer data and transmit power in the PD32. Two of the four pairs are generally utilized for data transmission, while all four pairs may be used to transmit power. The two data transmission wire pairs may be coupled to a data path38via transformers36. Current from all four wire pairs may travel through rectifier bridges40to a power path42. The power path42includes an electromagnetic interference (EMI) filter44, a PoE detection circuit46, a PoE classification circuit48, and a PoE isolation circuit50, all of which are described in more detail below. The filtered current then goes through a DC/DC converter52to ensure a stable supply of power to the PD32. An auxiliary power source54may also supply power to the PD32in the event that power from the PSE is insufficient or lost. Power from the auxiliary power source54goes through a separate DC/DC converter56. A smart switch58determines if power from the Ethernet network is lost or drops below an acceptable level and switches to the auxiliary power source54. After detection of the PD32, the PSE will supply power only if a minimum load is maintained. Accordingly, PoE is not reinitiated when sufficient power is again available from the PSE because there is no load on the circuit30due to the device32being powered by the auxiliary power source54.

FIG. 4illustrates a PoE circuit60in a powered device62in accordance with an embodiment of the present invention. An Ethernet connector64may be coupled to the cable (FIG. 1). In the illustrated embodiment, the Ethernet connector64is a standard modular jack with eight connection pins66. Each connection pin66is coupled to a wire68. The 1/2 and 3/6 wire pairs are utilized for data transfer via transformers70. A data path72transfers data from the transformers70to data processing components of the PD62.

The 1/2, 3/6, 4/5, and 7/8 wire pairs are utilized to provide power to the PD62. Bridge rectifiers74convert alternating current to direct current. The bridge rectifiers74may be coupled to an electromagnetic interference filter (EMI)76. The EMI filter76reduces noise in the current from electromagnetic radiation incident on the PoE circuit60. A PoE detection circuit78may then be utilized to alert to the PSE that the PD62is present and requires power. During detection, the PSE may transmit a 1.8-10 volt signal for approximately 500 mseconds. The PSE may measure resistance or capacitance of the detection circuit78, and if the measured value is within a standard range the PSE may supply power to the PD62. The detection circuit78may have a 25 kohm resistor signature to indicate that the PD62is compliant with IEEE 802.3af standards.

The level of power supplied to the PD62may be determined by supplying voltage to a classification circuit80. During classification, the PSE may transmit about 18 volts for approximately 50 mseconds. The classification is based on the current consumed by the PD62while a constant voltage is applied. According to IEEE standards, there are five PoE classifications, namely zero through four. Class zero is the default and indicates a maximum power level of 0.44-12.95 watts at the inlet of the PD32. Class one indicates a maximum of 0.44-3.84 watts, class two indicates a maximum of 3.84-6.49 watts, and class three indicates a maximum of 6.49-12.95 watts. After classification, power is supplied to the PD62from the PSE based on the determined classification. For example, the PSE may send 25-96 volts to the PD62, depending on need. Generally, the PSE may provide 48 volts and 15.4 watts of power to the PD62.

A PoE isolation circuit82enables current to pass through to the PD62when power is supplied from the PSE. For example, during detection and classification the isolation circuit82may prevent current from passing through to the PD62. When the voltage supplied by the PSE exceeds the values associated with detection and classification, the isolation circuit82may enable current to pass through and power the PD62.

In accordance with an aspect of the present invention, a minimum load may be maintained on the PoE circuit60by a minimum load circuit84. The minimum load circuit84may maintain a current of approximately 10 mA such that the PSE again supplies power to the PD62upon reconnection of the PD62to the PSE via the Ethernet network. That is, after detection of the PD62, the minimum load circuit84maintains a minimum load simulating powered components, thereby enabling the PSE to reinitiate PoE. Embodiments of the minimum load circuit84are described below. A DC/DC converter86may then be utilized to regulate the DC power supplied to the PD62from the PSE.

In addition to the PoE connection, the PD62may be coupled to an auxiliary power source88. The auxiliary power source88may be internal to the PD62or may be external, such as, for example, a battery backup, a UPS, a power grid, etc. If power via the Ethernet connection is lost or greatly reduced for any reason, the PD62may be powered by the auxiliary power source88. Generally, the PD62may switch to the auxiliary power source88if the power supplied from the PSE decreases to less than 24 volts. Because the minimum load circuit84enables the PD62to be rediscovered without restarting the PD62, the auxiliary power source88may supply power to the PD62until the Ethernet power is reconnected or reaches an adequate level to once again power the PD62. For example, the PD62may revert to PoE when the voltage supplied by the PSE14exceeds the voltage supplied by the auxiliary power source88. This feature enables continuous use of the PD62even after a power failure or network disconnection.

FIG. 5is a flow chart illustrating an exemplary process90by which the PoE circuit60(FIG. 4) may operate to maintain power to the PD62. Upon connection of the PD62to the Ethernet network18(FIG. 1), the PSE may detect or discover the PD62(block92). In the detection step (block92), the PSE may send a signal to the detection circuit78to determine if the PD62requires power via the network and to ensure that the PD62is properly configured to receive PoE. For example, the PSE may transmit a 1.8-10 volt signal for approximately 500 mseconds and measure the resistance of the detection circuit78. If the measured value is within an expected range, the detection step (block92) is successful. For example, a resistance signature of 25 kohms indicates that the PD62is IEEE compliant.

After detection, the PD62may be classified (block94). That is, the amount of power required to operate the PD62may be determined. In the classification step (block94), the PSE may send a signal to the classification circuit80to determine the proper power level class for the PD62. For example, the PSE may transmit a 12.5-25 volt signal to the classification circuit80for approximately 50 mseconds. The power level class may be based on a measured resistance in the classification circuit80. The appropriate level of power may then be supplied to the PD62(block96).

The PSE14may continue to supply power to the PD62until power is no longer drawn for a period of time, or a failure occurs (block98). For example, if the PD62draws less than 5 mA of current for 400 mseconds, the PSE may stop supplying power to the PD62. Failure may be a result of interruption of the Ethernet connection between the PSE14and PD62for any reason. For example, the PSE or the PD32may be disconnected from the Ethernet network18, or the lines providing the network18may be severed. Furthermore, if the PSE loses power it may no longer be able to provide power to the PD32.

Upon failure of the PoE, the PD63may begin to operate on auxiliary power (block100). The transition from PoE to auxiliary power may be automated such that the PD62does not power off during the transition. The PSE may again be able to supply power via the network to the PD62(block102). Upon recovery of the PoE, the PD62may again be discovered (block92) and classified (block94). Power to the PD62may then be supplied by the PSE (block98) rather than the auxiliary power source88.

FIGS. 6-9Dare schematics of exemplary PoE circuits as illustrated inFIG. 4. In an exemplary circuit110illustrated inFIG. 6, the detection circuit78may include a resistor112and a capacitor114in parallel (seeFIG. 9A). While the IEEE 802.3af standard calls for a signature resistance of about 25 kohms, pre-standard power equipment may detect the PD62(FIG. 4) based on signature capacitance. Accordingly, the detection circuit78may include both the resistor112and the capacitor114.

The classification circuit80may include multiple switches, for example, in the form of Zener diodes and transistors. The PSE classifies the PD62based on the overall resistance signature of the classification circuit80. A resistor116may be principally responsible for the detected resistance signature of the classification circuit80. The isolation circuit82operates as a switch to prevent power from passing through during detection and classification. When the PSE increases the voltage to the PD62enough to overcome a switch118, such as a Zener diode, current may flow through the isolation circuit82to the powered components of the PD62.

An exemplary minimum load circuit120(seeFIG. 9B) may continuously draw current even in the event that the PD62has switched to auxiliary power. The minimum load circuit120may include a resistor122. For example, the resistor122may have a resistance of 4.4 kohms such that a 44 volt signal across the resistor122produces 10 ampers of current. This current may be the minimum load to ensure that the PSE14detects and reconnects to the PD62after a failure. In addition, due to the nature of the minimum load circuit120, some power loss may occur even after the PD62is powered by the PSE14. The minimum load circuit120may then be coupled to the DC/DC converter86. Additionally, the auxiliary power source88may be coupled to the DC/DC converter86. Diodes124prevent current from leaking between the PoE circuit110and the auxiliary power source88and provide an automatic switch between the power sources. That is, when the power supplied to the DC/DC converter86by the PSE14becomes greater than that supplied by the auxiliary power source88, the PD62automatically switches to the PoE scheme.

FIG. 7illustrates an exemplary PoE circuit126, including many of the same elements described above. Another exemplary minimum load circuit128(seeFIG. 9C) may also provide at least a 10 mA current to ensure reconnection of the PD62to the PSE14in the event of a failure. A Zener diode130regulates voltage through the minimum load circuit128. In an exemplary embodiment, the Zener diode130may be a 1.25 volt diode. Current is then routed through a resistor132and a resistor134. In the illustrated embodiment, the resistor132is a 1 megaohm resistor, and the resistor134is a 250 kohm resistor. A comparator136, such as an operational amplifier, receives a non-inverting voltage input from the resistor134and a resistor138. An inverting voltage input to the comparator136may be supplied through a resistor140and a resistor142. In the illustrated embodiment, the resistor140is 100 ohms and the resistor142is 10 kohms. The output voltage from the comparator136may pass through a resistor144that is, for example, 1 kohm. If the voltage from the comparator136is greater than a threshold voltage of a switch146, such as a metal-oxide-semiconductor (MOSFET), the switch146may be turned on. When the voltage output from the comparator136decreases below the threshold voltage, the switch146may be turned off. While the switch146is open, current may transfer between the positive and negative channels of the PoE circuit128via the resistor140.

Additionally, the minimum load circuit128may maintain the minimum load only while operating power is not supplied to the PD62. That is, upon detection of a current through a resistor148, the minimum load circuit128may stop drawing power from the PoE circuit126. For example, if a comparator150, such as an operational amplifier, senses a voltage drop across the resistor148, the output voltage of the comparator150may be reduced via a resistor152then routed to a switch154, such as a junction gate field-effect transistor (JFET). If the voltage to the switch154becomes great enough to overcome the gate source voltage, the switch154may be turned off such that current is significantly impeded from traveling therethrough. By turning off the switch154, the inverting and non-inverting inputs to the comparator136are driven together, and voltage output from the comparator136approaches zero. When the voltage output from the comparator decreases below the threshold voltage of the switch146, the switch46is turned off such that current may not travel therethrough.

Finally, an exemplary PoE circuit having a minimum load circuit158is illustrated inFIG. 8. The minimum load circuit158seeFIG. 9D) includes a voltage regulator160. In the illustrated embodiment, the voltage regulator160output is 5 volts, however other voltage regulators may be utilized depending on the design of the circuit158. The output from the voltage regulator160is conducted through a resistor162. The resistor162may be designed such that the current flowing therethrough is 10 mA. For example, where a 5 volt regulator160is utilized, the resistor162may be 500 ohms.

In addition, the minimum load circuit158may be turned off upon detection of a current therethrough, as with the minimum load circuit128(FIG. 7). That is, if a comparator164, such as an operational amplifier, detects a voltage drop across a resistor166, an output voltage is transmitted from the comparator164to the regulator160. The voltage disables the regulator160, thereby substantially preventing the minimum load circuit158from draining current.