Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
  • G08C19/00—Electric signal transmission systems
• • G—PHYSICS
  • G08—SIGNALLING
  • G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
  • G08C25/00—Arrangements for preventing or correcting errors; Monitoring arrangements
  • G08C25/02—Arrangements for preventing or correcting errors; Monitoring arrangements by signalling back receiving station to transmitting station

Definitions

• Electronic circuit arrangement and method for continuously checking the electrical continuity of a conductor wire in particular a wire connecting a device emitting a digital electrical signal and a remote processing unit of said signal
• the present invention concerns electronic applications in general, and more specifically wired signal connections, for example, the connections between emitting devices of electrical state signals of a plant and a remote-control unit associated thereto.
• the present invention concerns the persistent verification of the electrical continuity of a conductor wire, in particular a connection wire for transmitting a state signal of a plant.
• the present invention concerns an electronic circuit arrangement and a method for the remote transmission via wire of a digital signal emitted by an emitting device of an electrical state signal, associated with a plant in the field, to a remote processing unit of said digital signal.
• the logic control circuits of a plant are obtained by programming control circuit equipment (PLC) to which sensors, actuators, buttons, selectors and other signal-providing devices used in the field, i.e. in the plant, refer.
• PLC programming control circuit equipment
• these sensors are physically quite far from the control equipment, and the electrical connection cables may be quite long.
• connection cables between the sensors and the control equipment, intervening promptly in the event of their degradation before the related sensor sends a relevant state signal to the control equipment, but needlessly if the connection cables are damaged or interrupted.
• a control portion including one or more electrical panels where the smart components that perform the programs reside and the application software is executed, and an actuation portion - separate from the control portion - residing in the field where the automated process or production for which a plant or a machine has been made takes place.
• These two entities are separate in that the electrical and electronic components that execute the control programs must be protected from the environment in which an industrial process or production takes place, normally to protect them from dust, possible excessive temperatures, the presence of chips or processing residues, harmful vapors, and any other condition that could damage them. Therefore, all these components are stored in one or more closed electrical panels, also equipped with an air conditioning system, located away from the actual machining area. Normally, these components include smart devices that run different software for each application, in most cases one or more PLCs (programmable logic controllers) specifically designed to operate in the industrial environment.
• PLCs programmable logic controllers
• Such controllers all work with similar criteria; they have a variable number of inputs and a variable number of outputs to be arranged according to the desired application.
• the inputs and outputs of a controller are normally used according to two distinct types of signals, digital or analog.
• Digital inputs and outputs are defined when the information is simplified in only two conditions, for example called“high signal” and“low signal”: when, at a relative terminal, there is a predetermined reference voltage or a voltage higher than a first reference threshold, a“high signal” condition is defined; when this voltage is not present or is lower than a second reference threshold, a“low signal” condition is defined.
• Analog inputs and outputs are defined when a variable number of intermediate values may be managed between a voltage of zero value and a maximum predetermined reference voltage.
• a digital signal normally has a reference voltage of 24V DC, so if a voltage of 24V is present at a terminal, a“high signal” state is recognized, otherwise a“low signal” state is recognized.
• the most common reference voltage is 10V DC, thus an analog input or analog output is sensitive to any intermediate value between OV and 10 V and may handle even hundreds of different states.
• the present invention applies to digital inputs.
• the sensors and actuators required to automatically perform a predetermined task are installed in the production area of an industrial process.
• Process control sensors are necessary to give a control circuit the information concerning the conditions and states of all the variables that are indispensable to the governance of an application. For example, there exist:
• inductive proximity sensors to identify the position of a mechanical component with respect to another following a manual or automated movement of the same
• - pressure sensors to determine the pressure level of a pneumatic or hydraulic plant
• position sensors to identify the position assumed by an element, such as a pneumatic rod or cylinder, following an automated movement of the same element
• thermosensors to detect when a component reaches a desired temperature or if the temperature at a specific point in a plant reaches an abnormal or dangerous value; - ultrasonic or capacitive sensors to determine, for example, the level of a fluid inside a tank.
• the process control actuators are instead indispensable for carrying out the commands given by the control circuit in the various production stages. They comprise, for example: - the rotation of electric motors, for moving parts of a machine, for driving devices such as fans and aspirators, for moving workpieces by means of conveyor belts;
• the controller of a plant gathers control devices protected in one or more electrical panels sheltered and accessible in a separate place from the place where the production or automated process takes place. Sensors and actuators are instead installed in the place where the production or automated process takes place.
• the distance between the electrical control panels from the environment where the sensors and actuators are installed may be as much as a few hundred meters and the electrical connections between the sensors and the controller are generally achieved by means of cables and terminal blocks, sometimes using intermediate electrical panels for connecting and collecting the signals.
• an electrical fault, an anomaly or a problem may occur, e.g. due to a cable breakage or an accidental short circuit between signal cables, which results in the modification or interruption of the same signals, resulting in a general plant problem.
• the controller or any other component associated thereto is able to generate an alarm and the malfunction becomes clear.
• the problem is not serious, and the anomaly does not appear until it is necessary to use the specific information that should be transported by the defective cable. At that time, however, it is too late to remedy the problem and the information obtained from the controller is clearly false or misleading.
• “high signals” and “low signals” flow to the controller’s inputs and are acquired using a technique designed to minimize possible failures.
• the operator in effect may verify that the machine has stopped due to the failure of the cable carrying the stop signal instead of voluntarily.
• the opposite situation would be much more dangerous.
• pressing the button results in signaling by means of a“high signal”, if the electrical continuity of the cable is interrupted, pressing the stop button would result in a signal that can no longer reach the controller and consequently the machine could not be stopped.
• a PLC may activate an output for moving a conveyor belt that transfers a workpiece from one station to the next.
• a sensor informs the PLC when the workpiece has reached its destination and the PLC consequently stops the conveyor belt. If the cable that transmits the signal from the sensor to the PLC is interrupted for any reason, the PLC will continue to move the belt with the result of transporting the workpiece in a wrong or dangerous position until there is a manual intervention by an operator or the intervention of a subsequent automated control by the PLC, which in any case will arrive too late. The workpiece will have already surpassed the programmed position.
• the object of the present invention is thus to provide a satisfactory solution to the problems described above, avoiding the drawbacks of the prior art. ln particular, the object of the present invention is to provide a solution that allows the verification of the electrical continuity of a conductor wire, and in particular a solution that allows the persistent verification of the electrical continuity of a conductor wire.
• this object is achieved by an electronic circuit arrangement for the remote transmission via wire of a digital signal emitted by an emitting device of an electrical state signal, associated in the field with a plant, to a remote processing unit of said digital signal, having the characteristics mentioned in claim 1.
• a further subject-matter of the invention is a method for the remote transmission via wire of a digital signal emitted by an emitting device of an electrical state signal associated in the field with a plant to a remote processing unit of said digital signal, having the characteristics referred to in claim 9.
• the present invention is based on the principle of embedding in a digital state signal, transmitted by a sensor or similar signal-providing or emitting device to a controller or similar remote receiver processing unit of said signal, by its nature having a binary value the evolution of which is unpredictable over time, periodic information that does not disrupt said digital state signal, but at the same time allows a continuous monitoring of the vitality of the wired connection between said emitting device and said remote processing unit.
• the main idea achieved by the invention is to continuously vary, in a constant and preferably rapid way, the state of the signal transmitted via the input wire to a control circuit (for example, a PLC of a control equipment) with a succession of high and low levels, which the control circuit will interpret as a correct connection of the sensor connected thereto, as a defect in the connection would have the effect of bringing the input always to a reference value, such as a low signal, due to the interruption of the cable, or a high signal because of the short circuit with a power supply voltage.
• a control circuit for example, a PLC of a control equipment
• an electronic circuit associated with a sensor is arranged to detect the signal emitted by such a sensor, representative of the state of the sensor,- i.e. indicative of the state of the component of the plant monitored by said sensor, and to generate a continuously variable composite signal to signal the state of the sensor and the state of the connection. This is done by using the connection cables of the sensor to the control circuit, and the continuous variability of the composite signal allows the control circuit to correctly interpret the state of the sensor and the integrity of the electrical connection that concerns it.
• the circuit arrangement covered by the invention is installed as close as possible to the sensors or transducers and is arranged to modify the signal emitted by the sensors or transducers and directed to the control circuit, providing additional information relative only to the state of the sensor or transducer.
• the composite signal generated by the circuit arrangement according to the invention is a repetitive wave over time, i.e.
• a periodic waveform signal with a variable frequency or duty cycle for example a square-wave signal that varies between a state identifiable as high (high signal) and a state identifiable as low (low signal), wherein the ratio between the duration of the high signal and the duration of the low signal is variable according to the state of the sensor.
• the composite signal sent to the control circuit is preferably a square-wave signal with a variable frequency or a variable duty cycle.
• the useful information on the state of the sensor is a high signal
• the information on the state of the connection is a low signal.
• the useful information on the state of the sensor is a low signal
• the information on the state of the connection is a high signal.
• the signal duration indicative of the information on the state of the connection is a fraction of the signal duration indicative of the information on the state of the sensor, or alternatively, the signal duration indicative of the information on the state of the connection is a fraction of the total signal duration including the signal duration indicative of the information on the state of the connection and the signal duration indicative of the information on the state of the sensor.
• the control circuit has therein logic circuits capable of deciphering the composite signal, acquiring information on the state of the sensor, but also extracting information added on the state of the wired connection between the sensor and the control circuit.
• the solution according to the invention resolves the drawbacks of the prior art by allowing a processing unit or control circuit to constantly check the state of the wired connection that puts it in communication with one or more sensors in the field, through a particular signal produced by such sensors.
• Figure 1 is a schematic diagram of an electronic circuit arrangement for the remote transmission via wire of a digital signal emitted by an emitting device of an electrical state signal, associated with a plant in the field, to a remote processing unit of said digital signal;
• Figure 2 is a schematic diagram of an electronic circuit arrangement according to the invention.
• Figures 3a and 3b are waveforms representative of a composite signal according to the invention.
• Figures 4a, 4b, 4c show diagrams representing the evolution over time of the signals exchanged between an emitting device and a remote processing unit, according to different embodiments of the invention, under different operating conditions;
• Figures 5a and 5b are alternative waveforms representative of a composite signal according to the invention.
• Figure 1 shows a circuit arrangement for controlling a plant, comprising a section F in the field and a control remote electrical panel Q.
• the section F in the field includes a plurality of sensors Sl, S2, S3 associated in the field with a plant and joined, through respective wired connections Sci, Sc2 and Sc3, to a transmission unit on the bus B.
• a bus signal wire emerges from the transmission unit on the bus B and runs from the section F in the field to the control remote cabinet Q, which comprises a circuit PLC or controller C.
• the sensors Sl, S2, S3 of the example embodiment described above are emitting devices of a digital electrical signal indicating the state of a part or a device of the plant.
• state refers to a physical condition of a part or device of the plant, such as its position with respect to a reference position (this is the case of limit sensors associated with a movable component of the plant) or the configuration thereof (this is the case of automatic circuit breakers).
• the representation of Figure 2 better describes the circuit arrangement covered by the invention at a sensor or signal provider S.
• the sensor or signal provider S has three outputs, respectively a first normally open output NA, a second normally closed output NC and a common output C.
• the sensor S in figure 2 is coupled to an electronic circuit for the generation of a digital composite signal for the transmission via wire to a remote processing unit.
• the circuit PLC or controller C represents said remote processing unit with which a signal recognition electronic circuit is associated.
• the electronic circuit for generating a composite digital signal, or signal composer circuit includes a detection circuit D, adapted to be connected to a signal output of the emitting device S and arranged to detect the value of said digital signal at predetermined detection time instants according to an assigned detection frequency, and a formation circuit G of said composite digital signal, adapted to generate a periodic digital signal, in the example a square-wave signal, at a predetermined signaling frequency, having a predetermined duty cycle in a signaling period, which is a function of the value of the detected digital signal.
• a detection circuit D adapted to be connected to a signal output of the emitting device S and arranged to detect the value of said digital signal at predetermined detection time instants according to an assigned detection frequency
• a formation circuit G of said composite digital signal adapted to generate a periodic digital signal, in the example a square-wave signal, at a predetermined signaling frequency, having a predetermined duty cycle in a signaling period, which is a function of the value of the detected digital signal.
• the switching of the normally open output being critical for communicating an anomalous state to the PLC C through a wired connection Sc, the detection circuit D and the formation circuit G of said composite digital signal are represented downstream of the path between the normally open output NA and the common connection C.
• the signal recognition electronic circuit at the circuit PLC or controller C is arranged to receive the composite digital signal and to verify the existence of at least one change in the logical state of said composite digital signal within a time interval corresponding to a signaling period.
• a composite digital signal is shown by way of example in Figures 3a and 3b. It comprises a signal portion representative of the logical state of the digital signal emitted by the emitting device and a signal portion for determining the electrical continuity of the transmission link.
• Figure 3a shows a composite signal of which the signal portion representative of the logical state of the digital signal emitted by the emitting device is representative of a“high signal”.
• Figure 3b shows a composite signal of which the portion of the signal representative of the logical state of the digital signal emitted by the emitting device is representative of a“low signal”.
• the composite digital signal is - in the example shown - a square- wave signal having a predetermined duty cycle in a signaling period, which is a function of the value of the digital signal detected.
• Each square wave period of the composite digital signal includes a first value corresponding to the logical state of said detected digital signal, which is maintained for at least a first time interval including a predetermined reading instant by the signal recognition circuit, and a second value complementary to said first value for a second interval of time.
• the first diagram reproduces the trend of a state signal Ss, normally low, emitted by the sensor S (or rather, by the normally open output NA of the sensor S), which, due to an anomalous event detected by the sensor S, switches at the time t c to the high level.
• t D6 is indicated a periodic succession of time instants when the state signal Ss is detected by the detection circuit D.
• the second diagram reproduces the trend of the composite digital signal present on the wired connection Sc between said emitting device and said remote processing unit.
• the composite digital signal is a square-wave signal in a signaling period corresponding to the period between each detection instant of the state signal Ss and is a function of the value of the digital signal detected at the instants tm, t D6 .
• the composite digital signal has a switching edge.
• the signaling frequency corresponds to the detection frequency
• the signaling frequency may also be a multiple or sub-multiple of the detection frequency.
• each square- wave period of the composite digital signal includes a first sub-period, wherein the composite digital signal has a high level, and a second sub-period, wherein the composite signal has a low level.
• the duration of the first sub-period is a function of the logical state of the detected digital signal, and specifically is greater at the time interval between the signaling time instant tsi and a subsequent reading time instant tm by the signal recognition circuit at the controller circuit C if the input digital signal has a high logical state, and less at the time interval between said signaling time instant tsi and a subsequent reading time instant tm by said signal recognition circuit if the input digital signal has a low logical state.
• the third diagram of Figure 4a shows a recognition signal SPLC of the state signal Ss and of the integrity of the wired connection at the control circuit C of the remote unit.
• t R i a recognition signal
• t R5 a recognition time instants of the state signal that may be triggered as a result of the leading edges at the time instants tsi, ..., tsr, with a predetermined delay.
• the signal recognition circuit detects a low signal logical state, and at instants tR 4 and tR 5, the signal recognition circuit detects a high signal logical state. Consequently, the recognition circuit emits respectively a low logical signal SPLC until the instant tR 4 , after which it emits a high logical signal.
• Figure 4b shows a succession of signals wherein - due to an anomaly in the wired connection - the composite signal on the connection Sc is no longer transmitted after the signaling time instant ts3 (the composite signal generated but never received by the PLC is indicated as a dashed line).
• the signal recognition circuit no longer detects a leading edge for a time greater than a predetermined time interval, for example at the signaling time interval Ts, it emits an anomaly signal SA (i.e. the signal SA switches from a low to a high level). Therefore, the remote processing unit is arranged to signal an anomaly if the associated signal recognition electronic circuit does not ascertain the existence of at least one change in the logical state of the composite digital signal within a time interval corresponding to a signaling period.
• a predetermined time interval for example at the signaling time interval Ts
• Figure 4c shows a series of diagrams in an embodiment wherein, for each signaling period, triads of successive state signal recognition time instants are indicated at t R i , t R i ’, t Ri ”,..., t 5, tR 5 ’, t R5 ”, independently reconstructed by the control circuit C synchronously with the signal composer circuit, i.e., the control circuit C knowing the duration of the square-wave period of the composite digital signal.
• the corresponding recognition time instants tm and tR,’ of each triad are triggered so as to fall at a first and second sub-period of the square wave of the composite signal, wherein said signal has a high and a low value respectively, or vice versa, independently of the value of the state signal Ss, while the recognition time instants t Ri ” are triggered so as to fall at a first and a second sub-period of the square wave of the composite signal, wherein said signal has respectively a high value and a low value depending on the value of the state signal Ss.
• the recognition circuit of the signal does not detect in a pair of corresponding recognition time instants t Ri and t R ,’ a high level and a low level, because, due to an anomaly on the wired connection, the composite signal on the connection Sc is no longer transmitted, it emits an anomaly signal S A .
• this is represented at the recognition time instants tR 5 and tR 5 ⁇ where, due to an anomaly, the signal on the connection Sc is always at the low value (the composite signal generated but never received by the PLC is indicated with a dashed line).
• the electronic signal recognition circuit is arranged to detect the time interval between a leading edge and the subsequent trailing edge of the composite digital signal and the time interval between the trailing edge and the subsequent leading edge.
• the remote processing unit is arranged to signal an anomaly if the associated signal recognition electronic circuit does not ascertain the existence of at least one change in the logical state of the composite digital signal within a time interval corresponding to a signaling period.
• the control circuit checks, after a predetermined time, for example 20ms, the value assumed by the signal. This value represents the state of the sensor.
• the PLC is able to verify that, on the input relative to the signaling by a certain sensor, the signal varies continuously, and this is indicative of the correct functioning of the connection cable. Conversely, if the signal remains constantly at the high or low value for a predetermined time, for example greater than a few verification cycles, for example l OOms, this condition is interpreted as an alarm condition due to a cable integrity problem.
• this technique is easily achievable on any state signal emitting device and on any control device and allows one to check the reliability of the connection for any signal-providing device that is considered important to monitor.
• the circuit for the generation of the composite signal according to the invention must be used in the vicinity of the signal- providing device to be monitored, and even better if it is integrated therein, so as to limit as much as possible the presence of electrical wires upstream of the connection cable that could also cause anomalies due to interruption of continuity or short circuit.
• this circuit may be miniaturized enough to be inserted directly into a container body of a sensor such as a limit sensor, making it an integral part thereof.
• the signal-providing or -emitting device could in effect transmit, by way of non-limiting example, with a sinusoidal waveform with variable frequency in the signaling period, a trapezoidal waveform with variable duty cycle, a sawtooth waveform of variable frequency, the latter shown by way of example in Figures 5a and 5b.
• the sawtooth composite signal is indicated at Sc, the digital signal (square wave) at SR interpreted at the receiver of the signal composed by comparison of the signal Sc with a high signal threshold VH and a low signal threshold VL.
• the information is acquired by the controller or the remote processing unit receiving the composite signal as a digital signal, and processed as if it were a square wave, freeing itself from the actual periodic waveform transmitted by the signal-providing or -emitting device.
• This allows the waveform of the composite signal to be adapted to different applications that may require adaptations to respect the electromagnetic compatibility in electrically“noisy” environments.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Programmable Controllers (AREA)
• Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
• Selective Calling Equipment (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=64316730

Family Applications (1)

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Family Cites Families (4)

• 2018
  • 2018-08-23 IT IT102018000008166A patent/IT201800008166A1/it unknown
• 2019
  • 2019-08-23 EP EP19773546.7A patent/EP3841563B1/de active Active
  • 2019-08-23 WO PCT/IB2019/057108 patent/WO2020039395A1/en unknown
  • 2019-08-23 MA MA053441A patent/MA53441A/fr unknown

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