RU2574353C2 - Communication system for process field device - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to field devices (102) for use in an industrial process. The device includes a process interface element (108) configured to measure or control a process variable. Communication circuitry (156) is configured to communicate with another location. A communication system is configured to provide communication between at least two components in the field device (102). A signal inverter (220) transmits an inverted signal from the communication system (192) to other circuitry to thereby reduce interference received by the other circuitry.

EFFECT: high reliability of the device.

18 cl, 5 dwg

Description

BACKGROUND

[0001] The present invention relates to field devices of the type used to monitor or control production processes. More specifically, the present invention relates to internal data transmissions in such field devices.

[0002] Production processes are used to perform various functions in processing or creating products from other components. Such processes include, for example, refineries, manufacturing plants, food processing plants, chemical plants and pharmaceutical plants. In such systems, field devices are used to monitor or control the progress of a process. One such device is a process transmitter that is configured to sense a process parameter and communicate with a centralized location based on a sensed process parameter. Examples of process parameters include flow, pressure, temperature, level, etc. The process controller is an example of another field device in which a control signal is received from a central location, and the process controller controls the process parameter in response. Communication with a centralized location may be via a wired or wireless process control loop.

[0003] Field devices often operate under power limitations. Additionally, such devices typically have a plurality of components and use a communication system to communicate between these components. In some cases, such as during operations using limited power, one communication system may interfere with data transmitted over another communication system. This “noise” can introduce errors into the device and even cause device failure.

SUMMARY OF THE INVENTION

[0004] A field device for use in a manufacturing process includes a process interface element configured to measure or control a process parameter. The communication scheme is configured to communicate with another location. The communication system is configured to provide communication between at least two components in a field device. A signal inverter is an element for introducing an inverted signal from a communication system into another circuit in order to thereby reduce interference received by another circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a simplified block diagram of a process control or monitoring system.

[0006] FIG. 2 is a simplified block diagram showing a field device of FIG. 1.

[0007] FIG. 3 is a diagram illustrating noise from a first data bus introduced into a second data bus.

[0008] FIG. 4 is a diagram illustrating the use of an inverter to reduce or eliminate noise shown in connection with FIG. 3.

[0009] FIG. 5 is a simplified block diagram showing an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to field devices used in process control and monitoring systems. As discussed in the Background Section, data communications in such field devices may introduce noise into other circuits, such as another communication system.

[0011] FIG. 1 is a simplified block diagram of a process control or monitoring system 100 including a field device 102 associated with a manufacturing process. In the example of FIG. 1, the field device 102 is connected to a process conduit 104 transferring the process fluid 106. A process interface element 108 is provided that can be configured to control a process (eg, a valve or the like) if the field device 102 is operating as a controller, or may be configured to measure a process parameter (such as temperature, pressure, flow, etc.) if the field device 102 is configured as a transmitter of the process parameter. Field device 102 may also work as other types of field devices, such as a stand-alone field device or field device that includes both control and measurement components, etc. 1, a field device 102 communicates with a central control point 110 via a process control loop 112. In the embodiment illustrated in FIG. 1, the process control loop 112 is a two-wire process control loop. Such process control loops often operate in accordance with communication standards such as the HART® digital communication standard, bus protocol with field devices, etc. For example, a two-wire process control loop can be used to power the field device 102, as well as transmit information between the field device 102 and the central location 110. Information can be transmitted in an analogous way, for example, as a current level that varies between 4 mA and 20 mA , and / or may be a digital signal that is modulated by the current flowing through circuit 112. In another exemplary configuration, process control circuit 112 satisfies wireless protocols that could It can include, for example, a mixed-type network protocol, and can operate in accordance with the HART® wireless protocol. The central location 110 is illustrated as including a load resistance 118 and a voltage source 116. Typically, other components, such as control equipment or monitoring equipment, are used at a central location 110 and may be monitored by an operator.

[0012] FIG. 1 also illustrates an auxiliary component 120 associated with a field device 102 via a local data bus 122. The auxiliary component 120 may be located inside or outside with respect to the field device 102. The data bus may operate in accordance with any suitable technology. One example is a CAN-based protocol (control area network) or other commercially available or custom protocols.

[0013] FIG. 2 is a simplified block diagram showing a field device 102 in more detail. Field device 102 includes an interface circuit 150 configured to operate with a process interface element 108. The interface circuit 150 is connected to a microprocessor 152, which operates in accordance with the instructions stored in the memory 154. A loop input / output circuit 156 is provided to allow communication on the process control loop 112. As illustrated in FIG. 2, the field device 102 also includes a local data bus communication circuit 160 for use in providing communication between the microprocessor 152 and an auxiliary component 120 on the local data bus 122. Auxiliary component 120 may include any component to which data is transmitted via data bus 122, and may be located in a field device 102, adjacent to a field device 102, or even remotely from a field device 102. Examples of an auxiliary component include sensors, controls, displays or another user interface, another field device, additional processing scheme, etc. Schemes 156 and 160 are examples of communication systems that are discussed herein.

[0014] FIG. 3 is a simplified block diagram illustrating interference between two communication systems 190, 192 in a field device 194. In FIG. 3, a first one-way transmitter 210 communicates with a first one-way receiver 212 via a first data bus 214. Similarly, the second one-way transmitter 200 communicates with the second one-way receiver 202 via the second data bus 204. As illustrated in FIG. 3, an interference signal from the data bus 214 is added to the data signal transmitted over the data bus 204, resulting in deterioration of the waveform of the data signal over the data bus 204. This interference signal may be added to or subtracted from the data signal depending on the phase of the interference. At low voltage levels, often present in field devices, an interference signal may cause erroneous data to be received by receiver 202.

[0015] One technology that can be used to eliminate this interference and improve the noise immunity of the system is the use of a differential signal transmission system, such as those commercially available in accordance with the RS-485 and RS-422 communication protocols. In such a system, a differential transmitter provides a signal with the same and opposite polarities on the differential transmission line. The differential transmission line consists of two conductors that are configured as a balanced pair, and therefore each conductor has the same impedance along its length and the same impedance to ground and another circuit. The correct implementation of this configuration requires that the circuitry comply with the rules of the physical layer of the network, which may entail requirements for synchronization, voltage level, and impedance characteristics. However, such a configuration increases the complexity of the device and also increases the manufacturing costs and the time required to design and manufacture such a device.

[0016] FIG. 4 is a simplified block diagram illustrating one exemplary embodiment of the present invention that eliminates the aforementioned interference problems. In the configuration of FIG. 4, elements that are similar to those shown in FIG. 3 have retained their numbering. 4, an inverting amplifier (inverter) 220 is connected to the output of a one-way transmitter 210. An inverting amplifier 220 is used to invert the signal on the data bus 214 and to input the inverted signal to the data bus 204. The inverter 220 is configured so that the amplitude, phase, and waveform of the input signal is similar to the inverse of the spurious interference signal from the data bus 214, which is input to the data bus 204. The closer these two signals are inverses of each other, the greater the effect of mutual compensation will be from the inverted signal from the inverter 220. Since the output signal from the inverter 220 is not used for data transmission, the output signal does not have to meet the requirements of the communication system to it. The output from inverter 220 should only be consistent with any requirements necessary for the desired level of noise reduction. Therefore, the inverter circuit 220 can be a relatively simple design solution compared to the complete configuration of the differential amplifier. In addition, since the configuration illustrated in FIG. 4 operates using one-way transmitters and receivers, the system does not require the more complex differential pathogens and receivers described above.

[0017] FIG. 5 is a simplified block diagram of a process control or monitoring system 250 including a field device 252 connected to a two-wire process control loop 254. Loop 254 is connected to loop power source 256 and load resistor 258 (or a read resistor). Data transmitted over the two-wire loop 254 can be sensed using a loop receiver 260 connected through a load resistor 258.

[0018] In FIG. 5, field device 252 is illustrated as having a housing that provides electrical ground 270, which is capacitively coupled to two-wire process control loop 254 via capacitors 272. Field device 252 includes a general circuit 274 that connects to loop 254 process control, with impedance Z1 and Z2. The circuit is configured to communicate with remote receiver 280 via data bus 282. This data bus can be implemented in accordance with the CAN protocol. The physical connection for the data bus 282 may include a center conductor and a cable shield 290. This cable shield is connected to the ground of the housing 270 and is capacitively connected to the central connector (also illustrated on element 282) through the cable capacitance 292. Data is broadcast to the remote receiver 280 using a signal source 294. As discussed above, the signal from the source 294 may introduce an interference signal into the two-wire process control loop 254, which manifests itself through the load resistance 258. However, in accordance with the present invention, an inverting amplifier 296 is provided and configured to transmit an inverted signal from the data bus 282 to the loop 254 process control. As illustrated in FIG. 5, the interference signal 298 from the signal source 294 is compensated or otherwise reduced in magnitude by the output signal from the inverting amplifier 296. In the configuration of FIG. 5, the connection between the field device 252 and the remote receiver 280 provides one data bus, in while the connection between the field device 252 and the loop receiver 260 through the two-wire process control loop 254 provides another data bus.

[0019] Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that changes can be made in form and detail without departing from the spirit and scope of the invention. Although the field device illustrated in this document includes only two local data buses, the invention can be applied with any number of data buses and is not limited to the specific configurations set forth herein. The inverter may be in accordance with any suitable inverter circuit and may comprise, for example, a simple inverting amplifier. In one exemplary configuration, one of the data buses comprises a two-wire or wireless process control loop that is used to connect a field device, for example, to a central control center or the like. In this configuration, the local data bus may cause noise to be introduced into the two-wire or wireless process control loop. Similarly, data transmitted over a two-wire or wireless process control loop can cause noise to be added to the local data bus. Alternatively, the one-way transmitter 200 illustrated in FIG. 4 operates as the input / output circuit 156 shown in FIG. 2. Although FIG. 4 illustrates one inverter 220 that delivers an inverted signal from one data bus to another data bus, in another exemplary configuration, a second inverter is implemented that injects an inverter signal in the opposite direction between the two data buses. In some configurations, one or more data buses may comprise a wireless data bus.

Claims (18)

1. Field device for use in the manufacturing process, containing:
a process interface element configured to measure or control a process parameter;
a first communication system including one-way transmitter and receiver;
a second communication system configured to provide communication between the at least two components, the second communication system comprising a signal source that generates a signal that is introduced into the first communication system as interference;
a signal inverter configured to invert the signal generated by said signal source to generate an inverted signal, which is also introduced into the first communication system in order to thereby reduce interference from the second communication system to the first communication system, while the inverted signal has a phase, amplitude and waveforms that are similar to inverting a signal from said signal source; and
wherein the field device is configured to communicate with another location in the manufacturing process. 2. The field device of claim 1, wherein the first communication system is configured to communicate with a different location in the manufacturing process. 3. The field device of claim 1, wherein the second communication system is configured to communicate with another location in the manufacturing process. 4. The field device of claim 1, wherein the first communication system includes a local data bus. 5. The field device of claim 1, wherein the second communication system includes a local data bus. 6. The field device according to claim 1, wherein the process interface element comprises a process parameter sensor. 7. The field device according to claim 1, wherein the process interface element comprises a control element. 8. The field device of claim 1, wherein at least one of the first and second communication systems includes a wireless data bus. 9. The field device according to claim 1, wherein at least one of the first and second communication systems comprises a one-way communication system. 10. The field device according to claim 1, comprising a second signal inverter configured to invert the signal transmitted in the first communication system to generate an inverted signal, which is also introduced into the second communication system, so as to reduce interference from the first communication system to the second communication system. 11. A method for use in a field device of the type used in the manufacturing process, the method being designed to provide communication between components and comprises the steps of:
interacting with said manufacturing process through a process interface configured to measure or control a process parameter;
transmitting data between at least two first components on a first data bus between a one-way transmitter and a one-way receiver;
transmitting data between at least two second components on a second data bus, wherein at least one of said two second components is located in said field device;
the communication signal is inverted in the second data bus to form an inverted signal, which is also introduced into the first data bus, so as to reduce the interference signal introduced into the first data bus from the second data bus, while the signal introduced into the first data bus has a phase, amplitude and waveform, which are similar to the inversion of the interference signal;
wherein the field device is configured to communicate with another location in said manufacturing process. 12. The method of claim 11, wherein the first data bus is configured to communicate with a different location in said manufacturing process. 13. The method of claim 11, wherein the second data bus is configured to communicate with another location in said manufacturing process. 14. The method of claim 11, wherein the first data bus includes a local data bus. 15. The method according to claim 11, wherein the second data bus includes a local data bus. 16. The method according to claim 11, wherein at least one of the first and second data buses includes a wireless data bus. 17. The method of claim 11, wherein at least one of the first and second data buses comprises a one-way data bus. 18. The method according to claim 11, comprising the step of providing a second inverted signal from the first data bus to the second data bus, thereby reducing interference.

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