WO2015180091A1

WO2015180091A1 - Control system having wire break detection capability

Info

Publication number: WO2015180091A1
Application number: PCT/CN2014/078781
Authority: WO
Inventors: Wei Liu; Axel Lohbeck; Huan SHI
Original assignee: Abb Technology Ltd
Priority date: 2014-05-29
Filing date: 2014-05-29
Publication date: 2015-12-03

Abstract

A control system (20) having wire break detection capability is provided. The control system (20) comprises a plurality of digital output channels, a timing division multiplexer (21) comprising a plurality of inputs and one output, wherein the plurality of inputs are connected to the corresponding plurality of digital output channels of the multi-channel device with digital outputs, respectively, and a wire break detection circuit (22) connected to the one output of the timing division multiplexer (21) and configured to perform wire break detection on corresponding one of the plurality of digital output channels, wherein the timing division multiplexer (21) is configured to in a detection period, enable the corresponding one of the plurality of digital output channels to connect with the wire break detection circuit (22) to perform wire break detection on the corresponding one digital output channel, and disable other digital output channels to connect with the wire break detection circuit (22).

Description

CONTROL SYSTEM HAVING WIRE BREAK DETECTION CAPABILITY

FIELD OF INVENTION [0001] Embodiments of the present disclosure generally relate to a control system, and more particularly, to a control system having wire break detection capability.

BACKGROUND OF INVENTION

[0002] Industrial control system is now frequently used in many industrial fields. A main purpose of the industrial control system is to automatically control devices in the field. Normally, the industrial control system comprises an engineering station, an operation station, a controller, an I/O station, terminal boards and devices in the field.

[0003] Digital output signal is widely used in process control for applications like an ON/OFF control and a relay output. A digital output branch will output high or low according to operation or control algorithms.

[0004] An advanced digital output branch usually supports multiple channels and also has diagnostic function. Wire break detection is one of important diagnostic information which can inform a user whether there is a cable loose or wire break in the field.

[0005] A prior art wire break detection solution uses a shunt to measure the current when an output is in the ON state. Response time of the shunt is fast enough and therefore accuracy can be guaranteed. However, for a digital output module with multiple output channels, using a shunt for each channel is rather expensive and space consuming.

SUMMARY OF INVENTION [0006] In order to address the foregoing and other potential problems, embodiments of the present disclosure proposes a control system having wire break detection capability.

[0007] According to embodiments of the present disclosure, there is provided a control system comprising: a plurality of digital output channels; a timing division multiplexer comprising a plurality of inputs and one output, wherein the plurality of inputs are connected to the corresponding plurality of digital output channels, respectively; and a wire break detection circuit connected to the one output of the timing division multiplexer and configured to perform wire break detection on corresponding one of the plurality of digital output channels, wherein the time division multiplexer is configured to in a detection period, enable the corresponding one of the plurality of digital output channels to connect with the wire break detection circuit to perform wire break detection on the corresponding one digital output channel, and disable other digital output channels to connect with the break detection circuit.

[0008] In one embodiment, the time divisional multiplexer comprises: a plurality of circuit branches in parallel each corresponding to one of the plurality of digital output channels, respectively, and a controller configured to provide a control signal to each of the plurality of circuit branches such that in the detection period, one of the plurality of circuit branches is enabled to connect corresponding one of the plurality of digital output channels with the wire break detection circuit, and other circuit branches are disabled to disconnect other digital output channels with the wire break detection circuit.

[0009] In one embodiment, each of the plurality of circuit branches comprises at least one switching element, wherein the controller is configured to provide a control signal to control the switching on or off of the switching element.

[0010] In one embodiment, the at least one switching element comprises two switching elements connected in series in opposite directions.

[0011] In one embodiment, the switching elements are of one of PMOS, NMOS, MOSFET, IGBT and BJT. [0012] In one embodiment, the wire break detection circuit comprises a detection element connecting to the output of the timing division multiplexer and output a detected signal.

[0013] In one embodiment, the detection element is a shunt.

[0014] In one embodiment, the wire break detection circuit further comprises: a comparator for comparing the detected signal with a reference signal to output a resulting signal. [0015] In one embodiment, the wire break detection circuit further comprises a pull-down resistor element, wherein one end of the pull-down resistor is connected between the output of the detection element and the input of the comparator and other end of the pull-down resister is connected ground.

[0016] In one embodiment, each of the plurality of digital output channels comprises a sampling resistor element. [0017] In one embodiment, each of the plurality of digital output channels comprises a switch element.

[0018] According to the embodiments of the present disclosure, the plurality of digital output chancels may share one wire break detection circuit by means of a time division multiplexer. [0019] Other features and advantages of embodiments of the present disclosure will also be understood from the following description of specific exemplary embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF DRAWINGS

[0020] Embodiments of the present disclosure will be presented in the sense of examples and their advantages are explained in greater detail below, with reference to the accompanying drawings, wherein:

[0021] FIG. 1 is a diagram illustrating a system comprising wire break detection used for a single digital output channel in the prior art;

[0022] FIG. 2 shows a wire break detection part of a control system having multi-channel digital output wire break detection capability according to an embodiment of the present disclosure;

[0023] FIG. 3 shows a specific circuitry of the timing division multiplexer and the wire break detection circuit according to one embodiment.

[0024] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION OF EMBODIMENTS

[0025] Hereinafter, the principle and spirit of the present disclosure will be described with reference to the illustrative embodiments. It should be understood, all these embodiments are given merely for the skilled in the art to better understand and further practice the present disclosure, but not for limiting the scope of the present disclosure. For example, features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions should be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0026] The disclosed subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the description with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

[0027] FIG. 1 is a diagram illustrating a system for a wire break detection on a single digital output channel in the prior art. As seen in Fig.l, the system 10 comprises a power supply 11, a detection element 12, a switch 13, a field wire 14, and a load 15. The load 15 will be connected to the ground (not shown). The detection element 12 is used for measuring or sensing the electrical properties of the system, such as current, voltage, power, and so on. Normally a shunt can be employed, which is a device for measuring a DC current, and converting the DC current to a voltage across a resistor in the shunt 12 when the current flowing in the resistor. [0028] For example, in the system shown Figure 1, the detection element 12 is a shunt and will measure the current in the loop. If the field wire 14 is correctly connected, the current measured in the detection element 12 will be in certain range and the converted voltage is also in a certain range. If the field wire 14 is broken, the obtained voltage will below certain point, and this voltage can be used to compare with a reference voltage to generate wire break signal.

[0029] In a distributed control system (DCS), there are usually 16-32 output channels. When applying the conventional wire break detection circuit as shown in Figure 1 to a plurality channels, each cancel needs to be arranged with a detection element as shown Figure 1. Thus, the number of the detection element should be as same as the number of the channels. The structure comprising a plurality of detection elements will be expensive and space consuming.

[0030] Embodiments of the present disclosure provide a control system having multi-channel digital output wire break detection capability. According to the embodiments of the present disclosure, the plurality of digital output chancels may share one wire break detection circuit by means of a time division multiplexer. The control system can be CCS (concentrated computer control system), DCS (distributed control system), FCS (fieldbus control system), and the like.

[0031] Details of the control system having multi-channel digital output wire break detection capability are described as follow. However, the present disclosure is not limited to those described therein. [0032] FIG. 2 shows a wire break detection part of a control system having multi-channel digital output wire break detection capability according to an embodiment of the present disclosure. The control system comprises a plurality of digital output channels.

[0033] According to an embodiment of the present disclosure, as shown in Figure 2, the control system 20 having multi-channel digital output wire break detection capability can comprise a timing division multiplexer 21 and a wire break detection circuit 22. The timing division multiplexer 21 can comprise a plurality of inputs and one output. The plurality of input of the timing division multiplexer 21 can be adapted to be connected to corresponding one of the plurality of digital output channels, Channel 1, Channel 2 ...Channel N, respectively. The output of the timing division multiplexer 21 can be adapted to be connected to the wire break detection circuit 22.

[0034] According to the embodiment of the present disclosure, the time division multiplexer 21 is configured to in a detection period, enable corresponding one of the plurality of digital output channels Channel 1, Channel 2... Channel N, to connect with the wire break detection circuit 22 to perform wire break detection on the corresponding one digital output channel, and disable other digital output channels to connect with the break detection circuit.

[0035] According to the embodiment of the present disclosure, when applying the timing division multiplexer 21 to the control system, it only desires one wire break detection circuit to perform wire break detection on all the digital output channels, thus reducing the cost and the space consuming.

[0036] Next, details of the timing division multiplexer 21 and the wire break detection circuit 22 will be described. It should be appreciated that these details are only for the understanding on the present disclosure, and the present disclosure is not limited thereto.

[0037] FIG. 3 shows a specific circuitry of the timing division multiplexer 21 and the wire break detection circuit 22 according to one embodiment. There are shown only two digital output channels, which is only illustrative not limiting. The present disclosure can be adapted to a plurality of channels and normally be applied to 16 or 32 channels when the control system is DCS.

[0038] As shown in Figure 3, the time divisional multiplexer 21 according to one embodiment of the present disclosure can comprise a plurality of circuit branches in parallel, for example, Branch 1, Branch 2,.... Each branch respectively corresponds to one of the plurality of digital output channels, for example, Channel 1, Channel 2,...

[0039] Further, the time divisional multiplexer 21 according to one embodiment of the present disclosure can comprise a controller (not shown) configured to provide a control signal (Select chl, Select_ch2...) to each of the plurality of circuit branches such that in a detection period, one of the plurality of circuit branches is enabled to connect corresponding one of the plurality of digital output channels with the wire break detection circuit, and other circuit branches are disabled to disconnect other digital output channels with the wire break detection circuit. In one embodiment, only one of the control signals will be output low in one detection circle to enable wire break detection for the corresponding channel. Also, the control signal can be output high to enable wire break detection for the corresponding channel. [0040] According to embodiments of the present disclosure, each of the branches (such as Branch 1 and Branch 2) can further comprise at least one switching element. In one example shown in Figure 3, each branch comprises two switching elements, namely, Branch 1 used for the digital output channel 1 comprises switching elements Ml and M2, and Branch 2 used for the digital output channel 2 comprises switching elements M3 and M4. There are two switching elements in one branch, because there is a body diode in some switching elements, such as PMOS. The PMOS can effectively shut off the current in one direction, which flows from the source to the drain of the PMOS, but the current in another direction (from drain to the source) will still conduct due to the body diode. The two switching elements are connected in series opposing relationship to completely turn off the current in both directions and guarantee that the channel selected to be measured will not be affected by other channels.

[0041] In one embodiment, the switching element is PMOS (positive channel Metal Oxide Semiconductor), and in other embodiments the switching element can be one of NMOS (N-Mental-Oxide-Semiconductor), MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), BJT (Bipolar Junction Transistor) and so on.

[0042] When using PMOS as the switching elements in the branches, the control signal will be output low in one detection circle to enable wire break detection used for one channel. After wire break detection for this channel is ended (detection period based on the character of the wire break detection circuit), control signal for next channel will be pull down to enable wire break detection for next channel.

[0043] According to embodiment of the present disclosure, the wire break detection circuit can comprise a detection element SI, which has two inputs for respectively connecting to a power supply and the output of the timing division multiplexer and an output for providing a wire break detection signal, as shown in Fig. 3. In one embodiment, the detection element can be a shunt. Also, in other embodiments, the detection element can be an ammeter or a similar element. [0044] Specifically, the detection element S 1 in the wire break detection circuit 22 can be a shunt in one embodiment. The shunt has two inputs and an output for providing a voltage signal. The two inputs of the shunt are respectively connected with the power supply Vs and the output of the timing division multiplexer 21. When Branch 1 is connected with the wire break detection circuit 22, the power supply Vs, the output digital channel 1, Branch 1 and the shunt constitutes a closed loop. Furthermore, the shunt can detect the DC current in the loop, and then output a voltage signal which has a relationship with the DC current depending on the character of the shunt. The shunt act as in the conventional wire break detection for single digital output channel, thus ensuring the accuracy of the wire break detection.

[0045] In one embodiment, the wire detection circuit 22 further comprises a pull-down resistor Rl . One end of the pull-down resistor 22 is connected between the output of the detection element SI and the input of the comparator Ul, and other end of the pull-down resister 22 is connected ground. The pull-down resistor Rl is used to pull down the output voltage of the detection element SI in order to be suitable to be detected or inputted to another device.

[0046] Furthermore, in one embodiment, the wire detection circuit 22 further comprises a comparator Ul . One of the input terminals of the comparator Ul is connected with the output voltage signal of the detection element SI, and the other input terminal of the comparator Ul is connected with the reference voltage V_ref. The comparator Ul is configured to compare the output voltage signal of detection element S 1 with the reference V_ref to output a resulting signal which can be considered as the wire break detection signal. For example, when the output voltage signal of the detection element SI is smaller than the reference signal V_ref, the comparator Ul outputs a wire break signal with value "0" to indicate the field wire in this channel to be detected is broken. Otherwise, the value 1 of the wire break signal can indicate the field wire in the corresponding channel works normally.

[0047] In one embodiment, there is also a sampling resistor in each of the plurality of digital output channels, which is used to sample the corresponding channel. As shown in Fig.3, the resistor R2 in channel 1 and the resistor R3 in channel 2 are the sampling resistor, the detection element SI can measure the current flowing in the sampling resistor and convert the current into voltage signal.

[0048] Moreover, each of the plurality of digital output channels comprises a switch element to control the status of the corresponding channel, such as the switch Ql in Channel 1 and the switch in Channel 2 as shown in the Fig.3. One end of the switch Ql or Q2 connects to the corresponding input of the multiplexer. Another end of the switch Ql or Q2 connects with the load (not shown) in the corresponding channel.

[0049] It should also be noted that the above described embodiments are given for describing rather than limiting the invention, and it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the invention and the appended claims. The protection scope of the invention is defined by the accompanying claims. In addition, any of the reference numerals in the claims should not be interpreted as a limitation to the claims. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The indefinite article "a" or "an" preceding an element or step does not exclude the presence of a plurality of such elements or steps.

Claims

WHAT IS CLAIMED IS:

1. A control system having wire break detection capability, comprising:

a plurality of digital output channels;

a timing division multiplexer comprising a plurality of inputs and one output, wherein the plurality of inputs are connected to the corresponding plurality of digital output channels, respectively, and

a wire break detection circuit connected to the one output of the timing division multiplexer and configured to perform wire break detection on corresponding one of the plurality of digital output channels,

wherein the time division multiplexer is configured to in a detection period, enable the corresponding one of the plurality of digital output channels to connect with the wire break detection circuit to perform wire break detection on the corresponding one digital output channel, and disable other digital output channels to connect with the break detection circuit.

2. The control system according to Claim 1, wherein the time divisional multiplexer comprises:

a plurality of circuit branches in parallel each corresponding to one of the plurality of digital output channels, respectively, and

a controller configured to provide a control signal to each of the plurality of circuit branches such that in the detection period, one of the plurality of circuit branches is enabled to connect corresponding one of the plurality of digital output channels with the wire break detection circuit, and other circuit branches are disabled to disconnect other digital output channels with the wire break detection circuit.

3. The control system according to Claim 2, wherein each of the plurality of circuit branches comprises at least one switching element, wherein the controller is configured to provide a control signal to control the switching on or off of the switching element.

4. The control system according to Claim 3, wherein the at least one switching element comprises two switching elements connected in series in opposite directions.

5. The control system according to Claim 3 or 4, wherein the switching elements are of one of PMOS, NMOS, MOSFET, IGBT and BJT.

6. The control system according to any of Claims 1-5, wherein the wire break detection circuit comprises a detection element connecting to the output of the timing division multiplexer, and output a detected signal.

7. The control system according to Claim 6, wherein the detection element is a shunt.

8. The control system according to Claim 6, wherein the wire break detection circuit further comprises a comparator for comparing the detected signal with a reference signal to output a resulting signal.

9. The control system according to Claim 8, wherein the wire break detection circuit further comprises a pull down resistor element, wherein one end of the pull-down resistor is connected between the output of the detection element and the input of the comparator, and other end of the pull-down resister is connected ground.

10. The control system according to any one of Claims 1-9, wherein each of the plurality of digital output channels comprises a sampling resistor element.

11. The control system according to any one of Claims 1-10, wherein each of the plurality of digital output channels comprises a switch element.