signal processing device

Abstract

The present application provides a signal processing device for two-wire sensor, which ensures that a two-wire cable can be used as the value of two-wire and 4-20mA output can be obtained, and high performance can be obtained without sacrificing performance. The signal processing device (300) has a sensor (10) and a signal converter (100) for converting the signal detected by the sensor, and a pair of output signal terminals (120, 130) for pulse and a pair of power terminals (140, 150) are provided at the external cable connection part (20) of the sensor, one of the pair of output signal terminals is connected to the + side of the power terminal through a specified resistor (160), and the other of the output signal terminals is short-circuited to the - side of the power terminal, forming an overlapping power line (210, 220) in which the current consumed by the pulse output circuit is superimposed on the current consumed by the power terminal of the sensor, the sensor and the signal converter are connected through the overlapping power line, and the signal converter extracts only the signal corresponding to the pulse output (304) from the overlapping current waveform flowing in the overlapping power line.

Description

Technical Field

[0001] This invention relates to a signal processing apparatus, and more specifically to a signal processing apparatus for a two-wire sensor. Background Technology

[0002] Sensors have various outputs depending on their application. For example, a Coriolis flow meter detects an analog signal of the torsion of the sensing tube and sends that signal out as a current (see Patent Document 1).

[0003] Among the methods of transmitting signals from sensors, there are generally "two-wire sensors" that use only two wires for both power supply and signal output, and "sensors consisting of three or more wires" where the power supply and signal system are separate. "Two-wire sensors" are a common technology in industrial applications, and are commercialized in products such as pressure transmitters and temperature transmitters, in addition to flow meters. "Two-wire" refers to controlling the current flowing in the power supply line supplying DC power to the device—that is, the device's current consumption—to a 4-20mA signal equivalent to an analog output for instrumentation, based on the device's measured value (see Patent Document 2).

[0004] In addition, in the "sensor consisting of three or more wires" where the power supply and signal lines to the electronic circuit of the sensor are separated, the circuit on the receiving side can be simplified, but compared with the "two-wire sensor", there is a problem of increased wiring time (wiring cost). Prior art literature Patent documents

[0005] Patent Document 1: Japanese Patent No. 4952820 Patent Document 2: Japanese Patent No. 3139502 Summary of the Invention (The problem that the invention aims to solve)

[0006] The current consumed by the device itself is lower than the analog output current, and must be basically below 4mA. Therefore, due to this design limitation, the two-wire device disclosed in Patent Document 1 is limited to a low-power measuring instrument that can operate with a current consumption of basically 4mA.

[0007] Furthermore, even when a two-wire system is possible, in flow meters that consume a large current, such as the Coriolis flow meter disclosed in Patent Document 1, the two-wire system is achieved by suppressing current consumption. Compared with Coriolis flow meters that are not two-wire systems, there is a tendency to sacrifice performance.

[0008] Furthermore, in the typical two-wire system disclosed in Patent Document 2, the obtained signal is a 4-20mA signal = instantaneous value, thus there is a problem that real-time cumulative flow information cannot be obtained in the flow meter. However, as mentioned above, compared with a three-wire system, which further increases the number of wires, the two-wire sensor significantly reduces wiring time, thereby enabling a reduction in the overall cost of the device and earlier startup of the device.

[0009] In the case of flow meters, there are mechanical (gear-type, turbine-type) flow meters with a long history that do not require an external power supply and have contact pulse output, capable of transmitting only a pulse signal equivalent to the accumulated flow using a two-wire cable. While real-time accumulated information can be obtained in these two-wire (mechanical) flow meters, on the other hand, due to their limitation to mechanical types that do not require an external power supply, there is a problem that they cannot be replaced by the latest electronic flow meters that are multifunctional, easy to use, and essentially maintenance-free.

[0010] Therefore, the present invention has been made in view of these actual circumstances, and its object is to provide a signal processing device for a two-wire sensor that ensures the use of a two-wire cable (which serves both as a power supply and signal transmission, thus reducing costs) and the ability to obtain a 4-20mA output (which can obtain a common instrument signal), without sacrificing performance and achieving high performance. (Technical solution used to solve the problem)

[0011] To address the aforementioned issues, the first technical solution of the present invention is a signal processing device, which includes a sensor and a signal converter for converting signals detected by the sensor. The signal processing device is characterized in that the external cable connection portion of the sensor has a pair of output signal terminals for semiconductor pulses and a pair of power supply terminals. One of the output signal terminals is connected to the positive side of the power supply terminal via a predetermined resistor, and the other of the output signal terminals is short-circuited to the negative side (0V) of the power supply terminal, forming an overlapping power line where the current consumed by the power supply terminal of the sensor overlaps with the current consumed by the pulse output circuit. The sensor and the signal converter are connected through the overlapping power line, and the signal converter extracts only the signal equivalent to the pulse output from the overlapping current waveform flowing in the overlapping power line.

[0012] To address the aforementioned issues, the second technical solution of the present invention is characterized in that the signal converter includes a specified current detection resistor and a frequency filter or comparator, or both the frequency filter and the comparator, to extract only a signal equivalent to the pulse output from the overlapping current waveform flowing in the overlapping power line.

[0013] To address the aforementioned issues, the third technical solution of the present invention is characterized in that the signal processing device further comprises a pulse signal extraction filter, which extracts only pulse signals from the overlapping current waveform through the current detection resistor and a frequency filter or comparator, or both the frequency filter and the comparator.

[0014] To address the aforementioned issues, the fourth technical solution of the present invention is characterized in that the signal processing device further comprises a frequency-to-current converter, which converts the pulse signal obtained from the pulse signal extraction filter into a specified current signal.

[0015] To address the aforementioned issues, the fifth technical solution of the present invention is characterized in that the sensor is a three-wire or four-wire flow meter.

[0016] To address the aforementioned issues, the sixth technical solution of the present invention is characterized by calculating the cumulative flow value and the instantaneous flow value based on the number of pulses and frequency information of the pulse signal obtained from the pulse signal extraction filter, and displaying the cumulative flow value, the instantaneous flow value, or an abnormal alarm based on the flow status through a pre-installed display.

[0017] To address the aforementioned issues, the seventh technical solution of the present invention is characterized in that an alarm output is issued when the frequency of the pulse signal obtained by the pulse signal extraction filter exceeds or falls below a predetermined frequency threshold. (Invention Effects)

[0018] According to the present invention, in a three-wire (or four-wire) sensor with high performance and open-collector pulse output, by connecting the power supply positive line and the open-collector positive line with a specified resistor, the flowmeter's original consumption current (which does not change drastically) is overlapped with the consumption current of the open-collector pulse (a pulse signal of about 1 Hz to several kH) on the power supply line. Furthermore, in the signal converter that serves as the interface with the upstream device, only the pulse signal can be extracted from the consumption current waveform using a specified frequency filter. Moreover, by performing frequency-to-current (F / I) conversion on the pulse signal, an output of 4 to 20 mA can be achieved, and pulse output is also possible.

[0019] Furthermore, according to the present invention, it is possible to provide an existing instrument system that effectively utilizes the advantages of sensors composed of three or more wires and consists of a two-wire flow meter (e.g., area type, differential pressure type, etc.) to suppress wiring costs. That is, if the signal processing device according to the present invention is used, it is possible to update the flow meter to a high-performance Coriolis flow meter that is not two-wire without changing the existing two-wire cable and the existing upstream receiving device.

[0020] For example, conventionally, mechanical two-wire flow meters that do not require an external power supply and have a contact pulse output (equivalent to cumulative flow) function cannot be replaced with Coriolis flow meters that require an external power supply. However, pulse output can also be obtained in the signal processing device involved in this invention, so without changing the existing two-wire cable and the existing upstream receiving device, it is possible to simply update the flow meter to a high-performance Coriolis flow meter that is not two-wire.

[0021] Therefore, the present invention provides a signal processing device for a two-wire sensor, ensuring that the two-wire cable, which is valued for its two-wire nature (it can be used for both power supply and signal transmission, thus reducing costs), can be used and that a 4-20mA output can be obtained (which can obtain a common instrument signal), without sacrificing performance and achieving high performance. Attached Figure Description

[0022] Figure 1 This is a block diagram illustrating a case where signal transmission overlaps with the power supply in one embodiment of the present invention. Figure 2 This is a block diagram illustrating the signal transmission using a three-wire sensor, a technology that has been used in the past. Figure 3 This is a block diagram illustrating the overall structure of a signal processing device including a sensor / power supply / signal conversion according to one embodiment of the present invention. Figure 4 This is an example of replacing the existing two-wire sensor in one embodiment of the present invention (one of them). Figure 5 This is a replacement example (second example) of the existing two-wire sensor in one embodiment of the present invention. Detailed Implementation

[0023] Hereinafter, a preferred embodiment of the signal processing apparatus of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a block diagram illustrating a case where signal transmission overlaps with a power supply in one embodiment of the present invention. Figure 2 This is a block diagram illustrating the signal transmission using a three-wire sensor, a technology that has been used in the past. Figure 3 This is a block diagram illustrating the overall structure of a signal processing device including a sensor / power supply / signal conversion according to one embodiment of the present invention.

[0024] First, in conventional two-wire sensor circuits, the signal line is shared with the power supply that drives the sensor itself. Therefore, when compared with the contact on / off signal, which is the simplest and easiest signal to process, the circuit drive current flows even in the state where no current should flow, i.e., when it is off.

[0025] Furthermore, even when the desired resistance and residual voltage are minimized, it is still necessary to ensure that the residual voltage can be used to drive the circuit as much as possible. This introduces various limitations for loads connected to sensors, and for connection methods involving multiple sensors, such as parallel or series connections.

[0026] In addition, there is a constraint that the current consumption of sensor elements must be set below the control current (usually below 4mA). Therefore, in sensors that consume a lot of current, there is a tendency that two-wire systems cannot be implemented or that performance must be sacrificed to reduce current consumption.

[0027] Next, as Figure 2 In the conventional three-wire system shown, the signal line is typically an open collector, and can also be a power supply different from the sensor power supply, thus reducing limitations compared to the conventional two-wire system. However, as... Figure 2 As shown, wiring based on three-wire cables is required, which increases wiring time.

[0028] Details will be discussed later. Figure 1 In the circuits involved in the embodiments of the present invention, regarding the output from the sensor, and Figure 2 Similarly, the three-wire system is configured such that it has a pair of semiconductor pulse signal terminals 620 and 630 and a pair of power supply terminals 640 and 650, starting from the external cable connection portion 520 of the sensor 510. Furthermore, the terminals can be either mechanical contacts or open-collector electrodes. Additionally, in Figure 2 The diagram schematically depicts the external cable connection 610, which in practice includes the aforementioned terminals and wires connected to the converter 600, each marked with its respective reference number.

[0029] Therefore, the output of sensor 510 is sent to converter 600 via external cable connection 520. Figure 2 In the previous three-wire technology, the converter 600 set the signal line 620 of the open collector as an independent cable.

[0030] The converter 600 and the power / signal processing unit 800 are connected via power lines 710, 730 and an open collector 720. The power / signal processing unit 800, upon receiving signals, performs composite processing on these signals, for example, into an analog output 802 and a pulse output 804.

[0031] On the other hand, in one embodiment of the present invention Figure 1 In the converter 100, one of the pair of output signal terminals, namely the open-collector output signal terminal 120, is connected to the positive-side power supply terminal 150 via a predetermined resistor 160. Furthermore, the other signal terminal 130 is short-circuited to the negative-side power supply terminal 140.

[0032] Through this circuit structure, the cables 210 and 220 connected to a pair of power terminals 140 and 150 become superimposed power lines 210 and 220, which are superimposed with the current consumed by the power terminals of the sensor and the current consumed by the pulse output circuit.

[0033] The converter 100 and the power / signal processing unit 300 are connected via two overlapping power lines 210 and 220. The power / signal processing unit 300 processes the received signals into analog output 302, pulse output 304, etc.

[0034] Next, refer to Figure 3 The power supply / signal processing device 300 will be described in detail below. The signal output from the sensor 10 is sent to the power supply / signal processing device 300 via the external cable connector 20, the converter 100, and the overlapping power lines 210 and 220.

[0035] The power supply / signal processing device 300 can be configured to include a specified current sensing resistor 310 and a frequency filter or comparator, or both a frequency filter and a comparator. Figure 3 In the illustrated embodiment, waveform filter 330 represents either a frequency filter or a comparator, or both. Additionally, overlapping power lines 210 and 220 are connected to power supply 320 for supplying power to the sensor.

[0036] The waveforms before and after the waveforms are shown in waveforms 312 and 332, respectively, and are appropriately filtered by the waveform filter 330.

[0037] The output of waveform filter 330 is sent to the arithmetic and control unit 340 and directly used as pulse output 304. Pulse output 304 can be output to the upper-level equipment of the measurement system for various processing and analysis.

[0038] In this embodiment, the calculation and control unit 340 can, for example, output a current output 302 of 4 to 20 mA through the frequency-to-current (F / I) converter 342, or output an alarm output 306 such as a warning message from the sensor 10 through the alarm control 344, or make the flow display 350 display the flow rate through the display control 346.

[0039] That is, according to this structure, by extracting only the signal equivalent to the pulse output from the overlapping current waveform flowing through the overlapping power lines, it is possible to convert it into various outputs.

[0040] Thus, one embodiment of the present invention maintains the structure of a high-performance three-wire (or four-wire) sensor with open-collector pulse output, and connects the power supply + line and the open-collector + line with a specified resistance.

[0041] Therefore, the pulsed current consumption of the open collector overlaps with the current consumption that does not change drastically. Furthermore, the power supply / signal processing device 300, by including a frequency filter and a comparator, extracts only the pulse signal from the current consumption waveform. Moreover, by performing frequency-to-current (F / I) conversion on the pulse signal, it can output 4 to 20 mA, and it can also output pulses.

[0042] The present invention provides a signal processing device for a two-wire sensor that ensures the usability of the two-wire cable (which serves both as a power supply and signal transmission, thus reducing costs) and provides a 4-20mA output (capable of providing a common instrument signal) without sacrificing performance and achieving high performance.

[0043] For typical two-wire sensors with an output of 4–20 mA, if the driving current is below 20 mA, and this current is considered sufficient for sensor driving (including computation and control), then processing is performed within the range of 4 mA or less. However, in one embodiment of the present invention, a high-performance and versatile sensor with a driving current exceeding 4 mA, which would otherwise be unsuitable for a two-wire system, can be used to construct a two-wire transmission system.

[0044] For example, in a high-performance Coriolis flow meter, which is one of the sensors consisting of three or more wires, the nominal current consumption is approximately 400mA. To make this high-current-consuming high-performance Coriolis flow meter compatible with conventional two-wire systems—that is, to drive the sensor with 4mA—it needs to be configured to reduce the energy used to approximately 1 / 100th. Common measures to reduce current consumption include: reducing the resolution of digital processing (reducing accuracy), and reducing the calculation frequency (degrading responsiveness), but these essentially degrade performance. On the other hand, this invention enables the application of conventional (and currently marketed) high-performance Coriolis flow meters consisting of three or more wires to two-wire systems without compromising performance.

[0045] Furthermore, generally speaking, for analog instruments such as Coriolis flow meters, the current consumption changes slowly during operation and does not change drastically. Therefore, as in this invention, it is relatively easy to separate and restore the pulse signal using a frequency filter using common techniques. Consequently, in this invention, even after separating and recombining temporarily overlapping signals, the possibility of the quality of the recombined signal deteriorating is relatively small.

[0046] Next, refer to Figure 4 , Figure 5 An example will be described in which the present invention is applied to replace a two-wire sensor with a sensor consisting of three or more wires when a two-wire sensor has already been provided.

[0047] Reference Figure 4 Even if a two-wire flow meter 512, such as a gear type, is already installed as shown in (A), it can be easily replaced with a four-wire high-performance Coriolis flow meter 12 as shown in (B).

[0048] exist Figure 4 In (A), the conventional method involves outputting a pulse signal 930 from a two-wire flow meter 512 (such as a gear type) to a higher-level system 900 via two-wire cables 910 and 920. On the other hand, in... Figure 4 In (B), the high-performance Coriolis flow meter 12, equipped with a converter 100 (not shown), is replaced with a two-wire flow meter 512. Then, Figure 4 The two wires 910 and 920 in (A) are used as overlapping power lines 210 and 220.

[0049] Signals (power) from the overlapping power lines 210 and 220 are sent to the power / signal processing device 300 according to this embodiment. In the power / signal processing device 300, they are converted into a pulse output 304 (or a current output 302, an alarm output 306, etc.) and output to the established upper-level system 900. As a result, the existing two-wire cables 910 and 920 (overlapping power lines 210 and 220) and the upper-level system 900 can be replaced by the high-performance Coriolis flow meter 12 without changing the existing cables.

[0050] Next, in Figure 5 In (A), the conventional method involves outputting a 4-20mA current signal 940 from a two-wire flowmeter 514 (such as an area-type or differential-pressure type) via two-wire cables 910 and 920 to the upper-level system 900. On the other hand, in... Figure 5 In (B), the high-performance Coriolis flow meter 12, equipped with a converter 100 (not shown), is replaced with a two-wire flow meter 514. Then, Figure 5 The two wires 910 and 920 in (A) are used as overlapping power lines 210 and 220.

[0051] The signals (power) from the overlapping power lines 210 and 220 are sent to the power / signal processing device 300 according to this embodiment. In the power / signal processing device 300, they are converted into a current output 302 (or a pulse output 304, an alarm output 306, etc.) and output to the established upper-level system 900. As a result, the existing two-wire cables 910 and 920 (overlapping power lines 210 and 220) and the upper-level system 900 can be replaced by the high-performance Coriolis flow meter 12 without changing the existing power lines 210 and 220.

[0052] Therefore, this invention solves the problems associated with conventional two-wire transmission (4-20mA output, pulse output = unidirectional signal transmission from the sensor to the higher-level device). Specifically, this invention provides a signal processing device for a two-wire sensor that, using existing wiring, ensures the use of the two-wire cable (which serves both power supply and signal transmission, reducing costs) and provides a 4-20mA output (capable of providing general-purpose instrument signals), without sacrificing performance and achieving high performance.

[0053] This invention achieves two-wire-based information transmission by converting the open-collector pulse signal output from the sensor into a current signal and superimposing it onto the power line. However, the transmitted signal is restored to a general-purpose instrument signal (4-20mA current signal, pulse signal) by the power supply / signal processing device 300. Therefore, it is also possible to acquire information using existing wiring relative to general-purpose upstream devices such as PLCs. Furthermore, several embodiments of this invention have been described, but the invention is not limited thereto. (Symbol Explanation)

[0054] 10, 12, 510, 512, 514: Sensors 20, 520: External cable connection part 100, 600: Converters 120, 130, 620, 630: Output signal terminals 140, 150, 640, 650: Power terminals 160: Resistance 210, 220: Overlapping power lines 300, 800: Power supply / signal processing unit 302, 802: Analog Output 304, 804, 930: Pulse output 306: Alarm Output 312, 332: Waveforms 310: Current sensing resistor 320: Power supply 330: Waveform Filter 340: Computation and Control Department 342: Frequency-to-current (F / I) conversion 344: Alarm Control 346: Display Control 350: Flow display 710, 730: Power cord 720: Open collector 900: Superior System 910, 920: Two-wire cable.

Claims

1. A signal processing apparatus comprising a sensor and a signal converter for converting a signal detected by the sensor, characterized in that, The external cable connection portion of the sensor includes a pair of semiconductor pulse output signal terminals and a pair of power supply terminals. One of the pair of output signal terminals is connected to the + side of the power supply terminal via a specified resistor, and the other of the output signal terminals is short-circuited to the - side of the power supply terminal, forming an overlapping power line where the current consumed by the sensor's power supply terminal overlaps with the current consumed by the pulse output circuit. The sensor and the signal converter are connected via the overlapping power line. The signal converter includes a specified current sensing resistor and a frequency filter or comparator, or both, and extracts only the signal corresponding to the pulse output from the overlapping current waveform flowing in the overlapping power line. The signal processing device further includes a pulse signal extraction filter, which extracts only pulse signals from the overlapping current waveform through the current detection resistor and a frequency filter or comparator, or both the frequency filter and the comparator.

2. The signal processing apparatus according to claim 1, characterized in that, The signal processing device also includes a frequency-to-current converter, which converts the pulse signal obtained from the pulse signal extraction filter into a specified current signal.

3. The signal processing apparatus according to claim 1 or 2, characterized in that, The sensor is a three-wire or four-wire flow meter.

4. The signal processing apparatus according to claim 1, characterized in that, The cumulative flow rate and instantaneous flow rate are calculated based on the number of pulses and frequency information of the pulse signal obtained by the pulse signal extraction filter. The cumulative flow rate and instantaneous flow rate or abnormal alarms based on the flow status are displayed on a pre-installed display.

5. The signal processing apparatus according to claim 1, characterized in that, An alarm is issued when the frequency of the pulse signal obtained by the pulse signal extraction filter exceeds or falls below a specified frequency threshold.

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