Condition monitoring system

Abstract

A state monitoring system (1) comprises a sensor amplifier (10) and a state monitoring device (20). The state monitoring device (20) includes an IEPE power supply (21). The sensor amplifier (10) includes: an arithmetic device (13) that outputs a signal corresponding to a signal which is output from a sensor (31); an output device (15) that outputs, as a signal compatible with that of the state monitoring device (20), the signal which is output from the arithmetic device (13); and a power converter (14) that draws, from the IEPE power supply (21), power corresponding to the sensor (31) and converts the power, which has been acquired from the IEPE power supply (21), into power for driving at least the arithmetic device (13).

Description

Condition Monitoring System

[0001] The present disclosure relates to a condition monitoring system.

[0002] Conventionally, as described in Japanese Patent No. 3305325 (Patent Document 1), there have been techniques that diagnose the condition of a machine performing rotary motion or reciprocating motion using a two-wire vibration sensor. In the technique of Patent Document 1, a two-wire vibration sensor is driven by a constant current source, and the obtained signal is processed to monitor the condition of the machine.

[0003] Japanese Patent No. 3305325

[0004] Patent Document 1 does not premise the use of sensors other than vibration sensors. In a condition monitoring system that monitors the condition of a machine, if many types of measurement can be performed, there are advantages such as improved diagnostic performance or enhanced versatility. However, when measuring the condition of a machine using sensors other than vibration sensors to perform many types of detection, dedicated input circuits and processing devices are required.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a condition monitoring system capable of measuring the condition of a machine using an arbitrary sensor.

[0006] The present disclosure relates to a condition monitoring system that monitors the condition of a machine. The condition monitoring system includes a sensor amplifier connected to a sensor attached to the machine, and a condition monitoring device that monitors the condition of the machine based on a signal transmitted from the sensor amplifier. The condition monitoring device includes a constant current source. The sensor amplifier includes: an arithmetic unit that outputs a signal corresponding to the signal output from the sensor; an output unit that outputs the signal output from the arithmetic unit as a signal compatible with the condition monitoring device; and a power converter that is driven by power obtained from the constant current source, draws power corresponding to the sensor from the constant current source, and converts the power obtained from the constant current source into at least power for driving the arithmetic unit.

[0007] According to the present disclosure, by using a sensor amplifier connected to the condition monitoring device, the condition of the machine can be measured using an arbitrary sensor.

[0008] This is a circuit diagram showing an example of a condition monitoring system. This is a circuit diagram showing the configuration of a constant current source.

[0009] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the embodiments described below, when numbers, quantities, etc. are mentioned, the scope of this disclosure is not necessarily limited to those numbers, quantities, etc., unless otherwise specified. The same reference numerals will be used for the same parts and equivalent parts, and redundant descriptions will not be repeated. It is intended from the outset that the configurations in the embodiments will be used in appropriate combinations.

[0010] Figure 1 is a circuit diagram showing an example of a condition monitoring system 1. The condition monitoring system 1 includes a sensor amplifier 10, a condition monitoring device 20, and connection terminals 51 to 55. The condition monitoring device 20 is connected to one end of the sensor amplifier 10, and a sensor 31 attached to a machine 30 is connected to the other end of the sensor amplifier 10. The condition monitoring system 1 is used in various industrial locations, such as monitoring the amount of vibration of the bearings of a wind power generation device, and is a system for monitoring the condition of the machine 30 that is to be monitored. Note that elements not related to this disclosure, such as storage devices and external servers, have been omitted from the description of the condition monitoring system 1. The sensor 31 may be included in the condition monitoring system 1.

[0011] The sensor amplifier 10 includes an AFE (Analog Front End) circuit 11, an ADC (Analog to Digital Converter) circuit 12, a calculation unit 13, a power converter 14, and an output unit 15. One end of the sensor amplifier 10 is connected to the sensor 31 by three wires via connection terminals 53 to 55, and the other end of the sensor amplifier 10 is connected to the state monitoring device 20 by two wires via connection terminals 51 and 52. Note that the connection between the sensor 31 and the sensor amplifier 10 in this disclosure is an example; if the sensor 31 includes a thermocouple or a clamp current sensor, the sensor 31 and the sensor amplifier 10 may be connected by two wires, and if the sensor 31 includes a high-precision resistance thermometer or a strain sensor, the sensor 31 and the sensor amplifier 10 may be connected by four wires. Thus, the number of wires between the sensor 31 and the sensor amplifier 10 can be appropriately changed depending on the configuration of the sensor 31.

[0012] Specifically, one end of the sensor amplifier 10 has a wire connected to terminal 53 for supplying power to the sensor 31, a wire connected to terminal 54 for receiving signals from the sensor 31, and a wire connected to terminal 55 for ground. The other end of the sensor amplifier 10 has a wire connected to terminal 51 for acquiring power from the status monitoring device 20 and outputting signals to the status monitoring device 20, and a wire connected to terminal 52 for ground.

[0013] The AFE circuit 11 is a circuit that processes the analog signal from the sensor 31. Specifically, the AFE circuit 11 is a circuit that receives the analog signal from the sensor 31 and converts the received analog signal into a signal suitable for A / D conversion. The analog signal output from the sensor 31 may be weak and contain noise components. Therefore, if it is input directly to the ADC circuit 12, it may not be possible to convert it into a digital signal properly. To address this, the AFE circuit 11 amplifies the signal or removes noise components with a filter to make it easier for the ADC circuit 12 to convert it into a digital signal. The AFE circuit 11 is composed of semiconductor chips including amplifiers and filters, as well as passive components such as resistors and capacitors.

[0014] The ADC circuit 12 is a circuit that converts the analog signal processed by the AFE circuit 11 into a digital signal and transmits it to the arithmetic unit 13. The ADC circuit 12 transmits the converted digital signal to the arithmetic unit 13. The ADC circuit 12 may be an independent IC (Integrated Circuit) or may be integrated into the AFE circuit 11 or the arithmetic unit 13. The ADC circuit 12 may be a 1-bit ADC that transmits a 1-bit signal. In this disclosure, the ADC circuit 12 is preferably a SAR (Successive Approximation Register) type or ΣΔ type ADC, which consume less power, rather than a flash type ADC which consumes more power.

[0015] The arithmetic unit 13 is a circuit that processes the digital signals converted by the ADC circuit 12. The arithmetic unit 13 is a computing entity (computer) that performs various processes by executing various programs. The arithmetic unit 13 is composed of a processor with digital computing capabilities, such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit). The arithmetic unit 13 outputs a signal to the output device 15 that corresponds to the signal output from the sensor 31 and obtained via the AFE circuit 11 and the ADC circuit 12.

[0016] The power converter 14 converts the power output from the state monitoring device 20 into a format usable by the AFE circuit 11, ADC circuit 12, arithmetic unit 13, etc. Here, since the power and voltage output from the state monitoring device 20 change according to the resistance of the sensor 31, adjustment by the power converter 14 is necessary. The power converter 14 has the function of drawing power according to the sensor 31 from a constant current source, which will be described later, and converting the power obtained from the constant current source into power for driving each device.

[0017] In this manner, the power converter 14 is driven by a constant current source and drives each device by adjusting the voltage and power to the voltage and power available to each device. Each device includes the AFE circuit 11, the ADC circuit 12, the arithmetic unit 13, and the sensor 31. Note that the sensor 31 may be one that does not require current. In such a case, the power converter 14 may not supply power to the sensor 31.

[0018] The output unit 15 outputs a signal to the status monitoring device 20 that corresponds to the signal output from the arithmetic unit 13. In this way, the output unit 15 has the function of outputting the signal output from the sensor 31 into a compatible signal that can be used by the status monitoring device 20. The output unit 15 uses semiconductor switches or mechanical switches to change the signal output in accordance with the sensor 31 connected to the sensor amplifier 10. Semiconductor switches include transistors controlled by current and FETs (Field Effect Transistors) controlled by voltage. Mechanical switches include reed relays and mechanical relays. The output unit 15 can be any configuration that can change the signal output in accordance with the sensor 31.

[0019] The condition monitoring device 20 monitors the state of the machine 30 to which the sensor 31 is attached based on signals transmitted from the sensor amplifier 10. The condition monitoring device 20 includes connection terminals 51 and 52, an IEPE (Integrated Electronics Piezo Electric) power supply 21, a capacitor 22, a switch 23, and an amplifier 24. Two connection terminals 51 and 52 are provided to correspond to a two-wire condition monitoring device 20. By connecting the sensor amplifier 10 in place of a two-wire vibration sensor, the condition monitoring device 20 can measure the state of the machine 30 to which the sensor 31 is attached, including sensors other than vibration sensors.

[0020] The capacitor 22 and the switch 23 are elements that switch between AC (Alternating Current) coupling and DC (Direct Current) coupling. When the switch 23 is ON, current flows through the switch 23, resulting in DC coupling, and the input signal is transmitted to the amplifier 24 as is. On the other hand, when the switch 23 is OFF, current flows through the capacitor 22, resulting in AC coupling, and the DC component of the input signal is cut off before it is transmitted to the amplifier 24. Note that the state monitoring device 20 may also be configured to include only the capacitor 22 that provides AC coupling, without the switch 23.

[0021] The amplifier 24 has the function of amplifying the signal. The signal amplified by the amplifier 24 is transmitted to an external computing device (not shown in the figure). The external computing device diagnoses the state of the machine 30 detected by the sensor 31 based on the received signal. Note that the computing device may be incorporated into the state monitoring device 20, and the device with the computing device incorporated may be referred to as the state monitoring device.

[0022] Sensor 31 is a sensor or device that measures the state of the machine 30 being monitored and outputs it as an analog signal. Various types of sensors can be used for sensor 31, such as AE (acoustic emission) sensors, temperature sensors (thermocouples, thermistors, resistance thermometers, etc.), ultrasonic sensors, acoustic sensors, strain sensors, load sensors, magnetic sensors (Hall sensors, magnetoresistive sensors, etc.), pH (Potential Hydrogen) sensors, and capacitance sensors. Sensor 31 may also include part of the configuration of sensor amplifier 10. Specifically, sensor 31 may include the functions of AFE circuit 11 and ADC circuit 12 and output the measured value on a digital bus. Sensor 31 may also include only the function of AFE circuit 11.

[0023] The IEPE power supply 21 is a constant current source capable of outputting a voltage of 14V or higher and having an output current in the range of 0.5mA to 40mA. The configuration of the IEPE power supply 21 will be explained using Figure 2. Figure 2 is a circuit diagram showing the configuration of a typical constant current source. As shown in Figure 2, the IEPE power supply 21, which is a constant current source, includes a constant voltage source 211 and a constant current diode 212.

[0024] The constant voltage source 211 generates a constant power supply voltage according to the characteristics of the connected sensor 31. One end of the constant voltage source 211 is connected to the grounding node 25. The grounding node 25 is connected to earth (ground). The other end of the constant voltage source 211 is connected to the constant current diode 212. The constant current diode 212 is configured to receive the current supplied from the constant voltage source 211 and supply a constant current to the connection terminal 51 by changing its resistance value and the potential difference across its terminals.

[0025] As shown in Figure 2, the IEPE power supply 21 differs from an ideal current source in that its output voltage is less than or equal to the voltage of the constant voltage source 211. Therefore, the output power increases or decreases depending on the characteristics of the connected sensor 31. Here, if the load (resistance) of the sensor 31 is Rs, the maximum voltage that the sensor 31 can output is Vmax, and the rated current of the constant current source is Ic, the output power Po is expressed by the following equation. Note that the load Rs changes depending on the load of the output device 15 and the input power of the power converter 14.

[0026] When Rs < Vmax / Ic

[0027]

[0028] When Rs > Vmax / Ic

[0029]

[0030] From equations (1) and (2), when Rs = Vmax / Ic, the IEPE power supply 21 supplies the maximum power to the sensor 31. However, when Rs = Vmax / Ic, the bias voltage required to operate the sensor 31 is equal to the maximum output voltage Vmax of the sensor 31, so the sensor 31 cannot output a measured value. Typical IEPE sensors control the bias voltage to be about half that of the IEPE power supply 21. Therefore, with Rs = Vmax / Ic / 2, the output power Po becomes Po = Vmax^2 / Rs / 2. Similar operation occurs in many cases even in constant current circuits using elements other than the constant current diode 212.

[0031] In this case, the sensor amplifier 10 has more processing power available when it receives more power than when it receives less. Therefore, the following methods are considered to increase the output power from the IEPE power supply 21.

[0032] One approach is to increase the resistance of the sensor amplifier 10 to increase the voltage applied to it. For example, if Rs is {Vmax / Ic*0.75}, increasing the bias voltage that operates the sensor amplifier 10 from half to 75% of Vmax will yield 1.5 times the power. This improves the bias voltage applied to the sensor 31, allowing the voltage applied to the output device 15 to exceed half of Vmax. Thus, it is preferable that the bias voltage of the sensor amplifier 10 exceeds half of the maximum voltage of the constant current source.

[0033] From equations (1) and (2), Po decreases whether Rs is too small or too large. Therefore, when the power demanded by the sensor amplifier 10 exceeds a certain value, the power converter 14 demands more current (Rs decreases), and the voltage of the IEPE power supply 21 decreases, resulting in a decrease in the power obtained. This creates a loop phenomenon. As a result, the power output from the IEPE power supply 21 to the sensor amplifier 10 decreases rapidly.

[0034] As a countermeasure to the above, for example, the power converter 14 should operate so that the power obtained from the constant current source is equal to the maximum value corresponding to the resistance of the sensor 31. One control method for maximizing such power is maximum power point control. The power converter 14 also operates so that the power or current obtained from the constant current source, or the power or current output to the outside, is below a specified value. By controlling the power converter 14 in this way, it is possible to prevent a sudden decrease in the power output to the sensor amplifier 10.

[0035] One way to increase the power obtained by the sensor amplifier 10 is to increase the rated current and maximum current of the IEPE power supply 21. Specifically, it is desirable that the IEPE power supply 21 have a rated current of 2mA or more and a maximum output voltage of 20V or more. Here, based on the ratings of various commercially available ICs, a power supply voltage of around 3.3V is appropriate for the sensor amplifier 10. Since keeping the output signal amplitude within the power supply voltage simplifies the circuit configuration, it is desirable to set the signal amplitude to 3.3Vpp. From this, the power obtained is Po = (Vmax - (3.3 / 2)) * Ic.

[0036] For example, consider a scenario where the sensor amplifier 10 has a power converter 14 with a conversion efficiency of approximately 80%, an output device 15 with 0.2 mW, a computing device 13 with 15 mW, an ADC circuit 12 with 0.5 mW + 2.5 mW (built into the computing device 13), an AFE circuit 11 with 10 mW, and a passive sensor 31. In such a case, the total power of the sensor amplifier 10 would be 28.2 / 0.8 = 35.25 mW, and from the relationship Po = (Vmax - (3.3 / 2)) * Ic, the sensor amplifier 10 can be driven if Vmax = 20 V and Ic = approximately 2 mA.

[0037] Next, we will consider the operation of the output unit 15. The output unit 15 needs to output a signal to the state monitoring device 20 that corresponds to the signal output from the arithmetic unit 13. Here, the vibration sensor is a two-wire sensor that shares power lines and signal lines, and it outputs a signal by adjusting the voltage ratio with the IEPE power supply 21 by changing the resistance. For this reason, in the sensor amplifier 10 of this disclosure, the output unit 15 also has the function of changing the load (resistance). In addition, since the state monitoring system 1 needs to obtain power to drive the sensor 31, the time-averaged load (resistance) needs to be kept within a certain range according to the power consumption of the sensor amplifier 10 and the driving capacity of the IEPE power supply 21. If the power consumption of the sensor amplifier 10 is Ps (excluding the power consumption on the output side of the output unit 15) and the variation range of the output voltage of the sensor amplifier 10 is 2*Vo, then the average value Ro of the load of the output unit 15 needs to be within the following range.

[0038]

[0039] Incidentally, the output signal of the sensor amplifier 10 in this disclosure has both an AC component and a DC component. A typical vibration sensor handles only the AC component as the output signal. In contrast, the sensor amplifier 10 in this disclosure can handle either the AC component or the DC component, or both, as the output signal. However, when handling an output signal that includes a DC component, the signal input of the state monitoring device 20 must be equipped with an input circuit that DC-couples while outputting the IEPE power supply 21. Note that equation (3) is calculated for the AC component; in the case of the DC component, Vo is doubled in the calculation.

[0040] From equation (3), considering the minimum Vmax and Ic required to increase the rated current and maximum current of the IEPE power supply 21, it can be seen that the output load Ro will be a large value (several kΩ to several hundred kΩ). Such a large output load Ro has a particularly negative impact on noise immunity and frequency, so it is desirable to have larger Vmax and Ic. Specifically, it is desirable that Vmax = 20V or more and Ic = 4mA or more.

[0041] [Modification] The output signal from the sensor 31 is superimposed on the IEPE power supply 21. For this reason, it is necessary to suppress fluctuations in the power supply voltage caused by the output device 15 and supply power to the power converter 14. In such a case, an inductance component may be added to the input side of the power converter 14 (between the output device 15 and the connection portion thereof). Furthermore, a capacitor with a large capacitance may be added downstream of the inductance component. A power factor correction circuit capable of controlling an input load (for example, a booster circuit) may be additionally provided on the input side of the power converter 14.

[0042] The output impedance of the sensor amplifier 10 is affected by the power consumption of the sensor amplifier 10. For this reason, it is desirable that the power consumption of the sensor amplifier 10 is low. Methods for suppressing the power consumption of the sensor amplifier 10 are listed below.

[0043] A method for suppressing the power consumption of the sensor amplifier 10 includes a method of keeping the power supply voltage in the sensor amplifier 10 low. For example, the power supply voltage in the sensor amplifier 10 may be set to 1.6 V or more and less than 3.3 V.

[0044] A method for suppressing the power consumption of the sensor amplifier 10 includes a method of causing at least one or more of the AFE circuit 11, the ADC circuit 12, and the arithmetic device 13 to operate intermittently. This makes it possible to suppress the time-averaged power consumption. Note that intermittent operation of the arithmetic device 13 is desirable because it is often easy to implement.

[0045] The arithmetic device 13 can be combined with a plurality of elements to switch between driving, non-driving, or modes. The power consumption of the sensor amplifier 10 may be suppressed by executing driving, non-driving, or mode switching for each component of the arithmetic device 13 as necessary.

[0046] Here, it is desirable that the impedance on the signal path from the first-stage amplifier of the AFE circuit 11 to the ADC circuit 12 is kept low in terms of signal quality. This is because lowering the impedance can suppress the influence of various noises. However, a path with low impedance allows a correspondingly larger amount of current to flow, resulting in increased power consumption. Therefore, it is desirable that the impedance on the signal path from the first-stage amplifier of the AFE circuit 11 to the ADC circuit 12 is within the range of 1 kΩ to 300 kΩ. This makes it possible to keep the influence of noise within an allowable range while setting the impedance as large as possible.

[0047] As a method for suppressing the power consumption of the sensor amplifier 10, there is a method of suppressing the amplitude of a signal flowing on the signal path of the AFE circuit 11. In a common AFE circuit, to suppress the influence of noise, signals are often handled with an amplitude of 50% or more of the power supply voltage. However, in the sensor amplifier 10 of the present disclosure, since it is necessary to suppress power consumption, there is an advantage of suppressing the signal amplitude even at the cost of some noise resistance. Specifically, it is desirable that the amplitude of a signal flowing on the signal path of the AFE circuit 11 is less than half of the driving voltage of the sensor amplifier 10.

[0048] [Supplementary Note] It will be understood by those skilled in the art that the exemplary embodiments described above are specific examples of the following aspects.

[0049] (Clause 1) The present disclosure relates to a condition monitoring system 1 that monitors the condition of a machine 30. The condition monitoring system 1 includes a sensor amplifier connected to a sensor attached to the machine, and a condition monitoring device that monitors the condition of the machine based on a signal transmitted from the sensor amplifier. The condition monitoring device includes a constant current source (IEPE power supply 21). The sensor amplifier includes: an arithmetic device that outputs a signal corresponding to a signal output from the sensor; an output device that outputs a signal output from the arithmetic device as a signal compatible with the condition monitoring device; and a power converter that draws electric power corresponding to the sensor from the constant current source (IEPE power supply 21) and converts electric power obtained from the constant current source (IEPE power supply 21) into electric power for driving at least the arithmetic device.

[0050] (Section 2) In the state monitoring system 1 described in Section 1, the power converter 14 operates so that the power obtained from the constant current source (IEPE power supply 21) is at its maximum value.

[0051] (Clause 3) In the status monitoring system 1 described in paragraph 1 or 2, the power converter 14 operates to keep the power or current obtained from the constant current source (IEPE power supply 21), or the power or current it outputs, below a specified value.

[0052] (Section 4) In the state monitoring system 1 described in Sections 1 to 3, the sensor amplifier 10 further comprises an analog front-end circuit (AFE circuit 11) that processes the analog signal from the sensor 31, and an analog-to-digital conversion circuit (ADC circuit 12) that converts the analog signal processed by the analog front-end circuit (AFE circuit 11) into a digital signal and transmits it to the arithmetic unit 13. The analog front-end circuit (AFE circuit 11) and the analog-to-digital conversion circuit (ADC circuit 12) are driven by the power output from the power converter 14.

[0053] (Article 5) In the status monitoring system 1 described in paragraphs 1 to 4, the output device 15 is a semiconductor switch.

[0054] (Section 6) In the condition monitoring system 1 described in Sections 1 to 5, the bias voltage of the sensor amplifier 10 is a value exceeding half of the maximum voltage of the constant current source (IEPE power supply 21).

[0055] (Section 7) In the condition monitoring system 1 described in Sections 1 to 6, one end of the sensor amplifier 10 is connected to the sensor 31 by three wires: a wire for supplying power, a wire for receiving signals, and a wire connected to ground. The other end of the sensor amplifier 10 is connected to the condition monitoring device 20 by two wires: a wire for acquiring power and outputting signals, and a wire connected to ground.

[0056] According to the state monitoring system 1 of the embodiment described above, by connecting the sensor amplifier 10 to the state monitoring device 20, the state of the machine 30 can be measured using any sensor 31.

[0057] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope of the claims are intended to be included.

[0058] 1. State monitoring system, 10. Sensor amplifier, 11. AFE circuit, 12. ADC circuit, 13. Calculation unit, 14. Power converter, 15. Output unit, 20. State monitoring device, 21. IEPE power supply, 22. Capacitor, 23. Switch, 24. Amplifier, 25. Ground node, 30. Machine, 31. Sensor, 51-55. Connection terminals, 211. Constant voltage source, 212. Constant current diode.

Claims

1. A condition monitoring system for monitoring the state of a machine, comprising: a sensor amplifier connected to a sensor attached to the machine; and a condition monitoring device that monitors the state of the machine based on a signal transmitted from the sensor amplifier, wherein the condition monitoring device includes a constant current source; and the sensor amplifier comprises: a computing device that outputs a signal corresponding to a signal output from the sensor; an output device that outputs the signal output from the computing device as a signal compatible with the condition monitoring device; and a power converter that draws power from the constant current source according to the sensor and converts the power obtained from the constant current source into power sufficient to drive at least the computing device.

2. The state monitoring system according to claim 1, wherein the power converter operates such that the power obtained from the constant current source is at its maximum value.

3. The status monitoring system according to claim 1, wherein the power converter operates to keep the power or current obtained from the constant current source, or the power or current output, below a specified value.

4. The state monitoring system according to claim 1, wherein the sensor amplifier further comprises an analog front-end circuit for processing an analog signal from the sensor, and an analog-to-digital conversion circuit for converting the analog signal processed by the analog front-end circuit into a digital signal and transmitting it to the computing device, and the analog front-end circuit and the analog-to-digital conversion circuit are driven by power output from the power converter.

5. The state monitoring system according to claim 1, wherein the output device is a semiconductor switch.

6. The state monitoring system according to claim 1, wherein the bias voltage of the sensor amplifier is greater than half the maximum voltage of the constant current source.

7. The status monitoring system according to claim 1, wherein one end of the sensor amplifier is connected to the sensor by three wires: a wire for supplying power, a wire for receiving signals, and a wire connected to ground, and the other end of the sensor amplifier is connected to the status monitoring device by two wires: a wire for acquiring power and outputting signals, and a wire connected to ground.

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