JP2013097520A - Two-wire transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect such abnormality as the deterioration or corrosion of a two-wire transmitter for controlling transmission currents by using an output circuit series-connected to an external circuit.SOLUTION: The two-wire transmitter 1 receives power supply from an external circuit 2 via two transmission lines L1 and L2, and transmits transmission currents i1 based on the measurement value of a sensor 3 to the external circuit 2. The two-wire transmitter 1 includes: an output circuit 6 series-connected to the external circuit 2 for controlling the transmission currents i1; a shunt regulator power source for controlling the voltage at the output side of the output circuit 6 to become a predetermined voltage by making shunt currents flow; and a signal processing circuit 4 for detecting shunt currents i4, and for obtaining the current consumption of the two-wire transmitter 1 on the basis of the shunt currents i4 and the transmission currents i1.

Description

  The present invention relates to a two-wire transmitter that receives a power supply from an external circuit via two transmission lines and transmits a transmission current based on a measured value of a sensor.

  The two-wire transmitter receives power from an external circuit via two transmission lines and transmits a transmission current of 4 to 20 mA. FIG. 3 is a block diagram showing a configuration of a conventional two-wire transmitter. The two-wire transmitter 101 in this figure is connected to the external circuit 102 via transmission lines L1 and L2. The external circuit 102 is connected in series with a DC power source Eb and a receiving resistor R1 necessary for supplying circuit power for the two-wire transmitter 101. The terminals T1 and T2 of the external circuit 102 are connected to the terminals T3 and T4 of the two-wire transmitter 101 via transmission lines L1 and L2.

  The two-wire transmitter 101 includes a sensor 103, a signal processing circuit 104, an EEPROM (Electrically Erasable Programmable Read Only Memory) 105, an output circuit 106, a power circuit 107, a control circuit 108, and an LCD (Liquid Crystal Display) 109. It is composed. The sensor 103 converts a physical quantity such as pressure and flow rate into an electrical signal and outputs the electrical signal to the signal processing circuit 104.

  The signal processing circuit 104 reads the linearity correction value stored in the EEPROM 105 with respect to this electric signal and performs signal processing. The signal processed signal is output to the output circuit 106. This signal is also output to the LCD 109 so that the value of this signal can be displayed.

  The output circuit 106 controls the transmission current i1 based on the signal from the signal processing circuit 104. The output circuit 106 is connected in series with the external circuit 102 and is limited to a transmission current (4 mA to 20 mA) i1 that can be used inside the two-wire transmitter 101. The limited transmission current i1 flows to the output side of the output circuit 106.

  The power supply circuit 107 supplies a voltage (for example, 3 volts) required by the signal processing circuit 104. The control circuit 108 is connected in series with the resistor R2, and the control circuit 108 and the resistor R2 constitute a shunt regulator power source. This shunt regulator power supply controls the voltage Vb on the output side of the output circuit 106 (for example, it is controlled so that Vb = 5 volts).

  The two-wire transmitter as described above is often installed and used in a harsh environment / atmosphere. When operated in such a harsh environment for a long period of time, the parts will deteriorate over time and the seal will deteriorate, causing corrosion of the transmitter due to the invasion of corrosive gas inside the 2-wire transmitter. It may lead to failure.

  If the two-wire transmitter 101 suddenly breaks down, a large loss in terms of safety, economics, etc. in plant facilities such as electricity, gas, water, sewage, and oil industry to which the two-wire transmitter 101 is attached. Will give. An electric circuit unit is disclosed in Patent Document 1 for such a problem. In this electric circuit unit, the lifetime of the electric circuit is predicted by calculating the integrated value of the measured value of the temperature sensor and the humidity sensor and the function of time.

  Further, Patent Document 2 discloses a diagnostic technique for predicting a failure of a process device before the failure occurs. In the technique of this Patent Document 2, the quiescent current consumption is measured, and based on the change in the quiescent current consumption, an electronic component or other failure is predicted to warn the operator.

Japanese Patent Laid-Open No. 2002-174652 Special table 2007-501980

  The electric circuit unit of Patent Document 1 has an advantageous effect in that the life of the electric circuit can be predicted based on temperature and humidity. However, the abnormality of the two-wire transmitter 101 also occurs due to deterioration or corrosion of parts. In the electric circuit unit of Patent Document 1, the detection accuracy of abnormality due to deterioration or corrosion of these parts is a cause. Becomes lower.

  In the process apparatus of Patent Document 2, a quiescent current consumption is measured, and a failure of an electronic component is predicted based on the quiescent current consumption. However, in the process apparatus of Patent Document 2, as shown in FIG. 3 of Patent Document 2, the shunt regulator 4-20 mA controller is shunted (parallel) to an external circuit, and the transmission current is reduced. It is configured to flow with a shunt.

  On the other hand, in the two-wire transmitter 101 as described in FIG. 3, the output circuit 106 for controlling the transmission current i1 is connected in series (series) to the external circuit 102, and the transmission current i1 flows in series. It has become. Therefore, the circuit configuration of the process apparatus of Patent Document 2 and the two-wire transmitter 101 as shown in FIG.

  Therefore, a method for measuring the quiescent current consumption in a process device in which a circuit for controlling transmission current (shunt regulator 4-20 mA controller of Patent Document 2) is shunt-connected to an external circuit is used to control transmission current i1. In order to apply the output circuit 106 to the two-wire transmitter 101 as shown in FIG. 3 connected in series to the external circuit 102, the circuit configuration must be significantly changed.

  Accordingly, an object of the present invention is to detect an abnormality such as deterioration or corrosion of a two-wire transmitter that controls a transmission current using an output circuit connected in series to an external circuit.

  In order to solve the above problems, a two-wire transmitter according to the present invention receives power from two external transmission lines and transmits a transmission current based on sensor measurement values to the external circuit. A two-wire transmitter that controls an output circuit connected in series to the external circuit that controls the transmission current and a shunt current that flows so that a voltage on the output side of the output circuit becomes a predetermined voltage. A shunt regulator power supply, and a signal processing circuit that detects the shunt current and obtains current consumption of the two-wire transmitter based on the shunt current and the transmission current are provided.

  According to this two-wire transmitter, the current consumption of the two-wire transmitter including an output circuit connected in series to an external circuit is detected based on the shunt current and the transmission current. By detecting the current consumption, an abnormality (or failure) of the two-wire transmitter can be determined based on the detected current consumption.

  Further, the signal processing circuit compares the current consumption detected by the signal processing circuit with a normal range of the current consumption to diagnose whether or not an abnormality has occurred in the two-wire transmitter. It is characterized by.

  Whether the signal processing circuit has an abnormality in the two-wire transmitter based on whether or not the detected current consumption is outside the normal range, with the range when the current consumption is normal as the normal range Can be diagnosed.

  Further, the signal processing circuit generates an abnormality in the two-wire transmitter based on a normal range of the current consumption corresponding to a temperature measured by a thermometer that measures the temperature inside the two-wire transmitter. It is characterized by performing a diagnosis of whether or not

  Since the current consumption varies with temperature, the normal range of current consumption at low temperatures is different from the normal range of current consumption at high temperatures. For this reason, the signal processing circuit can improve the diagnostic accuracy by comparing the normal range corresponding to the temperature with the detected current consumption and diagnosing the abnormality.

  Further, the signal processing circuit detects the abnormality of the two-wire transmitter based on humidity information measured by a hygrometer that measures the humidity inside the two-wire transmitter. It is characterized in that it is determined whether or not the cause of the abnormality of the transmitter is humidity.

  An abnormality of a two-wire transmitter detected based on current consumption may be caused by corrosion due to humidity. When an abnormality is detected based on the current consumption, it is possible to determine whether or not the cause of the detected abnormality is humidity by referring to the hygrometer.

  The present invention detects the consumption current of a two-wire transmitter that controls the transmission current by an output circuit connected in series with an external circuit based on the shunt current and the transmission current, thereby degrading the two-wire transmitter. And abnormalities such as corrosion can be detected.

It is a block diagram of a two-wire transmitter of an embodiment. It is a block diagram of the 2-wire type transmitter of a modification. It is a block diagram of the 2-wire type transmitter in a prior art.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a two-wire transmitter 1 according to an embodiment. The two-wire transmitter 1 is connected to an external circuit 2 via transmission lines L1 and L2. The terminal T1 of the external circuit 2 and the terminal T3 of the two-wire transmitter 1 are connected by the transmission line L1, and the terminal T2 of the external circuit 2 and the terminal T4 of the two-wire transmitter 1 are connected by the transmission line L2. Has been.

  The two-wire transmitter 1 is supplied with power from the external circuit 2 and transmits a transmission current i1 of 4 to 20 mA. The external circuit 2 is connected in series with a DC power source Eb and a receiving resistor R1 necessary for supplying circuit power for the two-wire transmitter 1. The two-wire transmitter 1 includes a sensor 3, a signal processing circuit 4, an EEPROM (Electrically Erasable Programmable Read Only Memory) 5, an output circuit 6, a power circuit 7, a control circuit 8, and an LCD (Liquid Crystal Display) 9. It is prepared and configured.

  The sensor 3 converts physical quantities such as pressure and flow rate into electrical signals. The sensor 3 outputs this electric signal (sensor signal) to the signal processing circuit 4. The signal processing circuit 4 reads the linearity correction value from the EEPROM 5 which is a nonvolatile memory, and performs signal processing on the sensor signal from the sensor 3.

  By performing this signal processing, the signal processing circuit 4 outputs a signal (transmission current control signal) for controlling the transmission current i1 to the output circuit 6. The transmission current control signal is also output to the LCD 9 so that the value of the transmission current can be displayed on the LCD 9 as a display device.

  The output circuit 6 inputs the transmission current control signal output from the signal processing circuit 4 and controls the transmission current i1 to 4 to 20 mA. The output circuit 6 is connected in series with the external circuit 2. Since the current that can be used inside the two-wire transmitter 1 is limited to the transmission current i1, the output circuit 6 controls the current from the external circuit 2 to flow with the transmission current i1.

  The power supply circuit 7 supplies a voltage (for example, 3 volts) required by the signal processing circuit 4. Based on this voltage, the signal processing circuit 4 operates. The control circuit 8 is connected in series with the resistor R2, and the control circuit 8 and the resistor R2 constitute a shunt regulator power source. This shunt regulator power supply is controlled so that the voltage on the output side of the output circuit 6 becomes Vb. For example, the voltage Vb is controlled to be 5 volts.

  As shown in FIG. 1, a sensor 3, a power supply circuit 7, and a control circuit 8 are connected to the output side of the output circuit 6. The sensor 3 operates based on the voltage Vb (for example, 5 volts) on the output side of the output circuit 6, and the current flowing through the sensor 3 is i2. In addition, the current flowing through the power supply circuit 7 that supplies a voltage (for example, 3 volts) necessary for the signal processing circuit 4 is i3. Furthermore, the current (shunt current) that the shunt regulator power supply passes through the resistor R2 for control is i4.

  The resistor R2 constituting the shunt regulator power supply has one end connected to the control circuit 8 and the other end grounded (COM in the figure). The signal processing circuit 4 is provided with an ADC (analog / digital converter) 11 and a voltage on the control circuit 8 side of the resistor R2 is inputted as Va. The ADC 11 converts the input voltage Va into a digital signal and uses it inside the signal processing circuit 4.

  The above is the configuration. Next, the operation will be described. The two-wire transmitter 1 is often installed and used in a harsh environment / atmosphere. If a long time elapses in a state where the two-wire transmitter 1 is installed in such a harsh environment, the aging of the parts will be caused, and the internal circuit of the two-wire transmitter 1 will be corroded. Failure may occur due to corrosion or the like due to the invasion of sex gases.

  The sudden failure of the two-wire transmitter 1 causes a large loss in terms of safety, economics, etc. in plant facilities such as electricity, gas, water, sewage, and petroleum industries to which the two-wire transmitter 1 is attached. May give. For this reason, it is extremely important to diagnose whether abnormality such as deterioration or corrosion has occurred in the two-wire transmitter 1. By diagnosing this abnormality, a warning for preventive maintenance can be given, and a fail-safe operation at the time of abnormality or failure can be performed.

As shown in FIG. 1, the output circuit 6 controls the current supplied from the external circuit 2 to the transmission current i1 (4 mA to 20 mA) based on the transmission current control signal output from the signal processing circuit 4. After the transmission current i1 is controlled by the output circuit 6, the output side of the output circuit 6 branches into three currents i2, i3, i4. Therefore, the following formula (1) is established.
i1 = i2 + i3 + i4 (Expression 1)

Among these currents i1 to i4, the current i2 is consumed by the sensor 3, and the current i3 is consumed by the signal processing circuit 4, the EEPROM 5, and the LCD 9. Therefore, the current consumption of the two-wire transmitter 1 is “i2 + i3”. Note that the shunt current i4 is a surplus current that flows through the resistor R2 in order for the shunt regulator power supply to control the voltage Vb, and therefore does not constitute the current consumption of the two-wire transmitter 1. When the shunt current i4 of the formula (1) described above is shifted to the left side, the following formula (2) is obtained.
i2 + i3 = i1-i4 (Formula 2)

  Among these, the transmission current i1 is a current controlled by the output circuit 6 based on the transmission current control signal output from the signal processing circuit 4. Accordingly, since the relationship between the transmission current control signal output from the signal processing circuit 4 and the transmission current i1 is known by design, the transmission current i1 has a value recognized by the signal processing circuit 4 in advance.

  On the other hand, the voltage Va on the control circuit 8 side of the resistor R2 is input to the ADC 11 of the signal processing circuit 4. The relationship between the voltage Va and the shunt current i4 is “i4 = Va / R2”. Since the resistor R2 is known, the signal processing circuit 4 can obtain the shunt current i4 by inputting the voltage Va converted into a digital signal by the ADC 11.

  Therefore, since the transmission current i1 and the shunt current i4 on the right side of Expression 2 can be obtained, the consumption of the two-wire transmitter 1 is performed by performing the calculation of “i1−i4 = i1− (Va / R2)”. A current “i2 + i3” can be obtained. The signal processing circuit 4 records the current consumption “i2 + i3” in the EEPROM 5 and compares whether the current consumption is in the normal range.

  The current consumption “i2 + i3” has a range (normal range) when the two-wire transmitter 1 is operating normally, and this normal range is obtained as known. This normal range is recognized by the signal processing circuit 4, and the signal processing circuit 4 determines whether the current consumption “i2 + i3” is within the normal range or out of the normal range.

  If the current consumption “i2 + i3” is within the normal range, there is no particular problem. However, when the current consumption is outside the normal range, it is diagnosed that the two-wire transmitter 1 has an abnormality such as deterioration or corrosion. When an abnormality is diagnosed, preventive maintenance can be performed by issuing a warning or the like. Further, a fail-safe operation at the time of abnormality or failure can be realized.

  At this time, the current consumption “i2 + i3” does not measure the current actually consumed, but simply measures the voltage Va on the control circuit 8 side of the resistor R2 through which the shunt current i4 flows. . In the case where current consumption is actually measured to obtain current consumption, it is necessary to measure the current i2 flowing through the sensor 3 and the current i3 flowing through the power supply circuit 7. For example, the current is measured by monitoring the voltage drop of a resistor that senses the current. Therefore, in order to directly measure the currents i2 and i3, it is necessary to provide current monitoring mechanisms in at least two places.

  In the present embodiment, the current consumption can be easily calculated simply by inputting the voltage Va on the control circuit 8 side of the resistor R2. That is, it is not necessary to provide special current monitoring mechanisms at two or more locations, and current consumption can be obtained with a simple circuit configuration. Then, based on the obtained current consumption, it is possible to detect whether or not an abnormality has occurred in the two-wire transmitter 1.

  The configuration of the two-wire transmitter 1 of the present embodiment is as shown in FIG. 1, and the output circuit 6 is connected in series (series) to the external circuit 2. Therefore, by detecting the shunt current i4 flowing in the shunt regulator power source for controlling the voltage Vb with the voltage Va, it is easily consumed by the circuit configuration of the two-wire transmitter 1 in which the output circuit 6 is connected in series to the external circuit 2. A current can be obtained.

  By the way, although the abnormality of the two-wire transmitter 1 is detected based on the consumption current “i2 + i3”, the consumption current greatly varies depending on the temperature of the usage environment of the two-wire transmitter 1. As a result, the abnormality may be diagnosed even though the abnormality is not caused in the two-wire transmitter 1 due to the temperature change. The reverse is also true. In particular, the power consumption may change greatly in an environment where the temperature changes drastically during the day and night.

  Therefore, the sensor 3 is provided with a thermometer. As this thermometer, a thermometer for temperature correction can be used. And the signal processing circuit 4 memorize | stores the normal range of the power consumption corresponding to temperature. For example, since the normal range of power consumption is different at each of high temperature, room temperature, and low temperature, the normal range of power consumption at each temperature is stored. The normal range of power consumption at each temperature can be obtained by measuring current consumption when the two-wire transmitter 1 is in a normal state and at high temperature, room temperature, and low temperature. For example, when the two-wire transmitter 1 is manufactured, a normal range of power consumption at each temperature can be obtained when performing temperature correction. The thermometer may be provided separately from the sensor 3, and a thermometer that measures the temperature of the two-wire transmitter 1 may be used.

  When the two-wire transmitter 1 is actually used, the signal processing circuit 4 acquires temperature information (temperature information) measured by a thermometer provided in the sensor 3. When determining the current consumption “i2 + i3”, the abnormality of the two-wire transmitter 1 is determined based on whether or not the current consumption is within the normal range corresponding to the temperature information.

  As a result, for example, when the two-wire transmitter 1 is used in a usage environment where the temperature changes drastically during the day and night, the current consumption can be compared based on the normal range corresponding to the corresponding temperature. Therefore, when an abnormality in current consumption is detected, it can be determined whether or not the cause is due to a temperature change. Thereby, the diagnostic system of the abnormality which has generate | occur | produced in the two-wire transmitter 1 improves.

  The sensor 3 can also be provided with a hygrometer. Information on humidity (humidity information) measured by the hygrometer is recorded. This humidity information can be recorded over a long period of time. The signal processing circuit 4 detects an abnormality of the two-wire transmitter 1 when the current consumption “i2 + i3” is outside the normal range. At this time, based on the recorded humidity information, the signal processing circuit 4 recognizes that the abnormality of the two-wire transmitter 1 is caused by humidity. The hygrometer may be provided separately from the sensor 3, and a hygrometer that measures the humidity of the two-wire transmitter 1 may be used.

  When the two-wire transmitter 1 is operated in a high humidity environment, an abnormality such as a decrease in insulation resistance due to corrosion between circuit patterns occurs. This is caused by corrosion due to humidity. The signal processing circuit 4 refers to the hygrometer of the sensor 3 (humidity information recorded by the sensor 3), so that the abnormality of the two-wire transmitter 1 Recognize that it is a factor.

  Next, application examples will be described. FIG. 2 shows a two-wire transmitter 1 as an application example. As shown in this figure, when a noise source 21 exists in the transmission line L1 and noise is applied to the two-wire transmitter 1 by the noise source 21, a shunt is connected via the output circuit 6 and the control circuit 8. The influence of noise appears in the current i4.

  The signal processing circuit 4 detects the shunt current i4 by inputting the voltage Va. Therefore, when noise appears in the shunt current i4, the signal processing circuit 4 can recognize the noise. The signal processing circuit 4 can recognize the magnitude of the noise by processing the influence of the noise. When the noise recognized at this time is large (for example, when it is higher than the set noise threshold), control may be performed so as to perform the fail-safe operation.

  Further, when an influence of a momentary interruption (instantaneous voltage drop) occurs in the direct current Eb constituting the external circuit 2 due to a lightning strike or the like, this influence also acts on the shunt current i4. Therefore, the signal processing circuit 4 can determine whether or not the DC current Eb has an instantaneous interruption based on whether the change in the shunt current i4 can be determined as an instantaneous interruption.

1 2-wire transmitter 2 External circuit 3 Sensor 4 Signal processing circuit 6 Output circuit 7 Power supply circuit 8 Control circuit 21 Noise source

Claims (4)

A two-wire transmitter for receiving a power supply from an external circuit via two transmission lines and transmitting a transmission current based on a measured value of a sensor to the external circuit;
An output circuit connected in series to the external circuit for controlling the transmission current;
A shunt regulator power supply for controlling the output side voltage of the output circuit by flowing a shunt current so as to be a predetermined voltage;
A signal processing circuit that detects the shunt current and obtains current consumption of the two-wire transmitter based on the shunt current and the transmission current;
A two-wire transmitter comprising: The signal processing circuit compares the current consumption detected by the signal processing circuit with a normal range of the current consumption to diagnose whether or not an abnormality has occurred in the two-wire transmitter. The two-wire transmitter according to claim 1. Whether the signal processing circuit has an abnormality in the two-wire transmitter based on a normal range of the current consumption corresponding to the temperature measured by a thermometer that measures the temperature inside the two-wire transmitter. The two-wire transmitter according to claim 2, wherein diagnosis of whether or not is performed. The signal processing circuit is configured to transmit the two-wire transmission based on humidity information measured by a hygrometer that measures the humidity inside the two-wire transmitter when an abnormality is detected in the two-wire transmitter. The two-wire transmitter according to claim 2 or 3, wherein it is determined whether or not the cause of the abnormality of the device is humidity.

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