JP2006323476A - Field instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a function without requiring a special operation, an additional device, or the like, using surplus power that does not contribute to driving of a two-wire system field instrument (two-wire system transmitter) itself. <P>SOLUTION: The two-wire system field instrument receives supply of transmission current from a load side via an output end, measures physical quantity, converts the transmission current correspondingly, and transmits it to the load side. The two-wire system field instrument has a charging means for covering a circuit power source with part of the transmission current and charging a capacitor using other part of the transmission current. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a two-wire field instrument that receives transmission current from the load side via an output terminal, measures a physical quantity, converts the transmission current to correspond to this, and transmits it to the load side. In particular, the present invention relates to a field instrument improved so as to improve the function by effectively utilizing a part of transmission current.

  FIG. 2 shows a configuration of a conventional two-wire transmitter described in FIG. The two-wire transmitter (two-wire field instrument) in this case is an example of a vortex flowmeter. Reference numeral 10 denotes a DC power source provided on the load side. A load resistor 11 is connected in series to the DC power source 10, and a series circuit constituted by these is connected to terminals 2 through terminals T 1 and T 2 and transmission lines L 1 and L 2. The output terminals of the linear transmitter 12 are connected to terminals T1 ′ and T2 ′, respectively.

A diode D1, a transistor Q1, a resistor R1, and a feedback resistor R2 are connected in series to the terminals T1 'and T2'. A series circuit of a resistor R3 and a Zener diode D2 is connected between a connection point A between the cathode of the diode D1 and the collector of the transistor Q2 and a connection point B between the resistor R1 and the feedback resistor R2.

Further, the collector and base of the transistor Q2 are connected to both ends of the resistor R3, and a primary voltage V1 is obtained between the emitter and the cathode of the Zener diode D2. Primary voltage V1 energizes amplifier 13 and the output of amplifier 13 controls the base voltage of transistor Q1.
The output of the signal processing circuit 14 energized by the primary voltage V1 is applied to the input terminal of the amplifier 13 and the feedback voltage Vf generated at both ends of the feedback resistor R2 is applied to the sensor side. Insulated.

The primary voltage is applied to a power supply circuit 16 that supplies a DC voltage Vd1 for galvanically insulating and energizing the signal processing circuit 17 on the sensor side. The input terminals are T3 and T4, and the output terminals are T5 and T6. For example, a vortex signal from a sensor 18 that converts the number of Karman vortices generated corresponding to the measured flow rate into a corresponding voltage signal is applied to the input end of the signal processing circuit 17.

Next, an outline of the operation of the two-wire transmitter 12 configured as described above will be described. The vortex signal generated by the sensor 18 corresponding to the measured flow rate is supplied with noise to the insulation circuit 15 after the noise is removed by the signal processing circuit 17. In the insulating circuit 15, the analog output of the signal processing circuit 17 is converted into a pulse signal and is galvanically isolated via a transformer, and is converted again into a voltage signal and output to the signal processing circuit 14.

The amplifier 13 calculates the deviation between the output of the signal processing circuit 14 and the feedback voltage Vf, and controls the base current of the transistor Q1 with the output voltage, so that the transmission current I0 matches the output of the signal processing circuit 14. To control. The transmission current I0 is selected so that, for example, the vortex flow rate 0% is 4 mA and 100% is 20 mA.

On the other hand, a part of the transmission current I0 is 4 mA to cover the circuit power supply of the two-wire transmitter 12. This power supply circuit 16 is a circuit in which the load 11 side and the sensor 18 side are insulated from each other by DC. The DC voltage Vd used in the above is provided.

  In other words, such a conventional two-wire transmitter is basically designed so that the circuit operates at a minimum current of 4 mA. Therefore, when the transmission current is 20 mA, a transmission current of 16 mA is used for the circuit operation. Is consumed by the transistor Q1 in the output stage as unnecessary. In other words, the transmission current I0 exceeding 4 mA is a wasteful heat loss.

  As a device using this transmission current, a two-wire instrument as shown in Non-Patent Document 1 described below has been proposed. Here, a maintenance switch is provided in a two-wire instrument. During maintenance, the maintenance switch is pressed to increase the output transmission current and increase the usable current of the instrument. The function is improved so that the operability can be improved and a diagnostic function can be added.

  In addition to this, an on-site instrument as shown in Patent Document 2 to be described later has been proposed in order to improve the function of the field instrument. This field-installed instrument has a charging circuit that charges the secondary battery inside, so that it is possible to introduce the field-installed instrument power into the secondary battery in an insulated state from external auxiliary devices as necessary. It is a thing. In other words, this on-site meter does not have a power generation means for charging in the meter itself, but introduces charging power from an external auxiliary device as necessary.

Japanese Patent Laid-Open No. 5-166093 JP 2003-297153 A Official Technical Number 2002-245 (Invention Association Technical Report)

  However, in the conventional two-wire transmitter described in Patent Document 1, the transmission current (4 mA to 20 mA) is determined according to the PV (process variable) value, but the two-wire transmitter itself (power supply voltage × 4 mA) Drive with less power consumption. That is, when the current is 4 mA or more, power is consumed by the output transistor as surplus power that does not contribute to the driving power of the two-wire transmitter, and this surplus power does not give any additional function as the two-wire transmitter. There is.

  In addition, the conventional two-wire instrument described in Non-Patent Document 1 uses the transmission current to improve the function. However, the transmission current is used only during maintenance, and a special operation is required. A certain switching operation is necessary, and there is a drawback that it is a limited functional improvement.

  Further, in the conventional field-installed instrument described in Patent Document 2, a charging circuit for charging the secondary battery is provided inside, and the secondary battery is charged from an auxiliary device which is an external additional device as necessary. It is a field-installed instrument and has the disadvantage of requiring an auxiliary device separately.

Therefore, the present invention uses a surplus power that does not contribute to the driving of the two-wire field instrument (two-wire transmitter) itself, and improves the function without requiring any special operation or additional device. Objective.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In a two-wire field instrument that receives a supply of transmission current from the load side via the output end, measures a physical quantity, converts the previous transmission current to correspond to this, and transmits it to the previous load side. And charging means for charging the capacitor using the other part of the previous transmission current and covering the circuit power supply with a part of the transmission current.

The invention described in claim 2 is characterized in that, in the invention described in claim 1, the power from the previous capacitor is used as the power source of the peripheral circuit.

According to a third aspect of the present invention, in the first aspect of the present invention, there is provided a determination means for determining whether or not the peripheral circuit is to be operated based on a result of inputting the state of charge in the previous charging means. Is.

As is apparent from the above description, the present invention has the following effects.
According to the first aspect of the present invention, the built-in storage battery is charged by the charging means using its own surplus power that does not contribute to the driving of the two-wire field instrument itself, and this charging power is used to specially Thus, there is an effect that an additional function can be added without requiring an operation or an additional device.

Further, according to the invention described in claim 2, in addition to the effect of the invention described in claim 1, there is an effect that it can be used as a power source for a peripheral circuit that requires a lot of power from the previous capacitor. .

Furthermore, according to the invention described in claim 2, in addition to the effect of the invention described in claim 1, the determination means can continuously monitor the charging state in the charging means and operate the peripheral circuit in terms of power. Therefore, there is an effect that a stable operation of the peripheral circuit can be ensured.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a two-wire field instrument according to the present invention. In FIG. 1, a sensor 20 detects a physical quantity such as a flow rate and pressure, converts it into an electrical signal, and outputs it as a sensor signal SS to a two-wire main circuit 21.

  The 2-wire main circuit 21 has a CPU (Central Processing Unit) mounted therein, removes noises and the like contained in the sensor signal SS, and performs signal processing such as span adjustment and zero adjustment to obtain a PV value signal. PV is output to the non-inverting input terminal (+) of the deviation amplifier 22.

  A DC power source 10 and a load resistor 11 provided on the load side are connected in series to terminals T7 and T8 of the field instrument 23. The load resistor 11 converts the transmission current I0 into a voltage and detects it as a voltage signal.

  The starting circuit 24, the collector and emitter of the output transistor 25, and the feedback resistor 26 are connected in series in this order to both ends of the terminals T7 and T8.

  A feedback voltage Vf2 generated in the feedback resistor 26 by the transmission current I0 is applied to the inverting input terminal (−) of the deviation amplifier 22, and the voltage at the output terminal of the deviation amplifier 22 is applied to the base of the output transistor 25.

  A constant voltage circuit 27 is connected between a connection point C between the starting circuit 24 and the collector of the output transistor 25 and a connection point D between the feedback resistor 26 and the emitter of the output transistor 25.

  The constant voltage circuit 27 includes a FET (field effect transistor) 28, a switch 29, an operational amplifier 30, a resistor 31, a resistor 32, a resistor 33, a Zener diode 34, and the like. The FET 28 has a source S at a connection point C and a connection point. A drain D is connected to each D. A series circuit of a resistor 31 and a resistor 32 and a series circuit of a resistor 33 and a Zener diode 34 are connected between the connection point C and the connection point D, respectively.

  The non-inverting input terminal (+) of the operational amplifier 30 is connected to the connection point between the resistor 31 and the resistor 32, and the inverting input terminal (−) of the operational amplifier 30 is connected to the connection point between the resistor 33 and the Zener diode 34. A switch 29 is connected between the output terminal 30 and the gate G of the FET 28.

  A charging circuit 35 is connected between the connection point C and the connection point D. The charging circuit 35 includes an FET 36, a diode 37, a charging capacitor 38 as a capacitor (including a secondary battery), a resistor 39, a resistor 40, a resistor 41, a Zener diode 42, a comparator 43, and the like.

  A series circuit of an FET 36, a diode 37, and a charging capacitor 38 is connected between the connection point C and the connection point D, and a series circuit of a resistor 39 and a resistor 40 is connected to both ends of the charging capacitor 38. Yes. In addition, a series circuit of a resistor 41 and a Zener diode 42 is connected between the connection point C and the connection point D.

  The inverting input terminal (−) of the comparator 43 is connected to the connection point between the resistor 39 and the resistor 40, and the non-inverting input terminal (+) of the comparator 43 is connected to the connection point between the resistor 41 and the Zener diode 42.

The opening / closing of the switch 44 is controlled by the overvoltage detection voltage V 0 appearing at the output terminal of the comparator 43, and the opening / closing of the switch 29 is also controlled via the inverter 45. Further, the overvoltage detection voltage V 0 at the output terminal of the comparator 43 is also applied to the two-wire main circuit 21.

  One end of the switch 44 is connected to the gate G of the FET 36, and the other end of the switch 44 is connected to the output terminal of the operational amplifier 30.

  Further, the connection point between the diode 37 and the charging capacitor 38 is connected to the power supply terminal of the peripheral circuit 47 through the diode 46. The peripheral circuit 47 is power-controlled by the determination signal Vj from the two-wire main circuit 21.

Next, the operation of the two-wire field instrument 23 configured as described above will be described. When the DC power supply 10 is initially turned on, the transmission current I 0 flows through the path of the DC power supply 10 → the start-up circuit 24 → the constant voltage circuit 27 → the feedback resistor 26 → the load resistor 11 → the DC power supply 10. A power supply voltage V2 of the linear main circuit 21 is generated.

  At the same time, a current also flows through the Zener diode 42 of the charging circuit 35 and a Zener voltage Vz1 is generated at both ends thereof. However, since the voltage Vc at both ends of the charging capacitor 38 is zero, the overvoltage detection voltage V0 at the output end of the comparator 43 is high. Level H.

  Therefore, the switch 44 is turned on, but the high level H of the overvoltage detection voltage V0 is inverted by the inverter 45 and becomes the low level L, so that the switch 29 is turned off.

  Since the power supply voltage V2 of the constant voltage circuit 27 is not established at the beginning of the DC power supply 10, the output terminal of the operational amplifier 30 of the constant voltage circuit 27 is at a low level L. The low level L is applied to the gate G of the FET 36 of the charging circuit 35, and the FET 36 is turned off.

  Next, the two-wire main circuit 21 operates by the power supply voltage V2 applied to the two-wire main circuit 21, and outputs a PV value signal PV. Therefore, the deviation amplifier 22 calculates a deviation between the feedback voltage Vf2 and the PV value signal PV, applies an output voltage to the base of the output transistor 25 so as to correspond to the PV value signal PV, and outputs the PV value signal PV. A transmission current I0 corresponding to is supplied.

  When the transmission current I0 flows, the power supply voltage V2 of the constant voltage circuit 27 is established, and the divided voltage obtained by dividing the charging voltage Vc of the charging capacitor 38 by the resistors 39 and 40 serves as a reference for switching charging / discharging of the capacitor 38. When the voltage is lower than the determined Zener voltage Vz1, the overvoltage detection voltage V0, which is the output of the comparator 43, is at the high level H, so that the switch 44 is turned on and the FET 36 is controlled by the operational amplifier 30 of the constant voltage circuit 27. The battery is charged while controlling the charging current flowing through the charging capacitor 38.

The high level H value of the overvoltage detection voltage V0 is also applied to the two-wire main circuit 21. At this time, since the battery is not fully charged, the two-wire main circuit 21 determines whether or not to operate the peripheral circuit 47 in consideration of power consumption. This determination result is incorporated in the two-wire main circuit 21. The CPU that has been used outputs a determination signal Vj from the two-wire main circuit 21 to the peripheral circuit 47 using a predetermined program, and the power supply of the peripheral circuit 47 is controlled by the determination signal Vj.
Do.

  Conversely, when the divided voltage obtained by dividing the charging voltage Vc of the charging capacitor 38 by the resistors 39 and 40 is higher than the Zener voltage Vz1 which is a predetermined value that determines the charging / stopping switching reference of the charging capacitor 38, the comparator 43 The output is at a low level L, so that the switch 44 is turned off, charging is stopped, and overcharging of the charging capacitor 38 is prevented. At this time, the level of the switch 29 is inverted by the inverter 45 and becomes H level. Therefore, the switch 29 is turned on, and the FET 28 of the constant voltage circuit 27 is controlled by the operational amplifier 30 so that surplus current flows.

That is, when the divided voltage obtained by dividing the charging voltage Vc of the charging capacitor 38 with the resistors 39 and 40 is lower than a predetermined value, the constant voltage circuit 27 controls the constant voltage while charging the charging capacitor 38 and When the voltage is high, charging is stopped and the constant current is controlled by the constant voltage circuit 27 while the surplus current is bypassed through the FET 28.
The electric power charged in the charging capacitor 38 is consumed by the peripheral circuit 47, but if it is consumed, it is removed from the overcharged state, so that it is charged again.

  The electric power charged in the charging capacitor 38 using the surplus power is used to drive the peripheral circuit 47. As the peripheral circuit 47, for example, a two-wire field meter has a large current consumption, so that it is mounted. Can be used for back-up to an EEPROM, etc. so that more parameters can be saved than before, such as an infrared setting switch, LCD backlight, dot matrix LCD with a large display screen, Many functions can be added to a linear instrument.

It is a block diagram which shows one Example of this invention. It is a block diagram which shows the structure of the conventional field instrument.

Explanation of symbols

10 DC power supply 11 Load resistor 12 2-wire resistor 13 Amplifier 14 Signal processing circuit 18, 20 Sensor 21 2-wire main circuit 22 Deviation amplifier 23 Field instrument 25 Output transistor 26 Feedback resistor 27 Constant voltage circuit 28, 36 FET
30 operational amplifiers 34, 42 Zener diode 35 charging circuit 38 charging capacitor 43 comparator 47 peripheral circuit

Claims (3)

  In the two-wire field instrument which receives the transmission current from the load side via the output end, measures the physical quantity, converts the transmission current to correspond to this, and transmits it to the load side. A field instrument characterized by comprising a charging means for covering a circuit power supply with a part of the power supply and charging a capacitor using another part of the transmission current.   2. The field instrument according to claim 1, wherein the electric power from the battery is used as a power source for a peripheral circuit. 2. The field instrument according to claim 1, further comprising a determination unit that determines whether or not to operate a peripheral circuit based on a result of input of a charging state in the charging unit.

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