WO2009154110A1 - Dispositif de mesure de flux électromagnétique, système de mesure de flux électromagnétique, convertisseur pour dispositif de mesure de flux électromagnétique - Google Patents

Dispositif de mesure de flux électromagnétique, système de mesure de flux électromagnétique, convertisseur pour dispositif de mesure de flux électromagnétique Download PDF

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Publication number
WO2009154110A1
WO2009154110A1 PCT/JP2009/060597 JP2009060597W WO2009154110A1 WO 2009154110 A1 WO2009154110 A1 WO 2009154110A1 JP 2009060597 W JP2009060597 W JP 2009060597W WO 2009154110 A1 WO2009154110 A1 WO 2009154110A1
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Prior art keywords
current
excitation
circuit
output
voltage
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PCT/JP2009/060597
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English (en)
Japanese (ja)
Inventor
敬祐 名越
正明 栖原
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株式会社キーエンス
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Priority to JP2010517860A priority Critical patent/JP5379937B2/ja
Publication of WO2009154110A1 publication Critical patent/WO2009154110A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
    • G01F1/60—Circuits therefor

Definitions

  • the present invention relates to an electromagnetic flow meter, an electromagnetic flow meter system, and a converter for an electromagnetic flow meter that detect a flow rate of a fluid to be detected by a capacitance method.
  • the electromagnetic flow meter generates an electromotive force proportional to the flow velocity of the detected fluid by flowing the detected fluid in the magnetic field, and calculates the flow rate based on the electromotive force detected by the electrode.
  • a connection method of such an electromagnetic flow meter a four-wire system in which a power line and a signal line are separated and a two-wire system in which a signal is integrated into the power line are known.
  • a two-wire electromagnetic flow meter is suitable for laying a long distance because of the small number of wires.
  • the amount of current supplied to the transmission line is limited to the range of 4 mA to 20 mA, and the flow amount information is transmitted by the amount of current. There is a problem that a sufficient amount of current cannot be supplied to the excitation circuit for exciting the excitation coil.
  • k is a constant
  • D is the diameter of the measuring tube
  • v is the average flow velocity
  • B is the generated magnetic flux density.
  • a main object of the present invention is to provide an electromagnetic flow meter, an electromagnetic flow meter system, and a converter for an electromagnetic flow meter that can detect a flow rate with high accuracy by removing the restriction of current consumption.
  • Another object of the present invention is to provide a converter and an electromagnetic flow meter that can be used regardless of the characteristics of the electromagnetic flow meter.
  • the electromagnetic flow meter according to the first invention is connected to an external power source via a pair of transmission lines and detects the flow rate of the fluid to be detected between the external power source Signal flow and power supply are performed on a common transmission line, and the flow that allows the fluid to be detected to pass is detected in an electromagnetic flow meter that can specify the flow rate by changing the power supply side current according to the detected flow rate.
  • a measurement tube constituting a path, at least a pair of excitation coils arranged orthogonal to the flow path of the measurement tube, an excitation circuit for energizing an excitation current for exciting the excitation coil, and the pair of excitations Based on a straight line connecting the coils, at least a pair of electrodes arranged to be orthogonal to the flow path of the measurement tube, and a detection signal detected by the electrodes, it passes through the flow path of the measurement tube.
  • Displays the flow rate of the fluid to be detected A current output circuit for adjusting a current value of an output current according to a flow rate of the fluid to be detected calculated by the calculation means, and a current value of the current output circuit connected to the current output circuit.
  • Current / voltage conversion means capable of converting the voltage into a voltage and outputting it to the outside, a normal mode for outputting an output voltage corresponding to the flow rate from the current / voltage conversion means to the transmission line as a detection signal, and a predetermined output current
  • the amplifier mode switching means capable of outputting to the current output circuit and the current / voltage conversion means an amplifier mode instruction signal for instructing switching of the amplifier mode to which the additional current is added and output, and the current / voltage conversion means
  • a voltage removal circuit for removing an additional voltage corresponding to the additional current from the output voltage when the amplifier mode instruction signal is received from the amplifier mode switching means; Kill.
  • the power source side current of the electromagnetic flow meter can be output as a larger voltage obtained by adding the additional voltage without limiting it to 4 mA to 20 mA. Thereby, the electric power which can supply sufficient exciting current to an exciting coil is ensured, and the highly accurate and stable flow measurement is attained.
  • the current output circuit can include a current addition circuit for adding an additional current to the output current.
  • the current adding circuit includes an operational amplifier, and the operational amplifier receives an amplifier mode instruction signal from the amplifier mode switching means and changes a reference voltage to change the current. It can be configured to switch the addition operation.
  • the base current can be increased without reducing the resolution. For example, instead of simply adding 20 mA to 4-20 mA to obtain 4-40 mA, the resolution can be maintained by shifting to 24-40 mA.
  • the excitation circuit receives an amplifier mode instruction signal from the amplifier mode switching means, and switches the excitation voltage applied to the excitation coil to a voltage source having a different voltage.
  • An excitation voltage control circuit for receiving the amplifier mode instruction signal from the amplifier mode switching means, a voltage application timing control circuit for controlling the timing of applying the excitation voltage to the excitation coil, and the amplifier mode switching means
  • An excitation constant current control circuit for receiving the amplifier mode instruction signal and changing the excitation current can be provided.
  • the output voltage output from the current / voltage conversion means varies in the range of 1-5V in the normal mode and in the range of 6-10V in the amplifier mode. it can.
  • processing can be performed in a general range of 1-5 V, and processing can be facilitated in terms of circuitry.
  • the additional voltage component removed from the output voltage by the current / voltage conversion means can be set to 1-10V. This allows continuous excitation by adding an additional current to the excitation circuit, realizing stable detection, and by subtracting the additional voltage from the output side for processing, in the general range of 1-5V Can output.
  • signal transmission of a detection signal connected to the converter via a pair of transmission lines and detecting the flow rate of the fluid to be detected between the converter and a power source A measuring tube that constitutes a flow path through which a fluid to be detected is passed in an electromagnetic flowmeter that can be supplied by a common transmission line and the flow rate can be specified by changing the converter side current according to the detected flow rate.
  • Calculation means to calculate and previous A current output circuit for adjusting the current value of the output current according to the flow rate of the fluid to be detected calculated by the calculation means, and detecting that the converter is externally connected to detect the output current according to the flow rate It is possible to switch from the normal mode, which is output to the converter via the transmission line as a signal, to the amplifier mode in which a predetermined additional current is added to the output current and output, and an amplifier mode instruction which instructs switching to the amplifier mode Amplifier mode switching means capable of outputting a signal to the current output circuit can be provided.
  • the converter receives the amplifier mode instruction signal, the converter can remove the additional voltage corresponding to the additional current from the output voltage and output it.
  • the voltage signal is easier to process than the current signal.
  • the electromagnetic flow meter is connected to the electromagnetic flow meter via a pair of transmission lines, and power is supplied to the electromagnetic flow meter via the transmission line
  • a current / voltage conversion means capable of converting the output current of the electromagnetic flow meter into a voltage and outputting the voltage to the outside, and according to the flow rate
  • An electromagnetic flow meter that can be switched from the normal mode in which the output current is output as a detection signal to the converter via the transmission line to the amplifier mode in which a predetermined additional current is added to the output current and output.
  • a voltage removing circuit for detecting and removing an additional voltage corresponding to the additional current from the output voltage of the current / voltage converting means.
  • the current / voltage conversion means can include a resistor.
  • the electromagnetic flow meter is connected to the electromagnetic flow meter via a pair of transmission lines, and the electric power obtained from the external power source is obtained.
  • a method for detecting a flow rate of a fluid to be detected in an electromagnetic flow meter system including a converter for an electromagnetic flow meter that supplies a detection signal related to a flow rate of the fluid to be detected detected by the electromagnetic flow meter while supplying to the electromagnetic flow meter And exciting at least a pair of excitation coils arranged perpendicular to the flow path through which the fluid to be detected is energized by exciting an excitation current, and the flow of the measurement tube
  • the electromagnetic flow meter detects that the output mode is switched from the normal mode that outputs the output current to the transmission line as a detection signal to the amplifier mode that outputs the output current by adding a predetermined additional current, the electromagnetic flow meter The converter removing an additional voltage corresponding to the additional current.
  • FIG. 1 is an external perspective view showing a two-wire electromagnetic flow meter according to Embodiment 1 of the present invention.
  • FIG. 2 is a front view of the two-wire electromagnetic flow meter of FIG. 1.
  • FIG. 2 is a side view of the two-wire electromagnetic flow meter of FIG. 1.
  • FIG. 2 is a block diagram of the two-wire electromagnetic flow meter of FIG. 1. It is a circuit diagram which shows the state which connected the 2-wire type electromagnetic flowmeter to the external power supply. It is a circuit diagram which shows the circuit example of a current output circuit. It is a circuit diagram which shows the circuit example of the switching circuit of a power supply part. It is a circuit diagram which shows the circuit example of an excitation circuit.
  • FIG. 5 is a block diagram showing a two-wire electromagnetic flow meter according to Embodiment 2.
  • FIG. It is a block diagram which shows the example which comprised the power supply part with the insulation type switching power supply. It is a block diagram which shows the example which comprised the power supply part with the non-insulated type power supply. It is a wave form diagram which shows operation
  • charge charge monitor circuit 28 ... excitation polarity switching circuit 29 ... exciting constant current circuit 30 ... electrode; 31 ... adder circuit; 33 ... amplifier mode switching 34 ... Detection circuit; 34C ... Signal amplification circuit 341 ... Buffer circuit; 342 ... Differential amplifier; 343 ... Differential amplifier 344 ... Offset compensation circuit; 38 ... A / D converter 40 ... Calculation means; 41 ... Addition / subtraction instruction circuit; 42 ... Memory unit; 43 ... Reference voltage switching circuit 44 ... Damping unit; 45 ... Auto mode switching unit 50 ... Display unit; 51 ... Display unit; 52 ... Display screen; 54 ... Operation panel 60 ... Output unit; 80 ... setting unit 110 ... main body; 111 ...
  • flow path port 180 180 ... residual voltage detection circuit; 192 ... power supply changeover switch 501 ... step-up power supply; 502 ... insulation transformer; 503 ... insulation type switching control circuit 504 ... current detection resistor; Voltage subtraction circuit; 506, pulse transformer 507, output circuit 601, step-up switching power supply, 602, conversion circuit, 604, electricity Detecting resistor 605 ... voltage subtracting circuit; 608 ... converter; 609 ... arithmetic unit; 610 ... converter 611 ... accumulated pulse alarm output circuit DL ... transmission line; PL ... power line; OL ... output line L ... coil R o ...
  • R E Excitation current detection resistances R a , R b , R c , R 1 , R 2 , R O1 , R O2 ... Resistance C C ... Charge capacitor; C C2 ... Second charge capacitor C S1 ... Smoothing capacitor; C 01 , C 02 ... hold capacitors Tr, Tr 5 , Tr 6 , Tr C ... transistors; Tr 1 to Tr 4 ... bridge transistors A 2 , A 5 , A 6 , A 7 ... operational amplifier A E1 ... error amplifier LPF ... low-pass filter DC ... external DC power source SW B1, SW B2, SW B3 , SW B4 ... bridge switch; SW O1, SW O2, SW 7 ... switch SW Vref ...
  • V ref1 Npumodo selector switch
  • V ref2, V ref3 , V ref4 reference voltage
  • V refc inverting input of the charge voltage command voltage V refo ... differential amplifier
  • V RE exciting current detection voltage V L ... low voltage; V H ... High voltage V O ... Output voltage;
  • V IO ... Output current indicating voltage;
  • V p ... Output current indicating voltage V c ... Charge voltage;
  • V 2 ... Charge voltage indicating voltage;
  • V S Output of differential amplifier;
  • V OS Differential amplifier output
  • V AI3 Transistor gate voltage;
  • V T1 Transformer primary side voltage
  • V n Voltage input to inverting input of error amplifier; V Tr ...
  • the embodiment described below exemplifies an electromagnetic flow meter, an electromagnetic flow meter system, and an electromagnetic flow meter converter for embodying the technical idea of the present invention
  • the present invention is an electromagnetic flow meter.
  • the electromagnetic flow meter system and the electromagnetic flow meter converter are not specified as follows.
  • the present specification by no means specifies the members shown in the claims as the members of the embodiments.
  • the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, but are merely described. It is just an example.
  • each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.
  • Example 1
  • FIG. 1 is an external perspective view of a two-wire electromagnetic flow meter
  • FIG. 2 is a front view of the two-wire electromagnetic flow meter of FIG. 1
  • FIG. 3 is a side view
  • FIG. 5 shows circuit diagrams in a state where the two-wire electromagnetic flow meter 100 is connected to an external power source.
  • This electromagnetic flow meter is a non-wetted capacity type. (appearance)
  • the two-wire electromagnetic flow meter shown in FIGS. 1 to 3 includes a main body 110 that constitutes a two-wire electromagnetic flow meter main body and a display unit 50.
  • This two-wire electromagnetic flow meter allows the fluid to be detected to pass through the flow passage port 111 opened at both end faces of the main body 110, detects the flow rate, outputs it through the transmission line DL, and displays it as necessary. Display on the unit 50.
  • the main body 110 may be made of metal or made of PPS resin or the like.
  • the main body 110 is provided with a flange-like flange portion on a cylindrical end surface, and opens a screw hole for screwing with a pipe such as a pipe and a screw.
  • the flange portion is preferably formed integrally with the main body 110 and metal.
  • the flow path port 111 opened in the flange portion forms a flow path with the measurement tube 10 built in the main body 110.
  • the diameter of the flow path is set to substantially the same diameter from one end to the other end of the flow path port 111 to reduce loss when the detected fluid flows in one direction in the flow path.
  • the display unit 50 is fixed to the upper surface of the main body 110 so as to be orthogonal as shown in FIG. By fixing the display surface of the display unit in a posture orthogonal to the cylindrical main body, the flow rate can be easily seen from the side surface through which the fluid to be detected flows through the pipe-shaped measuring tube 10. (Display unit 50)
  • the display unit 50 is a member for displaying information such as the flow rate of the fluid to be detected, and includes a display screen 52 as the display unit 51 as shown in FIG.
  • a 7-segment display is used as a numerical display area for displaying numerical values on the display screen 52, and the flow rate and the like are displayed numerically.
  • the 7-segment display displays numerical values such as instantaneous flow rate and integrated flow rate for the detected flow rate.
  • the display screen 52 shown in this figure includes two stages of 7-segment displays, and can display the integrated flow rate and the set value simultaneously.
  • a 7-segment display may be provided for only one screen so that the display of the integrated flow rate, instantaneous flow rate, set value, and the like can be switched.
  • a display screen using liquid crystal or organic EL can be used instead of the segment-type display screen 52 using LEDs or the like. In this way, the display screen 52 can display not only numerical values such as flow rate but also figures and images such as arrows or alternatively, and can easily display the detected flow rate information to the user. Can be displayed.
  • the display unit 50 includes an operation panel 54 as a setting unit 80 for performing various settings.
  • the operation panel 54 includes keys and buttons for performing various settings.
  • a 4-digit 7-segment display is arranged in two stages on the display screen 52, an operation panel 54 is provided below, and buttons are arranged.
  • the setting unit 80 functions as a reset setting unit for setting an initial value of the integrated flow rate or a predetermined reset value.
  • the display circuit that displays the display screen 52 incorporates a calculation means 40 that is connected to the detection circuit 34 and the excitation circuit 24 and controls them.
  • the calculation means can be constituted by individual members and incorporated in the main body 110. It is also possible to integrate a calculation means, a detection circuit, an excitation circuit, and the like.
  • the display unit 50 can include an input unit.
  • the input unit is an interface for inputting an input signal from an external device such as a temperature sensor, a reset signal for resetting the integrated value, and various setting information.
  • a communication unit capable of data communication, an I / O terminal, a memory card, or the like can be used as the input unit.
  • the display unit 50 is separated from the main body 110.
  • the display unit 50 may be integrated with the main body 110.
  • the display unit does not need to be fixed to the main body case 110, and may be a separation type in which the display unit is arranged at another position.
  • This two-wire electromagnetic flow meter can output an analog current corresponding to the measured instantaneous flow rate, integrated flow rate, etc., with the current value of the transmission line DL as an analog output.
  • an analog current is output in the range of 4 mA to 20 mA.
  • an analog current output circuit 16 is provided as an output unit. Analog currents have better noise immunity than voltage signals, and can be used for data recording and analysis by outputting them externally.
  • a two-wire electromagnetic flow meter 100 is wound around a measurement tube 10 that passes a detection fluid and a pole piece, and applies a magnetic field to the detection fluid from the outside of the measurement tube 10.
  • the calculation means 40 functions as a flow rate calculation unit capable of calculating the integrated flow rate based on the flow rate of the fluid to be detected detected by the main body case 110 constituting the flow rate detection means. Further, the calculation means 40 includes a memory unit 42 for adding or integrating the instantaneous flow rate calculated with the flow rate calculation value and holding the integrated flow rate. The integrated flow rate is updated by sequentially adding the newly measured instantaneous flow rate to the integrated flow rate, and the updated integrated value is held in the memory unit 42 as needed. Further, as necessary, an output unit 60 for outputting an output signal, an input unit 70 for inputting various input signals such as an external reset signal, a setting unit 80 for performing various settings, and the like are provided. Also good. The calculation means 40, the display unit 51, the output unit 60, the input unit 70, the setting unit 80, and the like are configured as a unit that is a separate member from the main body case 110 as the display unit 50. (Measurement tube 10)
  • the measuring tube 10 is an insulating lining that allows a fluid to be detected to pass through the inside of the tube.
  • the measuring tube 10 is required to have excellent chemical resistance as a pipe through which a fluid to be detected passes and electrical characteristics for constituting a capacitor.
  • the measuring tube 10 is a strength matrix that bears the force of tension or compression based on the expansion and contraction of the pipe due to pressure and temperature changes of the fluid to be detected, and the required inner diameter, thickness, and length to withstand it.
  • the electrode 30 is made of a material having a high dielectric constant in order to enhance the capacitive coupling between the electrode 30 attached around the measuring tube 10 and the fluid to be detected and to improve the S / N ratio.
  • a material can be made of ceramics, plastic, or PPS resin mixed with ceramics. In particular, the latter is relatively strong and can secure molding accuracy and high dielectric properties. PPS resin is excellent in oil resistance and chemical resistance. A lining is applied to the inner surface of the measuring tube 10 as necessary.
  • the fluid to be detected is water or a non-corrosive liquid, and a liquid having a predetermined conductivity.
  • non-wetted electromagnetic flowmeters measure even liquids that corrode electrodes that could not be used in the past because the electrode 30 is not in direct contact with the fluid to be detected. it can.
  • it can respond to various to-be-detected fluids by selecting the material of the measuring tube 10.
  • FIG. the material of the measuring tube 10 can be selected according to the dielectric constant required in accordance with the measurement accuracy and the resistance to the fluid to be detected.
  • the two-wire electromagnetic flowmeter uses the measuring tube 10 as a separate member from the main body 110, so that only the measuring tube 10 is changed and other components are shared, so that two-wires with various specifications are used.
  • a type electromagnetic flow meter can be configured, which is advantageous in terms of product preparation.
  • the measurement tube 10 is a separate member from the main body case 110.
  • condenser can be selected for the member which comprises the measurement pipe
  • FIG. On the other hand, a resin that can be easily molded into a complicated shape can be used for the main body 110.
  • the measuring tube 10 by making the measuring tube 10 a separate member from the main body 110, it can be configured by a member suitable for each.
  • the high dielectric material constituting the measuring tube is generally expensive, only necessary portions are made of expensive members, and the other members can be made of less expensive materials to reduce the overall cost.
  • the measuring tube 10 made of an appropriate material can be selected according to the accuracy required for the two-wire electromagnetic flow meter.
  • a measuring tube made of an appropriate material can be selected according to the detection purpose and application of the two-wire electromagnetic flow meter, the required specifications and cost. Further, by making it possible to set a plurality of measuring tubes on one 2-wire electromagnetic flow meter, the members of various types of 2-wire electromagnetic flow meters can be shared and provided at low cost. (Electrode 30)
  • the electrode 30 is disposed around the measuring tube 10.
  • an insulating tape such as polyimide coated with a copper foil can be used.
  • the electrode 30 is a planar conductor that is curved along the outer periphery of the cylindrical measurement tube 10, and the pair of electrodes 30 are disposed so as to face each other with the measurement tube 10 interposed therebetween.
  • Each electrode 30 is affixed to the outer periphery of the measuring tube 10 without a gap. Tape or adhesive can be used for pasting.
  • the electrode 30 is preferably made of a flexible member and can be fixed to the outer surface of the measuring tube 10 without a gap.
  • the conductor is preferably covered with an insulating layer.
  • a pair of electrodes is used in this example, two or more sets of electrodes can be used.
  • the positions of the electrodes are adjusted so that the electric field detected by each electrode is orthogonal to the magnetic field.
  • the measuring tube 10 that guides the fluid to be detected is generated by a pair of exciting coils 22 disposed on the left and right sides of the measuring tube 10 and is disposed so as to be orthogonal to the substantially parallel magnetic field guided to the pole piece.
  • the pair of electrodes 30 arranged to face the upper and lower surfaces of the measuring tube 10 are arranged so as to detect the electromotive force generated in the direction perpendicular to the magnetic field generated by the exciting coil 22 and the direction of passage of the fluid to be detected. Has been.
  • the moving speed (flow velocity) of the fluid to be detected is increased according to Faraday's law of electromagnetic induction. Proportional electromotive force is generated. At this time, the electromotive force is proportional to the product of the magnetic flux density, the flow velocity, and the measurement tube diameter according to Faraday's law.
  • the electrode 30 faces the fluid to be detected through the tube wall of the measuring tube 10 made of a derivative and is capacitively coupled, and functions to electrically extract an electromotive force generated in the fluid. The extracted electromotive force is transmitted to the calculation means 40, converted into a flow rate signal, displayed on the display unit 51, or output as an electrical signal.
  • a pair of excitation coils 22 are arranged apart from each other, and the excitation coil 24 is energized and excited by an excitation circuit 24 to generate a magnetic field between the excitation coils.
  • an electromotive force is generated in a direction orthogonal to the direction of movement of the liquid.
  • two excitation coils 22 are used and are provided on the left and right sides of the measurement tube 10.
  • the excitation coil may be one.
  • the output unit 60 can function as an integrated value output unit or an instantaneous value output unit. Note that the output unit may omit any of the control output, analog output, and timeout output, or may include another output terminal. Furthermore, you may provide the output indicator lamp which shows the output state of each output terminal.
  • a two-wire electromagnetic flow meter 100 shown in this figure detects a measurement tube 10, an electrode 30, an excitation coil 22, an excitation circuit 24 for exciting the excitation coil 22, and an analog signal detected by the electrode 30. And an A / D converter 38 for A / D converting the analog signal detected by the detection circuit 34, an arithmetic means 40, a control signal insulation circuit 12, and a power supply unit 14. Since members having the same names as those described above can be basically used, detailed description thereof is omitted. Further, only one excitation coil 22 is shown for the sake of simplicity, but it goes without saying that one pair or more may be used as described above.
  • a charge capacitor CC is connected in parallel to the secondary side output of the transformer 20 of the power supply unit 14 as a charging means for charging the electric charge from the power supply unit 14. Further the power supply unit 14 based on the power control signal from the operation means 40, primary-side input current for energizing the transmission line DL (the output current I O) capable of controlling the current output circuit 16, the current output circuit 16 And a switching circuit 18 capable of converting the DC power of the primary side input current supplied from the transmission line DL into a predetermined power and outputting it to the secondary side.
  • the secondary side output current IO isolated from the primary side by the switching circuit 18 can be arbitrarily set, and the excitation current IE of the excitation coil 22 can be set as the output current as in a conventional two-wire electromagnetic flow meter. Since a higher excitation current IE can be supplied without being restricted by I O or less, a high voltage signal can be obtained, and accurate flow rate detection can be realized. (Power supply unit 14)
  • the power supply unit 14 is connected to two transmission lines DL for the external power supply.
  • the power supply unit 14 includes a primary side input capable of connecting two transmission lines DL, and a secondary side output insulated from the primary side input.
  • the power supply unit 14 converts the DC power supplied from the transmission line DL into predetermined power and outputs it from the secondary output.
  • An excitation circuit 24, a detection circuit 34, and the like are connected to the secondary side output of the power supply unit 14. That is, the excitation circuit 24 and the detection circuit 34 are insulated from the current output circuit 16 arranged on the primary side input side by the power supply unit 14, and the power supply unit 14 can also be used as an insulation circuit.
  • the two transmission lines DL are composed of a pair of a HIGH-side first power supply line and a LOW-side first common line.
  • a measurement tube 10 that allows the fluid to be detected to pass through, an excitation coil 22 that is wound around the pole piece and applies a magnetic field to the fluid to be detected from the outside of the measurement tube 10, and excitation
  • An excitation circuit 24 for generating an alternating magnetic field in the coil 22, an electrode 30 for detecting an electromotive force generated by the detected fluid passing through the magnetic field generated in the excitation coil 22, and the electrode 30
  • a detection circuit 34 for detecting an electromotive force
  • an A / D converter 38 for converting an analog signal obtained by the detection circuit 34 into a digital signal
  • Arithmetic means 40 for sending a power supply control signal to the power supply unit 14 is arranged so that the primary side input current value corresponding to the flow rate is obtained from the detected signal.
  • the power supply unit 14 is an insulating switching power supply that DC / DC converts power supplied from an external power supply via the transmission line DL, and includes an output current detection resistor Ro , a current output circuit 16, and a switching circuit 18. Is done.
  • the current output circuit 16 controls the primary side input current value for energizing the transmission line DL based on the power supply control signal from the calculation means 40.
  • the switching circuit 18 includes a switching control circuit 19 and a transformer 20, and is controlled by the current output circuit 16, and a DC voltage obtained from the primary side input current supplied from the transmission line DL is converted into a predetermined voltage by DC / DC.
  • the converter circuit 17 performs DC / DC conversion, and outputs it to the secondary side of the transformer 20.
  • the power supply unit 14 shown in FIG. 5 is provided with an excitation circuit output connected to the excitation circuit 24 and a calculation means output connected to the calculation means 40 as secondary outputs of the transformer 20.
  • the number of turns for the primary winding can be adjusted and adjusted individually to the power required for driving the excitation circuit 24 and the calculation means 40.
  • the secondary side output may be shared, and the excitation circuit 24 and the arithmetic unit 40 may be connected and driven in parallel on the circuit. In this case, since the excitation circuit 24 and the computing means 40 are connected to the same second power supply line, a design such that both members can be driven at the same potential, or a voltage is divided by a resistor can be used.
  • the DC / DC conversion circuit 17 can be used to generate the minimum required output voltage, and the excitation circuit 24 with very little power loss can be configured.
  • the DC / DC conversion circuit 17 is a step-down converter that performs a switching operation, and there is little power loss when performing voltage conversion, and an advantage that power loss can be extremely reduced is obtained.
  • this configuration is different from the configuration in which the calculation means 40 such as a CPU, the excitation circuit 24, and the detection circuit 34 such as an analog signal amplification circuit are arranged on the primary side.
  • the calculation means 40 such as a CPU
  • the excitation circuit 24, and the detection circuit 34 such as an analog signal amplification circuit are arranged on the primary side.
  • Arrangement on the side, that is, the exciting coil 22 side insulated from the input current has various advantages. Specifically, the electromotive force detected by the analog signal amplifier circuit can be directly input to the CPU as a flow rate analog signal without insulation. Therefore, the insulation circuit between them, which has been conventionally required, becomes unnecessary, and the problem of signal corruption caused by insulation can be avoided.
  • the number of power supply circuits can be reduced by using the power supply unit 14 in which an insulated power supply for an analog signal detection circuit and a power supply for an excitation circuit, which are conventionally required, are integrated. In other words, it is possible to simplify the configuration by reducing the number of power supply circuits by sharing the essential insulated power supply for the analog signal amplifier circuit also for the excitation circuit.
  • the control circuit isolation circuit 12 that separates the common potential (ground) between the CPU and the current output circuit 16 of the power supply unit 14 is sufficient.
  • the circuit configuration can be further simplified in that the number of insulating circuits can be reduced.
  • the switching circuit 18 and the current output circuit 16 exist on the primary side of the transformer 20 in the configuration of FIG. 5, it is possible to deal with a wide range of power supply voltages with respect to the external power supply on the input side.
  • the secondary voltage can be boosted by increasing the duty ratio of the switching circuit 18 or increasing the number of turns of the transformer 20. Therefore, even if it is difficult to operate in the past, such as when the voltage required for driving the excitation circuit 24 is higher than the external power supply voltage, the operation is boosted by the isolated switching power supply according to the present embodiment. Can be made.
  • the circuit configuration is simplified when excitation is performed by the intermittent excitation method. That is, if the excitation current is increased with a conventional two-wire electromagnetic flow meter having an excitation circuit on the primary side, it is conceivable to perform intermittent excitation instead of continuous excitation. In this case, since the fluctuation of the primary side input current value according to the flow rate is large, the fluctuation of the consumption current in the excitation circuit is also large, and a large-capacity capacitor is required to keep the output current constant, There is a problem that the load on the current output circuit becomes large. In the configuration of FIG.
  • the current output circuit 16 is connected in parallel with the switching circuit 18 between the two transmission lines DL, that is, between the HIGH-side first power supply line and the LOW-side first common line. ing.
  • a circuit example of such a current output circuit 16 is shown in FIG.
  • the output current adjustment circuit 166 includes an operational amplifier 167, a transistor 168, and a resistor. The + input terminal of the operational amplifier 167 is grounded, and the output is connected to the base side of the transistor 168.
  • the emitter of the transistor 168 is grounded to the first common line, and is connected to the output current detection resistor Ro through the first common line.
  • an arithmetic means (not shown in FIG. 6) sends an output current instruction signal as a power supply control signal to the current output circuit 16 via the control signal insulation circuit 12 in the PWM method.
  • the current output circuit 16 converts the PWM signal into an output current instruction voltage V p using a low-pass filter LPF and an operational amplifier 162.
  • the adder 164 and the output current adjustment circuit 166 adjust the output current I O to the instructed current value.
  • the switching circuit 18 of the power supply unit 14 in FIG. 5 includes a switching control circuit 19 and a transformer 20.
  • a circuit example of the switching control circuit 19 is shown in FIG.
  • the switching control circuit 19 shown in this figure includes a smoothing capacitor C S1 connected in parallel to the primary side of the transformer 20, and a switching connected to the first common line side between the smoothing capacitor C S1 and the transformer 20.
  • An element 181 and an oscillation circuit 182 connected to the switching element 181 are provided.
  • a power MOSFET or the like can be used for the switching element 181.
  • the oscillation circuit 182 includes an operational amplifier, a resistor, and a capacitor.
  • the switching circuit 18 generates a driving pulse by the oscillation circuit 182, and inputs the driving pulse to the gate of the transistor Tr to perform ON / OFF switching, thereby driving the transformer 20 and adjusting the output on the secondary side.
  • the power supply unit 14 that drives the switching element 181 with the switching control circuit 19 to control the power ON / OFF and stabilize the output can be configured to be small and light. (Measurement tube 10)
  • the measuring tube 10 constitutes a flow path through which the fluid to be detected passes.
  • a pair of exciting coils 22 and electrodes 30 are arranged so as to be orthogonal to the flow path of the measuring tube 10.
  • the excitation coil 22 and the electrode 30 are fixed to each other so that the pair of the excitation coil 22 and the electrode 30 face each other so that the measurement tube 10 is sandwiched therebetween.
  • the electrode 30 is fixed to the outside of the measuring tube 10 and is isolated from the fluid to be detected and does not come into contact.
  • the computing means 40 computes the flow rate of the fluid to be detected that passes through the flow path of the measuring tube 10 based on the voltage signal detected by the detection circuit 34.
  • the computing means 40 outputs an excitation control signal for controlling the drive state of the excitation circuit 24 to the excitation circuit 24, and further outputs a power supply control signal for controlling the drive state of the power supply unit 14 to the power supply unit 14. Based on these signals, the calculation means 40 controls the amount of current from the transmission line DL supplied to the primary side input of the power supply unit 14 according to the calculated flow rate of the fluid to be detected.
  • the computing means 40 is composed of a CPU or the like. (Control signal insulation circuit 12)
  • the control signal insulation circuit 12 sends a power control signal from the computing means 40 to the power supply unit 14 while separating the common potential between the primary side input and the computing means 40.
  • the calculation means 40 since the calculation means 40 is disposed at the secondary output of the power supply unit 14, it can be connected to the output side of the detection circuit 34. As a result, the excitation circuit 24 and the calculation means 40 can be arranged on the secondary side output and insulated from the primary side input with the transmission line DL. An insulation circuit can be eliminated. Further, the power supply unit 14 can be controlled from the calculation unit 40 with high reliability in a state where the calculation unit 40 and the power supply unit 14 are insulated from the common potential. Furthermore, since the number of parts to be insulated can be reduced, the number of necessary insulation circuits can also be reduced. (Detection circuit 34)
  • the detection circuit 34 shown in FIG. 5 includes an analog signal amplification circuit that amplifies the voltage signal detected by the electrode 30.
  • the analog signal amplifier circuit includes a buffer circuit 341 connected to each electrode 30, a differential amplifier 342 that inputs an output of the buffer circuit 341, and an amplifier 343 that inputs an output of the differential amplifier 342.
  • the buffer circuit 341 constitutes a preamplifier that amplifies the signal detected by the electrode 30.
  • the capacitive coupling between the electrode 30 and the fluid to be detected is generally as small as several tens of pF, the impedance of the resistance when providing a filter for passing an electrical signal is extremely high. For this reason, the buffer circuit 341 is connected to each electrode 30 to reduce the impedance.
  • the electric signals detected by the electrodes 30 are respectively input to the inputs of the differential amplifier 342 via the buffer circuit 341, and after the difference is amplified by the amplifier 343, the arithmetic means 40 via the A / D converter 38. Is output.
  • the analog signal amplifier circuit may be provided with a periodic reset circuit as necessary as a circuit for resetting a voltage detected by receiving a reset signal periodically sent from the computing means 40. (Excitation circuit 24)
  • an exciting circuit 24 is used.
  • Power supply unit 14 as a constant voltage power supply for driving the excitation circuit 24, a low voltage V L and the high voltage V H.
  • the excitation circuit 24 connects a low voltage V L and a high voltage V H of a constant voltage power source and an excitation constant current circuit 29 (described later) to the excitation coil 22 via an excitation polarity switching circuit.
  • a constant current is generated by the excitation constant current circuit 29 by a constant DC voltage supplied from the low voltage V L and the high voltage V H , and switching is performed by an excitation polarity switching circuit having a switch connected in a bridge shape to generate an alternating current.
  • An alternating current is passed through the coil 22.
  • the excitation circuit 24 is connected to a second power supply line of the secondary side output of the power supply unit 14.
  • FIG. 8 shows an example of the excitation circuit 24.
  • Excitation circuit 24 shown in this figure the transistors Tr1 ⁇ 4 which are connected like a bridge, and the exciting coil 22 connected to the center of the bridge, the coil current I L to be energized exciting coil 22 to a constant value
  • the excitation constant current circuit 29 is provided.
  • the coil current I L is a current that is passed through the excitation coil 22 and is an alternating current
  • the excitation current I E is a current that is passed from the excitation coil 22 through the bridge circuit to the excitation constant current circuit 29. It is a direct current. That excitation current I E is equal to the absolute value of the coil current I L.
  • the exciting coil 22 is disposed in the center of the bridge for the sake of explanation. However, in an actual apparatus, the exciting coil 22 is disposed in the vicinity of the measuring tube 10 as shown in FIG. (Excitation constant current circuit 29)
  • Exciting the constant current circuit 29 includes transistors Tr 5, an operational amplifier A 2, and the reference voltage V ref1, constituted by the excitation current detecting resistor R E.
  • the inverting input ( ⁇ ) of the operational amplifier A 2 is connected to the exciting current detection resistor R E
  • the non-inverting input (+) is connected to the reference voltage V ref1
  • the output side is input to the gate of the transistor Tr 5 .
  • the excitation current I E is detected by the excitation current detection resistor R E , converted into the excitation current detection voltage V RE and input to the inverting input ( ⁇ ) of the operational amplifier A 2 .
  • the operational amplifier A 2 controls the transistor Tr 5 so that the excitation current detection voltage V RE becomes equal to the reference voltage V ref1 .
  • the gates of the bridge transistors Tr 1 to Tr 4 are connected to the calculation means 40 (not shown in FIG. 8), and each bridge transistor is used as an excitation control signal sent from the calculation means 40 by an excitation timing signal SET. Tr 1 to Tr 4 are driven ON / OFF.
  • the calculating means 40 controls the timing of causing the coil current IL to flow through the exciting coil 22 by the bridge transistors Tr 1 to Tr 4 by the excitation timing signal S ET .
  • the operational amplifier A 2 controls the transistor Tr 5 so that the excitation current detection voltage V RE becomes equal to the reference voltage V ref1 , thereby making the excitation current IE constant.
  • FIG. 9 shows an example of a waveform pattern of the coil current I L and the excitation current I E flowing through the excitation coil 22.
  • (a) is a bridge transistor Tr 1 , Tr 4
  • (b) is a bridge transistor Tr 2 , Tr 3
  • (c) is a coil current I L
  • (d) is a waveform pattern of an excitation current IE.
  • the direction of the coil current I L flowing through the exciting coil 22 is changed by alternately turning on / off the bridge transistors Tr 1 , Tr 4 and Tr 2 , Tr 3 of FIG.
  • An alternating magnetic field can be generated by changing in the directions of A and B shown in FIG. Thereby, the AC coil current IL can be obtained from the DC excitation current IE .
  • FIG. 10 An example of such a circuit is shown in FIG. 10 as a two-wire electromagnetic flow meter 200 according to the second embodiment.
  • the two-wire electromagnetic flow meter 200 shown in this figure can use the same configuration as that in FIG. 5 on the primary side.
  • the member similar to FIG. 5 can be utilized also for the member of a secondary side, these detailed description is abbreviate
  • the excitation circuit 24 connects the excitation circuit 24 to the excitation circuit power supply line which is the second power supply line of the secondary side output of the power supply unit 14. Further, the calculation means 40 and the A / D converter 38 are connected in series with the excitation circuit 24 and then connected to the circuit common line of the secondary output. The arithmetic means 40 and the A / D converter 38 are connected in parallel, and are connected to the excitation circuit common line via the excitation circuit 24. Therefore, the excitation circuit common line becomes a circuit power supply line other than the excitation circuit, such as the arithmetic means 40 and the A / D converter 38.
  • the circuit common line other than the excitation circuit such as the arithmetic unit 40 is different from the excitation circuit common line. For this reason, since the level of the excitation control signal sent from the arithmetic means 40 to the excitation circuit 24, that is, the excitation timing signal SET is different, it is necessary to insulate them. Therefore, an excitation signal insulation circuit 12B is provided on the excitation timing signal line between the excitation circuit 24 and the calculation means 40. (Power supply unit 14)
  • the two-wire electromagnetic flow meter shown in this figure shows a simplified configuration of the secondary output of the power supply unit 14.
  • the DC / DC conversion circuit 17 and the current output circuit 16 are integrated as an insulating switching power supply, and the secondary output and the output current IO are adjusted.
  • the power supply unit 14 shown in this figure includes a switching element 181, an oscillation circuit 182 that controls ON / OFF of the switching element 181, an output current detection resistor Ro , a transformer 20, and a smoothing capacitor C S1 .
  • the power supply unit 14 performs a switching operation using the switching element 181 and smoothes it with the smoothing capacitor C S1 .
  • a power transistor Tr such as a MOSFET can be used as the switching element 181.
  • the oscillation circuit 182 can change the switching pattern of the switching element 181 by adjusting the oscillation frequency and the duty.
  • the output current I O is adjusted by changing the switching pattern of the switching element 181 by the oscillation circuit 182.
  • the power supply unit 14 does not have a configuration in which the excess current that cannot be consumed in the circuit as in the prior art is applied to the transistor and consumed as heat so as to match the book. Instead, the oscillation circuit 182 adjusts the duty of the transistor Tr so that the instructed output current I O is obtained, and the power sent to the secondary side of the switching power source is made variable, so that the output current I O is reduced. It is adjusted. As a result, it is resistant to fluctuations in the power supply voltage and output current IO , and can be maintained at a high efficiency with a wide power supply voltage and output current. In particular, any power supply voltage or output current is DC / DC converted so that power is sent to the secondary side with a switching power supply as much as possible, so no extra power is generated and consumed as heat.
  • the excitation power circuit consumes the largest amount of power, so a circuit for intermittent excitation with a constant excitation current (described later) or a circuit for dynamically changing the excitation current. Even in the configuration, highly efficient operation can be realized.
  • FIG. 12 shows such a two-wire electromagnetic flow meter as a modification.
  • the power supply unit of the two-wire electromagnetic flow meter shown in this figure includes a smoothing capacitor C S1 , a switching element 181B, a coil L, a charge capacitor C C, and an oscillation circuit 182B.
  • this two-wire electromagnetic flow meter is almost the same as that of the above-described isolated switching power supply, and by operating the oscillation circuit 182B so that the output current I O becomes a value indicated by the output current instruction signal, Adjust the output current IO .
  • FIG. 13 shows an operation when the output current I O is reduced
  • FIG. 14 shows an operation when the output current I O is increased
  • FIG. 15 shows an operation when the power supply voltage is increased
  • FIG. 16 shows a decrease.
  • V AI3 indicates the gate voltage of the transistor Tr shown in FIG. 11, and V T1 also indicates the primary voltage of the transformer 20.
  • the output current I O is changed by changing the duty ratio for switching the primary side of the transformer 20.
  • the method of changing the output current is not limited to this configuration, and the same change can be realized by changing the switching frequency, for example.
  • the switching power supply also functions as a stabilized power supply that maintains a stable output even when the power supply voltage of the external power supply fluctuates. For example, as shown in FIG. 15, when the power supply voltage increases, the primary side voltage V T1 of the transformer 20 also increases and the amplitude value increases. In this case, the power that can be transmitted by switching the transformer 20 once increases. In other words, the current consumption for switching the transformer 20 once increases. Therefore, the oscillation circuit 182 works so as to lengthen the off time Toff for switching the transformer 20, so that the current can be relatively reduced and the output current IO can be maintained at the indicated value.
  • the switching power supply can respond to the change even when the power supply voltage changes.
  • the output current IO can be kept constant, and the output can be stabilized and the reliability can be improved.
  • the switching power supply can perform the maximum switching with respect to the power supply voltage that is currently supplied and the output current IO that is currently output, and the power can be efficiently transferred to the output side of the switching power supply at all times.
  • the oscillation circuit 182 performs switching so that the output current value is determined according to the detected flow rate, unnecessary current consumption is eliminated, and the efficiency is improved with the instructed output current value. Switching can be performed well. For this reason, compared with the conventional system, there is no part which converts electric power into heat and is consumed, and it is excellent in efficiency. In particular, this feature is beneficial because the two-wire electromagnetic flowmeter originally has less power available. In addition, a strong advantage is obtained against fluctuations in the power supply voltage, and even if the power supply voltage fluctuates, the switching duty can be adjusted so that the indicated current value is obtained at the power supply voltage. (Surplus current adjustment circuit 185)
  • This two-wire electromagnetic flow meter includes a DC / DC conversion circuit 17 as an insulating switching power supply, an oscillation circuit 182 including a duty adjustment circuit, a surplus current adjustment circuit 185 including a transistor Tr 6 and a resistor, a transistor Tr 6 includes a transistor control circuit 184 for controlling 6 , an output current detection resistor Ro, and a control signal insulation circuit 12.
  • the two-wire electromagnetic flow meter shown in this figure uses a current output circuit 16B similar to the conventional one in combination with the switching power supply described above. That is, when the power that can be transmitted by a switching power supply has reached the upper limit, the excess current regulating circuit 185 for consumption by energizing the surplus current to the transistor Tr 6, is provided on the primary side of the transformer 20 .
  • the surplus current adjustment circuit 185 can also be arranged on the output side of the switching power supply.
  • FIG. 18 is a graph showing the relationship between the flow rate and the output current IO .
  • the surplus current adjusting circuit 185 consumes the surplus current in the range equal to or higher than the switching power transmission upper limit indicated by cross hatching in FIG. That is, the transistor Tr 6 is turned ON, and the surplus is consumed by the resistor and the transistor Tr 6 .
  • Example 3 Excitation circuit that performs intermittent excitation
  • an excitation circuit with variable power can be used on the output side of the switching power supply.
  • a two-wire electromagnetic flow meter using such an excitation circuit is shown in FIG.
  • a two-wire electromagnetic flow meter 300 shown in this figure includes a power supply unit 14 including a DC / DC conversion circuit 17, an excitation circuit 24 connected to the secondary side of the power supply unit 14, and a charge voltage supplied to the excitation circuit 24.
  • a charge charge monitoring circuit 26 which monitors the V c
  • calculation means for outputting the excitation timing signal S ET instructing excitation start of excitation circuit 24 receives the charging completion signal from the charge charge monitoring circuit 26 to the excitation circuit 24 40, a constant voltage power supply 25 for supplying power to the arithmetic means 40 and performing signal amplification, a measuring tube 10, an electrode 30, a detection circuit 34, and an A / D converter 38.
  • the members having the same names as those described above are basically the same as those in the above-described embodiment, and detailed description thereof will be omitted.
  • the excitation circuit 24 maintains the coil current I L for exciting the excitation coil 22 substantially constant. If the coil current is changed as in a conventional electromagnetic flow meter, the linearity of the signal may deteriorate. However, by keeping the coil current constant at an appropriate value without changing the coil current, the linearity is improved and the flow rate is highly accurate. Detection can be realized. Further, when the output current value is made constant, setting of the value is important. In other words, if the current value is set low, it is necessary to design the excitation circuit so that the excitation coil can be excited with the low current value. However, if the output current value is high in this design, the current that is not consumed by the excitation circuit increases. It is wasted due to heat and the like.
  • the current value is not set to the lowest current value but is set to a higher current value.
  • intermittent excitation is performed in this range to temporarily stop the excitation.
  • the specific current value is set to a current value at a flow rate of 50% (12 mA when the output current IO is in the range of 4-20 mA).
  • continuous excitation can be performed in a current range of 50% or more, and highly accurate flow rate detection can be stably performed.
  • the current range of 50% or less by performing as intermittent excitation described above, it maintains the coil current I L at a constant value. Further, the rising characteristics are improved by using the charging of the rising voltage (high voltage V H ) of the exciting coil 22 described later without throwing away the surplus current even in the region of 50% or more.
  • the power exceeding the power required for circuit drive is stored during the excitation pause period, and when the excitable power is obtained, the pause period is switched to the excitation period. Start.
  • the excitation period is again switched to the rest period, and switching from discharging to charging is performed. Specifically, charging of the power to the charge capacitor is started at the timing when the excitation current is turned off.
  • a constant voltage power supply 25 and a charge charge monitor circuit 26 are connected in parallel with the excitation circuit 24.
  • the constant voltage power supply 25 performs DC / DC conversion on the electric power received from the power supply unit 14, and adjusts and supplies it to a voltage value for driving the computing means 40.
  • charge the charge monitor circuit 26 monitors the voltage necessary to supply the coil current I L to the excitation circuit 24. Time Specifically, the when the charge voltage instruction signal from the excitation circuit 24 to the charge charge monitoring circuit 26 during the intermittent excitation is instructed, the start of the charge to the charge capacitor C C, a predetermined voltage is charged To supply the charge voltage V c to the excitation circuit 24.
  • FIG. 20 shows a two-wire electromagnetic flow meter that constitutes such an excitation circuit.
  • the two-wire electromagnetic flow meter shown in this figure shows an excitation circuit 24 and its peripheral circuit in the secondary side portion of the power supply unit 14.
  • the two-wire electromagnetic flow meter includes a switching control circuit 19, a transformer 20, a charge capacitor C C that generates a voltage for exciting the excitation coil 22 on the secondary side of the power supply circuit, and a charge capacitor C as a charging means.
  • the calculating means 40 for delivering the excitation timing signal S ET to indicate the timing of the excitation on the basis of the monitoring result of the charge charge monitor circuit 26, the excitation circuit 24 as, an exciting coil 22, an exciting polarity switching circuit 28 for switching the polarity of the excitation of the exciting coil 22, an exciting constant current circuit 29 to keep the coil current I L flowing through the exciting coil 22 constant, the residual voltage detection circuit 180 Is provided.
  • an excitation circuit 24 using a charge charge monitor circuit 26 is provided on the secondary side of the power supply unit 14 which is a switching power supply, and intermittent excitation is performed.
  • Charge charge monitor circuit 26 monitors the charge is charged from the power supply unit 14 during the excitation dead time to charge the capacitor C C, when the prescribed power is able to charge, and sends a charging completion signal CHG_COMP to computing means 40 .
  • Computing means 40 upon receiving the charge completion signal CHG_COMP, each bridge switches SW B1 ⁇ SW B4 constituting a bridge-like excitation polarity switching circuit 28 sends an excitation timing signal S ET, starts excitation.
  • the arithmetic means 40 sends a residual voltage detection timing signal S RV to the residual voltage detection circuit 180 and maintains the residual voltage of the exciting coil 22 constant.
  • the exciting constant current circuit 29, the residual voltage is caused by the voltage drop of the transistor Tr 5 and the exciting current detection resistor R E. In particular the voltage drop of the transistor Tr 5 causes fever becomes the power loss.
  • This residual voltage is detected by the residual voltage detection circuit 180 and controlled so that the residual voltage becomes small.
  • the residual voltage detection circuit 180 sends a charge voltage instruction signal for instructing the charge voltage V c to the charge charge monitor circuit 26 so that the current consumption in the excitation constant current circuit 29 is reduced.
  • the charge charge monitor circuit 26 monitors the amount of charge stored in the charge capacitor C C with the charge voltage V c .
  • the charge voltage V c for determining that excitation can be started is set so that the residual voltage of the excitation coil 22 becomes constant.
  • the charge voltage V c corresponding to the excitation coil 22 is set and the power is adjusted to an appropriate power regardless of the size and characteristics of the excitation coil, so that wasteful current consumption can be reduced to a minimum.
  • the charge voltage V c is the same as the low voltage V L described above. (Intermittent excitation)
  • the excitation polarity switching circuit 28 of FIG. 20 includes four bridge switches SW B1-B4 connected in a bridge shape with the central excitation coil 22 interposed therebetween.
  • a pair of bridge switches SW B1 and SW B4 and SW B2 and SW B3 positioned obliquely with respect to the exciting coil 22 are simultaneously turned ON / OFF, and these sets are alternately turned ON / OFF, thereby exciting the pair.
  • the coil 22 is energized the coil current I L alternately in forward and reverse directions.
  • the coil current I L P side excitation the excitation of the forward (rightward in FIG. 8), the reverse excitation of the N side exciting.
  • FIG. 21 shows a pattern of continuous excitation, in which P-side excitation and N-side excitation are alternately repeated.
  • FIG. 22 repeats the operation of performing the P-side excitation and the N-side excitation again after the P-side excitation and the N-side excitation are continuously excited as a set, and then a pause period is provided.
  • intermittent excitation is not limited to this pattern.
  • FIG. 23 after an odd number of excitations such as P-side excitation, N-side excitation, P-side excitation, N-side excitation, and P-side excitation are continued, And starts from N-side excitation when restarting.
  • the polarity of the excitation that is initially performed at every excitation can be alternately switched, and excitation can be performed in a well-balanced manner.
  • FIG. 24A shows the basic period of excitation
  • FIG. 24B shows the voltage across the excitation coil 22
  • FIG. 24C shows the coil current I L
  • FIG. 24D shows the excitation current detection voltage.
  • V RE shows the power supply switching signal S VH output from the computing means 40
  • FIG. 24F shows the low voltage V L
  • FIG. 24G shows the charge completion signal output from the charge charge monitor circuit 26.
  • CHG_COMP and FIG. 24H show the waveforms of the residual voltage detection timing signal S RV , respectively.
  • FIG. 24A shows the basic period of excitation
  • FIG. 24B shows the voltage across the excitation coil 22
  • FIG. 24C shows the coil current I L
  • FIG. 24D shows the excitation current detection voltage.
  • V RE shows the power supply switching signal S VH output from the computing means 40
  • FIG. 24F shows the low voltage V L
  • FIG. 24G shows the charge completion signal output from the charge charge monitor circuit 26.
  • CHG_COMP and FIG. 24H show the waveform
  • FIG. 24A shows the timing for alternately performing P-side excitation and N-side excitation in intermittent excitation with a pause period.
  • SW B1 -B4 of the excitation polarity switching circuit 28 provided with the excitation coil 22 shown in FIG. 20
  • SW B1 and SW B4 and SW B2 and SW B3 are alternately paired, and the lower right part of FIG. It is to oN / OFF by the excitation timing signal S ET from the calculating means 40 shown, energized alternately an alternating current to the exciting coil 22 generates an alternating magnetic field.
  • FIG. 24 illustrates an example in which the excitation with the excitation period of one (odd number) is repeated, in which the P-side excitation is performed once and then the N-side excitation is performed once with a pause period in between.
  • Excitation is started by instructing the excitation timing signal SET from the calculation means 40 to the bridge switches SW B1 to SW B4 .
  • a voltage is applied to the exciting coil 22
  • the power source switching signal S VH is turned off and the power source switching switch 192 is turned off as shown in FIG.
  • the voltage is switched to the low voltage V L and applied to the exciting coil 22.
  • the coil current I L becomes a substantially constant value as shown in FIG.
  • the broken line shown in FIG. 24C indicates that the coil current I L increases when the low voltage V L is applied from the beginning.
  • the excitation coil 22 has poor rise characteristics. Therefore, by increasing the applied voltage at the time of voltage application, it becomes possible to obtain a stable excitation in a short time with a sharp rise.
  • the residual voltage detection circuit 180 is set so that the excitation coil residual voltage becomes a predetermined value when the excitation coil starts up and shifts to a normal constant current. Has been adjusted. Further, when the charge completion signal CHG_COMP charge charge monitor circuit 26 of FIG. 24 (g) is inputted to the arithmetic unit 40, is output excitation timing signal S ET from the arithmetic unit 40 to the excitation polarity switching circuit 28, FIG. 24 ( Excitation is started as shown in a).
  • the pause period during intermittent excitation is not constant, and the circuit performs the excitation by determining that the pause period is as short as possible.
  • the most efficient excitation can be performed within the supplied power.
  • the CPU constituting the calculation means 40 also reduces power consumption and performs only a minimum operation.
  • a method of reducing the power consumption of the CPU a method of lowering the operating frequency such as clock division and having a sub clock separately from the main clock can be used.
  • Each bridge switches SW B1-B4 of the excitation polarity switching circuit 28 is constituted by bridge transistors Tr 1 ⁇ Tr 4, the ON / OFF control by the excitation timing signal S ET from the calculating means 40, not shown. (Charge Charge Monitor Circuit 26)
  • FIG. 26 shows a waveform pattern for controlling the pause period by the charge charge monitor circuit 26 during intermittent excitation.
  • 26A shows the excitation timing
  • FIG. 26B shows the charge voltage V c
  • FIG. 26C shows the waveform of the charge completion signal CHG_COMP.
  • the excitation period the flows excitation current I E, Vc due to the discharge of the charge capacitor C C is reduced.
  • the excitation is ended quiescent period, the exciting current I E is stopped, the charge to the charge capacitor C C is started.
  • Vc rises, and reaches the charge voltage command voltage V 2, is output from the operation unit 40 shown in FIG. 20 the excitation timing signal S ET bridge switches SW B1-B4, again exciting current I E is the excitation coil 22 is energized. Power stored in the charge capacitor C C in this way, is consumed by the excitation coil 22 to the exciting period, it is charged from the power supply unit 14 to pause.
  • the excitation circuit 24, without the pause period is constant, dynamically changes according to the charge amount of the charge voltage command voltage V 2 and a charge capacitor C C. That is, since the rapidly energized upon reaching the charge voltage command voltage V 2 which is instructed is started, the charging of the charge capacitor C C is completed earlier, is shortened rest period by that amount. The shorter the pause period, the longer the period of excitation, which can contribute to improved flow rate detection accuracy and stable operation.
  • FIG. 27 shows an operation example in the case where the output current I O increases and the continuous excitation can be maintained.
  • (a) shows the excitation timing
  • (b) shows the charge voltage V c
  • (c) shows the waveform of the charge completion signal CHG_COMP.
  • the exciting current I E Can be continuously excited to maintain the current. For this reason, by adding an output current in an amplifier mode, which will be described later, continuous excitation can be maintained without performing intermittent excitation, and highly accurate flow rate detection can be performed.
  • the charge charge monitor circuit 26 determines the timing of intermittent excitation. Although it is conceivable that the intermittent excitation cycle is defined by the output current value, in this method, it is necessary to consider an offset or the like, and the current is wasted. In this embodiment the contrary, to monitor the amount of charge charge charge monitoring circuit 26 is stored in the charge capacitor C C, because it configured to discharge when it becomes chargeable voltage, the charge amount of the actual It is possible to operate in accordance with high efficiency driving without wasting current. In this method, since the actual voltage value is monitored, the actual charge amount can always be monitored and the excitation possible timing can be determined even if the characteristics of the excitation coil etc. are changed. The advantage is also obtained.
  • FIG. 28 shows an example of charging means for generating a voltage V H higher than the normal low voltage V L as the voltage at the time of starting up the coil.
  • This charging means includes a plurality of coils, rectifier diodes, and charge capacitors CC having different turns on the secondary side of the power supply unit 14 so as to supply a high voltage V H and a low voltage V L.
  • a second charge capacitor C C2 is further stacked on the charge voltage V c to obtain a high voltage V H.
  • V H since the high voltage V H is generated based on the charge voltage V C , V H also fluctuates up and down together with the up and down fluctuation of Vc.
  • a charge voltage V c that is a normal voltage (low voltage V L ) and a high voltage V H for starting up the exciting coil.
  • V L normal voltage
  • V H high voltage
  • the bridge transistors Tr 1 to Tr 4 constituting the bridge switches SW B1 to B4 of the excitation polarity switching circuit 28 are a combination of Tr 1 ⁇ Tr 4 and Tr 2 ⁇ Tr 3 , and apply both positive and negative excitation voltages to the excitation coil 22. As a result, an alternating current flows through the exciting coil 22.
  • FIG. 1 The bridge transistors Tr 1 to Tr 4 constituting the bridge switches SW B1 to B4 of the excitation polarity switching circuit 28 are a combination of Tr 1 ⁇ Tr 4 and Tr 2 ⁇ Tr 3 , and apply both positive and negative excitation voltages to the excitation coil 22. As a result, an alternating current flows through the exciting coil 22.
  • the excitation constant current circuit 29 includes an operational amplifier A 2 , a transistor Tr 5 , an excitation current detection resistor R E , and a reference voltage V ref1 .
  • the non-inverting input of the operational amplifier A 2 and the reference voltage V ref1, inverting input and between the exciting current detection resistor R E and the transistor Tr 5, are connected, and the output side is connected to the transistor Tr 5.
  • the excitation constant current circuit 29 controls the transistor Tr 5 so that the excitation current detection voltage V RE approaches the reference voltage V ref1 . Specifically, when the excitation current detection voltage V RE is lower than a predetermined reference value, the excitation coil 22 is driven by the high voltage V H by turning on the transistor Tr 6 constituting the power supply switch 192. Conversely, when it is high, the transistor Tr 6 is turned off and the exciting coil 22 is driven by the charge voltage V c .
  • the electromagnetic flow meter can also have an amplifier mode switching function for switching to an amplifier mode in which the output current is increased in order to improve measurement accuracy.
  • the amplifier mode for example, by operating at 24-40 mA, which is a 4-20 mA consumption current plus an additional current (base current) of 20 mA, the excitation current IE is increased and the electromotive force is increased, resulting in more stable performance. It will be obtained. As a result, it is possible to reduce or eliminate the pause period of intermittent excitation and realize stable measurement with continuous excitation.
  • FIG. 400 An electromagnetic flow meter having such an amplifier mode switching function is shown in FIG.
  • the electromagnetic flow meter 400 shown in this figure has substantially the same configuration as the electromagnetic flow meter 300 in FIG. 19 except that the calculation means 40 functions as a mode switching means, and detailed description of the same members as those in FIG. 19 is omitted.
  • Calculation means 40 outputs the normal mode, the amplifier mode instruction signal S AP instructing switching of adding a predetermined additional current to the output current to the amplifier mode to output, to the power unit 14 and the excitation circuit 24.
  • Power supply unit 14 and the excitation circuit 24 receives the amplifier mode instruction signal S AP, the process proceeds to the operation of the amplifier mode with add additional current.
  • the output current I O is increased, so that an external device that receives the output current also needs a mechanism for detecting the flow rate corresponding to the increase in current.
  • the converter corresponding to amplifier mode is connected and it converts into the flow volume which considered the increase in electric current appropriately.
  • the amplifier mode switching means may also be configured to automatically detect that it is connected to an amplifier mode compatible external device such as a converter and switch to the amplifier mode.
  • FIG. 31 shows an example of an output current adjusting circuit of an electromagnetic flow meter having an amplifier mode switching function.
  • the electromagnetic flow meter shown in this figure includes a DC / DC conversion circuit 17 that is an insulating switching power supply, and an oscillation circuit 182 that includes a duty adjustment circuit as a switching control circuit 19 that performs switching control of the DC / DC conversion circuit 17; Low-pass filter LPF, calculation means 40, control signal insulation circuit 12 that insulates the power supply control signal from calculation means 40 and sends it to the current output circuit 16, and amplifier mode from calculation means 40 that includes amplifier mode switching means 33 an instruction signal S amp mode changeover switch for switching the ON / OFF at AP, and the instruction signal insulation circuit 12C for insulating the amplifier mode instruction signal S AP, as an additional programmable current output circuit an additional current without lowering the resolution, additional the output current I o and Anpumo so as to be able to effectively take advantage of the current consumption and the amplifier mode An adding circuit 31 for adding the reference voltage V a at the time.
  • the calculation means 40 serves also as an amplifier mode switching means 33 switches the reference voltage at the amplifier mode instruction signal S AP. Specifically, the two controls are switched so as to stabilize the operation of the electromagnetic flowmeter by raising the excitation current IE and the excitation voltage by changing the reference voltage. That is, (A) the threshold value of timing for switching the excitation voltage of the excitation coil 22 from V H to V L is switched. (B) to switch the range of the excitation current I E, to increase the partial excitation current I E plus additional current.
  • the amplifier mode instruction signal S AP from the amplifier mode switching means 33 switches the ON / OFF of the amplifier mode switch.
  • the amplifier mode selector switch is OFF, the normal mode is selected, and when it is ON, the amplifier mode is selected.
  • the output current adjusting circuit in the amplifier mode by sending the amp mode instruction signal S AP to the arithmetic unit 40 is the adding circuit 31, by shifting the current range 24-40MA, remains current consumption maintaining the resolution It is configured to allow base up.
  • the voltage input to the duty adjustment circuit is V p , and is a voltage suitable for PWM control of the duty adjustment circuit through the low-pass filter LPF.
  • the voltage V n of the duty adjustment circuit is set so that the amplifier mode selector switch is OFF in the normal mode.
  • V n R b / R a ⁇ I o R o It becomes.
  • the amplifier mode changeover switch is turned ON, and the addition circuit 31 works.
  • V n R b / R a ⁇ I o Ro ⁇ R b / R c ⁇ V a It becomes.
  • I o R a / R o ⁇ (V p / R b + V a / R c ) It becomes. That is, in addition to the output current I O in the normal mode, the amplifier mode changeover switch is turned ON / OFF in the amplifier mode to add the current R a / R o ⁇ V a / R c as the additional current I add. It can be energized.
  • the span can be set arbitrarily in normal mode and amplifier mode, so it can be switched to 4-20mA or 24-40mA current output without reducing the resolution of PWM control in the duty adjustment circuit. And can.
  • the amplifier mode is set for operation. Since the obtained signal has an additional current of 20 mA, it is necessary to subtract 20 mA on the signal receiving side.
  • a dedicated converter corresponding to the amplifier mode operation is used. In such a dedicated converter, the obtained signal is received by a resistor of, for example, 250 ⁇ , and converted to a voltage signal of 6-10V. That is, by subtracting the voltage of 5 V corresponding to the additional current of 20 mA, it can be converted into a voltage signal of 1-5 V. This 1-5V voltage signal is a commonly used voltage signal and can be easily processed.
  • the excitation current can be secured to a certain level regardless of the output current.
  • the 30 mA excitation current IE can be intermittently supplied.
  • the excitation current can be set to any value, but if intermittent excitation is performed, the number of excitations in a fixed time is smaller than that in continuous excitation, so the amplifier mode is used more frequently and requires high accuracy. Set the excitation current so that continuous excitation is possible with the output current value.
  • the offset compensation circuit In intermittent excitation, the offset compensation circuit is used and offset compensation is performed by an analog circuit in order to remove the low frequency offset component without increasing the number of A / D conversions as much as possible.
  • a reference setting function for adding half-period excitation for setting the reference may be provided.
  • Conventional offset compensation circuits cannot be used as they are because accuracy is deteriorated in intermittent excitation.
  • odd-numbered half-period excitation is performed, and sampling is not performed by the first one-time excitation, and only the offset compensation circuit is driven, thereby enabling offset compensation without reducing accuracy. Yes.
  • the electromagnetic flow meter shown in this figure includes an exciting coil 22, an exciting circuit 24, a measuring tube 10, an electrode 30, a signal amplifying circuit 34C, an A / D converter 38, and a computing means 40.
  • the signal amplification circuit 34C includes an offset compensation circuit 344 between the differential amplifier 342 and the differential amplifier 343 of the detection circuit.
  • the offset compensation circuit 344 includes switches SW O1 and SW O2 , resistors R O1 and R O2 , and hold capacitors C O1 and C O2 .
  • the reason why the offset compensation circuit 344 has two charging / discharging paths in this way is to correspond to P-side excitation and N-side excitation, respectively.
  • the output V S of the differential amplifier 342 is connected to the inverting input of the differential amplifier 343.
  • the switch SW O1 of the offset compensation circuit 344 is connected to the output V S of the differential amplifier 342, and the switch SW O2 is connected to the non-inverting input of the differential amplifier 343. That is, the offset compensation circuit 344 receives the output V S of the differential amplifier 342, charges one of the hold capacitors C O1 and C O2 , and outputs it to discharge the non-inverting input of the differential amplifier 343. .
  • the calculation means 40 outputs the reference voltage switching signal S refs to the offset compensation circuit 344, and switches the switches SW O1 and SW O2 . As shown in FIG. 33, the switches SW O1 and SW O2 are turned ON / OFF so that one is connected to the hold capacitor C O1 and the other is connected to the hold capacitor C O2 . As a result, a sample-and-hold circuit is configured in which the output of the differential amplifier 342 is charged and held in one of the hold capacitors C O1 and C O2 , and the comparison result with the output V S of the previous stage is output from the differential amplifier 343. Is done.
  • sampling is always performed in the order of P-side excitation ⁇ N-side excitation.
  • the polarity is alternately changed every excitation period.
  • N-side excitation ⁇ P-side excitation Set the polarity of the excitation to be started to be reversed.
  • the P-side excitation and the N-side excitation can be handled equally.
  • half-period excitation is generated an odd number of times in the excitation period.
  • FIG. 34A shows the timing of the excitation pattern
  • FIG. 34B shows the reference voltage switching signal S refs output from the calculation means 40
  • FIG. 34C shows the output V S of the differential amplifier 342 (ie, the offset compensation circuit 344)
  • (D) is the inverting input V refo of the differential amplifier 343 (ie, the output of the offset compensation circuit 344)
  • (e) is the output V OS of the differential amplifier 343
  • (f) is the calculation means 40.
  • the timing for sampling the detection signal is shown. In this example, it is assumed that there is an offset portion linearly inclined as shown in FIG. 34C in the output V S of the differential amplifier 342 which is an analog circuit.
  • the first half-cycle excitation is the reference excitation, and no signal sampling is performed as shown in FIG.
  • the output V refo of the offset compensation circuit 344 is offset because of sample hold.
  • the last voltage before a half cycle is output even in the idle period. This situation is shown in the table of FIG. If the excitation periods of PNP ⁇ NPN ⁇ PNP... Are expressed as 1, 2, 3,..., 2n,.
  • the voltage Vs in the k-th state is expressed as Vs (k).
  • differential amplification can be performed regardless of the offset component.
  • a half-cycle excitation is added to the pair of signals on the P-side excitation and the N-side excitation first as a reference excitation, so that a total of three half-cycle excitations are performed within the excitation period. . Further, since a half cycle may be added to the even number of times of excitation such as P ⁇ N ⁇ P ⁇ N, the total may be 5 or 7 times.
  • signal sampling is actually performed 2n times excluding the first reference excitation, and thus signal sampling is not performed at a rate of 1 / (2n + 1). Therefore, it is desirable to take n as large as possible from the viewpoint of efficiency. Therefore, it is preferable to perform sampling of the maximum number possible in a charge amount accumulated in the charge capacitor C C. Thereby, even if an offset occurs on either the P side or the N side, it can be effectively eliminated.
  • FIG. 36 is a circuit diagram of an analog reset circuit
  • FIG. 37 shows operation waveforms when continuous excitation is performed in this circuit.
  • 37A shows the input waveform of the analog detection signal
  • FIG. 37B shows the waveform of the reset signal AN_RES_T1
  • FIG. 37B shows the waveform of the reset signal AN_RES_T2.
  • the circuit in FIG. 36 has a sample hold circuit dedicated to P side excitation and N side excitation, respectively, as in FIG. 33.
  • Each sample hold circuit includes hold capacitors C 01 and C 02 and is operated via a switch. Connected to the non-inverting input of amplifier 343. The switch can be switched ON / OFF by a reset signal.
  • each analog switch shows a low state
  • the P side is connected to the non-inverting input side of the operational amplifier 343.
  • the hold capacitors C 01 and C 02 can be charged even during signal sampling.
  • the N-side excitation value before the half cycle is used as a reference
  • the P-side excitation before the half cycle is used.
  • the value of as a reference As a result, as shown in FIG. 37, one hold capacitor is charged during each A / D sampling period, and at the same time, the voltage of the other hold capacitor is maintained, thereby enabling a reference operation. (Modification)
  • FIG. 38 shows an example of such a driving method.
  • FIG. 38A when intermittent excitation of P ⁇ N ⁇ pause ⁇ P ⁇ N is performed, signal sampling is performed using the circuit of FIG. An output as shown in FIG. 38 (b) is obtained.
  • FIG. 38 (b) the number of excitations and the number of signal samplings are the same, so that unnecessary excitation current is eliminated and efficient excitation can be performed with low consumption.
  • FIG. 39 shows a waveform pattern in the case where odd-numbered half-period excitations such as P ⁇ N ⁇ P ⁇ pause ⁇ N ⁇ P ⁇ N are continued by this method as in FIG. Also in FIG. 39, (a) shows the timing of the excitation pattern, (b) shows the reference voltage switching signal S refs output by the computing means 40, (c) shows the output V S of the differential amplifier 342, and (d). Is the inverting input V refo of the differential amplifier 343, (e) is the output V OS of the differential amplifier 343, and (f) is the timing at which the computing means 40 samples the detection signal. Also in this example, it is assumed that the output V S of the differential amplifier 342 which is an analog circuit has a linearly inclined offset as shown in FIG. 39C.
  • the signal of the first one out of the odd number of half-period excitations is halved. Since the offset compensation circuit 344 has a gain, the gain is lowered because there is no signal before the half cycle in the first excitation after the pause period. Therefore, this can be dealt with by performing an operation with gain only for the first signal, or by performing an operation with the first signal set as P and N. For example, when an odd number of half-period excitations such as P ⁇ N ⁇ P ⁇ pause ⁇ N ⁇ P ⁇ N are continued as shown in FIG. 40 (a), each excitation period is shown in FIG. 40 (b). The low gains A and B appearing at the beginning of the signal are combined into one signal. This makes it possible to compensate for a gain that is halved, and it can be handled in the same way as an excitation signal for a normal half cycle.
  • the offset compensation method is not limited to the above method, and for example, offset compensation can also be realized by a method in which the output voltage of the amplifier 343 is fed back and used as an input reference. (converter)
  • FIG. 41 shows an example of a two-wire electromagnetic flow meter system in which a converter is connected to such a two-wire electromagnetic flow meter.
  • the converter 500 shown in this figure includes a step-up power supply 501, an insulation transformer 502, an insulation type switching control circuit 503, a current detection resistor 504, a voltage subtraction circuit 505, an insulation type pulse transformer 506, and an output circuit 507. Is provided.
  • the converter 500 converts the power received from the external DC power source DC through the power line PL by a switching method, and supplies the converted power to the two-wire electromagnetic flow meter 400 through the transmission line DL, while the two-wire electromagnetic flow rate.
  • the output current I O corresponding to the flow rate detected by the total 400 is converted into an output voltage V O and output from the output circuit as a 1-5 V voltage signal via the output line OL.
  • FIG. 42 shows an example of another two-wire electromagnetic flow meter system.
  • This converter 600 is a high-functional type provided with an integrated pulse alarm output that outputs an integrated pulse of flow rate in addition to a normal voltage output.
  • the converter 600 includes a step-up switching power supply 601, a current detection resistor 604, a voltage subtraction circuit 605, an A / D converter 608, a calculation unit 609, a DC / DC conversion circuit 602, and an F / V conversion circuit 610. And an integrated pulse alarm output circuit 611.
  • the converter 600 subtracts the additional voltage from the output current I O corresponding to the flow detected by the two-wire electromagnetic flow meter 400 by the voltage subtracting circuit 605, and then the A / D converter 608.
  • the A / D converted signal is sent to the calculation unit 609.
  • the calculation unit 609 calculates the flow rate based on the detected digital signal, and outputs the digital signal whose frequency is changed according to the flow rate to the F / V conversion circuit 610 and the integrated pulse alarm output circuit 611.
  • the F / V conversion circuit 610 performs frequency / voltage conversion and outputs a voltage signal of 1-5V corresponding to the flow rate.
  • the integrated pulse alarm output circuit 611 outputs the integrated value of the flow rate signal as a transistor output. Thereby, an alarm output is obtained based on the integrated value of the flow signal. (Amplifier mode switching function)
  • These two-wire electromagnetic flow meters can be switched to an amplifier mode in which an additional current is added in order to improve measurement accuracy in addition to the normal mode in which the output current I O is operated at 4-20 mA. Switching between the normal mode and the amplifier mode is performed by the amplifier mode switching means 33.
  • Amp mode switching unit 33 outputs the amp mode instruction signal S AP, instructs the switching of the normal mode and the amp mode.
  • an additional current of 20 mA is added to the output current in the amplifier mode.
  • the converter switches the output signal according to the presence / absence of the amplifier mode or ON / OFF.
  • the output voltage is subtracted by an additional voltage (for example, 5V) by the voltage subtracting circuit and insulated via the pulse transformer, and then the output circuit 1-5V, a voltage signal of 1-5V corresponding to the flow rate is output in both the normal mode and the amplifier mode.
  • FIG. 1 An example of a two-wire electromagnetic flow meter having such an amplifier mode switching function is shown in FIG.
  • the two-wire electromagnetic flow meter shown in this figure is connected to an external DC power source DC by a pair of transmission lines DL, and a current output circuit 16 is provided between the transmission lines DL.
  • the current output circuit 16 includes an operational amplifier A 6 and a transistor.
  • the current output circuit 16 is connected to the addition / subtraction instruction circuit 41.
  • the addition / subtraction instruction circuit 41 includes an operational amplifier A 7 and a resistor.
  • the switch SW 7 is connected to the inverting input of the operational amplifier A 7 via a resistor.
  • Switch SW 7 is switched to ON / OFF the amplifier mode instruction signal S AP output from the amplifier mode switching means 33 of the internal circuit.
  • the inverting input of the operational amplifier A 7 is connected to the internal circuit via a further resistor. As a result, the output current instruction signal SVO output from the internal circuit is input to the inverting side input side via the resistor
  • the internal circuit of FIG. 43 is designed to consume 4-20 mA in accordance with the flow rate range in the normal mode.
  • an additional current is added. In this case, for example, if 20 mA is simply added as an additional current, an instruction circuit that consumes 4-40 mA is required for the flow rate range, and the resolution is lowered.
  • the amplifier mode switch SW 7 by an amplifier mode instructing signal S AP is ON or OFF, to change the reference voltage of the subtraction instruction circuit 41.
  • the operation of the current output circuit 16 is switched to operate so that the output current I O changes in a range of 24-40 mA instead of 4-40 mA. In this way, the current offset can be added without reducing the resolution of the output current instruction signal SVO by the addition / subtraction instruction circuit 41 in the amplifier mode.
  • FIG. 44 shows an example of an excitation circuit having an excitation control function capable of controlling the excitation current and voltage corresponding to such an amplifier mode.
  • the excitation circuit 24 switches between three controls in order to realize a stable operation of the electromagnetic flow meter. That is, (1) the excitation current IE is switched. (2) The timing for switching the excitation voltage of the excitation coil 22 is switched. Here, the threshold value of the timing for switching the excitation voltage from V H to V L is switched by the excitation constant current circuit 29. (3) The voltage supplied to the exciting coil 22 is increased. In other words, the excitation current IE is changed. When the excitation current IE is changed, the residual voltage needs to be changed. As a result of changing the residual voltage, the charge voltage instruction signal V ref from the residual voltage detection circuit 180 to the charge charge monitor circuit 26 changes. And control charge charge monitoring circuit 26, changes the charge voltage command voltage V 2. As a result, the coil voltage V L increases. With such a configuration, the efficiency can be further improved by adjusting the excitation timing in addition to the switching operation to the amplifier mode. (Damping function)
  • this electromagnetic flow meter has a damping function to stabilize the signal.
  • damping is weighting of averaging in the moving averaging process or the like
  • FIG. 45 shows an outline of the damping process (averaging process).
  • the output value after the damping process for the input value is output as shown in FIG. 45 (c) when the input changes stepwise as shown in FIG. 45 (b). Is defined as the time to reach 63%.
  • FIG. 46 shows an example of an electromagnetic flow meter having such a damping function.
  • the electromagnetic flow meter 700 shown in this figure further includes a damping means 44 and an auto mode switching means 45, and is further connected to a setting unit 80 for performing these settings.
  • the damping means 44 is a member for performing a damping calculation based on the set damping amount.
  • the auto mode switching means 45 is a means for switching between manual mode and auto mode.
  • the setting unit 80 is a member that sets a damping amount, an auto mode switching timing, and the like, and includes a console, a display monitor, a communication port, and the like as necessary.
  • the damping unit 44 and the auto mode switching unit 45 are integrated with a calculation unit 40 that performs flow rate calculation.
  • the damping means 44 and / or the auto mode switching means 45 can be provided separately from the calculation means.
  • the damping unit 44 performs a damping process and the auto mode switching unit 45 can switch between a manual mode and an auto mode.
  • the manual mode is a mode in which the damping unit 44 maintains the damping amount for performing the damping calculation at a predetermined value
  • one auto mode is a mode in which the damping unit 44 changes the damping amount according to the flow rate. It is a mode to make it.
  • the electromagnetic flow meter can perform stable measurement by switching the damping amount from a fixed value to a variable value and increasing the damping amount by the automatic mode switching means 45 switching from the manual mode to the automatic mode according to the predetermined conditions. The result can be obtained.
  • this process will be described in detail. (Damping calculation)
  • the damping amount is typically a damping time constant indicating the time for performing the averaging process, and is variable in the range of 0.5 s to 30 s, for example.
  • the reference for making the damping amount variable that is, the timing for switching from the manual mode to the auto mode is determined by the auto mode switching means 45.
  • the reference for switching is an area where the damping process needs to be increased, and the flow rate, output current, etc. can be used. For example, when the calculated flow velocity is in the low flow velocity range (0 m / s to 0.5 m / s, etc.), the signal value is small, so stabilization is necessary. Even in the range where the analog output of the output current IO is 4 to 12 mA, the excitation current is small, so the detection signal is also small, and similarly stabilization by damping processing is necessary.
  • the auto mode and the manual mode may be switched at an arbitrary timing designated by the user.
  • the mode can be shifted to the auto mode, and the stability can be improved by increasing the damping amount as the flow rate decreases.
  • the damping amount increases, it is possible to reduce the averaging process and increase the responsiveness to changes in the flow rate, thereby making it possible to maintain both measurement accuracy and improve stability.
  • Fig. 49 shows an image for setting the damping.
  • a setting screen displayed on the monitor of the setting unit 80 is shown, and the user sets each item from the console. From this screen, the damping time constant in the manual mode can be switched between 0.5 s, 1.0 s, and 1.5 s as the setting of the damping amount that the damping means 44 performs the damping process. It is not limited to the selection of such a fixed value, but the user may be able to specify an arbitrary value.
  • the operation of the auto mode switching means 45 is selected from specified conditions (level 1, 2, 3, etc.). Each level is defined by, for example, a flow velocity value, an excitation current value, or the like. It is also possible to select the operation in the manual mode in which the auto mode is turned off, that is, the damping amount is maintained at a constant value without being limited to the flow velocity.
  • the span is a flow velocity or a flow rate when outputting 20 mA that is the maximum value of the analog output of the output current IO .
  • the user can also assign the auto mode switching threshold.
  • FIG. 50 shows an example of such a span setting and a change in analog output with respect to the flow velocity.
  • the analog output linearly changes from 4 mA to 20 mA from the flow velocity 0 toward the span flow velocity value.
  • Such a span can be set in units of a flow rate (m / s), a flow rate (L / min), a mass flow rate (kg / s), or the like.
  • An example of setting such a span is shown in FIG.
  • This example also shows a setting screen image of the setting unit 80 as in FIG.
  • a span is selected as a setting item, and the user can select a desired value from choices (for example, a flow rate of 500 L / min, a flow rate of 2 m / s, and a mass flow rate of 100 kg / h).
  • the electromagnetic flow meter, electromagnetic flow meter system, and electromagnetic flow meter converter of the present invention can be suitably applied as a capacitive electromagnetic flow meter that detects the flow rate of a conductive liquid in a non-wetted state.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Volume Flow (AREA)

Abstract

Selon l'invention, la limitation du courant consommé est supprimée, de façon à permettre une détection de flux de haute précision. À cet effet, l'invention porte sur un circuit de sortie de courant (16) destiné à régler la valeur de courant d'un courant de sortie Io en réponse au flux du flux cible pour la détection, calculée par un moyen de calcul ; un moyen de conversion courant/tension qui est connecté au circuit de sortie de courant (16) et qui peut convertir la valeur de courant du circuit de sortie de courant (16) en une tension et la délivrer en sortie à l'extérieur ; un moyen de commutation de mode d'amplificateur (33) qui peut délivrer en sortie un signal d'indication de mode d'amplificateur SAP au circuit de sortie de courant (16) et au moyen de conversion courant/tension, ledit signal SAP indiquant la commutation entre le mode normal, dans lequel la tension de sortie correspondant au débit de flux est prise comme signal de détection et est délivrée en sortie du moyen de conversion courant/tension aux lignes de transmission DL, et le mode d'amplificateur, qui ajoute le courant ajouté spécifié au courant de sortie Io pour la sortie ; et un circuit de suppression de tension pour éliminer de la tension de sortie la composante de tension ajoutée correspondant au courant ajouté, lorsque le moyen de conversion courant/tension reçoit le signal d'indication de mode d'amplificateur SAP à partir du moyen de commutation de mode d'amplificateur (33).
PCT/JP2009/060597 2008-06-20 2009-06-10 Dispositif de mesure de flux électromagnétique, système de mesure de flux électromagnétique, convertisseur pour dispositif de mesure de flux électromagnétique WO2009154110A1 (fr)

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Cited By (2)

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JP2016540985A (ja) * 2013-12-20 2016-12-28 ローズマウント インコーポレイテッド 動作設定値自動選定機能を有する電磁式流量計
CN113189389A (zh) * 2020-01-14 2021-07-30 西门子股份公司 一种电流传感器单元和电流检测电路

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JPH08285646A (ja) * 1995-04-18 1996-11-01 Hitachi Ltd 一体形電磁流量計
JPH09126849A (ja) * 1995-11-01 1997-05-16 Hitachi Ltd 二線式電磁流量計

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JP3131758B2 (ja) * 1994-07-05 2001-02-05 株式会社山武 電磁流量計用ディストリビュータ

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JPH08285646A (ja) * 1995-04-18 1996-11-01 Hitachi Ltd 一体形電磁流量計
JPH09126849A (ja) * 1995-11-01 1997-05-16 Hitachi Ltd 二線式電磁流量計

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Publication number Priority date Publication date Assignee Title
JP2016540985A (ja) * 2013-12-20 2016-12-28 ローズマウント インコーポレイテッド 動作設定値自動選定機能を有する電磁式流量計
US10641627B2 (en) 2013-12-20 2020-05-05 Rosemount Inc. Magnetic flowmeter with automatic operating setpoint selection
CN113189389A (zh) * 2020-01-14 2021-07-30 西门子股份公司 一种电流传感器单元和电流检测电路

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