JP5726558B2 - Electromagnetic flow meter - Google Patents

Description

  In the present invention, a magnetic flux that crosses the measurement flow path is generated by an exciting coil, and a potential difference generated between two points of the measurement flow path according to the magnetic flux density of the magnetic flux and the flow velocity of the fluid flowing in the measurement flow path is a pair. The present invention relates to an electromagnetic flowmeter that detects the flow rate of a fluid by detecting between the detection electrodes.

  Conventionally, as this type of electromagnetic flow meter, one that operates only with an internal power source (for example, a battery), one that operates only with an external power source (for example, a commercial power source or a constant current power source with 4-20 mA output), A device that operates on any one of external power sources is known (for example, Patent Document 1).

JP 2010-237113 A (FIGS. 1 to 3)

  By the way, in any type of electromagnetic flow meter described above, the higher the magnetic flux density of the magnetic flux generated by the exciting coil, the greater the detection voltage detected by the pair of detection electrodes, resulting in noise resistance. Improve measurement accuracy.

  However, the higher the magnetic flux density, the larger the exciting current that flows through the exciting coil and the higher the power consumption. Therefore, the exciting coil outputs a magnetic flux with a lower magnetic flux density than the maximum magnetic flux density that can be output to the exciting coil. Was set to do. For this reason, there are cases where sufficient measurement accuracy cannot be obtained in an environment that is susceptible to noise. In particular, an electromagnetic flow meter that can be operated with an internal power supply has a high need for power saving, and therefore has a problem that the magnetic flux density is set lower than that of an electromagnetic flow meter that operates only with an external power supply, and the measurement accuracy is also low. It was. In addition, it is more susceptible to noise when measuring the instantaneous flow rate per unit time than when measuring the integrated flow rate, and it is difficult to obtain sufficient measurement accuracy when measuring the instantaneous flow rate. there were.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an electromagnetic flow meter capable of measuring a flow rate with higher measurement accuracy than before.

In order to achieve the above object, an electromagnetic flowmeter according to the invention of claim 1 is configured to generate a magnetic flux crossing a measurement flow path in an exciting coil, and the magnetic flux density of the magnetic flux and the flow velocity of the fluid flowing in the measurement flow path. the potential difference between two points of the measurement flow path in accordance with the bets are detected by between a pair of sensing electrodes, an electromagnetic flowmeter for measuring the flow rate of a fluid, the external power connection connectable to an outside power source, When power is not received from the internal power supply and external power supply, magnetic flux is generated in the excitation coil by the power from the internal power supply to enter the power saving measurement mode, while power from the external power supply is received when receiving power from the external power supply. A power-related mode switching means for switching the excitation coil to generate a magnetic flux higher than the power saving measurement mode and setting the high accuracy measurement mode, an integrated flow measurement mode for measuring the integrated flow of the fluid passing through the measurement flow path, and measurement Instantaneous / integrated switching operation unit for switching to instantaneous flow rate measurement mode for measuring instantaneous flow rate, which is the flow rate per unit time of fluid passing through the passage, and receiving high-precision measurement from an external power source It is characterized in that it can be switched from the integrated flow rate measurement mode to the instantaneous flow rate measurement mode on condition that the mode is set.

The invention according to claim 2 is the electromagnetic flow meter according to claim 1 , wherein the main body case having a measurement flow path and holding a pair of detection electrodes accommodates the exciting coil and the internal power source, and the internal power source alone. A main unit that can measure the flow rate of fluid and an external unit that holds an external power supply connection in an external case that can be attached to and detached from the main body case. It is characterized in that power can be supplied from the external power source to the exciting coil by transformer coupling with the secondary coil.

According to a third aspect of the present invention, in the electromagnetic flowmeter according to the second aspect of the present invention, an external arithmetic processing circuit is provided that is housed in an external case and receives and operates from an external power source through an external power source connection portion, and is held by the main body case The flow rate measurement result can be given from the main unit to the external calculation processing circuit through the photocoupler composed of the light emitting element and the light receiving element held by the external case, and the external calculation processing circuit It is characterized in that a pulse output unit for externally outputting a pulse signal is held in an external case.

[Invention of Claim 1]
According to the configuration of the electromagnetic flow meter of claim 1, it is possible to switch between the power saving measurement mode in which the magnetic flux density of the magnetic flux generated by the exciting coil is relatively low and the high accuracy measurement mode in which the magnetic flux density is relatively high. Therefore, it becomes possible to measure the flow rate with higher measurement accuracy than the conventional one in which the magnetic flux density is set to be constant low.

Further , according to the configuration of the electromagnetic flow meter of claim 1, when the internal power supply having an upper limit for the total power supply is supplying power to the excitation coil, the power saving measurement mode is set, while the external power supply for the total power supply has no upper limit. When the power supply is supplying power to the excitation coil, it automatically switches to the high-accuracy measurement mode, so the usable period (life) of the internal power supply can be extended and the need for power saving is relatively low. The flow rate can be measured with high accuracy when the power supply is used.

  Whether the electromagnetic flow meter for switching between the power saving measurement mode and the high-accuracy measurement mode is equipped with a power saving switching operation switch, whether it is connected to an external power source, regardless of whether it is in the integrated flow rate measurement mode or the instantaneous flow rate measurement mode. Regardless, it may be switched to any one of the power saving measurement mode and the high-accuracy measurement mode according to the operation of the power saving switching operation switch.

Further, the electromagnetic flow meter according to claim 1 can switch from the integrated flow rate measurement mode to the instantaneous flow rate measurement mode on condition that the power is received from the external power source and is in the high accuracy measurement mode. In order to measure the instantaneous flow rate during use, the high-accuracy measurement mode is switched to greatly reduce the remaining capacity of the internal power supply, or the instantaneous flow rate is not measured with low accuracy during the power saving measurement mode. That is, it is possible to measure the instantaneous flow rate with high accuracy without greatly reducing the remaining capacity of the internal power supply.

[Invention of claim 2 ]
The electromagnetic flow meter according to claim 2 can be divided into a main unit having an internal power source and an external unit having an external power source connection portion. When the external flow source is not connected, the external unit is removed. The flow rate can be measured only with the main unit. In addition, power can be supplied between the main unit and the external unit by transformer coupling, so the main unit can be easily waterproofed and dust-proof, and noise from the external power supply to the main unit is reduced. Can be made.

[Invention of claim 3 ]
According to the configuration of claim 3 , the flow rate measurement result externally output by the electromagnetic flow meter is received by a device other than the electromagnetic flow meter, for example, monitoring of an abnormal flow rate, adjustment of a valve for adjusting the flow rate, etc. Can be used for processing. According to the third aspect of the present invention, the flow rate measurement result is given from the main unit to the external arithmetic processing circuit of the external unit through a photocoupler, and the external arithmetic processing circuit converts the flow rate measurement result into an electric pulse signal. Because it outputs to the outside, the waterproofing and dustproofing of the main unit can be easily achieved.

The block diagram of the electromagnetic flowmeter which concerns on 1st Embodiment of this invention. Time chart for explaining operation of electromagnetic flowmeter Block diagram of an electromagnetic flow meter according to the second embodiment Block diagram of electromagnetic flow meter according to modification

[First Embodiment]
Hereinafter, a first embodiment according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing the electrical configuration of the electromagnetic flow meter 10 of the present embodiment. The electromagnetic flow meter 10 includes a flow meter case 40 having a circuit housing chamber 42 on the side of the measurement tube 41. The inner side of the measurement pipe 41 is the measurement flow path 11 according to the present invention. Both ends of the measurement pipe 41 are connected to, for example, a pipe (not shown), and the fluid flowing through the pipe passes through the measurement flow path 11. In addition, the measurement tube 41 is held in a state where the pair of detection electrodes 12 and 12 penetrates, and the distal ends of the pair of detection electrodes 12 and 12 are exposed in the measurement flow channel 11 and the measurement flow channel. 11 are opposed to each other in a direction intersecting with 11 axial directions (fluid flowing directions). On the other hand, the base ends of the pair of detection electrodes 12, 12 are exposed in the circuit housing chamber 42 and connected to the main control circuit 16 via the amplifier circuit 15.

  In the circuit housing room 42, a pair of exciting coils 13 and 13 are arranged at positions facing each other with the measuring tube 41 interposed therebetween. The pair of excitation coils 13 and 13 are connected in series between a pair of output units in the excitation circuit 14 housed in the circuit housing room 42. Then, an exciting current that periodically reverses the exciting circuit 14 is applied to the exciting coils 13 and 13. Further, the excitation coils 13 and 13 are excited by a common excitation current to generate magnetic fluxes in the same direction, and the magnetic flux crosses the portion sandwiched between the detection electrodes 12 and 12 in the measurement channel 11. It has become. Thereby, a potential difference corresponding to the flow velocity of the fluid flowing through the measurement flow path 11 and the magnetic flux density of the magnetic flux is generated as a detection voltage between the pair of detection electrodes 12 and 12, and the detection voltage is generated by the amplifier circuit 15. Amplified and taken into the main control circuit 16. The main control circuit 16 calculates the flow velocity of the fluid passing through the measurement channel 11 from the acquired detection voltage and the magnetic flux density of the magnetic flux generated by the exciting coil 13, and the fluid flow rate of the measurement channel 11 is calculated as the flow velocity. Multiply the area to calculate the flow and output. If a display switch (not shown) provided in the electromagnetic flow meter 10 is turned on, the flow rate calculated by the main control circuit 16 can be visually recognized on the monitor 17 provided in the electromagnetic flow meter 10.

  Further, the electromagnetic flow meter 10 is provided with, for example, an instantaneous / integrated switching operation unit 35, and by operating the instantaneous / integrated switching operating unit 35, the integrated flow rate of the fluid passing through the measurement flow path 11 is determined. It is possible to switch between the integrated flow rate measurement mode for measuring and the instantaneous flow rate measurement mode for measuring the instantaneous flow rate that is the flow rate per unit time of the fluid passing through the measurement flow path 11. Specifically, in the instantaneous flow rate measurement mode and the integrated flow rate measurement mode, the instantaneous flow rate is calculated from the average value of the latest n measurement results. The value of n is set smaller in the instantaneous flow rate measurement mode than in the integrated flow rate measurement mode. For this reason, in the instantaneous flow rate measurement mode, for example, when a sudden abnormal value is measured due to noise, the calculated instantaneous flow rate is easily affected by the abnormal value. The average value may be obtained by simply averaging the latest n measurement results, or by performing an exponential averaging process based on the latest measurement results and the previous n-1 measurement results. You may go.

  The electromagnetic flow meter 10 includes first and second power supply circuits 21 and 22 and a battery 20A corresponding to the “internal power supply” of the present invention housed in a circuit housing chamber 42, and a power receiving connector 31 and a pulse signal. The output connector 32 and the 4-20 mA signal output connector 33 are provided on the outer surface of the flow meter case 40 as the “external power supply connection portion” according to the present invention.

  The second power supply circuit 22 includes one input unit and at least two output units. The second power supply circuit 22 receives a DC output from the external power supply 55 connected to the power receiving connector 31 and transforms it into a control DC voltage. While outputting from an output part, it converts into alternating current and outputs from the other output part.

  The first power supply circuit 21 includes two input units and at least two output units. The first power supply circuit 21 receives either DC output from the battery 20A or AC output from the second power supply circuit 22, and is controlled from one output unit. A DC voltage for output is output and a DC voltage for excitation and amplification is output from the other output section. Further, the AC output from the second power supply circuit 22 is taken into the first power supply circuit 21 via the transformer 24. Specifically, when receiving power from the external power supply 55 through the second power supply circuit 22 and the transformer 24, the first power supply circuit 21 cuts off the power receiving line from the battery 20A and uses the power from the external power supply 55. The control DC voltage and the excitation / amplification DC voltage are output. On the other hand, when the first power supply circuit 21 is not receiving power from the external power supply 55, it outputs only the control DC voltage using the power received from the battery 20A, and does not output the excitation / amplification DC voltage. Here, when the output voltage of the battery 20A is the first voltage, the excitation / amplification DC voltage output from the first power supply circuit 21 is a second voltage higher than the first voltage.

  The power receiving connector 31 can be connected to a connector of an external power source 55 which is a known constant current power source of 4-20 mA output, and receives 4-20 mA output of the external power source 55. The external power supply 55 corresponds to an “external power supply” according to the present invention, and operates by receiving power from a commercial power supply.

  The pulse signal output connector 32 is provided to output the flow rate measurement result by the electromagnetic flow meter 10 as an electrical pulse signal. The 4-20 mA signal output connector 33 is provided to output the flow rate measurement result by the electromagnetic flow meter 10 as a 4-20 mA current signal. In addition, in order to generate the electric pulse signal and the 4-20 mA current signal, a sub control circuit 26 is provided in the circuit accommodating room 42 separately from the main control circuit 16, and the sub control circuit 26 includes a second control circuit 26. It operates by receiving a control DC voltage from the power supply circuit 22 and acquires the output of the main control circuit 16 via the photocoupler 25. Then, the sub control circuit 26 converts the calculation result such as the flow rate obtained from the main control circuit 16 into a pulse signal according to the protocol with the external device 56 to which the pulse signal output connector 32 is connected. While outputting to the pulse signal output connector 32, it converts into a 4-20mA current signal according to the protocol with the external device 56 to which the 4-20mA signal output connector 33 is connected, and outputs a 4-20mA signal. Output to the connector 33. Note that the sub-control circuit 26 takes in the 4-20 mA output from the external power supply 55 through the power receiving connector 31 in order to generate a 4-20 mA current signal.

  When the electromagnetic flow meter 10 is not receiving power from the external power source 55, the electromagnetic flow meter 10 is in the power saving measurement mode according to the present invention, while in the state where power is being received from the external power source 55, it is in the high accuracy measurement mode according to the present invention. That is, the electromagnetic flow meter 10 is switched to either the power saving measurement mode or the high accuracy measurement mode depending on whether or not the power is supplied from the external power source 55. Specifically, either the battery 20A or the output part of the excitation / amplification DC voltage in the first power supply circuit 21 is selectively connected to the excitation circuit 14 via the switching circuit 18. ing. In addition, an amplifier circuit 15 is commonly connected together with the switching circuit 18 to the output part of the excitation / amplification DC voltage in the first power supply circuit 21. When the switching circuit 18 does not receive the excitation / amplification DC voltage from the first power supply circuit 21, the switching circuit 18 conducts between the switching circuit 18 and the battery 20A.

  Thus, when the electromagnetic flow meter 10 is not receiving power from the external power supply 55 (see the period from t0 to t1 in FIG. 2), the excitation circuit 14 switches the output voltage of the first voltage from the battery 20A at a predetermined cycle. When applied to the excitation coils 13, 13, a magnetic flux having a magnetic flux density B 1 (see FIG. 2) corresponding to the first voltage is generated across the measurement flow path 11. The amplifier circuit 15 amplifies the detection voltage between the detection electrodes 12 and 12 and applies it to the main control circuit 16 with a first gain corresponding to the output voltage of the first voltage from the battery 20A.

On the other hand, when the electromagnetic flow meter 10 is receiving power from the external power supply 55 (see the period from t1 to t3 in FIG. 2), the excitation circuit 14 outputs the output voltage of the second voltage from the first power supply circuit 21 for a predetermined period. And the magnetic flux having a magnetic flux density B2 (see FIG. 2) corresponding to the second voltage is generated across the measurement flow path 11. The amplifier circuit 15 amplifies the detection voltage between the detection electrodes 12 and 12 with a second gain corresponding to the output voltage of the second voltage from the first power supply circuit 21 and applies the amplified voltage to the main control circuit 16. The switching circuit 18, the first power supply circuit 21 and the excitation circuit 14 described above constitute “power-related mode switching means” according to the present invention.
Here, the present embodiment is configured to be able to switch from the integrated flow rate measurement mode to the instantaneous flow rate measurement mode on condition that power is received from the external power supply 55 and the high accuracy measurement mode is set. Thereby, in order to measure the instantaneous flow rate during use of the battery 20A, the remaining capacity of the battery 20A is not greatly reduced by switching to the high-accuracy measurement mode, or the instantaneous flow rate is not measured with low accuracy. That is, it is possible to measure the instantaneous flow rate with high accuracy without greatly reducing the remaining capacity of the battery 20A.

  The main control circuit 16 acquires a determination signal from the first power supply circuit 21 as to whether or not the first power supply circuit 21 is receiving power from the external power supply 55. Then, the calculation process for the case where the first power supply circuit 21 is not receiving power from the external power supply 55 and the calculation process for the case where the first power supply circuit 21 is receiving power from the external power supply 55 are switched to change the flow rate from the detected voltage. Is calculated. That is, the main control circuit 16 stores the values of the magnetic flux densities B1 and B2 and the values of the first and second gains. When the first power supply circuit 21 is not receiving power from the external power supply 55, the main control circuit 16 uses an arithmetic expression including the magnetic flux density B1 and the first gain, or for the magnetic flux density B1 and the first gain. The flow rate is obtained from the detection voltage using a correspondence map between the detection voltage and the flow rate set in advance. On the other hand, when the first power supply circuit 21 is receiving power from the external power supply 55, the main control circuit 16 is an arithmetic expression including the magnetic flux density B2 and the second gain, or for the magnetic flux density B2 and the second gain. The flow rate is obtained from the detection voltage using a correspondence map between the detection voltage and the flow rate set in advance.

  In the lowermost end portion of FIG. 2, a change in the 4-20 mA current signal output from the pulse signal output connector 32 of the electromagnetic flow meter 10 when the power saving measurement mode and the high accuracy measurement mode are switched. It is shown.

As described above, when the electromagnetic flow meter 10 of the present embodiment is operated by the battery 20A (internal power source) having an upper limit in the total supply of electric power, the magnetic flux density of the magnetic flux output from the exciting coils 13 and 13 is relatively low. In the power saving measurement mode with low power consumption, when operating with the external power supply 55 that has no upper limit on the total supply of power, the magnetic flux density of the magnetic flux output from the exciting coils 13 and 13 is relatively high, and high accuracy. Since it automatically switches to a high-accuracy measurement mode in which measurement is possible, the usable period (life) of the battery 20A can be extended, and the need for power saving is relatively low when using the external power supply 55. The flow rate can be measured with accuracy.
Here, especially when measuring the instantaneous flow rate of fluid, it is easily affected by sudden noise during measurement, and if the magnetic flux density is relatively low as in the prior art, it is difficult to measure accurately. . However, in the present embodiment, since the instantaneous flow rate can be measured in the high-accuracy measurement mode with a relatively high magnetic flux density, the instantaneous flow rate can be measured with high accuracy.
In addition, since the power from the external power supply 55 is applied to the first power supply circuit 21 through the transformer 24, noise from the external power supply 55 can be reduced. Further, since the electromagnetic flow meter 10 outputs the measurement result from the pulse signal output connector 32 and the 4-20 mA signal output connector 33 to the outside, the measurement result is received by the external device 56 other than the electromagnetic flow meter 10. For example, it can be used for processing such as monitoring of an abnormality in the flow rate and adjustment of a valve for adjusting the flow rate. Further, since the photocoupler 25 is provided between the main control circuit 16 and the pulse signal output connector 32 and the 4-20 mA signal output connector 33, the pulse signal output connector 32 and the 4-20 mA signal output connector 33 are provided. Even if noise is input, the main control circuit 16 is not affected.

[Second Embodiment]
The electromagnetic flow meter 10V of the present embodiment is shown in FIG. 3 and has a configuration in which the electromagnetic flow meter 10 of the first embodiment is divided into a main unit 10H and an external unit 10J. That is, the flow meter case 40V of the electromagnetic flow meter 10V is divided into a main body case 45 and an external case 46, and the external case 46 is detachably coupled to the main body case 45. In addition, the external power supply circuit 22 and the sub control circuit 26 described in the first embodiment, the primary coil L1 in the transformer 24, and the phototransistor T1 in the photocoupler 25 (the “light receiving element” of the present invention) are provided in the external case 46. The external unit 10J is configured by fixing the power receiving connector 31, the pulse signal output connector 32, and the 4-20 mA signal output connector 33 to the outer surface of the external case 46. . In addition, all electric components of the electromagnetic flow meter 10 that are not packaged in the external case 46, including the secondary coil L <b> 2 in the transformer 24 and the light emitting diode D <b> 1 in the photocoupler 25 (corresponding to “light emitting element” of the present invention) The circuit is packaged in the main body case 45 to constitute the main body unit 10H, and the main body unit 10H can measure the flow rate of the fluid only by the battery 20A. By combining the main unit 10H and the external unit 10J, the primary coil L1 and the secondary coil L2 are disposed adjacent to each other so that power can be supplied from the external unit 10J to the main unit 10H. D1 and the phototransistor T1 are disposed adjacent to each other so that a signal can be transmitted from the main unit 10H to the external unit 10J. The sub-control circuit 26 in the present embodiment corresponds to the “external arithmetic processing circuit” of the present invention.

  When the electromagnetic flow meter 10V of this embodiment is not connected to the external power supply 55, the flow rate can be measured only by the main unit 10H from which the external unit 10J is removed. In addition, since power can be supplied between the main unit 10H and the external unit 10J by the transformer coupling of the primary coil L1 and the secondary coil L2, the main unit 10H can be easily waterproofed and dustproof. Can do. In addition, since the flow rate measurement result is given from the main unit 10H to the external unit 10J through the photocoupler 25 including the light emitting diode D1 and the phototransistor T1, the main unit 10H can be easily waterproofed and dustproof. it can.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

(1) Like the electromagnetic flow meter 10X shown in FIG. 6, the secondary battery 20B is provided instead of the battery 20A of the first embodiment, the switching circuit 18 is excluded, and the output of the secondary battery 20B The excitation / amplification DC voltage output section in the first power supply circuit 21 may be commonly connected to the excitation circuit 14 and the amplification circuit 15. With this configuration, when the first power supply circuit 21 outputs the second voltage (when receiving power from the external power supply 55), the potential becomes higher than the first voltage of the secondary battery 20B. The first power supply circuit 21 is connected to the excitation circuit 14 and the amplifier circuit 15 and can charge the secondary battery 20B. When the first power supply circuit 21 does not output the second voltage (from the external power supply 55) Since the first voltage of the secondary battery 20B is higher than the output of the first power supply circuit 21 when the power is not being received, the secondary battery 20B is connected to the excitation circuit 14 and the amplifier circuit 15.

10, 10V, 10W, 10X, 10Y Electromagnetic flow meter 10H Main unit 10J External unit 11 Measurement flow path 12 Detection electrode 13 Excitation coil 14 Excitation circuit 16 Main control circuit 20A, 20B Internal power supply 24 Transformer 25 Photocoupler 26 Sub control circuit 35 Instantaneous / integration switching operation section 45 Body case 46 External case 55 External power supply L1 Primary coil L2 Secondary coil

Claims (3)

A magnetic flux that crosses the measurement flow path is generated by an exciting coil, and a pair of potential differences generated between two points of the measurement flow path are detected according to the magnetic flux density of the magnetic flux and the flow velocity of the fluid flowing through the measurement flow path. In an electromagnetic flowmeter that detects between the electrodes and measures the flow rate of the fluid,
An external power connection that can be connected to an external power source;
An internal power supply,
When not receiving power from the external power source, the magnetic flux is generated in the exciting coil with the power from the internal power source to enter the power saving measurement mode, while when receiving power from the external power source, Power-related mode switching means for switching the excitation coil to generate a magnetic flux higher than the power saving measurement mode and to be in a high accuracy measurement mode with power,
Switching between an integrated flow rate measurement mode for measuring the integrated flow rate of the fluid passing through the measurement flow path and an instantaneous flow rate measurement mode for measuring an instantaneous flow rate that is a flow rate per unit time of the fluid passing through the measurement flow path. And an instantaneous / total switching operation section for
An electromagnetic flow meter characterized in that it can be switched from the integrated flow rate measurement mode to the instantaneous flow rate measurement mode on condition that power is received from the external power source and the high-accuracy measurement mode is set. A main body unit comprising the measurement flow path and holding the pair of detection electrodes and housing the exciting coil and the internal power source, the main body unit capable of measuring the flow rate of the fluid only with the internal power source, An external unit that holds the external power supply connection portion in an external case that can be attached to and detached from the main body case, and a transformer coupling between a primary coil housed in the external case and a secondary coil housed in the main body case The electromagnetic flow meter according to claim 1, wherein power can be supplied from the external power source to the excitation coil. Provided in the external case, provided with an external arithmetic processing circuit that operates by receiving power from the external power source through the external power source connection part,
The flow rate measurement result can be given from the main body unit to the external arithmetic processing circuit through a photocoupler including a light emitting element held by the main body case and a light receiving element held by the external case, and the external attachment 3. The electromagnetic flow meter according to claim 2, wherein a pulse output unit is provided in the external case for the arithmetic processing circuit to externally output the flow rate measurement result as an electric pulse signal.

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