Empty pipe detection circuit and electromagnetic flowmeter

Abstract

The utility model discloses an empty pipe detection circuit and an electromagnetic flowmeter, the empty pipe detection circuit comprises an electromagnetic flow sensor, a filter circuit, a double operational amplifier in-phase input differential amplification circuit, an analog-to-digital conversion circuit, an MCU controller and an alarm circuit which are connected in sequence, and the empty pipe detection circuit also comprises a pulse signal conditioning circuit, the pulse signal conditioning circuit is provided with two signal input ends and two signal output ends, and the two pulse signal output ends of the MCU controller are connected with the two signal input ends of the pulse signal conditioning circuit in a one-to-one correspondence mode. The two signal output ends of the pulse signal conditioning circuit are connected with the signal output positive electrode end and the signal output negative electrode end of the electromagnetic flow sensor in a one-to-one correspondence mode, and the two pulse signal output ends of the MCU output two paths of complementary and symmetrical pulse signals. According to the utility model, the accuracy of the empty pipe state detection result of the electromagnetic flowmeter can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of flow detection, in particular to an empty pipe detection circuit and an electromagnetic flowmeter. Background Art

[0002] The electromagnetic flowmeter is an instrument that uses the principle of electromagnetic induction to measure the flow rate of conductive fluid based on the induced electromotive force generated when the conductive fluid passes through an external magnetic field.

[0003] The electromagnetic flowmeter detects the flow signal of the conductive fluid in the pipeline through the electromagnetic flow sensor. The flow signal output by the electromagnetic flow sensor is a weak alternating signal of microvolt to millivolt level, and the internal impedance of the signal is very high. The amplitude of the noise signal is much larger than the flow detection signal output by the electromagnetic flow sensor. Therefore, the flow signal needs to be filtered and amplified, and then output to the processor for flow conversion and analysis after analog-to-digital conversion.

[0004] When installing and using the electromagnetic flowmeter, it is necessary to ensure that the measuring pipe of the electromagnetic flowmeter is filled with the measured liquid. This is because when the measuring pipe is not full, the data detected by the electromagnetic flow sensor cannot correctly reflect the flow rate of the measured fluid. If the measuring electrode in the measuring pipe of the electromagnetic flow sensor is completely exposed to the air, the electromagnetic flow sensor will generate a large interference signal, and its output signal will have a large swing, which will seriously affect the normal use of the electromagnetic flowmeter.

[0005] In actual engineering measurement applications, it is difficult to ensure that the pipeline is always full of liquid. Therefore, real-time detection of empty pipe status and giving an alarm are crucial for the signal processing of the electromagnetic flowmeter.

[0006] Therefore, how to accurately detect the empty pipe status with electromagnetic flowmeter is a problem that needs to be solved urgently. Utility Model Content

[0007] In view of the defects in the prior art, the utility model aims to provide an empty pipe detection circuit and an electromagnetic flowmeter which can improve the accuracy of the empty pipe status detection result.

[0008] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0009] According to the first aspect of the utility model, the utility model provides an empty pipe detection circuit, including an electromagnetic flow sensor, a filter circuit, a dual operational amplifier in-phase input differential amplifier circuit, an analog-to-digital conversion circuit, an MCU controller, an alarm circuit and a pulse signal conditioning circuit, wherein:

[0010] The filter circuit has two signal input terminals and two signal output terminals. The two signal input terminals of the filter circuit are connected to the positive signal output terminal and the negative signal output terminal of the electromagnetic flow sensor in a one-to-one correspondence.

[0011] The dual operational amplifier common-phase input differential amplifier circuit has two signal input terminals and one signal output terminal. The two signal input terminals of the dual operational amplifier common-phase input differential amplifier circuit are connected to the two signal output terminals of the filter circuit in a one-to-one correspondence.

[0012] The signal input end of the analog-to-digital conversion circuit is connected to the signal output end of the differential amplifier circuit, the signal output end of the analog-to-digital conversion circuit is connected to the signal input end of the MCU controller, and the alarm signal output end of the MCU controller is connected to the signal input end of the alarm circuit.

[0013] The MCU controller has two pulse signal output terminals, which output two complementary and symmetrical pulse signals. The pulse signal conditioning circuit has two signal input terminals and two signal output terminals. The two pulse signal output terminals of the MCU controller are connected one-to-one with the two signal input terminals of the pulse signal conditioning circuit. The two signal output terminals of the pulse signal conditioning circuit are connected one-to-one with the signal output positive terminal and the signal output negative terminal of the electromagnetic flow sensor.

[0014] Preferably, the pulse signal conditioning circuit comprises a first pulse signal conditioning subcircuit and a second pulse signal conditioning subcircuit, wherein:

[0015] The first pulse signal conditioning subcircuit includes a first resistor, a second resistor, a third resistor, a first capacitor and a second capacitor, one end of the first resistor is connected to a pulse signal output end of the MCU controller, the other end of the first resistor is connected to one end of the second resistor and one end of the first capacitor, the other end of the second resistor is connected to one end of the second capacitor and one end of the third resistor, the other end of the third resistor and the other end of the first capacitor are grounded, and the other end of the second capacitor is connected to the signal output positive terminal of the electromagnetic flow sensor;

[0016] The second pulse signal conditioning subcircuit includes a fourth resistor, a fifth resistor, a sixth resistor, a third capacitor and a fourth capacitor, one end of the fourth resistor is connected to another pulse signal output end of the MCU controller, the other end of the fourth resistor is connected to one end of the fifth resistor and one end of the third capacitor, the other end of the fifth resistor is connected to one end of the fourth capacitor and one end of the sixth resistor, the other end of the sixth resistor and the other end of the third capacitor are grounded, and the other end of the fourth capacitor is connected to the signal output negative terminal of the electromagnetic flow sensor.

[0017] Preferably, the filtering circuit comprises a first RC low-pass filtering sub-circuit and a second RC low-pass filtering sub-circuit, wherein:

[0018] The first RC low-pass filter subcircuit includes a seventh resistor and a fifth capacitor, one end of the seventh resistor is connected to the signal output positive terminal of the electromagnetic flow sensor, the other end of the seventh resistor is connected to one end of the fifth capacitor and one input end of the dual operational amplifier in-phase input differential amplifier circuit, and the other end of the fifth capacitor is grounded;

[0019] The second RC low-pass filter sub-circuit includes an eighth resistor and a sixth capacitor, one end of the eighth resistor is connected to the signal output negative terminal of the electromagnetic flow sensor, the other end of the eighth resistor is connected to one end of the sixth capacitor and the other input end of the dual operational amplifier common-phase input differential amplifier circuit, and the other end of the sixth capacitor is grounded.

[0020] Preferably, the dual operational amplifier common-phase input differential amplifier circuit comprises a first operational amplifier, a second operational amplifier, a ninth resistor, a tenth resistor, an eleventh resistor and a twelfth resistor, wherein:

[0021] The non-inverting input terminal of the first operational amplifier is connected to a signal output terminal of the filter circuit, the inverting input terminal of the first operational amplifier is connected to one end of the ninth resistor and the tenth resistor, the other end of the ninth resistor is connected to the output terminal of the first operational amplifier and the signal input terminal of the analog-to-digital conversion circuit, the other end of the tenth resistor is connected to the output terminal of the second operational amplifier and one end of the eleventh resistor, the other end of the eleventh resistor is connected to the inverting input terminal of the second operational amplifier and one end of the twelfth resistor, and the other end of the twelfth resistor is connected to the reference voltage.

[0022] Preferably, the first operational amplifier and the second operational amplifier are both TLV2211 operational amplifiers.

[0023] Preferably, the ninth resistor, the tenth resistor, the eleventh resistor and the twelfth resistor are precision resistors with the same resistance value.

[0024] Preferably, the analog-to-digital conversion circuit includes an A / D converter, and the A / D converter is a low-noise analog-to-digital converter of model AD7193.

[0025] Preferably, the MCU controller adopts a single chip microcomputer of model MSP430F5418A.

[0026] According to the second aspect of the utility model, the present application provides an electromagnetic flowmeter, comprising the empty pipe detection circuit described in any one of the first aspects above.

[0027] The utility model filters out high frequency and stray useless interference signals in the flow detection signal output by the electromagnetic flow sensor through a filtering circuit, and amplifies the filtered weak flow detection signal through a dual operational amplifier in-phase input differential amplifier circuit, so that the weak flow detection signal is converted into a stable analog voltage signal and output to the analog-to-digital conversion circuit, and after the analog-to-digital conversion, it is converted into a digital signal that can be recognized by the processor of the electromagnetic flow meter and output to the MCU controller for subsequent flow analysis and processing;

[0028] By setting up an alarm circuit and a pulse signal conditioning circuit, when an empty pipe is detected, the two pulse signal output terminals of the MCU controller output two complementary and symmetrical pulse signals. The two pulse signals are regulated by the pulse signal conditioning circuit and output to the positive and negative signal output terminals of the electromagnetic flow sensor respectively. When the pipe is empty, the electrodes of the electromagnetic flow sensor are exposed to the air, and the electrode signals are in a suspended state. The two in-phase input terminals of the dual op amp in-phase input differential amplifier circuit have no DC bias, which will make the op amp output voltage unstable or saturated. When a pulse signal for empty pipe detection is applied, the dual op amp in-phase input The two operational amplifiers of the differential amplifier circuit will be in a saturated state, and the signal collected by the analog-to-digital conversion circuit is also saturated. When the electromagnetic flow sensor is in a full-pipe state, the two in-phase input terminals of the dual operational amplifier in-phase input differential amplifier circuit will have a DC bias. At this time, the operational amplifier works in an amplification state. Even if a pulse signal for empty pipe detection is applied, the operational amplifier will never reach a saturated state after voltage division and capacitor DC isolation filtering. The signal amplitude obtained when the pipe is empty can be clearly distinguished, thereby realizing accurate detection of the empty pipe state. When the empty pipe state is detected, the MCU controller controls the alarm circuit to output an alarm prompt signal.

[0029] In summary, the utility model can effectively improve the accuracy of the empty pipe state detection result of the electromagnetic flowmeter.

[0030] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation of the utility model or the technical solution in the prior art, the following is a brief introduction to the drawings required for the specific implementation or the prior art description. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0032] Figure 1 This is a circuit principle block diagram of an empty pipe detection circuit in one embodiment of the utility model;

[0033] Figure 2 It is a circuit schematic diagram of a pulse signal conditioning circuit in one embodiment of the utility model;

[0034] Figure 3 It is a circuit principle diagram of a filter circuit and a dual operational amplifier common-phase input differential amplifier circuit in one embodiment of the utility model. DETAILED DESCRIPTION

[0035] The following embodiments of the technical solution of the utility model are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the utility model, and are therefore only used as examples, and cannot be used to limit the protection scope of the utility model.

[0036] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by technicians in the field to which the utility model belongs.

[0037] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] In addition, the terms "first", "second", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0039] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this utility model can be understood according to specific circumstances.

[0040] In the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being “above”, “above”, and “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, and “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0041] like Figure 1-3 As shown, the embodiment of the utility model provides an empty pipe detection circuit, including an electromagnetic flow sensor 1, a filter circuit 2, a dual operational amplifier in-phase input differential amplifier circuit 3, an analog-to-digital conversion circuit 4, an MCU controller 5, an alarm circuit 6 and a pulse signal conditioning circuit 7, wherein:

[0042] The filter circuit 2 has two signal input terminals and two signal output terminals. The two signal input terminals of the filter circuit 2 are connected to the positive terminal and negative terminal of the signal output of the electromagnetic flow sensor 1 in a one-to-one correspondence.

[0043] The dual operational amplifier common-phase input differential amplifier circuit 3 has two signal input terminals and one signal output terminal. The two signal input terminals of the dual operational amplifier common-phase input differential amplifier circuit 3 are connected to the two signal output terminals of the filter circuit 2 in a one-to-one correspondence.

[0044] The signal input end of the analog-to-digital conversion circuit 4 is connected to the signal output end of the differential amplifier circuit, the signal output end of the analog-to-digital conversion circuit 4 is connected to the signal input end of the MCU controller 5, and the alarm signal output end of the MCU controller 5 is connected to the signal input end of the alarm circuit 6.

[0045] The MCU controller 5 has two pulse signal output terminals, and the two pulse signal output terminals of the MCU controller 5 output two complementary and symmetrical pulse signals. The pulse signal conditioning circuit 7 has two signal input terminals and two signal output terminals. The two pulse signal output terminals of the MCU controller 5 are connected one-to-one with the two signal input terminals of the pulse signal conditioning circuit 7, and the two signal output terminals of the pulse signal conditioning circuit 7 are connected one-to-one with the signal output positive terminal SIG+ and the signal output negative terminal SIG- of the electromagnetic flow sensor 1.

[0046] The empty pipe detection circuit of this embodiment filters out high frequency and spurious useless interference signals in the flow detection signal output by the electromagnetic flow sensor 1 through the filter circuit 2, and amplifies the filtered weak flow detection signal through the dual operational amplifier in-phase input differential amplifier circuit 3, so that the weak flow detection signal is converted into a stable analog voltage signal and output to the analog-to-digital conversion circuit 4, which is converted into a digital signal recognizable by the processor of the electromagnetic flowmeter after analog-to-digital conversion and output to the MCU controller 5 for subsequent flow analysis and processing;

[0047] By setting an alarm circuit 6 and a pulse signal conditioning circuit 7, when an empty pipe is detected, the two pulse signal output terminals of the MCU controller 5 output two complementary and symmetrical pulse signals, which are regulated by the pulse signal conditioning circuit 7 and output to the positive signal output terminal and the negative signal output terminal of the electromagnetic flow sensor 1 respectively. When the pipe is empty, the electrodes of the electromagnetic flow sensor 1 are exposed to the air, and the electrode signals are in a suspended state. The two in-phase input terminals of the dual operational amplifier in-phase input differential amplifier circuit 3 have no DC bias, which will make the operational amplifier output voltage unstable or saturated. When a pulse signal for empty pipe detection is applied, the dual operational amplifier in-phase output The two operational amplifiers input into the differential amplifier circuit 3 will be in a saturated state, and the signal collected by the analog-to-digital conversion circuit 4 is also saturated. When the electromagnetic flow sensor 1 is in a full-tube state, the two in-phase input terminals of the dual operational amplifier in-phase input differential amplifier circuit 3 will have a DC bias. At this time, the operational amplifier works in an amplification state. Even if a pulse signal for empty pipe detection is applied, after voltage division and capacitor DC isolation filtering, the operational amplifier will never reach a saturated state, and the signal amplitude obtained when the pipe is empty can be clearly distinguished, thereby realizing accurate detection of the empty pipe state. When the empty pipe state is detected, the MCU controller 5 controls the alarm circuit 6 to output an alarm prompt signal.

[0048] In one embodiment, the pulse signal conditioning circuit 7 includes a first pulse signal conditioning subcircuit 71 and a second pulse signal conditioning subcircuit 72, wherein:

[0049] The first pulse signal conditioning subcircuit 71 includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1 and a second capacitor C2, one end of the first resistor R1 is connected to a pulse signal output end of the MCU controller 5, the other end of the first resistor R1 is connected to one end of the second resistor R2 and one end of the first capacitor C1, the other end of the second resistor R2 is connected to one end of the second capacitor C2 and one end of the third resistor R3, the other end of the third resistor R3 and the other end of the first capacitor C1 are grounded, and the other end of the second capacitor C2 is connected to the signal output positive terminal of the electromagnetic flow sensor 1;

[0050] The second pulse signal conditioning subcircuit 72 includes a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a third capacitor C3 and a fourth capacitor C4, one end of the fourth resistor R4 is connected to another pulse signal output end of the MCU controller 5, the other end of the fourth resistor R4 is connected to one end of the fifth resistor R5 and one end of the third capacitor C3, the other end of the fifth resistor R5 is connected to one end of the fourth capacitor C4 and one end of the sixth resistor R6, the other end of the sixth resistor R6 and the other end of the third capacitor C3 are grounded, and the other end of the fourth capacitor C4 is connected to the signal output negative terminal of the electromagnetic flow sensor 1.

[0051] The first pulse signal conditioning subcircuit 71 and the second pulse signal conditioning subcircuit 72 condition the two complementary and symmetrical pulse signals output from the two pulse signal output terminals of the MCU controller 5 respectively and output them to the signal output positive terminal and the signal output negative terminal of the electromagnetic flow sensor 1 respectively, and then are processed by the filter circuit 2, the dual operational amplifier in-phase input differential amplifier circuit 3 and the analog-to-digital conversion circuit 4, and then the MCU controller 5 judges the signal state output by the analog-to-digital conversion circuit 4 to judge whether the operational amplifier of the dual operational amplifier in-phase input differential amplifier circuit 3 has reached the saturation stage, thereby judging whether the current state is an empty pipe state.

[0052] In one embodiment, the filter circuit 2 includes a first RC low-pass filter sub-circuit 21 and a second RC low-pass filter sub-circuit 22, wherein:

[0053] The first RC low-pass filter subcircuit 21 includes a seventh resistor R7 and a fifth capacitor C5, one end of the seventh resistor R7 is connected to the positive terminal of the signal output of the electromagnetic flow sensor 1, the other end of the seventh resistor R7 is connected to one end of the fifth capacitor C5 and one input end of the dual operational amplifier in-phase input differential amplifier circuit 3, and the other end of the fifth capacitor C5 is grounded;

[0054] The second RC low-pass filter sub-circuit 22 includes an eighth resistor R8 and a sixth capacitor C6, one end of the eighth resistor R8 is connected to the signal output negative terminal of the electromagnetic flow sensor 1, the other end of the eighth resistor R8 is connected to one end of the sixth capacitor C6 and the other input end of the dual operational amplifier in-phase input differential amplifier circuit 3, and the other end of the sixth capacitor C6 is grounded.

[0055] In this embodiment, the seventh resistor R7 and the fifth capacitor C5 as well as the eighth resistor R8 and the sixth capacitor C6 respectively constitute a low-pass filter circuit 2 for filtering out high-frequency and stray useless interference signals in the flow detection signal output by the electromagnetic flow sensor 1.

[0056] In one embodiment, the dual operational amplifier common-phase input differential amplifier circuit 3 includes a first operational amplifier U1, a second operational amplifier U2, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11 and a twelfth resistor R12, wherein:

[0057] The non-inverting input terminal of the first operational amplifier U1 is connected to a signal output terminal of the filter circuit 2, the inverting input terminal of the first operational amplifier U1 is connected to one end of the ninth resistor R9 and the tenth resistor R10, the other end of the ninth resistor R9 is connected to the output terminal of the first operational amplifier U1 and the signal input terminal of the analog-to-digital conversion circuit 4, the other end of the tenth resistor R10 is connected to the output terminal of the second operational amplifier U2 and one end of the eleventh resistor R11, the other end of the eleventh resistor R11 is connected to the inverting input terminal of the second operational amplifier U2 and one end of the twelfth resistor R12, and the other end of the twelfth resistor R12 is connected to the reference voltage Ref.

[0058] In this embodiment, the first operational amplifier U1 and the second operational amplifier U2 form a series dual operational amplifier with common-phase input and high common-mode rejection ratio differential amplifier circuit, so that the common-phase interference signal is suppressed.

[0059] In one embodiment, the first operational amplifier U1 and the second operational amplifier U2 are both operational amplifiers of model TLV2211. In the dual operational amplifier common-phase input differential amplifier circuit 3, a dual operational amplifier common-phase input high common-mode rejection ratio differential amplifier circuit composed of two micro-power single operational amplifiers TLV2211 is selected, which can well suppress the common-phase interference signal.

[0060] In one embodiment, the ninth resistor R9, the tenth resistor R10, the eleventh resistor R11 and the twelfth resistor R12 are precision resistors with the same resistance. The ninth resistor R9, the tenth resistor R10, the eleventh resistor R11 and the twelfth resistor R12 use precision resistors with the same resistance to ensure accurate matching of the circuit. These four precision resistors have a small temperature drift coefficient and good consistency, and can have a very high suppression ability for common-mode signals. At the same time, since the signal is input from the in-phase terminal of the operational amplifier, the circuit has a very high input impedance. Specifically, the ninth resistor R9, the tenth resistor R10, the eleventh resistor R11 and the twelfth resistor R12 use precision resistors with an accuracy of 0.1%.

[0061] In one embodiment, the analog-to-digital conversion circuit 4 includes an A / D converter, and the A / D converter uses a low-noise analog-to-digital converter of model AD7193. The AD7193 analog-to-digital converter is suitable for high-precision measurement and has low noise. It has a built-in PGA (programmable gain amplifier) ​​that can directly input small signals, so that the analog signal amplification factor of only about 200 can meet all measurement requirements.

[0062] In one embodiment, the MCU controller 5 uses a single-chip microcomputer of model MSP430F5418A. The MSP430 series single-chip microcomputer has rich internal resources and various analog circuit interfaces, low power consumption, and strong signal operation and processing capabilities, and is suitable for the new empty traffic detection circuit used in this invention.

[0063] An embodiment of the present application also provides an electromagnetic flowmeter, comprising the empty pipe detection circuit in any of the above embodiments.

[0064] It should be noted that, since the electromagnetic flowmeter includes the empty pipe detection circuit in the above embodiment, the electromagnetic flowmeter has the same working principle and technical effect as the empty pipe detection circuit in the above embodiment, which will not be repeated here.

[0065] In the specification of the present utility model, a lot of specific details are described. However, it is understood that the embodiments of the present utility model can be practiced without these specific details. In some examples, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this specification.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the utility model, and they should all be included in the scope of the claims and specification of the utility model.

Claims

1. An empty pipe detection circuit, characterized in that: It includes an electromagnetic flow sensor, a filter circuit, a dual operational amplifier common-phase input differential amplifier circuit, an analog-to-digital conversion circuit, an MCU controller, an alarm circuit and a pulse signal conditioning circuit, wherein: The filter circuit has two signal input terminals and two signal output terminals. The two signal input terminals of the filter circuit are connected to the positive signal output terminal and the negative signal output terminal of the electromagnetic flow sensor in a one-to-one correspondence. The dual operational amplifier common-phase input differential amplifier circuit has two signal input terminals and one signal output terminal. The two signal input terminals of the dual operational amplifier common-phase input differential amplifier circuit are connected to the two signal output terminals of the filter circuit in a one-to-one correspondence. The signal input end of the analog-to-digital conversion circuit is connected to the signal output end of the differential amplifier circuit, the signal output end of the analog-to-digital conversion circuit is connected to the signal input end of the MCU controller, and the alarm signal output end of the MCU controller is connected to the signal input end of the alarm circuit. The MCU controller has two pulse signal output terminals, which output two complementary and symmetrical pulse signals. The pulse signal conditioning circuit has two signal input terminals and two signal output terminals. The two pulse signal output terminals of the MCU controller are connected one-to-one with the two signal input terminals of the pulse signal conditioning circuit. The two signal output terminals of the pulse signal conditioning circuit are connected one-to-one with the signal output positive terminal and the signal output negative terminal of the electromagnetic flow sensor.

2. The empty pipe detection circuit according to claim 1, characterized in that: The pulse signal conditioning circuit comprises a first pulse signal conditioning subcircuit and a second pulse signal conditioning subcircuit, wherein: The first pulse signal conditioning subcircuit includes a first resistor, a second resistor, a third resistor, a first capacitor and a second capacitor, one end of the first resistor is connected to a pulse signal output end of the MCU controller, the other end of the first resistor is connected to one end of the second resistor and one end of the first capacitor, the other end of the second resistor is connected to one end of the second capacitor and one end of the third resistor, the other end of the third resistor and the other end of the first capacitor are grounded, and the other end of the second capacitor is connected to the signal output positive terminal of the electromagnetic flow sensor; The second pulse signal conditioning subcircuit includes a fourth resistor, a fifth resistor, a sixth resistor, a third capacitor and a fourth capacitor, one end of the fourth resistor is connected to another pulse signal output end of the MCU controller, the other end of the fourth resistor is connected to one end of the fifth resistor and one end of the third capacitor, the other end of the fifth resistor is connected to one end of the fourth capacitor and one end of the sixth resistor, the other end of the sixth resistor and the other end of the third capacitor are grounded, and the other end of the fourth capacitor is connected to the signal output negative terminal of the electromagnetic flow sensor.

3. The empty pipe detection circuit according to claim 1, characterized in that: The filter circuit includes a first RC low-pass filter subcircuit and a second RC low-pass filter subcircuit, wherein: The first RC low-pass filter subcircuit includes a seventh resistor and a fifth capacitor, one end of the seventh resistor is connected to the signal output positive terminal of the electromagnetic flow sensor, the other end of the seventh resistor is connected to one end of the fifth capacitor and one input end of the dual operational amplifier in-phase input differential amplifier circuit, and the other end of the fifth capacitor is grounded; The second RC low-pass filter sub-circuit includes an eighth resistor and a sixth capacitor, one end of the eighth resistor is connected to the signal output negative terminal of the electromagnetic flow sensor, the other end of the eighth resistor is connected to one end of the sixth capacitor and the other input end of the dual operational amplifier common-phase input differential amplifier circuit, and the other end of the sixth capacitor is grounded.

4. The empty pipe detection circuit according to claim 1, characterized in that: The dual operational amplifier common-phase input differential amplifier circuit comprises a first operational amplifier, a second operational amplifier, a ninth resistor, a tenth resistor, an eleventh resistor and a twelfth resistor, wherein: The non-inverting input terminal of the first operational amplifier is connected to a signal output terminal of the filter circuit, the inverting input terminal of the first operational amplifier is connected to one end of the ninth resistor and the tenth resistor, the other end of the ninth resistor is connected to the output terminal of the first operational amplifier and the signal input terminal of the analog-to-digital conversion circuit, the other end of the tenth resistor is connected to the output terminal of the second operational amplifier and one end of the eleventh resistor, the other end of the eleventh resistor is connected to the inverting input terminal of the second operational amplifier and one end of the twelfth resistor, and the other end of the twelfth resistor is connected to the reference voltage.

5. The empty pipe detection circuit according to claim 4, characterized in that: The first operational amplifier and the second operational amplifier are both TLV2211 operational amplifiers.

6. The empty pipe detection circuit according to claim 4, characterized in that: The ninth resistor, the tenth resistor, the eleventh resistor and the twelfth resistor are precision resistors with the same resistance value.

7. The empty pipe detection circuit according to claim 1, characterized in that: The analog-to-digital conversion circuit includes an A / D converter, and the A / D converter adopts a low-noise analog-to-digital converter of model AD7193.

8. The empty pipe detection circuit according to any one of claims 1 to 7, characterized in that: The MCU controller adopts a single chip microcomputer of model MSP430F5418A.

9. An electromagnetic flowmeter, characterized in that: The invention comprises the empty pipe detection circuit as described in any one of claims 1 to 8.

Images