CN105651348A - Excitation circuit for electromagnetic flow meter - Google Patents
Excitation circuit for electromagnetic flow meter Download PDFInfo
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- CN105651348A CN105651348A CN201610000813.XA CN201610000813A CN105651348A CN 105651348 A CN105651348 A CN 105651348A CN 201610000813 A CN201610000813 A CN 201610000813A CN 105651348 A CN105651348 A CN 105651348A
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- circuit
- switch drive
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- bridge circuit
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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
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Volume Flow (AREA)
Abstract
The invention discloses an excitation circuit for an electromagnetic flow meter. The excitation circuit comprises a constant current circuit, a sensing coil, an H-bridge circuit and an H-bridge circuit control loop; the constant current circuit provides a constant current for the sensing coil through the H-bridge circuit, all control signal output ends of the H-bridge circuit control loop are connected to all control ends of the H-bridge circuit respectively, and the two ends of the sensing coil are connected to the two output ends of the H-bridge circuit respectively; the constant current circuit is a switching-mode constant current circuit and comprises a switch driving chip, a starting circuit, a switch frequency selection circuit, an error amplification and compensation circuit and an output filtering circuit; the output end of the switch driving chip is connected to a positive input of the H-bridge circuit through the output filtering circuit, a negative input of the H-bridge circuit is grounded through a current sampling resistor, and the switch driving chip collects a current signal through the current sampling resistor, so that voltage input to the H-bridge circuit is variable direct voltage, and the current passing through the sensing coil is constant.
Description
Technical field
The present invention relates to electromagnetic flowmeter technology, particularly relate to electromagnet flow meter sensor coil and adopt switching mode constant current field circuit.
Background technology
Electromagnetic flowmeter is a kind of instrument for measuring fluid flow. Field circuit is the indispensable important component part of electromagnetic flowmeter, and its effect is to produce size and the controlled exciting current of sequential, carrys out stimulus sensor coil, thus producing magnetic field. Fluid is cutting magnetic line in the duct, produces induction electromotive force at signal electrode two ends, the size of induction electromotive force and magnetic induction, the flow velocity of fluid and direct ratio.
Existing electromagnetic flowmeter is all realize keeping magnetic field intensity constant by control exciting current, existing typical case's field circuit that electromagnetic flowmeter is adopted all includes power supply, constant-current source produces loop, and for controlling H bridge and the associated control circuitry thereof of the sense of current.
Fig. 2 is the one existing typical case field circuit that tradition electromagnetic flowmeter adopts, in this circuit, V+ is H bridge power supply is that cell winding is powered, VCC is that linear constant current circuit is powered, (Ai) being linear constant current source circuit in frame, operational amplifier U1, audion Q, current sampling resistor Ri, reference power supply source R1 and D1 form linear constant current source circuit together. Li1 is cell winding. Hi is H-bridge circuit part. U0 is H bridge control circuit. This traditional linear constant current mode, the method is due to all very big through the electric current of audion Q and the voltage drop at its two ends, and therefore power loss is very big. The method needs to use radiator, thus adding the overall power of system cost and circuit board size and electromagnetic flowmeter.
The China Patent No. is separately had to be: 201380013712.0, disclose the field circuit of a kind of electromagnetic flowmeter, switching circuit (11) is based on excitation signal (SA, SB), by diode (D1, D2) the driving electric current that will flow from current input terminal (Tin) to current output terminal (Tout) supplies to magnet exciting coil (L) switching as exciting current (Iex), charge-discharge circuit (13) charges to capacity cell (C) by the counter electromotive force of diode bridge (DB) self-excitation coil (L) in the future, (SW1 by high resistance to pressure condition, SW2), be consistent ground with the polarity of exciting current (Iex), the discharge current of self-capacitance element (C) supplies to magnet exciting coil (L) in the future.Thereby, it is possible to avoid the damage of the on-off circuit caused by high voltage, simultaneously effective utilize the counter electromotive force of magnet exciting coil, make the rising of exciting current quickly carry out. The constant-current circuit of above-mentioned patent adopts operational amplifier and transistor composition analog linearity constant-current circuit, it is very big that it deposits power loss equally, need to use radiator, heat produced by radiator can make circuit board temperature raise, circuit board performance is had certain impact, and owing to using radiator, circuit board size can increase, the holistic cost of its circuit design is high, it is crucial that owing to the overall power of electromagnetic flowmeter is increased greatly a lot by the useless power of loss.
Summary of the invention
In order to overcome the defect of above-mentioned prior art, the invention provides a kind of field circuit for electromagnetic flowmeter, its objective is that provide a kind of substitutes traditional linear model constant current circuit based on switching mode constant current circuit, thus eliminating the power loss using linear current source, and systematic function can be significantly improved.
In order to solve above-mentioned technical problem, the technical solution used in the present invention is:
Field circuit for electromagnetic flowmeter, including constant-current circuit, sensor coil, H-bridge circuit, H-bridge circuit controls loop, described constant-current circuit provides constant electric current by H-bridge circuit for sensor coil, each control signal outfan in described H-bridge circuit control loop is coupled with each control end of H-bridge circuit, the two ends of described sensor coil are coupled with two outfans of H-bridge circuit, it is characterized in that: described constant-current circuit is switch-mode constant current circuit, it includes switch drive chip, start-up circuit, switching frequency selection circuit, error amplifies compensation circuit, output filter circuit and booster circuit, the outfan of switch drive chip is connected to the positive input of H-bridge circuit by output filter circuit, the negative input of H-bridge circuit passes through current sampling resistor ground connection, switch drive chip gathers current signal by current sampling resistor, described start-up circuit one end is connected with switch drive chip, the other end is connected with earthing potential, described switching frequency selection circuit one end is connected with switch drive chip, the other end is connected with earthing potential, described error is amplified compensation circuit on one side and is connected with switch drive chip, the other end is connected with earthing potential, described booster circuit one end is connected with switch drive chip output pin, and the other end is connected with switch drive chip boosting pin.
Described start-up circuit includes starting resistance R1, R2, R3 and Zener diode D1, described startup resistance R1, R2, R3 connect, its one end is connected with starting power supply VCC, the other end is connected with earthing potential GND, 6 feet of switch drive chip are connected to startup between resistance R2, R3, the cathode terminal of described Zener diode D1 is connected to startup between resistance R1, R2, and the anode terminal of Zener diode D1 is connected with earthing potential GND.
Described switching frequency selection circuit includes selecting resistance R4, and described one end of selection resistance R4 is connected with 5 feet of switch drive chip, and the other end is connected with earthing potential GND.
Described error is amplified compensation circuit and is included compensating resistance R5 and compensating electric capacity C4, described compensation resistance R5 connecting with compensating electric capacity C4, and one end of compensation resistance R5 is connected with 2 feet of switch drive chip, and the other end compensating electric capacity C4 is connected with earthing potential GND.
Described output filter circuit includes output inductor L1 and output filter capacitor C1, one end of output inductor L1 and the positive input being connected to H-bridge circuit, one end of described output filter capacitor C1 is connected between output inductor L1 and the positive input of H-bridge circuit, the other end is connected with earthing potential GND, and 8 feet of switch drive chip are connected to output inductor L1.
Described booster circuit includes boost capacitor C2, described boost capacitor C2 and is connected between output pin 8 foot of switch drive chip and boosting pin 10 foot.
Also including power filtering capacitor C3, one end of described power filtering capacitor C3 is connected with 11 feet of switch drive chip, and the other end is connected with 12 feet of switch drive chip and earthing potential GND respectively.
The invention have the advantages that
1, the input voltage of switch-mode constant current of the present invention is direct voltage source, switch drive chip converts the direct voltage source of input to by the fixed frequency adjusted in circuit the switching voltage source output of corresponding frequencies, it is added to the voltage of H bridge input through output filter circuit and is similarly the voltage source of linear change, constant current loop feeds back to switch drive chip by the voltage signal that current sampling resistor acquisition is directly proportional to electric current to carry out the dutycycle of fixed frequency is adjusted, so that the current constant of cell winding is arrived in output, eliminate the power loss using linear current source.
2, the start-up circuit of the present invention, starting function for system electrification is to mono-electrifying startup signal of U1, makes normal circuit operation.
3, the 5 foot outer meeting resistance R4 of the switching frequency selection circuit of present invention circuit within U1 and U1 form oscillating circuit, and the size of R4 resistance value directly determines its frequency of oscillation value, is also equivalent to determine switching frequency size.
4, the error of the present invention amplifies compensation circuit, and its function is mainly used in compensating foreign current detection loop, accurately adjusts the dutycycle of fixed switching frequency so that output electric current is adjusted to desirable value.
5, the output filter circuit of the present invention is LC filter circuit construction form, it is bigger that its circuit advantage applies to load current, require the occasion that output voltage pulsation is less, switching frequency produced by U1 is significantly high, the driving electric current of cell winding is generally hundreds of milliampere, is therefore especially suitable for by this LC filter circuit construction form.
6, the electric capacity C3 of the present invention is the power filtering capacitor that U1 internal circuit is powered, the output that 11 feet are U1 internal low-voltage dropout regulator of U1, this pin is internal controller and drive circuit is powered, it is powered filtering so that it is the work that internal circuit is more reliable and more stable at an indirect electric capacity C3 of this pin Yu power supply ground.
7, the electric capacity C2 that states of the present invention is boost capacitor, forms booster circuit with switch drive chip internal circuits, and its effect is to realize high efficiency output when switch drive chip operation is when high duty ratio. It is connected to switch drive chip 8(SW) foot and 10(BST) between boost capacitor C2 and function critically important because it is related to light loading functional and the efficiency of whole circuit.
Accompanying drawing explanation
Fig. 1 is the electrical block diagram of the present invention;
Fig. 2 is the electrical block diagram of prior art.
Detailed description of the invention
Below in conjunction with accompanying drawing, invention is described further:
Embodiment 1
As shown in Figure 1, field circuit for electromagnetic flowmeter, field circuit is by constant-current circuit Ai, sensor coil Li1, H-bridge circuit Hi, H-bridge circuit controls loop U0 composition, constant-current circuit Ai provides constant electric current by H-bridge circuit Hi for sensor coil Li1, each control signal outfan of H-bridge circuit control loop U0 is coupled with each control end of H-bridge circuit Hi, the two ends of sensor coil Li1 are coupled with two outfans of H-bridge circuit Hi, to realize the electric current that H-bridge circuit Hi offer is constant.
Constant-current circuit Ai is switch-mode constant current circuit, it is by switch drive chip U1(or claims synchronous buck DC-DC regulator chip), start-up circuit, switching frequency selection circuit, error amplifies compensation circuit and output filter circuit, the outfan of switch drive chip U1 is connected to the positive input of H-bridge circuit Hi by output filter circuit, the negative input of H-bridge circuit Hi passes through current sampling resistor Ri ground connection, switch drive chip U1 gathers current signal by current sampling resistor Ri, start-up circuit one end is connected with switch drive chip U1, the other end is connected with earthing potential GND, described switching frequency selection circuit one end is connected with switch drive chip U1, the other end is connected with earthing potential GND, described error is amplified compensation circuit on one side and is connected with switch drive chip U1, the other end is connected with earthing potential GND. the input voltage of switch-mode constant current is direct voltage source, switch drive chip converts the direct voltage source of input to by the fixed frequency adjusted in circuit the switching voltage source output of corresponding frequencies, it is added to the voltage of H bridge input through output filter circuit and is similarly the voltage source of linear change, constant current loop feeds back to switch drive chip by the voltage signal that current sampling resistor acquisition is directly proportional to electric current to carry out the dutycycle of fixed frequency is adjusted, so that the current constant of cell winding is arrived in output
Start-up circuit is by starting resistance R1, R2, R3 and Zener diode D1, start resistance R1, R2, R3 series connection, after series connection, one end of R1 is connected with starting power supply VCC, one end of R3 connects ground potential GND, 6 feet (SS/TRK foot) of switch drive chip U1 are connected to startup between resistance R2, R3, the cathode terminal of Zener diode D1 is connected to startup between resistance R1, R2, the anode terminal of Zener diode D1 is connected with earthing potential GND, starting function for system electrification is to mono-electrifying startup signal of U1, makes normal circuit operation.
Switching frequency selection circuit includes selecting resistance R4, selects one end of resistance R4 to be connected with 5 feet (FREQ foot) of switch drive chip U1, and the other end is connected with earthing potential GND. The 5 foot outer meeting resistance R4 of switching frequency selection circuit circuit within U1 and U1 form oscillating circuit, and the size of R4 resistance value directly determines its frequency of oscillation value, is also equivalent to determine switching frequency size.
Error is amplified compensation circuit and is formed with compensation electric capacity C4 by compensating resistance R5, compensate resistance R5 and connect with compensating electric capacity C4, after series connection, the one end compensating resistance R5 is connected with 2 feet (COMP foot) of switch drive chip U1, the other end compensating electric capacity C4 is connected error amplification compensation circuit with earthing potential GND, its function is mainly used in compensating foreign current detection loop, accurately adjusts the dutycycle of fixed switching frequency so that output electric current is adjusted to desirable value.
Output filter circuit is made up of output inductor L1 and output filter capacitor C1, output inductor L1 connects with output filter capacitor C1, one end of output inductor L1 and the positive input being connected to H-bridge circuit Hi, one end of output filter capacitor C1 is connected between output inductor L1 and the positive input of H-bridge circuit Hi, the other end is connected with earthing potential GND, and 8 feet (SW foot) of switch drive chip U1 are connected to output inductor L1 and output. Output filter circuit is LC filter circuit construction form, it is bigger that its circuit advantage applies to load current, require the occasion that output voltage pulsation is less, switching frequency produced by U1 is significantly high, the driving electric current of cell winding is generally hundreds of milliampere, is therefore especially suitable for by this LC filter circuit construction form.
Boost capacitor C2, forms booster circuit with switch drive chip internal circuits, and its effect is to realize high efficiency output when switch drive chip operation is when high duty ratio. It is connected to switch drive chip 8(SW) foot and 10(BST) between boost capacitor C2 and function critically important because it is related to light loading functional and the efficiency of whole circuit.
Also including power filtering capacitor C3 in the present invention, one end of described power filtering capacitor C3 is connected with 11 feet (VCC foot) of switch drive chip U1, and the other end is connected with 12 feet (AGND foot) of switch drive chip U1 and earthing potential GND respectively. Electric capacity C3 is the power filtering capacitor that U1 internal circuit is powered, the output that 11 feet are U1 internal low-voltage dropout regulator of U1, this pin is internal controller and drive circuit is powered, it is powered filtering so that it is the work that internal circuit is more reliable and more stable at an indirect electric capacity C3 of this pin Yu power supply ground.
Above-mentioned beginning driving chip U1 is a fixed frequency, Controlled in Current Mode and Based, blood pressure lowering synchronous switching regulator, and the N-channel power MOSFET of its symmetrical complement being internally integrated can provide high conversion efficiency under middle and high load.
1 foot (FB) regulates input pin for sampling feedback, one electric current of outside need turning voltage sample resistance provides feedback regulation voltage VFB. for this pin
2 feet (COMP) error amplifier compensation pin, outside need series resistance and electric capacity are connected to ground.
3 feet (EN) are accurate enables pin, when this pin is high level, and chip operation; During for low level, chip quits work.
4 feet (PGOOD) are the good output identification pin of the effective power supply of high level, this pin output high level when chip normal operation exports, and when chip output is not in prescribed limit, pin becomes low level.
5 feet (FREQ) select pin for switching frequency, and working frequency of chip size thus pin outer meeting resistance value is determined.
6 feet (SS/TRK) are soft start/with following the tracks of input pin, and this pin external circuit has two kinds of connections and chip to power on normal to start connection and chip delayed starts connection, and this circuit adopts chip to power on and directly initiates connection. Delayed startup connection is connect a delay capacitor on the basis of this circuit connecting again on this pin, its effect is that to allow this pin power on be that voltage slowly rises, make its whole circuit power on stable after normal operation output again, this circuit advantage is that the surge voltage to output is little. This circuit does not adopt delayed to be a powering up directly initiating, it is because the H bridge of electromagnetic flowmeter to power on and be in off-state, output voltage is not had to be added to cell winding, its whole system powered on rear H bridge control loop just can export control signal turn it on can cell winding power, therefore its delayed startup method has little significance.
7 feet (PGND) are chip power ground pin, and this pin is directly connected with power supply ground.
8 feet (SW) switch output pin, and this pin inner portions connects the midpoint of the N-channel power MOSFET of symmetrical complement, and the mutual conduction of internal two MOSET makes its midpoint output high level and low level, reach switching frequency output purpose.
9 feet (VIN) power pins input, this pin is directly connected with positive source. Power for its whole circuit.
10 feet (BST) boost pin, and this pin uses ceramic condenser to be connected to SW foot, to form the floating power supply of upper end N-channel power MOSFET driver, improve delivery efficiency.
The output (output pin of interior voltage-stabilized power supply) of 11 feet (VCC) internal voltage regulator.
12 feet (AGND) simulation ground, this pin be control function internally, with power supply be connected.
Claims (7)
1. for the field circuit of electromagnetic flowmeter, including constant-current circuit, sensor coil, H-bridge circuit, H-bridge circuit controls loop, described constant-current circuit provides constant electric current by H-bridge circuit for sensor coil, each control signal outfan in described H-bridge circuit control loop is coupled with each control end of H-bridge circuit, the two ends of described sensor coil are coupled with two outfans of H-bridge circuit, it is characterized in that: described constant-current circuit is switch-mode constant current circuit, it includes switch drive chip, start-up circuit, switching frequency selection circuit, error amplifies compensation circuit, output filter circuit and booster circuit, the outfan of switch drive chip is connected to the positive input of H-bridge circuit by output filter circuit, the negative input of H-bridge circuit passes through current sampling resistor ground connection, switch drive chip gathers current signal by current sampling resistor, described start-up circuit one end is connected with switch drive chip, the other end is connected with earthing potential, described switching frequency selection circuit one end is connected with switch drive chip, the other end is connected with earthing potential, described error is amplified compensation circuit on one side and is connected with switch drive chip, the other end is connected with earthing potential, described booster circuit one end is connected with switch drive chip output pin, and the other end is connected with switch drive chip boosting pin.
2. the field circuit for electromagnetic flowmeter according to claim 1, it is characterized in that: described start-up circuit includes starting resistance R1, R2, R3 and Zener diode D1, described startup resistance R1, R2, R3 connect, its one end is connected with starting power supply VCC, the other end is connected with earthing potential GND, 6 feet of switch drive chip are connected to startup between resistance R2, R3, the cathode terminal of described Zener diode D1 is connected to startup between resistance R1, R2, and the anode terminal of Zener diode D1 is connected with earthing potential GND.
3. the field circuit for electromagnetic flowmeter according to claim 1, it is characterized in that: described switching frequency selection circuit includes selecting resistance R4, described one end of selection resistance R4 is connected with 5 feet of switch drive chip, and the other end is connected with earthing potential GND.
4. the field circuit for electromagnetic flowmeter according to claim 1, it is characterized in that: described error is amplified compensation circuit and included compensating resistance R5 and compensating electric capacity C4, described compensation resistance R5 connects with compensating electric capacity C4, the one end compensating resistance R5 is connected with 2 feet of switch drive chip, and the other end compensating electric capacity C4 is connected with earthing potential GND.
5. the field circuit for electromagnetic flowmeter according to claim 1, it is characterized in that: described output filter circuit includes output inductor L1 and output filter capacitor C1, one end of output inductor L1 and the positive input being connected to H-bridge circuit, one end of described output filter capacitor C1 is connected between output inductor L1 and the positive input of H-bridge circuit, the other end is connected with earthing potential GND, and 8 feet of switch drive chip are connected to output inductor L1.
6. the field circuit for electromagnetic flowmeter according to claim 1, it is characterised in that: described booster circuit includes boost capacitor C2, described boost capacitor C2 and is connected between output pin 8 foot of switch drive chip and boosting pin 10 foot.
7. the field circuit for electromagnetic flowmeter according to claim 1, it is characterized in that: also include power filtering capacitor C3, one end of described power filtering capacitor C3 is connected with 11 feet of switch drive chip, and the other end is connected with 12 feet of switch drive chip and earthing potential GND respectively.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201610000813.XA CN105651348A (en) | 2016-01-04 | 2016-01-04 | Excitation circuit for electromagnetic flow meter |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201610000813.XA CN105651348A (en) | 2016-01-04 | 2016-01-04 | Excitation circuit for electromagnetic flow meter |
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| CN105651348A true CN105651348A (en) | 2016-06-08 |
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| CN201610000813.XA Pending CN105651348A (en) | 2016-01-04 | 2016-01-04 | Excitation circuit for electromagnetic flow meter |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110998248A (en) * | 2017-08-09 | 2020-04-10 | 代傲表计有限公司 | Measuring device for determining a fluid parameter relating to a fluid and/or a fluid flow |
| CN113230540A (en) * | 2021-06-09 | 2021-08-10 | 黄翠娟 | Medical electrotherapy therapeutic instrument control circuit |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110998248A (en) * | 2017-08-09 | 2020-04-10 | 代傲表计有限公司 | Measuring device for determining a fluid parameter relating to a fluid and/or a fluid flow |
| CN113230540A (en) * | 2021-06-09 | 2021-08-10 | 黄翠娟 | Medical electrotherapy therapeutic instrument control circuit |
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Application publication date: 20160608 |
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