CN211978013U - Electromagnetic water meter circuit with high efficiency and small interference - Google Patents

Abstract

The utility model relates to an efficient electromagnetic water meter circuit that disturbs for a short time especially relates to excitation circuit design, power supply circuit design, include: the device comprises a current control voltage source high-efficiency excitation circuit, a power supply circuit without a negative power supply, an amplification and processing circuit for isolating polarization voltage, an A/D conversion circuit, an air traffic control detection circuit, an excitation voltage detection circuit and a coil current detection circuit; the invention can improve the excitation efficiency, reduce the excitation power consumption and the whole machine power consumption, simplify the power supply types, filter the polarization voltage interference, further reduce the battery consumption and improve the flow measurement precision.

Description

Electromagnetic water meter circuit with high efficiency and small interference

Technical Field

The utility model relates to an electromagnetic water meter and electromagnetic flow meter flow measurement field especially relates to excitation circuit design, power supply circuit design, adopts the utility model discloses can improve excitation efficiency, reduce electromagnetic water meter consumption, filtering polarization voltage interference, be applicable to the electromagnetic water meter of battery powered, adopt the utility model discloses can prolong electromagnetic water meter life-span, improve flow measurement accuracy.

Background

The electromagnetic water meter has many advantages when being used for measuring the flow velocity of fluid, compared with other water meters such as an ultrasonic water meter and a mechanical water meter, the electromagnetic water meter has the advantages of high metering precision, good linearity, wide range ratio, wear resistance, no temperature influence and the like, so the electromagnetic water meter is widely applied to the urban water supply industry and the agricultural irrigation industry; the principle of electromagnetic measurement of fluid flow is as follows: according to Faraday's law of electromagnetic induction, when a conductive fluid flows through a uniformly distributed magnetic field, an induced electromotive force proportional to the average velocity of the fluid can be detected on the electrodes of the conductor due to the action of cutting magnetic lines, and therefore, the volume flow is calculated according to the cross-sectional area of the pipeline by detecting the induced electromotive force; at present, there is excitation efficiency low, the complete machine consumption is big, mains voltage kind is many, polarization voltage to the great scheduling problem of signal influence in current electromagnetic water meter circuit, and in order to solve above-mentioned problem, my company has developed an efficient electromagnetic water meter detection circuitry that disturbs for a short time, adopts the utility model discloses a can improve excitation efficiency, reduce excitation consumption and complete machine consumption, simplify the mains kind, filtering polarization voltage interference further reduces the battery quantity, improves flow measurement accuracy.

Disclosure of Invention

The utility model aims at providing an efficient little electromagnetic water meter circuit of interference mainly is applicable to the electromagnetic water meter field of battery powered.

The utility model discloses a solve the technical scheme that its technical problem adopted and be:

the utility model provides an electromagnetic water meter circuit that high efficiency is little disturbed, by the high-efficient excitation circuit of current control voltage source, the power supply circuit of no negative power supply, the amplification and processing circuit of isolation polarization voltage, AD converting circuit, empty pipe detection circuitry, excitation voltage detection circuitry and coil current detection circuitry constitute characterized by: the current control voltage source high-efficiency excitation circuit generates a constant current to excite the sensor coil; the power supply circuit without a negative power supply mainly generates a stable power supply to supply power to the microprocessor, the remote computing amplifier and the like; the amplifying and processing circuit of the isolated polarization voltage filters and amplifies the induced electromotive force signal generated on the electrode; the A/D conversion circuit is used for converting the voltage signal output by the amplification and processing circuit of the isolation polarization voltage from an analog signal to a digital signal and transmitting the conversion result to the microprocessor, and the microprocessor calculates the flow according to the measured digital signal through a corresponding software algorithm; the empty pipe detection circuit is used for detecting whether the pipeline is full; an excitation voltage detection circuit that detects an excitation voltage; and a coil current detection circuit for detecting whether or not a current is present in the coil. The details are as follows:

1. the high-efficiency excitation circuit of the current control voltage source: the constant current source of the high-efficiency excitation circuit of the current control voltage source is used for sampling the voltage of a tiny precise resistor in the excitation circuit, converting the current into the voltage, amplifying the sampled voltage through a remote computing amplifier, inputting the amplified voltage to the feedback end of the DC-DC, controlling the output voltage of the DC-DC by the constant current source, and regulating the output current by regulating the output voltage so as to realize the constant current;

the excitation circuit mainly comprises a DC-DC integrated module U72, a power supply feedback circuit U73B, an H-bridge circuit Q710 and the like, a coil L and a micro sampling resistor R738, the DC-DC integrated module U72, the power supply feedback circuit U73B and the micro sampling resistor R738 form a constant current source, DC-DC output voltage is loaded on the excitation coil L through an H bridge, the DC-DC output voltage is adjusted in real time according to the sampling voltage to realize constant current, and the excitation voltage is low, the voltage utilization rate is high, so that the energy consumption is extremely low; according to the expression F = NI (N is the number of turns of the exciting coil, I is the exciting current) of the magnetic potential of the sensor, the current must be ensured to be constant in order to ensure that the magnetic potential is not changed according to a formula;

according to the constant-current excitation, the power supply voltage is variable, an adjusting switch is not required to be added, the DC-DC conversion efficiency reaches 95%, the excitation voltage is loaded on the coil by 98%, and the excitation efficiency is high; according to ohm's law

R is coil resistance, when the temperature rises, the coil resistance is increased, the coil current is reduced, the sampling voltage is reduced, the feedback voltage is reduced, and the DC-DC quickly adjusts the duty ratio to improve the excitation voltage V; when the temperature is reduced, the resistance of the coil is reduced, the current of the coil is increased, the sampling voltage is increased, the feedback voltage is increased, and the duty ratio of the DC-DC quick regulation is reducedAn excitation voltage V; through a feedback circuit and DC-DC dynamic adjustment, regardless of the change of R, the excitation voltage always changes in the same proportion with R in the same direction, and further the constant current is realized;

constant current source: the DC-DC integrated module U72, the voltage feedback circuit operational amplifier U73B and the like, the tiny sampling resistor R78 and the like form a constant current source, the voltage of the sampling resistor R738 is amplified by an operational amplifier and then input to a DC-DC feedback end, the voltage and the internal reference voltage Ref of the DC-DC integrated module are subjected to differential amplification and comparison processing, when the exciting current reaches a set value, the voltage amplified by the operational amplifier U73B is approximately equal to Ref, and the circuit enters a constant current state; when the exciting current is smaller than a set value, the amplified voltage of the U73B is smaller than Ref, the DC-DC module U72 adjusts the duty ratio to increase the output voltage, and the exciting current is increased; when the exciting current is larger than a set value, the voltage amplified by the U73B is larger than Ref, the DC-DC module U72 adjusts the duty ratio to reduce the output voltage, and the exciting current is reduced; the output voltage of the DC-DC module is regulated by innovatively utilizing a signal obtained by amplifying the voltage of the sampling resistor by the operational amplifier as feedback, constant current is realized by regulating the voltage, and the excitation efficiency is further improved;

h bridge circuit: the H bridge circuit is an H bridge switch composed of four field effect transistors Q710, Q711, Q714 and Q715, so that the tube voltage drop of a semiconductor device during conduction is reduced, heating is reduced, thermal stability is enhanced, and measurement accuracy is improved.

2. Power supply circuit without negative power supply

The power supply circuit without the negative power supply comprises main power supplies VCC and 1/2VCC reference power supplies, wherein the main power supply VCC is obtained by reducing the voltage of a lithium battery through a Low Dropout (LDO) linear voltage regulator, and the VCC mainly supplies power for the MCU and the operational amplifiers U86A and U86B; the reference power supply is firstly reduced by a main power supply VCC through a reference chip, then is input into a voltage follower after being divided by a high-precision low-temperature drift resistor, and 1/2VCC output by the voltage follower is used as a signal ground level in the whole signal amplification circuit;

the main power VCC is obtained by a battery voltage through a low-voltage drop linear regulator and mainly comprises a field effect transistor Q73, a resistor R73 and a LDO regulator U71, a 3.6V lithium battery is connected with the drain electrode of the field effect transistor Q73, the grid electrode of the Q73 is grounded through a resistor R73, the source electrode of the Q73 is connected with the 2-pin (VIN) input end of the low-voltage drop (LDO) U71 linear regulator, and the 3-pin (VOUT) is the output end which is the main power VCC;

reference power supply: the main power supply is firstly reduced in voltage through a high-precision and micro-power-consumption voltage reference chip Q81, then is divided into 1/2VCC 'through high-precision and low-temperature drift resistors R81 and R84, then 1/2VCC' voltage is input to the positive input end of a voltage follower U81, the voltage follower U81 outputs 1/2VCC to serve as a reference power supply of the whole signal circuit, and the voltage follower is adopted to effectively isolate front and rear voltages without mutual influence; the circuit innovatively takes 1/2VCC as an electrode reference power supply, and an induced electromotive force signal is automatically raised to 1/2VCC, so that negative induced electromotive force does not exist, the operational amplifier differentially amplifies the electromotive force signal without a negative power supply and outputs saturated electricity without exceeding an operational amplifier, and the whole circuit has no negative power supply and only one positive power supply, so that the whole power supply circuit is simple and efficient; the reference power supply mainly comprises a reference chip Q81, a voltage follower U81, R81, R84 and R86 and mainly provides a reference point for the signal amplification circuit.

3. Amplifying and processing circuit for isolating polarization voltage

The amplifying and processing circuit of the isolated polarization voltage is mainly used for filtering the polarization voltage and high-frequency interference in the induced electromotive force, then amplifying a useful flow signal and further converting the useful flow signal into an analog signal which can be effectively identified by the AD conversion circuit; the circuit mainly comprises an RC filter circuit, a voltage follower U81, operational amplifiers U86A and U86B, gain resistors R830, R831, R832 and R833 and a polarization voltage processing circuit; the flow signal induced by the sensor is the potential difference between electrodes, and the voltage obtained on the electrodes due to electromagnetic induction, electrostatic induction, electrochemical potential and the like is not only the electromotive force which is in direct proportion to the flow velocity, but also contains various interference components, so that the interference must be eliminated for correctly measuring the flow velocity, and the signal circuit mainly plays a role in filtering additional noise unrelated to the flow velocity and amplifying the flow signal into a signal which can be effectively collected by AD;

the working mode of the signal circuit is as follows: in the amplifying circuit, weak voltage signals output from two electrodes pass through a filter circuit composed of two stages of RC to filter high-frequency interference signals, and then are directly input into an A/D converter U31 after being amplified by a first-stage operational amplifier U86A and U86B to be subjected to A/D conversion, wherein the fundamental reason why the amplifying circuit only passes through first-stage amplification without multi-stage amplification is that: a polarization voltage processing circuit is arranged between the amplifiers, polarization voltage in the signals is main interference, and after the polarization voltage processing circuit effectively removes the polarization voltage, the residual signals are useful flow signals, so that the amplification factor can be directly enlarged, and the first-stage amplifier cannot be saturated;

the polarization voltage circuit is mainly used for eliminating electrode polarization voltage, and the reason why the polarization voltage is generated is as follows: when the metal electrode contacts with the measuring liquid, ions in the measuring medium move to the electrode, so that a certain potential is formed between the electrode and the measuring medium, and when the material or the surface state of the electrode is different, a polarization voltage is generated between the two electrodes; the depolarization circuit mainly comprises a resistor and a capacitor between the two operational amplifiers;

polarization voltage is doped in signals induced on the electrodes, and when the polarization voltage is larger, flow signals can be submerged, so that the flow signals are distorted, and flow measurement is inaccurate; when the polarization voltage is small, because the superposed polarization voltage is in drift variation, the output swing of the flow signal is also large, and how to reduce the polarization voltage becomes an important factor of the measurement accuracy of the instrument; this patent utilizes the characteristic of electric capacity "direct current of blocking to pass mutually", utilizes the electric capacity coupling to keep apart polarization voltage interference, then eliminates common mode interference through differential amplification to the polarization voltage has been eliminated under the condition that does not reduce input impedance.

4. A/D conversion circuit

The A/D conversion circuit mainly converts the analog signal to the digital signal of the voltage signal that the signal amplification circuit outputs, in order to the microprocessor calculates the flowrate through the corresponding software algorithm according to the digital signal obtained, its main composition is AD conversion chip U31, R32, R33, etc. make up, two routes of flowrate signal enter AD two differential inputs through R32, R33, AD convert the signal difference into the digital signal according to the reference voltage, transmit to microprocessor U91 through DOUT; A/D chip U31 selects 24 bit AD chip, the core part of the converter mainly comprises a ∑ A/D modulator module, a low-pass digital filter module and a decimator module, the basic principle is: the Δ ∑ modulator samples the analog input sampling signal in an oversampling manner, modulates the sampling value, outputs a one-bit encoded data stream reflecting the amplitude of the input signal, and performs decimation and low-pass digital filtering to remove noise to obtain a multi-bit encoded output.

5. Empty pipe detection circuit

In actual measurement, the pipeline is difficult to be ensured to be filled with fluid all the time, so that the real-time detection of the empty pipe state and the alarm information given by the microprocessor are of great importance to the signal processing of the electromagnetic flowmeter; completing empty tube detection according to different resistance values at two ends of the signal electrode in the full tube state and the empty tube state; the empty tube detection circuit mainly comprises two analog switches U82, U83, an operational amplifier U86A, U86B and an A/D conversion chip U31, wherein a pin 82 of a microprocessor and a pin 49 of the microprocessor are respectively connected with control pins of the two analog switches U82 and U83, when the pin 82 and the pin 49 of the microprocessor both output high levels during each detection, 5 pins (COM) and 6 pins (NO) of the two analog switches U82 and U83 are respectively connected, at the moment, a pin 51 of the microprocessor outputs high levels, a pin 50 outputs low levels, the next empty tube detection period, a pin 51 outputs low levels, a pin 50 outputs high levels (alternately outputting high and low levels mainly used for circuit signal balance), and the high levels and the low levels are loaded on the two electrodes after being subjected to resistance voltage division respectively to form two sampling loops; when the tube is empty, two electrodes without fluid in the tube are equivalent to open circuit, and a voltage of about dozens of mV is arranged between the electrodes; when the tube is full, the fluid in the tube is equivalent to a resistance of dozens of K, the voltage difference between the two electrodes is almost zero, the difference voltage of the two electrodes enters the AD conversion circuit through amplification, the tube is judged to be full when the AD difference is small, and the tube can be judged to be empty when the AD difference is large.

6. Excitation voltage detection circuit

The excitation voltage detection circuit mainly has the function of detecting whether the DC-DC output voltage is normal or not, and mainly comprises a resistor R720 and a 12-bit ADC in a microprocessor, when the excitation circuit works, the voltage of a micro sampling resistor R738 is amplified by operational amplifiers U86A and U86B and then input into the 12-bit ADC in the microprocessor for conversion processing, when the conversion result is lower than a judgment standard, the excitation voltage is low, when the conversion result is higher than the judgment standard, the excitation voltage is high, and only when the conversion result is in a judgment range, the excitation voltage is judged to be normal.

7. Coil current detection circuit

The coil current detection circuit is mainly used for detecting whether current passes through the coil or not and detecting whether the coil is broken or not; the circuit mainly comprises two analog switches U84 and U85, operational amplifiers U86A and U86B, R825, R826, R827, R828 and an A/D converter, two ends of the excitation coil are respectively connected with a resistor R826, R827 in series, when excited, the two ends of the coil are passed by current, and can produce a pulse voltage of several hundred mv, and said pulse signal can be introduced into output end of operational amplifier U86A or U86B by means of analog switch, when U84 directs the coupled signal to the output of amplifier U86A, U85 is turned off, so that one coupled signal and one normal signal are input to the AD through R32 and R33, respectively, when the AD conversion result is larger, the coil is proved to have current passing through, when the AD conversion result is smaller, the coil is proved to have no current, because the coil current detection does not need real-time detection, therefore, the detection is only needed once when the system is powered on, and the detection is only needed once every a period of time (such as 24 hours) after the system is powered on; when the excitation signal alternates direction, U84 and U85 alternately conduct.

8. The coil current detection, the empty pipe detection and the flow detection are carried out in a time-sharing mode and are not interfered with one another.

The utility model has the advantages that:

(1) constant-current control excitation voltage source, high excitation efficiency and low power consumption

In the excitation circuit, the excitation voltage converted from DC-DC is loaded on the excitation coil, and the constant current is realized by directly adjusting the excitation voltage.

(2) No negative power supply, no high-frequency interference

The circuit innovatively takes 1/2VCC as an electrode reference signal, and leads an induced electromotive force signal to be automatically raised to 1/2VCC, so that the operational amplifier amplifies the electromotive force signal in a differential mode under the condition that a negative power supply is not needed and does not exceed the output saturation voltage of an operational amplifier, and simultaneously, the digital power supply and an analog power supply are combined into a whole through ingenious design, so that the whole circuit has no negative power supply and only one positive power supply, and the whole power supply circuit is simple and efficient. The traditional negative power supply of the electromagnetic power supply is generated based on DC-DC, the voltage of the negative power supply can be superposed with a high-frequency ripple wave caused by the on and off of a switching power supply, the frequency of the negative power supply is equal to the working frequency of the DC-DC and generally fluctuates by 30-200 mv, and the power supply can be directly loaded on the negative power supply of the operational amplifier, so that large noise can be generated on a circuit, the stable work of the operational amplifier is influenced for the first time, and the final measurement result is influenced by the superposition of the power supply into an induction signal, so that the small-flow measurement precision of the electromagnetic water meter is reduced. This patent induced electromotive force is with 1/2VCC as the benchmark, and is undulant near 1/2VCC, so this circuit does not need the negative supply, and signal positive supply VCC is battery voltage and obtains through LDO simultaneously, so this patent power ripple is little, the noise is low, no high frequency interference.

(3) Depolarization of signals

This patent utilizes the characteristic of electric capacity "blocking direct traffic", can guarantee that flow signal passes through, can be with polarization voltage filtering again, and the circuit that depolarizes can eliminate the polarization and disturb, keeps the instrument error stable for a long time.

(4) Analog power supply normally open

Because the power consumption of the electromagnetic detection circuit is extremely low, the power supply of an analog device of the excitation and signal detection part is normally open, and the consistency of the measurement precision in a normal use state and a calibration state is ensured; the electromagnetic instrument has two working states, a calibration state and a normal use state, the traditional circuit method simulates the normal open of a device power supply in the calibration state, and ensures that the measurement performance is optimal in the calibration state, the simulation device power supply is only opened in the normal use state (one time after ten seconds, if the power consumption of the simulation power supply is large), the measurement precision is greatly deviated due to the fact that the power supply is opened normally and opened in the use, the precision of the instrument in the normal use can not be ensured, because the power consumption of the electromagnetic detection circuit is extremely low, the excitation and signal detection part can be ensured to be normally opened, the error caused by the power switch is eliminated, and the measurement precision is improved; in addition, the conventional power supply is frequently started to cause voltage fluctuation and interference, so that measurement is unstable.

Drawings

Fig. 1 and fig. 2 are the utility model relates to an efficient electromagnetic water meter circuit schematic diagram with small interference.

Fig. 3 is a schematic diagram of a conventional constant current excitation circuit.

Fig. 4 is a typical DC-DC schematic.

Detailed Description

The technical solution of the present invention will be described in further detail with reference to the following embodiments, and the scope of the present invention is not limited by the following statements.

In the present patent, some parameters, such as a voltage value, a current value, etc., are introduced for the purpose of explaining the problem, and these are introduced only for convenience of explaining the problem, and in the implementation process, parameters, such as an excitation current, an excitation voltage, a power supply voltage, etc., of the present circuit may be adjusted according to parameters, such as different calibers, range ratios, etc., but the present patent should also be protected as long as the circuit or the similar structure of the present patent is adopted.

Referring to fig. 1 and 2, an electromagnetic water meter circuit with high efficiency and low interference is composed of a current control voltage source high-efficiency excitation circuit a, a power supply circuit B without a negative power supply, an amplification and processing circuit C, AD conversion circuit D for isolating polarization voltage, an empty pipe detection circuit E, an excitation voltage detection circuit F, a coil current detection circuit G and the like.

1. High-efficiency excitation circuit of current control voltage source

The constant current source of the high-efficiency excitation circuit of the current control voltage source is characterized in that the current is converted into voltage by sampling the voltage of a tiny precise resistor in the excitation circuit, the sampled voltage is amplified by a remote computing amplifier and then input to a feedback end of a DC-DC, the output voltage of the DC-DC is proportional to the excitation current, and the output voltage is adjusted to adjust the output current, so that the constant current is realized.

In the traditional constant-current excitation, the power supply voltage is constant, in order to realize constant current, a regulating switch is designed in a circuit, the regulating switch reserves allowance for the resistance change of a coil and the voltage change of a battery, and part of excitation energy is consumed on the regulating switch, so that the efficiency is reduced, and the energy consumption is wasted.

According to the constant-current excitation, the power supply voltage is variable, an adjusting switch is not required to be added, the DC-DC conversion efficiency reaches 95%, the excitation voltage is loaded on the coil by 98%, and the excitation efficiency is high;

the current electromagnetic water meter mostly adopts a constant current excitation mode, namely, the current added to an excitation coil is constant current, and the excitation current is constant current when the voltage of a battery fluctuates and the resistance of the coil fluctuates, but the circuit has the defects that: the constant current excitation reserves allowance for the change of the resistance value of the coil (the temperature affects the resistance of the coil) and the voltage fluctuation of the battery, thereby wasting the power consumption and reducing the efficiency;

traditional constant current excitation: fig. 3 is a schematic diagram of a conventional constant current excitation, and the main working principle is as follows: sampling is carried out through a sampling resistor, negative feedback is input into an operational amplifier, the constancy of coil current is realized through the adjustment of the operational amplifier on a G pole of a field effect transistor, the coil current is constant, the magnetic potential can be constant, and a constant magnetic field can be obtained.

The traditional constant-current excitation working mode is as follows: according to ohm's law

(R is coil resistance, R 'is adjusting switch resistance), when the temperature rises, the coil resistance R becomes large, and the impedance R' is reduced by adjusting the G pole of the field effect transistor by the operational amplifier; when the temperature decreases, the coil resistance R becomes smallThe impedance R' is increased by adjusting the G pole of the field effect transistor through the operational amplifier; when V is not changed, R + R' is always kept unchanged through dynamic adjustment of the adjusting switch, so that constant current is kept.

The traditional constant current excitation circuit causes the current in the excitation coil to be not constant due to the change of the resistance value of the excitation coil (influenced by temperature) and the fluctuation of the voltage of a battery, and needs to additionally introduce electronic elements such as an MOS (metal oxide semiconductor) tube and the like to adjust the resistance, so that the current in the excitation coil is always kept constant, and the traditional constant current excitation circuit has the following problems:

(1.1) the traditional constant-current excitation reserves allowance for battery voltage fluctuation, so that power consumption is wasted, and efficiency is reduced; for example, as shown in fig. 4, the regulated voltage of the MOS transistor is different at different excitation voltages, the electromagnetic instrument is powered by a lithium-thionyl chloride battery, the working voltage of the battery is generally 3.0V to 3.6V, and the battery cannot support the normal operation of the instrument when the working voltage is lower than 3.0V under a standard load. From 3.0V to 3.6V, the MOS tube reserves 0.58V allowance for battery voltage fluctuation, namely consumes 0.58V voltage, which is about 0.58V/3.6V =16% of battery voltage, namely consumes 16% of excitation energy;

(1.2) the constant-current excitation circuit reserves adjustment allowance for the temperature change of the coil resistor, so that power consumption is wasted; the following table shows that the consumption voltage of the MOS tube is different at different temperatures, the temperature is from 0 ℃ to 40 ℃, the resistance of the coil changes by 16%, and the MOS tube reserves 0.36V allowance for the fluctuation of the battery voltage, namely, the voltage of 0.36V is adjusted, the battery voltage accounts for 0.36V/3.6V =10%, and the excitation energy of 10% is consumed.

The utility model discloses an in order to solve above-mentioned problem, adopted a mode of new constant current excitation, both all voltages all load to excitation coil in, realize the constant current through adjusting excitation voltage.

The excitation circuit of the utility model comprises four parts (1), a DC-DC excitation power supply (2), an H bridge (3) and a micro sampling resistor (4) voltage feedback circuit; the DC-DC outputs a stable excitation power supply, the excitation power supply is completely loaded to the excitation coil and the tiny sampling resistor through the H bridge, the sampling voltage is amplified and output to the feedback end of the DC-DC by the voltage feedback circuit, and the DC-DC adjusts the output voltage according to the feedback voltage, so that constant current is realized; fig. 4 is a typical DC-DC schematic diagram of the present patent, and it is the idea of the present patent that parameters and the like are slightly changed as long as the principle of constant current excitation by a current control voltage source is adopted, and the present patent shall be protected.

The specific working principle is as follows:

according to ohm's law

R is coil resistance, when the temperature rises, the coil resistance is increased, the coil current is reduced, the sampling voltage is reduced, the feedback voltage is reduced, and the DC-DC quickly adjusts the duty ratio to improve the excitation voltage V; when the temperature is reduced, the resistance of the coil is reduced, the current of the coil is increased, the sampling voltage is increased, the feedback voltage is increased, and the DC-DC rapid regulation duty ratio reduces the excitation voltage V; through a feedback circuit and DC-DC dynamic adjustment, regardless of the change of R, the excitation voltage is always changed in the same proportion with R in the same direction, and further the constant current is realized.

The patent innovatively utilizes the low-power-consumption high-efficiency synchronous buck converter DC-DC to output the excitation voltage, when an excitation circuit works, the voltage of a sampling resistor R738 is amplified by an operational amplifier U73B and then is compared with the internal reference voltage of a DC-DC module U72, when the voltage amplified by the operational amplifier U73B is less than 0.5V, the DC-DC module U72 adjusts the duty ratio to increase the output voltage, when the voltage is more than 0.5V, the DC-DC module U72 adjusts the duty ratio to reduce the output voltage, which is also the core principle of constant-current excitation, 1V excitation voltage and a coil 50 omega are taken as examples for explanation, when the coil resistance is 50 omega, the excitation voltage is 1V, the excitation current is 20mA, when the coil resistance is increased to 55 omega by temperature, the excitation voltage is simultaneously and rapidly adjusted to increase to 1.1V, the excitation current is still 20mA, under the condition that the current is kept constant, and adjusting the excitation voltage to ensure that the excitation voltage and the resistance in the excitation circuit are changed in the same proportion and the same direction.

The excitation circuit of the patent has the following characteristics:

(1) the DC-DC conversion efficiency is high; the low-power-consumption high-efficiency synchronous buck converter DC-DC integrated module is selected, the conversion efficiency reaches 95%, the input voltage can be as low as 1.2V and as high as 5V, the working range of the battery voltage can be completely covered (taking a lithium-thionyl chloride battery as an example, the working range of the battery voltage is 3.0V-3.6V), and meanwhile, the electric quantity of the battery can be used up to the limit; the DC-DC module is a synchronous pulse width converter, integrates N-channel and P-channel MOSFET switches, improves the efficiency of synchronous rectification and reduces the count of external elements.

(2) The constant-current excitation efficiency is high, and the power consumption is low; only excitation coil and a small sampling resistor in this patent circuit, excitation voltage more than 98% load to the coil on, because it is the regulated voltage to realize the constant current, in addition need not the electronic regulating switch among the excitation circuit, so the required excitation voltage of circuit is extremely low, and this patent excitation voltage high-usage, so the consumption is minimum.

(3) The constant current excitation solves the problem of battery voltage fluctuation; the constant-current excitation power supply is obtained by reducing the voltage of the DC-DC, the fluctuation of the voltage of the battery cannot influence the output voltage because the output voltage is far lower than the voltage of the battery, namely when the voltage of the battery is 3.6V, the DC-DC outputs stable 1V excitation voltage (taking 1V excitation as an example), and when the voltage of the battery is reduced to 3.0V, the DC-DC still keeps stable 1V output so as to ensure the normal work of an excitation circuit.

The constant-current excitation working mode of the patent is as follows: as shown in fig. 1, in the excitation circuit, a sampled voltage is connected to a forward input end of an operational amplifier U73B, amplified by an operational amplifier U73B and resistors R727 and R729, and then input to a pin 5 (FB) of a DC-DC module U72, the pin 5 (FB) of the DC-DC module U72 is connected to a collector of a triode Q76(PNP) through a resistor R714, one path of a base of the triode Q76 is connected to a collector of the Q72 through a resistor, and is connected to a pin 9 (SW) of the DC-DC module U72 through an inductor L71, a base of the triode Q72(PNP) is connected to a pin 48 (output high level) of a microprocessor through a resistor R75, an output of the operational amplifier U73B is connected to a pin 96 (a 1) of the microprocessor through a resistor R720, and a 12-bit ADC processing inside the microprocessor is utilized, thereby completing detection of the entire excitation voltage; the high level output by the pin 6 of the microprocessor is input to the positive input end of a comparator U73A after voltage division through a precision resistor R723 and a precision resistor R724, one path of the output end of the comparator U73A is grounded through a resistor R725, the other path is connected to the grid of a field effect transistor Q718, and one path of the drain of the Q718 is grounded through resistors R726 and R729; the other path is connected to the reverse input end of the operational amplifier U73B through a resistor R727; in the excitation power supply circuit, on one hand, the voltage drop on the sampling resistor is amplified by using the operational amplifier, and on the other hand, the voltage drop on the sampling resistor is amplified and then used as feedback to regulate output voltage, so that the precision is further improved;

in the H-bridge circuit, an H-bridge switch is composed of four MOS transistors Q710, Q711, Q714 and Q715; the four MOS tubes control the on and off of the H bridge switch; the excitation coil of the sensor is connected with the diagonal line of the bridge switch, when the pin 2 of the microprocessor is at a high level and the pin 4 of the microprocessor is at a low level or the pin 2 of the microprocessor is at a low level and the pin 4 of the microprocessor is at a high level; exciting current passes through two diagonal MOS tubes, a coil L and a sampling resistor R738 respectively; the voltage of the sampling resistor R738 is amplified and then input to the FB end of the excitation power supply, and the output excitation voltage is regulated, so that a closed-loop feedback loop is formed, and constant-current excitation current is achieved.

The essence of the patent is that constant current negative feedback is carried out on a DC-DC voltage source, so that voltage variable excitation is realized, and the circuit is slightly modified but has the same essence as the circuit and also belongs to the protection scope of the patent.

2. Power supply circuit without negative power supply

As shown in fig. 1, the power supply of this patent includes a main power supply and a reference power supply, and is described by taking the main power supply as 2.8V and the reference power supply as 1.4V as an example, the 2.8V main power supply is obtained by passing a battery voltage through a low dropout regulator U71, a 3.6V lithium battery is connected to the drain of a P-channel fet Q73, the gate of Q73 is grounded through a resistor, the source is connected to a 2-pin (VIN) input terminal of a Low Dropout (LDO) regulator U71, a 3-pin (VOUT) is used as an output terminal, and the main power supply mainly supplies power to a microprocessor U91, an operational amplifier U86, an AD chip U31, and the like.

Reference power supply: the 2.8V main power supply is firstly reduced to 1.6V through a high-precision and micro-power-consumption voltage reference chip Q81, then the voltage is divided into 1.4V through high-precision and low-temperature drift resistors R81 and R84, then the 1.4V voltage is input into the positive input end of a voltage follower U81, the voltage follower outputs 1.4V to be used as the reference power supply of the whole electromagnetic detection circuit, and the voltage follower is adopted to effectively isolate the front voltage and the rear voltage without influencing each other; the circuit innovatively takes 1.4V as an electrode reference signal, and an induced electromotive force signal is automatically raised to 1.4V, so that the operational amplifier differentially amplifies the electromotive force signal without exceeding an operational amplifier to output saturated electricity under the condition of not needing a negative power supply, the whole circuit has no negative power supply, and only one positive power supply is provided, so that the whole power supply circuit is simple and efficient.

The following table shows the type of the power supply of the conventional electromagnetic circuit, including a positive power supply and a negative power supply of an amplifying circuit, because the induced electromotive force of the conventional circuit is based on 0V, and the induced electromotive force is a differential signal with equal magnitude and opposite polarity, the induced electromotive force will drift up and down near the zero point, and the circuit needs to add a negative power supply to amplify the negative induced electromotive force.

The traditional negative power supply of the electromagnetic power supply is generated based on DC-DC, the voltage of the negative power supply can be superposed with a high-frequency ripple wave caused by the on and off of a switching power supply, the frequency of the negative power supply is equal to the working frequency of the DC-DC and generally fluctuates by 30-200 mv, and the power supply can be directly loaded on the negative power supply of the operational amplifier, so that large noise can be generated on a circuit, the stable work of the operational amplifier is influenced for the first time, and the final measurement result is influenced by the superposition of the power supply into an induction signal, so that the small-flow measurement precision of the electromagnetic water meter is reduced.

This patent induced electromotive force is with 1/2VCC as the benchmark, and is undulant near 1/2VCC, so this circuit does not need the negative supply, and signal positive power VCC is battery voltage and obtains through LDO simultaneously, and this patent power ripple is little, the noise is low, and interference immunity is strong.

3. Amplifying and processing circuit for isolating polarization voltage

The amplifying and processing circuit of the isolated polarization voltage is mainly used for filtering the polarization voltage and high-frequency interference in the induced electromotive force, then amplifying a useful flow signal and further converting the useful flow signal into an analog signal which can be effectively identified by AD (analog-to-digital);

the flow signal induced by the sensor is the potential difference between electrodes, and the voltage obtained on the electrodes due to electromagnetic induction, electrostatic induction, electrochemical potential and the like is not only the electromotive force which is in direct proportion to the flow velocity, but also contains various interference components, so that the interference must be eliminated for correctly measuring the flow velocity, and the signal circuit mainly plays a role in filtering additional noise unrelated to the flow velocity and amplifying the flow signal into a signal which can be effectively collected by AD;

the working mode of the signal circuit is as follows:

the positive and negative signals are respectively filtered by RC and then enter the positive input ends of operational amplifiers U86A and U86B, according to the principle of 'virtual short' break, the negative input of U86A is equal to the positive input, the negative input of U86B is equal to the positive input, a polarization voltage processing circuit H is arranged between the two negative input ends and mainly comprises a capacitor and a resistor, because the signal voltage is alternating current and the polarization voltage is direct current, the polarization voltage is isolated by utilizing the characteristic of the capacitor 'blocking direct current and alternating current', the signals pass through the polarization voltage processing circuit, the flow signals are amplified by operational amplifiers U86A, U86B, gain resistors R833, R831, R832, R829 and R830 and are directly input into an A/D converter U31 for A/D conversion, and the fundamental reason that the amplification circuit only carries out one-stage amplification without multistage amplification is that: a polarization voltage processing circuit is arranged between the amplifiers, polarization voltage in signals is main interference, and after the polarization voltage processing circuit effectively removes the polarization voltage, residual signals are useful flow signals, the amplification factor can be directly enlarged, and primary amplifier saturation cannot be caused.

This patent utilizes the characteristic of electric capacity "direct current of blocking to pass mutually", utilizes the electric capacity coupling to keep apart polarization voltage interference, then eliminates common mode interference through differential amplification to the polarization voltage has been eliminated under the condition that does not reduce input impedance.

4. A/D conversion circuit

A 3 pin of the microprocessor is connected with a CLK pin to be used as a system clock signal control line; pin 2 is connected with SCLK pin as serial clock signal control line; the 4 pin is connected with the DOUT pin and used for receiving serial output data converted by the A/D converter; pins 5 and 6 are connected with a MUX0 pin and a MUX1 pin respectively and used as input channel signal control lines; two input signals of the A/D converter are connected with pins AINP1 and AINN1, and the result of the A/D converter is transmitted to the microprocessor through DOUT.

5. Empty pipe detection circuit

Pin 82 of the microprocessor and pin 49 of the microprocessor are respectively connected with pin 1 (IN) of the two analog switches, and pin 5 (COM) and pin 6 (NO) of the two analog switches are respectively switched on when pin 82 and pin 49 of the microprocessor both output high level during each detection; at the moment, a pin 51 of the microprocessor outputs a high level, a pin 50 outputs a low level, the next empty pipe detection period, the pin 51 outputs a low level, the pin 50 outputs a high level (alternately outputting the high and low levels which are mainly used for balancing circuit signals), and the high level and the low level are respectively loaded on two electrodes after being subjected to voltage division by resistors to form two sampling loops; when the tube is empty, two electrodes without fluid in the tube are equivalent to open circuit, and a voltage of about dozens of mV is arranged between the electrodes; when the tube is full, the fluid in the tube is equivalent to a resistance of dozens of K, the voltage difference between the two electrodes is almost zero, the difference voltage of the two electrodes enters the AD conversion circuit through amplification, the tube is judged to be full when the AD conversion difference is small, and the tube can be judged to be empty when the AD difference is large.

Meanwhile, in order to prevent the interference of the empty pipe pulse signal on flow measurement, the empty pipe detection and the flow detection are carried out in a time-sharing mode, and when the flow detection is carried out, the empty pipe detection is closed; when empty pipe detection is performed, flow detection is turned off.

6. Excitation voltage detection circuit

After the voltage of the sampling resistor R738 is amplified by the operational amplifier U73B, one path of the voltage is sent to the feedback end of the DC-DC module U72, and the other path of the voltage is sent to a 96 pin (A1) of the microprocessor through a resistor R720, and the feedback voltage is detected by utilizing a 12-bit ADC in the microprocessor.

When the AD conversion result is lower than the set standard, the excitation voltage is low, when the AD conversion result is higher than the set standard, the excitation voltage is high, and when the detection result is abnormal, the MCU gives an alarm in real time and displays the alarm on the liquid crystal display screen.

7. Coil current detection circuit

The coil current detection circuit is mainly used for detecting whether current passes through the coil, whether the coil is open or short-circuited, and the specific working mode is as follows:

as shown in FIG. 1, two ends of the exciting coil are respectively connected with a resistor R826 and a resistor R827 in series to couple hundreds of mv pulse signals on the exciting coil, when the analog switch U84 guides the coupled signals into the amplifying circuit, the analog switch U85 is closed, so that two paths of signals are input into the AD through R32 and R33, when the AD conversion result is large, the coil is proved to have current passing, and when the AD conversion result is small, the coil is proved to have no current.

When the excitation signal alternates direction, U84 and U85 alternately conduct.

The current control voltage source high-efficiency excitation circuit comprises a current control voltage source high-efficiency excitation circuit, a power supply circuit without a negative power source, an amplification and processing circuit for isolating polarization voltage, an AD conversion circuit, an air traffic control detection circuit, an excitation voltage detection circuit, a coil current detection circuit and other circuits, wherein the current control voltage source high-efficiency excitation circuit and the power supply circuit without the negative power source are core circuits, other circuits are matched with the core circuits for use, and form a system with the core circuits.

The above is a specific implementation mode of the circuit of each part of the electromagnetic water meter circuit with high efficiency and small interference.

Claims (9)

1. The utility model provides an electromagnetic water meter circuit that high efficiency is little disturbed, by the high-efficient excitation circuit of current control voltage source, the power supply circuit of no negative power supply, the amplification and processing circuit of isolation polarization voltage, AD converting circuit, empty pipe detection circuitry, excitation voltage detection circuitry and coil current detection circuitry constitute characterized by: the current control voltage source high-efficiency excitation circuit generates a constant current to excite the sensor coil; the power supply circuit without a negative power supply mainly generates a stable power supply to supply power to the microprocessor and the remote computing amplifier; the amplifying and processing circuit of the isolated polarization voltage filters and amplifies the induced electromotive force signal generated on the electrode; the A/D conversion circuit is used for converting the voltage signal output by the amplification and processing circuit of the isolation polarization voltage from an analog signal to a digital signal and transmitting the conversion result to the microprocessor, and the microprocessor calculates the flow according to the measured digital signal through a corresponding software algorithm; the empty pipe detection circuit is used for detecting whether the pipeline is full; an excitation voltage detection circuit that detects an excitation voltage; and a coil current detection circuit for detecting whether or not a current is present in the coil.

2. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the constant current source of the high-efficiency excitation circuit of the current control voltage source is used for sampling the voltage of a tiny precise resistor in the excitation circuit, converting the current into the voltage, amplifying the sampled voltage through a remote computing amplifier, inputting the amplified voltage to the feedback end of the DC-DC, controlling the output voltage of the DC-DC by the constant current source, and regulating the output current by regulating the output voltage so as to realize the constant current;

the excitation circuit mainly comprises a DC-DC integrated module U72, a power supply feedback circuit U73B, an H-bridge circuit Q710, a coil L and a micro sampling resistor R738, the DC-DC integrated module U72, the power supply feedback circuit U73B and the micro sampling resistor R738 form a constant current source, DC-DC output voltage is loaded on the excitation coil L through an H bridge, the DC-DC output voltage is adjusted in real time according to the sampling voltage to realize constant current, and the excitation voltage is low, the voltage utilization rate is high, so that the energy consumption is extremely low; according to the expression F = NI of the magnetic potential of the sensor, N is the number of turns of the excitation coil, I is the excitation current, and the current must be ensured to be constant in order to ensure the magnetic potential to be constant according to a formula;

constant current excitation, the supply voltage being variable, without the need forAn adjusting switch is added, the DC-DC conversion efficiency reaches 95%, the excitation voltage is loaded to the coil by 98%, and the excitation efficiency is high; according to ohm's law

R is coil resistance, when the temperature rises, the coil resistance is increased, the coil current is reduced, the sampling voltage is reduced, the feedback voltage is reduced, and the DC-DC quickly adjusts the duty ratio to improve the excitation voltage V; when the temperature is reduced, the resistance of the coil is reduced, the current of the coil is increased, the sampling voltage is increased, the feedback voltage is increased, and the DC-DC rapid regulation duty ratio reduces the excitation voltage V; through a feedback circuit and DC-DC dynamic adjustment, regardless of the change of R, the excitation voltage always changes in the same proportion with R in the same direction, and further the constant current is realized;

constant current source: the DC-DC integrated module U72, the voltage feedback circuit operational amplifier U73B and the tiny sampling resistor R78 form a constant current source, the voltage of the sampling resistor R738 is amplified by the operational amplifier and then input to the DC-DC feedback end, the voltage is subjected to differential amplification and comparison processing with the internal reference voltage Ref of the DC-DC integrated module, when the exciting current reaches a set value, the voltage amplified by the operational amplifier U73B is approximately equal to Ref, and the circuit enters a constant current state; when the exciting current is smaller than a set value, the amplified voltage of the U73B is smaller than Ref, the DC-DC module U72 adjusts the duty ratio to increase the output voltage, and the exciting current is increased; when the exciting current is larger than a set value, the voltage amplified by the U73B is larger than Ref, the DC-DC module U72 adjusts the duty ratio to reduce the output voltage, and the exciting current is reduced;

h bridge circuit: the H-bridge circuit is characterized in that an H-bridge switch is composed of four field effect transistors Q710, Q711, Q714 and Q715, a sensor excitation coil L is connected to a diagonal line of the H-bridge switch, and a microprocessor outputs high and low levels through a pin 2 and a pin 4 of an I/O port to control the on and off of the MOS transistors Q710, Q711, Q714 and Q715 when exciting the excitation coil L, so that a magnetic field is generated in the excitation coil L.

3. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the power supply circuit without the negative power supply comprises main power supplies VCC and 1/2VCC reference power supplies, wherein the main power supply VCC is obtained by reducing the voltage of a lithium battery through a low-voltage-drop linear voltage regulator, and the VCC mainly supplies power for the MCU and the operational amplifiers U86A and U86B; the reference power supply is firstly reduced by a main power supply VCC through a reference chip, then is input into a voltage follower after being divided by a high-precision low-temperature drift resistor, and 1/2VCC output by the voltage follower is used as a signal ground level in the whole signal amplification circuit; the main power VCC is obtained by a battery voltage through a low-voltage drop linear voltage stabilizer and mainly comprises a field effect transistor Q73, a R73 and a LDO voltage stabilizer U71, a 3.6V lithium battery is connected with the drain electrode of the field effect transistor Q73, the grid electrode of the Q73 is grounded through a resistor R73, the source electrode of the Q73 is connected with the input end of a pin 2 of the low-voltage drop U71 linear voltage stabilizer, and the output end of the pin 3 is the main power VCC;

reference power supply: the main power supply is firstly reduced in voltage through a high-precision and micro-power-consumption voltage reference chip Q81, then is divided into 1/2VCC 'through high-precision and low-temperature drift resistors R81 and R84, then 1/2VCC' voltage is input to the positive input end of a voltage follower U81, the voltage follower U81 outputs 1/2VCC to serve as a reference power supply of the whole signal circuit, and the voltage follower is adopted to effectively isolate front and rear voltages without mutual influence; the circuit innovatively takes 1/2VCC as an electrode reference power supply, and an induced electromotive force signal is automatically raised to 1/2 VCC; the reference power supply mainly comprises a reference chip Q81, a voltage follower U81, R81, R84 and R86 and mainly provides a reference point for the signal amplification circuit.

4. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the amplifying and processing circuit of the isolated polarization voltage is mainly used for filtering the polarization voltage and high-frequency interference in the induced electromotive force, then amplifying a useful flow signal and further converting the useful flow signal into an analog signal which can be effectively identified by the AD conversion circuit; the circuit mainly comprises an RC filter circuit, a voltage follower U81, operational amplifiers U86A and U86B, gain resistors R830, R831, R832 and R833 and a polarization voltage processing circuit;

the working mode of the signal circuit is as follows: in the amplifying circuit, weak voltage signals output from the two electrodes pass through a filter circuit formed by two stages of RC (resistor-capacitor) circuits to filter high-frequency interference signals, are amplified by a first-stage operational amplifier U86A and U86B and then are directly input into an A/D (analog-to-digital) converter U31 to be subjected to A/D (analog-to-digital) conversion.

5. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the A/D conversion circuit mainly converts the analog signal to the digital signal of the voltage signal that the signal amplification circuit outputs, in order to the microprocessor calculates the flowrate through the corresponding software algorithm according to the digital signal obtained, it mainly makes up for AD conversion chip U31, R32, R33, two routes of flowrate signals enter AD two differential inputs through R32, R33, AD converts the signal difference into the digital signal according to the reference voltage, transmit to microprocessor U91 through DOUT; A/D chip U31 selects 24 bit AD chip, the core part of the converter mainly comprises a ∑ A/D modulator module, a low-pass digital filter module and a decimator module, the basic principle is: the Δ ∑ modulator samples the analog input sampling signal in an oversampling manner, modulates the sampling value, outputs a one-bit encoded data stream reflecting the amplitude of the input signal, and performs decimation and low-pass digital filtering to remove noise to obtain a multi-bit encoded output.

6. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the empty tube detection circuit mainly comprises two analog switches U82, U83, an operational amplifier U86A, U86B and an A/D conversion chip U31, wherein a pin 82 of a microprocessor and a pin 49 of the microprocessor are respectively connected with control pins of the two analog switches U82 and U83, when the pin 82 and the pin 49 of the microprocessor output high levels each time detection is carried out, pins 5 (COM) and 6 (NO) of the two analog switches U82 and U83 are respectively connected, at the moment, pin 51 of the microprocessor outputs high levels, pin 50 outputs low levels, the next empty tube detection period, pin 51 outputs low levels, pin 50 outputs high levels, and the high levels and the low levels are loaded on the two electrodes after being subjected to resistance voltage division respectively to form two sampling loops; when the tube is empty, the two electrodes without fluid in the tube are equivalent to open circuit, and a voltage of about dozens of mV is arranged between the electrodes.

7. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the excitation voltage detection circuit mainly has the function of detecting whether the DC-DC output voltage is normal or not, and mainly comprises a resistor R720 and a 12-bit ADC in a microprocessor, and when the excitation circuit works, the voltage of a micro sampling resistor R738 is amplified by operational amplifiers U86A and U86B and then is input into the 12-bit ADC in the microprocessor for conversion processing.

8. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the coil current detection circuit is mainly used for detecting whether current passes through the coil or not and detecting whether the coil is broken or not; the circuit mainly comprises two analog switches U84 and U85, operational amplifiers U86A and U86B, R825, R826, R827, R828 and an A/D converter, wherein two ends of a magnet exciting coil are respectively connected with a resistor R826 and R827 in series, when the magnet exciting coil is excited, two ends of the coil pass through current to generate pulse voltage of hundreds of mv, the pulse signal is led to the output end of the operational amplifier U86A or U86B through the analog switches, when the U84 leads the coupling signal to the output end of the amplifier U86A, the U85 is closed, and thus, the coupled signal and the normal signal are respectively input to AD through R32 and R33.

9. The circuit of an electromagnetic water meter with high efficiency and low interference as claimed in claim 1, wherein: the coil current detection, the empty pipe detection and the flow detection are carried out in a time-sharing mode and are not interfered with one another.

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