CN204330080U - A kind of liquid level detection circuit based on sampling capacitance - Google Patents
A kind of liquid level detection circuit based on sampling capacitance Download PDFInfo
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- CN204330080U CN204330080U CN201420745560.5U CN201420745560U CN204330080U CN 204330080 U CN204330080 U CN 204330080U CN 201420745560 U CN201420745560 U CN 201420745560U CN 204330080 U CN204330080 U CN 204330080U
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Abstract
The utility model discloses a kind of liquid level detection circuit based on sampling capacitance, comprising: electric capacity and voltage conversion circuit, voltage modulate circuit and voltage and current converter circuit; Described electric capacity is connected the output terminal of capacitance probe with the input end of voltage conversion circuit, and another input end connects the output terminal of crystal oscillator, and described electric capacity is connected the input end of described voltage modulate circuit with the output terminal of voltage conversion circuit; The output terminal of described voltage modulate circuit connects the input end of voltage and current converter circuit; Described voltage is connected external control devices with the output terminal of current converter circuit.Solve the low problem low with repeatability index of anti-interference of existing level sensing treatment circuit, be applicable to the elevation carrection of liquid coolant in fuel level in tank height in aviation field and liquid cooling system.
Description
Technical field
The utility model relates to technical field of liquid level measurement, especially a kind of liquid level detection circuit based on sampling capacitance.
Background technology
In industrial processes, there is a lot of place to need to carry out Liquid level to the medium in container, make it high-precision and remain on a given numerical value, at aviation field, liquid level in fuel tanker or in liquid cooling pipeline needs to control, and liquid level information is passed to control system and identifies.At present, the measurement of most of fuel tank internal combustion oil mass still adopts classic method, and namely fuel-quantity transducer connects a Metallic rod by slidably float, and the afterbody of Metallic rod is connected to a variable resistor via moveable contact.Variable resistor one end ground connection, the other end is connected on the fuel level gauge of panel board.The change of liquid level drives float movement thus causes the change of variable resistor resistance.But the measuring method precision of this Purely mechanical is low, reproducibility error is high, and is not suitable for long-distance transmissions.
Utility model content
The utility model provides a kind of liquid level detection circuit based on sampling capacitance, with the low problem low with repeatability index of the anti-interference solving existing level sensing treatment circuit, be applicable to the elevation carrection of liquid coolant in fuel level in tank height in aviation field and liquid cooling system.
The utility model provides a kind of liquid level detection circuit based on sampling capacitance, comprising: electric capacity and voltage conversion circuit, voltage modulate circuit and voltage and current converter circuit;
Described electric capacity is connected the output terminal of capacitance probe with the input end of voltage conversion circuit, and another input end connects the output terminal of crystal oscillator, and described electric capacity is connected the input end of described voltage modulate circuit with the output terminal of voltage conversion circuit;
The output terminal of described voltage modulate circuit connects the input end of voltage and current converter circuit;
Described voltage is connected external control devices with the output terminal of current converter circuit.
Further, described electric capacity and voltage conversion circuit comprise and frequently press conversion chip, the first resistance, the 3rd resistance, the 4th resistance, the 5th resistance, the 6th resistance, the 11 resistance, the 8th electric capacity and the 9th electric capacity and the tenth electric capacity; The collection pin of described frequency pressure conversion chip connects one end of capacitance probe and the 11 resistance, another termination 15V voltage of 11 resistance, threshold pin is connected with the common port of the tenth electric capacity and the 4th resistance, the other end of the tenth electric capacity connects the output terminal of crystal oscillator, the other end of the 4th resistance connects the common port of the 3rd resistance and the 8th electric capacity, the other end of the 3rd resistance connects the pressure input pin of conversion chip and one end of the 5th resistance frequently, and the reseting pin of pressure conversion chip connects one end of the 6th resistance frequently;
Frequently the output pin of pressure conversion chip connects one end of the first resistance, and described 9th Capacitance parallel connection is in the two ends of the first resistance, and the output pin of pressure conversion chip connects the input end of voltage modulate circuit frequently.
Further, described voltage modulate circuit comprises low-pass filter circuit and signal conversion circuit, described signal conversion circuit is subtraction circuit, described electric capacity is connected the in-phase input end of described low-pass filter circuit with the output terminal of voltage conversion circuit, the output terminal of described low-pass filter circuit connects the in-phase input end of described subtraction circuit, the inverting input of described subtraction circuit connects one end of the 13 resistance, and the other end of the 13 resistance connects the output terminal of the second voltage stabilizing chip.
Further, described low-pass filter circuit comprises the first operational amplifier, the 8th resistance, the 9th resistance, the tenth resistance, the 11 electric capacity, the 12 electric capacity and the 15 electric capacity;
Described electric capacity is connected one end of the 8th resistance with the output terminal of voltage conversion circuit, the other end of the 8th resistance connects the common port of the tenth resistance and the 11 electric capacity, the other end of the tenth resistance connects in-phase input end and the 12 electric capacity of the first operational amplifier, and the other end of the 11 electric capacity connects the output terminal of the first operational amplifier; The inverting input of described operational amplifier connects one end of the 9th resistance, and the other end of the 9th resistance connects the output terminal of described first operational amplifier, described 9th resistance two ends the 15 electric capacity in parallel.
Further, described signal conversion circuit comprises the second operational amplifier, the 12 resistance, the 13 resistance, the 17 resistance and the 18 resistance, and wherein the 13 resistance and the 17 resistance are all adjustable resistances;
The output terminal of described low-pass filter circuit connects one end of the 12 resistance, and the other end of the 12 resistance connects one end of the 17 resistance, and the 12 resistance is connected the in-phase input end of the second operational amplifier with the common port of the 17 resistance;
One end of 13 resistance connects the output terminal of the second voltage stabilizing chip, and the other end of the 13 resistance connects the inverting input of the second operational amplifier, connects the 18 resistance between the inverting input of the second operational amplifier and output terminal.
Further, described voltage and current converter circuit comprise voltage and electric current conversion chip, the 3rd diode, the 4th diode, the 16 electric capacity and the 17 electric capacity;
Described voltage is connected the output terminal of described voltage modulate circuit with the input pin of electric current conversion chip, described voltage is connected the anode of described 3rd diode, the negative electrode of the 4th diode and the common port of the 17 electric capacity with the output pin of electric current conversion chip, the negative electrode of described 3rd diode connects 15V power supply, the plus earth of described 4th diode, the other end ground connection of described 17 electric capacity, one termination 15V power supply of described 16 electric capacity, other end ground connection; Described voltage and electric current conversion chip export 4mA ~ 20mA standard current signal.
Further, multiple power circuit is comprised;
First power circuit comprises the first voltage stabilizing chip, the first diode, the first voltage stabilizing diode and the first electric capacity, the voltage source of 28V connects the anode of the first diode, the negative electrode of the first diode connects the negative electrode of the first voltage stabilizing diode, the anode of described first voltage stabilizing diode connects the input end of the first voltage stabilizing chip, the output terminal of the first voltage stabilizing chip connects the input end of the second voltage stabilizing chip, and the first voltage stabilizing chip exports 15V voltage;
Second source circuit comprises the second voltage stabilizing chip, the second resistance, the 7th resistance, the 4th electric capacity and the 5th electric capacity, and the second resistance is adjustable resistance; One end of described 4th electric capacity connects fixed contact and the moving contact of the second resistance, the input end of the second voltage stabilizing chip connects the common port of the 4th electric capacity and the second resistance, another fixed contact of second resistance connects one end of the 7th resistance, the other end of the 7th resistance connects the output terminal of the second voltage stabilizing chip, second resistance is connected the earth terminal of the second voltage stabilizing chip with the common port of the 7th resistance, the output terminal of the second voltage stabilizing chip connects the input end of voltage modulate circuit, and the second voltage stabilizing chip exports 5V voltage.
Further, the 3rd power circuit and the 4th power circuit is also comprised;
3rd power circuit comprises the 3rd voltage stabilizing chip, the second voltage stabilizing diode, the second electric capacity and the 3rd electric capacity; The input end of described 3rd voltage stabilizing chip connects the anode of the second voltage stabilizing diode, the negative electrode of described second voltage stabilizing diode is connected the output terminal of described first voltage stabilizing chip with the common port of the second electric capacity, the other end of the second electric capacity connects one end of the 3rd electric capacity, the other end of the 3rd electric capacity connects the output terminal of the 3rd voltage stabilizing chip, second electric capacity is connected the earth terminal of the 3rd voltage stabilizing chip with the common port of the 3rd electric capacity, the output terminal of the 3rd voltage stabilizing chip connects the input end of crystal oscillator, and the 3rd voltage stabilizing chip exports 5V voltage;
4th power circuit comprises level transferring chip, the 3rd voltage stabilizing diode, the 6th electric capacity and the 7th electric capacity; The voltage input end of described level transferring chip connects the anode of the 3rd voltage stabilizing diode, the negative electrode of described 3rd voltage stabilizing diode connects the output terminal of the first voltage stabilizing chip, the storage capacitor positive terminal of described level transferring chip connects the positive pole of the 6th electric capacity, storage capacitor negative pole end connects the negative pole of the 6th electric capacity, the negative supply input end of the output terminal concatenation operation amplifier of described level transferring chip and the negative pole of the 7th electric capacity, the plus earth of the 7th electric capacity, described level transferring chip exports-15V voltage.
The utility model provides a kind of liquid level detection circuit based on sampling capacitance, the crystal oscillation signal effect that the capacitance signal inputted capacitance probe by electric capacity and voltage conversion circuit and crystal oscillator are exported produces the voltage signal that is proportional to described capacitance signal, 0V ~ 10V voltage signal is exported by the process of voltage modulate circuit, this voltage signal exports 4mA ~ 20mA standard current signal through voltage and current converter circuit effect, to realize that measuring accuracy is high, reproducibility error is low, circuit anti-interference ability is strong, and the object such as signal long-distance transmissions is unattenuated.
Accompanying drawing explanation
Fig. 1 is the theory diagram of the liquid detecting circuit based on sampling capacitance that the utility model provides;
Fig. 2 is the electric capacity of the liquid detecting circuit based on sampling capacitance that the utility model provides and the circuit theory diagrams of voltage conversion circuit;
Fig. 3 is the circuit theory diagrams of the voltage modulate circuit of the liquid detecting circuit based on sampling capacitance that the utility model provides;
Fig. 4 is the voltage of the liquid detecting circuit based on sampling capacitance that the utility model provides and the circuit theory diagrams of current converter circuit;
Fig. 5 is the circuit theory diagrams of the power circuit of the liquid detecting circuit based on sampling capacitance that the utility model provides.
In figure:
1. capacitance probe 2. electric capacity and voltage conversion circuit 3. voltage modulate circuit
4. voltage and current converter circuit 5. opertaing device
Embodiment
The capacitance probe 1 that the utility model adopts utilizes inside and outside concentric metal bar and metal tube to be made, outer wall has several holes, freely can enter liquid, metal bar and metal tube are isolated by insulating sleeve, respectively draw a wire from the inside and outside wall of capacitance probe 1, form the two poles of the earth of electric capacity.Capacitance due to capacitance probe 1 belongs to pF level weak capacitive, be vulnerable to the impact of stray capacitance and line distribution capacitance in external environment and circuit board, gather comparatively difficulty, so the liquid level detection circuit based on sampling capacitance that the utility model provides carries out corresponding filtering to it after collection capacitance signal, signal amplifies and conditioning, final output current signal form gathers for the opertaing device 5 on aircraft.
The technical solution of the utility model is further illustrated by embodiment below in conjunction with accompanying drawing.
With reference to shown in Fig. 1, the utility model provides a kind of liquid level detection circuit based on sampling capacitance, comprising: electric capacity and voltage conversion circuit 2, voltage modulate circuit 3 and voltage and current converter circuit 4;
Described electric capacity is connected the output terminal of capacitance probe 1 with the input end of voltage conversion circuit 2, and another input end connects the output terminal of crystal oscillator, and described electric capacity is connected the input end of described voltage modulate circuit 3 with the output terminal of voltage conversion circuit 2;
The output terminal of described voltage modulate circuit 3 connects the input end of voltage and current converter circuit 4;
Described voltage is connected external control devices 5 with the output terminal of current converter circuit 4.
Fig. 2 is the electric capacity of the liquid detecting circuit based on sampling capacitance that the utility model provides and the circuit theory diagrams of voltage conversion circuit;
Shown in composition graphs 2, on the basis of the above description, described electric capacity and voltage conversion circuit 2 can specifically be built by following components and parts.Described electric capacity and voltage conversion circuit 2 comprise presses conversion chip U5 frequently, the chip model that can select is LM331, the first resistance R1, the 3rd resistance R3, the 4th resistance R4, the 5th resistance R5, the 6th resistance R6, the 11 resistance R11, the 8th electric capacity C8 and the 9th electric capacity C9 and the tenth electric capacity C10, the collection pin RC of described frequency pressure conversion chip U5 connects one end of capacitance probe the 1 and the 11 resistance R11, another termination 15V voltage of 11 resistance R11, threshold pin THRES is connected with the common port of the tenth electric capacity C10 and the 4th resistance R4, the other end of the tenth electric capacity C10 connects the output terminal of crystal oscillator U8, the other end of the 4th resistance R4 connects the common port of the 3rd resistance R3 and the 8th electric capacity C8, the other end of the 3rd resistance R4 connects the input pin IN of pressure conversion chip U5 and one end of the 5th resistance R5 frequently, the equal ground connection of the other end of the 5th resistance R5 and the 8th electric capacity C8, frequently the reseting pin REF of pressure conversion chip U5 connects one end of the 6th resistance R6, the other end ground connection of the 6th resistance R6, wherein CX represents capacitance signal,
Frequently the output pin OUT of pressure conversion chip U5 connects one end of the first resistance R1, the other end ground connection of the first resistance R1, described 9th electric capacity C9 is parallel to the two ends of the first resistance R1, and the output pin V5 of pressure conversion chip U5 connects the input end of voltage modulate circuit 3 frequently.
In described electric capacity and voltage conversion circuit 2, C8 and C9 plays the effect of stabilization signal, the value of C10 converts speed and the output voltage ripple of voltage signal to by affecting capacitance signal, if increase C10, output voltage ripple then can be made to reduce, but slewing rate can reduce, reduce C10 and then can improve slewing rate, but voltage ripple can increase.In order to reach preferably slewing rate and less voltage ripple, C10 value is between 180PF to 270PF.
As mentioned above, convert capacitance signal to voltage signal by electric capacity and voltage conversion circuit 2 and export, overcome the shortcoming that capacitance signal is unstable in mimic channel, not easily change, there is the features such as Low Drift Temperature, low dissipation power and high linearity.Inside circuit has crystal oscillator, and the high-frequency signal itself brought to circuit is all eliminated by the low-pass filter circuit of inside circuit, and circuit anti-interference is stronger.The voltage signal exported is directly proportional to the described capacitance of capacitance probe 1 and the crystal oscillator frequency of crystal oscillator.Again because the direct proportion change with the change of liquid level of the capacitance of described capacitance probe 1, so electric capacity is directly proportional to the liquid level of fluid to be measured to the output voltage signal of voltage conversion circuit 2, can by detecting output voltage signal detection of liquid level height.
Fig. 3 is the circuit theory diagrams of the voltage modulate circuit of the liquid detecting circuit based on sampling capacitance that the utility model provides;
Shown in composition graphs 3, on the basis of the above description, described voltage modulate circuit 3 can specifically be built by following components and parts.Described voltage modulate circuit 3 comprises low-pass filter circuit and signal conversion circuit, described signal conversion circuit is subtraction circuit, described electric capacity is connected the in-phase input end of described low-pass filter circuit with the output terminal of voltage conversion circuit 2, the output terminal of described low-pass filter circuit connects the in-phase input end of described subtraction circuit, the inverting input of described subtraction circuit connects one end of the 13 resistance R13, and the other end of the 13 resistance R13 connects the output terminal V2 of the second voltage stabilizing chip U2.
Wherein, described low-pass filter circuit comprises the first operational amplifier U6A, the 8th resistance R8, the 9th resistance R9, the tenth resistance R10, the 11 electric capacity C11, the 12 electric capacity C12 and the 15 electric capacity C15;
Described electric capacity is connected one end of the 8th resistance R8 with the output terminal V5 of voltage conversion circuit 2, the other end of the 8th resistance R8 connects the common port of the tenth resistance R10 and the 11 electric capacity C11, the other end of the tenth resistance R10 connects in-phase input end and the 12 electric capacity C12 of the first operational amplifier U6A, the other end of the 11 electric capacity C11 connects the output terminal of the first operational amplifier U6A, the other end ground connection of the 12 electric capacity C12; The inverting input of described operational amplifier U6A connects one end of the 9th resistance R9, and the other end of the 9th resistance R9 connects the output terminal of described first operational amplifier U6A, described 9th resistance R9 two ends the 15 electric capacity C15 in parallel.
Wherein, described signal conversion circuit comprises the second operational amplifier U6B, the 12 resistance R12, the 13 resistance R13, the 17 resistance R17 and the 18 resistance R18, and wherein the 13 resistance R13 and the 17 resistance R17 is all adjustable resistances;
The output terminal of described low-pass filter circuit connects one end of the 12 resistance R12, the other end of the 12 resistance R12 connects one end of the 17 resistance R17, the other end ground connection of the 17 resistance R17, the 12 resistance R12 is connected the in-phase input end of the second operational amplifier U6B with the common port of the 17 resistance R17;
One end of 13 resistance R13 connects the output terminal of the second voltage stabilizing chip U6B, the other end of the 13 resistance R13 connects the inverting input of the second operational amplifier U6B, connects the 18 resistance R18 between the inverting input of the second operational amplifier U6B and output terminal.The model of operational amplifier can adopt LM258.
The mathematical model of voltage signal conditioning is:
Suppose that zero liquid level is with under full liquid level state, the voltage signal exported through electric capacity and voltage conversion circuit 2 and low-pass filter circuit is respectively Va and Vb, by described signal conversion circuit process, can be 0V ~ 10V voltage signal by its linear transformation, before and after conditioning, voltage corresponding relation be:
Utilize operational amplification circuit to realize above-mentioned function, the pass between op-amp output voltage and input voltage is:
From the relation between above-mentioned op-amp output voltage and input voltage, can by the Gain tuning regulating R13 and R17 to realize operational amplifier.Shown in composition graphs 5, in second source circuit, by the output voltage V2 regulating the size of R2 to adjust the second voltage stabilizing chip U2, until the first pin output voltage V1 is equal in Vout and U6B, thus the adjustment of zero point offset amount parameter can be realized.
As mentioned above, removed by the high-frequency signal comprised in the voltage signal that pressure conversion chip U5 is converted to frequently by low-pass filter circuit, avoid high-frequency signal to affect subsequent conditioning circuit and export, improve circuit stability.By signal conversion circuit, linear function conversion (namely return to zero and adjust gain factor) is carried out to filtered voltage signal, export 0V ~ 10V voltage signal, there is circuit simple, the feature of the adjustment of signal zero and gain can be realized by the resistance adjusting several resistance.
Fig. 4 is the voltage of the liquid detecting circuit based on sampling capacitance that the utility model provides and the circuit theory diagrams of current converter circuit;
With reference to shown in Fig. 4, on the basis of the above description, described voltage and current converter circuit 4 can specifically be built by following components and parts.Described voltage and current converter circuit 4 comprise voltage and electric current conversion chip U7, the 3rd diode D3, the 4th diode D4, the 16 electric capacity C16 and the 17 electric capacity C17;
Described voltage is connected the output terminal V6 of described voltage modulate circuit 3 with the input pin of electric current conversion chip U7, described voltage is connected the anode of described 3rd diode D3, the negative electrode of the 4th diode D4 and the common port of the 17 electric capacity C17 with the output pin of electric current conversion chip U7, the negative electrode of described 3rd diode D3 connects 15V power supply, the plus earth of described 4th diode D4, the other end ground connection of described 17 electric capacity C17, the one termination 15V power supply of described 16 electric capacity C16, other end ground connection; Described voltage and electric current conversion chip U7 export 4mA ~ 20mA standard current signal.
The chip model of described voltage and electric current conversion chip U7 is the AD694 of AD company, this chip is a single-chip current transmitters, high level signal input can be accepted to export 4mA ~ 20mA standard current signal, thus control outside sets, such as, in process control conventional valve, actuator and other equipment.Input signal generally adopts input amplifier, and this input amplifier can be utilized to adjust the output of input signal or a buffering current-mode DAC (Digital to Analog Converter, digital to analog converter).Can be realized the selection of the voltage range of pre-calibration by simple pin binding, the input range that can select is 0V ~ 2V or 0V ~ 10V.Other scope can be arranged by non-essential resistance.
As mentioned above, realize 0V ~ 10V voltage signal by voltage and current converter circuit 4 and be converted into 4mA ~ 20mA standard current signal, avoid causing signal attenuation because of long range propagation.
Fig. 5 is the circuit theory diagrams of the power circuit of the liquid detecting circuit based on sampling capacitance that the utility model provides.
With reference to shown in Fig. 5, the described liquid level detection circuit based on sampling capacitance comprises multiple power circuit, and described power circuit can specifically be built by following components and parts.
First power circuit comprises the first voltage stabilizing chip U1, the first diode D1, the first voltage stabilizing diode D5 and the first electric capacity C1, the voltage source of 28V connects the anode of the first diode D1, the negative electrode of the first diode D1 connects the negative electrode of the first voltage stabilizing diode D5, the anode of described first voltage stabilizing diode D5 connects the input end of the first voltage stabilizing chip U1, the output terminal of the first voltage stabilizing chip U1 connects the input end of the second voltage stabilizing chip U2, and the first voltage stabilizing chip U1 exports 15V voltage;
Second source circuit comprises the second voltage stabilizing chip U2, the second resistance R2, the 7th resistance R7, the 4th electric capacity C4 and the 5th electric capacity C5, and the second resistance R2 is adjustable resistance; One end of described 4th electric capacity C4 connects fixed contact and the moving contact of the second resistance R2, the input end of the second voltage stabilizing chip U2 connects the common port of the 4th electric capacity C4 and the second resistance R2, another fixed contact of second resistance R2 connects one end of the 7th resistance R7, the other end of the 7th resistance R7 connects the output terminal of the second voltage stabilizing chip U2, second resistance R2 is connected the earth terminal of the second voltage stabilizing chip U2 with the common port of the 7th resistance R7, the output terminal V2 of the second voltage stabilizing chip U2 connects the input end of voltage modulate circuit 3, the output 5V voltage of the second voltage stabilizing chip U2.
Further, the 3rd power circuit and the 4th power circuit is also comprised;
3rd power circuit comprises the 3rd voltage stabilizing chip U3, the second voltage stabilizing diode D2, the second electric capacity C2 and the 3rd electric capacity C3, the input end of described 3rd voltage stabilizing chip U3 connects the anode of the second voltage stabilizing diode D2, the negative electrode of described second voltage stabilizing diode D2 is connected the output terminal of described first voltage stabilizing chip U1 with the common port of the second electric capacity C2, the other end of the second electric capacity C2 connects one end of the 3rd electric capacity C3, the other end of the 3rd electric capacity C3 connects the output terminal of the 3rd voltage stabilizing chip U3, second electric capacity C2 is connected the earth terminal of the 3rd voltage stabilizing chip U3 with the common port of the 3rd electric capacity C3, the output terminal V3 of the 3rd voltage stabilizing chip U3 connects the input end of crystal oscillator, 3rd voltage stabilizing chip U3 exports 5V voltage,
4th power circuit comprises level transferring chip (can select the ICL7660 of Maxim company) U4, the 3rd voltage stabilizing diode D6, the 6th electric capacity C6 and the 7th electric capacity C7; The voltage input end of described level transferring chip U4 connects the anode of the 3rd voltage stabilizing diode D6, the negative electrode of described 3rd voltage stabilizing diode D6 connects the output terminal of the first voltage stabilizing chip U1, the storage capacitor positive terminal CAP+ of described level transferring chip U4 connects the positive pole of the 6th electric capacity C6, storage capacitor negative pole CAP-holds the negative pole of connection the 6th electric capacity C6, the negative supply input end of output terminal concatenation operation amplifier U6A of described level transferring chip U4 and the negative pole of the 7th electric capacity C7, the plus earth of the 7th electric capacity C7, described level transferring chip U4 exports-15V voltage.
As mentioned above, realized by 28V DC power supply by multiple power circuit, power with airplane power source and match.
This circuit belongs to mimic channel, utilize 3 acp chips (frequently pressing conversion chip, operational amplifier and voltage and electric current conversion chip) that the Acquire and process of signal can be realized, modulate circuit is simple, by the adjustment regulating several resistance can realize signal zero and gain.For realizing the collection of capacitance signal, inside circuit has crystal oscillator, and the high-frequency signal itself brought to circuit is all eliminated by the low-pass filter circuit of inside circuit, and circuit anti-interference is stronger.The linearity major part of circuit depends on the linearity of capacitance probe 1, the structural symmetry of capacitance probe 1 own, and inside circuit process chip can not cause larger distorted signals, and therefore the linearity of processing of circuit can be guaranteed.Circuit, by 28V DC power supply, is powered with airplane power source and is matched, output signal as 4mA ~ 20mA current signal, uses long-distance transmissions unattenuated.
It should be noted that and above are only preferred embodiment of the present utility model and institute's application technology principle.Skilled person in the art will appreciate that the utility model is not limited to specific embodiment described here, various obvious change can be carried out for a person skilled in the art, readjust and substitute and protection domain of the present utility model can not be departed from.Therefore, although be described in further detail the utility model by above embodiment, but the utility model is not limited only to above embodiment, when not departing from the utility model design, can also comprise other Equivalent embodiments more, and scope of the present utility model is determined by appended right.
Claims (8)
1. based on a liquid level detection circuit for sampling capacitance, it is characterized in that, comprising: electric capacity and voltage conversion circuit, voltage modulate circuit and voltage and current converter circuit;
Described electric capacity is connected the output terminal of capacitance probe with the input end of voltage conversion circuit, and another input end connects the output terminal of crystal oscillator, and described electric capacity is connected the input end of described voltage modulate circuit with the output terminal of voltage conversion circuit;
The output terminal of described voltage modulate circuit connects the input end of voltage and current converter circuit;
Described voltage is connected external control devices with the output terminal of current converter circuit.
2. the liquid level detection circuit based on sampling capacitance according to claim 1, it is characterized in that, described electric capacity and voltage conversion circuit comprise presses conversion chip, the first resistance, the 3rd resistance, the 4th resistance, the 5th resistance, the 6th resistance, the 11 resistance, the 8th electric capacity and the 9th electric capacity and the tenth electric capacity frequently; The collection pin of described frequency pressure conversion chip connects one end of capacitance probe and the 11 resistance, another termination 15V voltage of 11 resistance, threshold pin is connected with the common port of the tenth electric capacity and the 4th resistance, the other end of the tenth electric capacity connects the output terminal of crystal oscillator, the other end of the 4th resistance connects the common port of the 3rd resistance and the 8th electric capacity, the other end of the 3rd resistance connects the pressure input pin of conversion chip and one end of the 5th resistance frequently, and the reseting pin of pressure conversion chip connects one end of the 6th resistance frequently;
Frequently the output pin of pressure conversion chip connects one end of the first resistance, and described 9th Capacitance parallel connection is in the two ends of the first resistance, and the output pin of pressure conversion chip connects the input end of voltage modulate circuit frequently.
3. the liquid level detection circuit based on sampling capacitance according to claim 1, it is characterized in that, described voltage modulate circuit comprises low-pass filter circuit and signal conversion circuit, described signal conversion circuit is subtraction circuit, described electric capacity is connected the in-phase input end of described low-pass filter circuit with the output terminal of voltage conversion circuit, the output terminal of described low-pass filter circuit connects the in-phase input end of described subtraction circuit, the inverting input of described subtraction circuit connects one end of the 13 resistance, and the other end of the 13 resistance connects the output terminal of the second voltage stabilizing chip.
4. the liquid level detection circuit based on sampling capacitance according to claim 3, it is characterized in that, described low-pass filter circuit comprises the first operational amplifier, the 8th resistance, the 9th resistance, the tenth resistance, the 11 electric capacity, the 12 electric capacity and the 15 electric capacity;
Described electric capacity is connected one end of the 8th resistance with the output terminal of voltage conversion circuit, the other end of the 8th resistance connects the common port of the tenth resistance and the 11 electric capacity, the other end of the tenth resistance connects in-phase input end and the 12 electric capacity of the first operational amplifier, and the other end of the 11 electric capacity connects the output terminal of the first operational amplifier; The inverting input of described operational amplifier connects one end of the 9th resistance, and the other end of the 9th resistance connects the output terminal of described first operational amplifier, described 9th resistance two ends the 15 electric capacity in parallel.
5. the liquid level detection circuit based on sampling capacitance according to claim 3, it is characterized in that, described signal conversion circuit comprises the second operational amplifier, the 12 resistance, the 13 resistance, the 17 resistance and the 18 resistance, and wherein the 13 resistance and the 17 resistance are all adjustable resistances;
The output terminal of described low-pass filter circuit connects one end of the 12 resistance, and the other end of the 12 resistance connects one end of the 17 resistance, and the 12 resistance is connected the in-phase input end of the second operational amplifier with the common port of the 17 resistance;
One end of 13 resistance connects the output terminal of the second voltage stabilizing chip, and the other end of the 13 resistance connects the inverting input of the second operational amplifier, connects the 18 resistance between the inverting input of the second operational amplifier and output terminal.
6. the liquid level detection circuit based on sampling capacitance according to claim 1, is characterized in that, described voltage and current converter circuit comprise voltage and electric current conversion chip, the 3rd diode, the 4th diode, the 16 electric capacity and the 17 electric capacity;
Described voltage is connected the output terminal of described voltage modulate circuit with the input pin of electric current conversion chip, described voltage is connected the anode of described 3rd diode, the negative electrode of the 4th diode and the common port of the 17 electric capacity with the output pin of electric current conversion chip, the negative electrode of described 3rd diode connects 15V power supply, the plus earth of described 4th diode, the other end ground connection of described 17 electric capacity, one termination 15V power supply of described 16 electric capacity, other end ground connection; Described voltage and electric current conversion chip export 4mA ~ 20mA standard current signal.
7. the liquid level detection circuit based on sampling capacitance according to claim 1, is characterized in that, comprises multiple power circuit;
First power circuit comprises the first voltage stabilizing chip, the first diode, the first voltage stabilizing diode and the first electric capacity, the voltage source of 28V connects the anode of the first diode, the negative electrode of the first diode connects the negative electrode of the first voltage stabilizing diode, the anode of described first voltage stabilizing diode connects the input end of the first voltage stabilizing chip, the output terminal of the first voltage stabilizing chip connects the input end of the second voltage stabilizing chip, and the first voltage stabilizing chip exports 15V voltage;
Second source circuit comprises the second voltage stabilizing chip, the second resistance, the 7th resistance, the 4th electric capacity and the 5th electric capacity, and the second resistance is adjustable resistance; One end of described 4th electric capacity connects fixed contact and the moving contact of the second resistance, the input end of the second voltage stabilizing chip connects the common port of the 4th electric capacity and the second resistance, another fixed contact of second resistance connects one end of the 7th resistance, the other end of the 7th resistance connects the output terminal of the second voltage stabilizing chip, second resistance is connected the earth terminal of the second voltage stabilizing chip with the common port of the 7th resistance, the output terminal of the second voltage stabilizing chip connects the input end of voltage modulate circuit, and the second voltage stabilizing chip exports 5V voltage.
8. the liquid level detection circuit based on sampling capacitance according to claim 7, is characterized in that, also comprises the 3rd power circuit and the 4th power circuit;
3rd power circuit comprises the 3rd voltage stabilizing chip, the second voltage stabilizing diode, the second electric capacity and the 3rd electric capacity; The input end of described 3rd voltage stabilizing chip connects the anode of the second voltage stabilizing diode, the negative electrode of described second voltage stabilizing diode is connected the output terminal of described first voltage stabilizing chip with the common port of the second electric capacity, the other end of the second electric capacity connects one end of the 3rd electric capacity, the other end of the 3rd electric capacity connects the output terminal of the 3rd voltage stabilizing chip, second electric capacity is connected the earth terminal of the 3rd voltage stabilizing chip with the common port of the 3rd electric capacity, the output terminal of the 3rd voltage stabilizing chip connects the input end of crystal oscillator, and the 3rd voltage stabilizing chip exports 5V voltage;
4th power circuit comprises level transferring chip, the 3rd voltage stabilizing diode, the 6th electric capacity and the 7th electric capacity; The voltage input end of described level transferring chip connects the anode of the 3rd voltage stabilizing diode, the negative electrode of described 3rd voltage stabilizing diode connects the output terminal of the first voltage stabilizing chip, the storage capacitor positive terminal of described level transferring chip connects the positive pole of the 6th electric capacity, storage capacitor negative pole end connects the negative pole of the 6th electric capacity, the negative supply input end of the output terminal concatenation operation amplifier of described level transferring chip and the negative pole of the 7th electric capacity, the plus earth of the 7th electric capacity, described level transferring chip exports-15V voltage.
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| CN104880235A (en) * | 2015-06-24 | 2015-09-02 | 西安华舜测量设备有限责任公司 | Indicator for measuring oil level inside transformer sleeve through electric field and measurement method thereof |
| CN105445562A (en) * | 2015-11-27 | 2016-03-30 | 贵州铜仁高新区科创互联生产力促进中心 | Capacitor capacity test circuit, liquid level height detection circuit, and application method of the liquid level height detection circuit |
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| CN107782410A (en) * | 2016-08-29 | 2018-03-09 | 佛山市顺德区美的电热电器制造有限公司 | Liquid level detection device and electrical equipment |
| CN107782409A (en) * | 2016-08-29 | 2018-03-09 | 佛山市顺德区美的电热电器制造有限公司 | Liquid level detection device and electrical equipment |
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| CN104880235A (en) * | 2015-06-24 | 2015-09-02 | 西安华舜测量设备有限责任公司 | Indicator for measuring oil level inside transformer sleeve through electric field and measurement method thereof |
| CN104880235B (en) * | 2015-06-24 | 2018-06-01 | 西安华舜测量设备有限责任公司 | The indicator and its measuring method of oil level in a kind of electric field measurement bushing shell for transformer |
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| CN105445562B (en) * | 2015-11-27 | 2018-11-02 | 泉州市天龙电子科技有限公司 | The application method of capacitance test circuit, liquid level detection circuit, liquid level detection circuit |
| CN105675082A (en) * | 2016-01-22 | 2016-06-15 | 桂林优利特医疗电子有限公司 | Liquid level induction device, biochemical analyzer and liquid level induction method |
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