CN206876262U - The detection circuit and liquid level gauge for the liquid level height that monitoring electrical conductivity is not zero - Google Patents
The detection circuit and liquid level gauge for the liquid level height that monitoring electrical conductivity is not zero Download PDFInfo
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- CN206876262U CN206876262U CN201720584516.4U CN201720584516U CN206876262U CN 206876262 U CN206876262 U CN 206876262U CN 201720584516 U CN201720584516 U CN 201720584516U CN 206876262 U CN206876262 U CN 206876262U
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Abstract
The detection circuit for the liquid level height that monitoring electrical conductivity is not zero, including single-chip microcomputer, operational amplifier, first analog switch, standard capacitance known to second analog switch and capacity, the operational amplifier connects into voltage follower, the input of first analog switch and an I/O mouth of single-chip microcomputer connect, the output end of first analog switch is connected with the input of the second analog switch, the input of one end of standard capacitance and voltage follower known to the output end and capacity of second analog switch connects, the control terminal of first analog switch and the second analog switch is connected with an I/O mouth of single-chip microcomputer respectively, the output end of the voltage follower and the AD mouths of single-chip microcomputer connect, the other end of standard capacitance known to the capacity is signally connected with the detection circuit.Liquid level gauge is made up of above-mentioned detection circuit and capacitance level transducer.
Description
Technical field
The utility model belongs to liquid level height monitoring field, more particularly to a kind of liquid for monitoring electrical conductivity and being not zero
The capacitance type liquid level detection circuit and capacitance level gauge of liquid level.
Background technology
The capacitance level gauge for the liquid level height that monitoring electrical conductivity is not zero is by capacitance level transducer and detection
Circuit is formed.Existing capacitance level transducer is generally the coaxial cylindrical capacitance type sensor shown in Fig. 1, Fig. 2, by exhausted
The cylindrical electrode 1 and annular bare electrode 2 of edge homogeneous media parcel form, and the internal diameter of annular bare electrode is more than cylinder electricity
The external diameter of pole.In use, the cylindrical electrode 1 uniformly wrapped up by dielectric and annular bare electrode 2 are put into monitored liquid
In the liquid of position height, it is interior and naked with annular that the cylindrical electrode 1 that is uniformly wrapped up by dielectric be located at annular bare electrode 2
Electrode coaxial line is placed, and the liquid 2-1 that the electrical conductivity of monitored liquid level is not zero is filled between two electrodes, is formed such as
Equivalent circuit shown in Fig. 3.In Fig. 3, CxTo be monitored electric capacity, corresponding relation be present with liquid level H, in measurement CxWhen, quilt
The impedance R for the liquid 2-1 that the electrical conductivity of monitoring liquid level is not zero0And C0Parallel connection come equivalent, the R0It is with being monitored
The equivalent resistance for the liquid electric conductivity correlation that the electrical conductivity of liquid level is not zero, C0It is the electrical conductivity with monitored liquid level
The equivalent capacity for the liquid dielectric correlation being not zero, the liquid that electrical conductivity is not zero are situated between as in the presence of the conductive of a constant impedance
Matter and annular bare electrode 3 are monitored electric capacity C in pie graph 3 togetherxAn electrode, cylindrical electrode 1 is electric capacity CxIt is another
Individual electrode, the dielectric 1-1 for being uniformly wrapped in cylindrical electrode outer surface surrounded by the liquid that electrical conductivity is not zero are electricity
Hold CxMedium.If from figure 3, it can be seen that electric capacity CxMedium have stable dielectric constant, leakage current are very small (to choose and close
Suitable insulating materials, such as polyester, polypropylene can be achieved), and R0Sufficiently small or R0With C0It is sufficiently stable, CxSize just only
With the height correlation for the liquid for being enclosed in its dielectric surface, but in most cases R0Not small enough and R0And C0Be it is unstable or
It is uncertain, and the existing detection circuit supporting with such capacitance level transducer can not eliminate the liquid that electrical conductivity is not zero
The influence that is brought to measurement result of impedance, therefore the fluid impedance that the monitoring accuracy of liquid level is not zero by electrical conductivity is not true
Qualitatively influence is the mortal wound of this kind of liquid level gauge, even if in the very big conducting medium of application demand --- the level monitoring neck of water
Domain is also more seldom to use capacitance level gauge using the throw-in type liquid level sensor based on pressure measxurement principle.Furthermore coaxially
Cylindrical capacitor is vertical type rigid structure, not easy cleaning, and application is limited (for example, vertical type is rigid after electrode is contaminated
Structure cannot be used for water level monitoring of the equipment of tumbling-box washing machine etc etc.).
Utility model content
The purpose of this utility model is overcome the deficiencies in the prior art, there is provided a kind of liquid for monitoring electrical conductivity and being not zero
The detection circuit and liquid level gauge of liquid level, to eliminate the equiva lent impedance for the liquid that the electrical conductivity of monitored liquid level is not zero
The uncertain harmful effect to caused by liquid level monitoring result, and make the capacitance level transducer structure of composition liquid level gauge
Various, application is wide wider.
The detection circuit for the liquid level height that monitoring electrical conductivity described in the utility model is not zero, based on " electric charge measuring cup "
Method build, its principle as shown in Figure 4, Figure 5, i.e., by electric capacity CxA capacity unknown " charge container " is regarded as, by the way that C will be filledx
In the electric charge transfer known capacity that is referred to as " electric charge measuring cup " to one or more standard capacitance in, measure (base in other words
In the scale " reading " of measurable " electric charge measuring cup ") by CxInverse goes out the electric charge being transferred in the standard capacitance of known capacity again
CxValue.Illustrated below with Fig. 4 and eliminate the principle that the equiva lent impedance for the liquid that electrical conductivity is not zero influences：
1. single-chip microcomputer controls the first analog switch K1Connect, the second analog switch K2Disconnect, when a length of △ T1.First simulation
Switch K1After connection, electrode 1 and reference power supply VrefConnection, reference power supply VrefThrough the R in parallel relationship0And C0To CxCharging.
With in above-mentioned charge circuit by R0、C0And CxThe loop time constant, τ of decision1Compare, △ T1It is bigger, CxThe voltage V at both endsCxThen get over
Close to reference power supply Vref, as △ T1It is big enough in VCxWith VrefBetween error when can ignore, CxIn charge Q=Cx
×Vref；
2. through △ T1Afterwards, single-chip microcomputer controls the second analog switch K2Connect, the first analog switch K1Disconnect, when a length of △ T2。
Second analog switch K2After connection, CxIn charge Q pass through in parallel relationship R0And C0To the standard capacitance C of known capacity1Transfer.
In transfer process, CxThe voltage V at both endsCxWith CxThe outflow of middle electric charge and decline, and the standard capacitance C of known capacity1Both ends
Voltage VC1Then with C1The inflow of middle electric charge and rise.This transfer is the constant Q of total amount in CxAnd C1In reallocation, transfer
After completing (or reaching poised state), VC1=VCx.With in above-mentioned electric charge transfer loop by R0、C0、CxAnd C1The loop time of decision
Constant, τ2Compare, △ T2It is bigger, VCxAnd VC1Closer to balance (or equal), as △ T2It is big enough in VCxWith VC1Between
Unbalanced error when can ignore, VC1=VCx=Q/ (Cx+C1), it can thus be concluded that：
In above formula, due to C1And Vref, it is known that by measuring VC1It can obtain Cx。
Based on principles above, as long as charging duration △ T1With electric charge transfer duration △ T2Relative to the timeconstantτ foot in loop
It is enough big, the liquid that the electrical conductivity that the detection circuit can eliminates monitored liquid level in great scope is not zero etc.
Effect impedance uncertainty influences to caused by measurement result.
As shown in figure 5, with the standard capacitance of two (or multiple) known capacities, by corresponding analog switch gamut
It is divided into two sections (or multistages), can further improves the resolution ratio of gamut and detect the signal to noise ratio of circuit.
The detection circuit for the liquid level height that monitoring electrical conductivity described in the utility model is not zero, including single-chip microcomputer, fortune
Calculate amplifier, the first analog switch, the second analog switch and standard capacitance known to capacity, the operational amplifier and connect into electricity
Follower is pressed, the input of first analog switch and an I/O mouth of single-chip microcomputer connect, the output end of the first analog switch
It is connected with the input of the second analog switch, one end of standard capacitance and electricity known to the output end and capacity of the second analog switch
Press the input connection of follower, the control terminal of first analog switch and the second analog switch, one with single-chip microcomputer respectively
I/O mouths connect, and the output end of the voltage follower and the AD mouths of single-chip microcomputer connect, and standard capacitance is another known to the capacity
One end is signally connected with the detection circuit.
In order to improve the resolution ratio of gamut and detect the signal to noise ratio of circuit, standard capacitance is by first known to the capacity
Standard capacitance parallel combination known to standard capacitance known to capacity and the second capacity forms, and is additionally arranged the 3rd analog switch,
The output end of second analog switch connects with the input of one end of standard capacitance and voltage follower known to the first capacity
Connect, the input of the 3rd analog switch is connected with the output end of the second analog switch, the output end and second of the 3rd analog switch
One end connection of standard capacitance known to capacity, the control terminal of the 3rd analog switch and an I/O mouth of single-chip microcomputer connect, described
Signal ground of the other end of standard capacitance with the detection circuit known to standard capacitance known to first capacity and the second capacity
Connection.
The liquid level gauge of liquid level height that monitoring electrical conductivity described in the utility model is not zero, by above-mentioned detection circuit and
Capacitance level transducer is formed, and the capacitance level transducer is by an electrode uniformly wrapped up by insulating materials and one
It can be formed in the bottom limit level of monitored target setting with the bare electrode that liquid directly contacts, the electricity uniformly wrapped up by insulating materials
Pole is connected with the output end of the first analog switch, and bare electrode is signally connected with detection circuit.
Above-mentioned liquid level gauge, the horizontal stroke of the electrode uniformly wrapped up by insulating materials and bare electrode in its capacitance level transducer
Cross sectional shape is shaft-like, banding or arcuation for circular, ellipse or polygon, global shape.
Above-mentioned liquid level gauge, between the electrode and bare electrode that are uniformly wrapped up by insulating materials in its capacitance level transducer
Position relationship do not restricted, can be if necessary in arbitrarily being placed in monitored liquid.
Compared with prior art, the utility model has the advantages that：
1st, because detection circuit provided by the utility model efficiently solves the equiva lent impedance for the liquid that electrical conductivity is not zero
The uncertain harmful effect to caused by liquid level monitoring result, thus the measurement accuracy of liquid level can be increased substantially.
2nd, measurement accuracy and monitored liquid of the circuit to liquid level are detected due to liquid level gauge described in the utility model
Equiva lent impedance it is unrelated, thus form the shape of two electrodes of the capacitance level transducer of liquid level gauge, mutual position
Put that relation is unrestricted, as long as placing the metal bare electrode of an arbitrary shape in the bottom of monitored liquid, you can utilize quilt
Another electrode that insulating materials uniformly wraps up monitors the liquid level in the container of arbitrary shape or height.
3rd, two electrode shapes of the liquid level sensor in liquid level gauge described in the utility model and mutual alignment relation is any
Property, cost of manufacture can be not only reduced, and the scope of application of such liquid level gauge can be expanded.
Brief description of the drawings
Fig. 1 is the structural representation of coaxial cylindrical capacitance level transducer and in monitored liquid in the prior art
In placement schematic diagram；
Fig. 2 is Fig. 1 top view；
Fig. 3 be formed in the liquid that the electrical conductivity of the monitored liquid level of capacitance level transducer insertion is not zero etc.
Imitate circuit diagram；
Fig. 4 is the basic principle schematic of the detection circuit described in the utility model based on " electric charge measuring cup " method structure；
Fig. 5 is the further principle schematic for improving and detecting circuit gamut resolution ratio and circuit signal to noise ratio；
Fig. 6 is the first knot of the detection circuit for the liquid level height that monitoring electrical conductivity described in the utility model is not zero
Structure schematic diagram；
Fig. 7 is second of knot of the detection circuit for the liquid level height that monitoring electrical conductivity described in the utility model is not zero
Structure schematic diagram；
Fig. 8 is the structural representation of the liquid level gauge for the liquid level height that monitoring electrical conductivity described in the utility model is not zero
Figure；
Fig. 9 is the structural representation of capacitance level transducer in application examples 1；
Figure 10 is the structural representation of capacitance level transducer in application examples 2；
In figure, the 1-electrode that is uniformly wrapped up by insulating materials, 1-1-insulating materials, 2-bare electrode, 2-1-monitored
The liquid that is not zero of electrical conductivity, 3-single-chip microcomputer, 4-operational amplifier, 5-support, 5-1-guide plate, 6-drum type washing
Clothing machine water tank, K1- the first analog switch, K2- the second analog switch, K3- the three analog switch, C1Standard known to-capacity
Electric capacity C1-1Standard capacitance known to-the first capacity, C1-2Standard capacitance known to-the second capacity.
Embodiment
Below by embodiment and application examples and with reference to accompanying drawing to the liquid described in the utility model for monitoring electrical conductivity and being not zero
The capacitance type liquid level detection circuit and capacitance level gauge of body liquid level are described further.
Embodiment 1
In the present embodiment, the detection circuit for the liquid level height that monitoring electrical conductivity is not zero is as shown in fig. 6, including monolithic
Machine 3, operational amplifier 4, the first analog switch K1, the second analog switch K2With a capacity known to standard capacitance C1, the fortune
Calculate amplifier 4 and connect into voltage follower, the first analog switch K1Input and single-chip microcomputer an I/O mouths P05 connect
Connect (by the I/O mouths of single-chip microcomputer through the first analog switch K1To measured capacitance CxCharge power supply is provided, that is, provided in Fig. 4
“Vref"), the first analog switch K1Output end and the second analog switch K2Input connection, the second analog switch K2Output
End and standard capacitance C known to capacity1One end connected with the input of voltage follower, the first analog switch K1With
Two analog switch K2Control terminal be connected respectively with I/O mouths P04, P03 of single-chip microcomputer, the output end and list of the voltage follower
The AD mouths connection of piece machine, standard capacitance C known to the capacity1The other end and the detection circuit be signally connected.
Embodiment 2
In the present embodiment, the detection circuit for the liquid level height that monitoring electrical conductivity is not zero is as shown in fig. 7, comprises monolithic
Machine 3, operational amplifier 4, the first analog switch K1, the second analog switch K2, the 3rd analog switch K3, the first capacity is known marks
Pseudo-capacitance C1-1With the second capacity known to standard capacitance C1-2, the operational amplifier 4 connects into voltage follower, and described first
Analog switch K1Input and single-chip microcomputer an I/O mouths P05 connection (by the I/O mouths of single-chip microcomputer through the first analog switch K1To
Measured capacitance CxCharge power supply is provided, that is, " the V in Fig. 5 is providedref"), the first analog switch K1Output end and the second mould
Intend switch K2Input connection, the second analog switch K2Output end and the first capacity known to standard capacitance C1-1One end and
The input connection of voltage follower, the 3rd analog switch K3Input and the second analog switch K2Output end connection, the 3rd
Analog switch K3Output end and the second capacity known to standard capacitance C1-2One end connection, the first analog switch K1,
Two analog switch K2With the 3rd analog switch K3Control terminal be connected respectively with I/O mouths P04, P03, P02 of single-chip microcomputer, the electricity
The output end of follower and the AD mouths of single-chip microcomputer is pressed to connect, standard capacitance C known to first capacity1-1With the second capacity
The standard capacitance C known1-2The other end be signally connected with the detection circuit.
Embodiment 3
In the present embodiment, the liquid level gauge for the liquid level height that monitoring electrical conductivity is not zero is as shown in figure 8, by monitoring conductance
The detection circuit and capacitance level transducer for the liquid level height that rate is not zero are formed；What the monitoring electrical conductivity was not zero
The detection circuit of liquid level height is same as Example 2, and the capacitance level transducer is equal by insulating materials 1-1 by one
The electrode 1 of even parcel and a bare electrode 2 that can be directly contacted with liquid in the bottom limit level of monitored target setting form, electricity
The cross section of pole 1 is rectangle, and the cross section of bare electrode 2 is circle, the global shape of electrode 1 and bare electrode 2 be it is shaft-like, they
Between be separated by a spacing and be placed in the liquid that the electrical conductivity of monitored liquid level is not zero；The electrode 1 and first is simulated
Switch K1Output end connection, the bare electrode 2 and capacitance type liquid level detect being signally connected for circuit.
When liquid level gauge monitors liquid level described in the present embodiment, workflow is as follows：
1. the electrode 1 uniformly wrapped up by insulating materials in capacitance level transducer and bare electrode 2 are inserted monitored
In the liquid of liquid level, and make detection circuit in running order；
2. single-chip microcomputer 3 is detected by aforementioned principles after start, the liquid level of monitored liquid is provided.
Application examples 1
The application example is used to monitor the liquid level in humidifier, electric shown in circuit and Fig. 9 using being detected described in embodiment 2
The liquid level gauge that appearance formula liquid level sensor is formed.
Circuit is detected as shown in fig. 7, in the circuit, standard capacitance C known to the first capacity1-1=100P, the second capacity is
The standard capacitance C known1-2=1000P, the model N76E003, the first analog switch K of single-chip microcomputer 31, the second analog switch K2,
Three analog switch K3Be model CD4066 4 path analoging switch in three path analoging switch；Operational amplifier 4 is model
In LT1013 single supply two-way operational amplifier all the way；Detect circuit to power using 5V dc sources, i.e. VCC=5V.
Capacitance level transducer is as shown in figure 9, be thickness by the electrode 1 and bare electrode 2 that insulating materials uniformly wraps up
0.5mm, wide 5mm stainless steel band, the lower end of the electrode 1 uniformly wrapped up by insulating materials is L-shaped, wraps up the insulation material of electrode 1
Material 1-1 is the polyester material that thickness is 0.15mm；The electrode 1 and bare electrode 2 uniformly wrapped up by insulating materials is with 20mm spacing
Symmetrically it is fixed on support 5, the both sides of support 5 are provided with the guide plate 5-1 matched with the guide groove in humidifier water tank side wall, make
Used time, support 5 are inserted into by the guide plate of both sides in the guide groove of humidifier water tank side wall, can be slided along guide groove, humidifier
Bottom limit level is determined by the terminal position for the bare electrode 2 being fixed on support 5, in the application example, bottom limit level to water tank bottom
Height be 15mm, the electrode 1 uniformly wrapped up by insulating materials is located at the L-shaped section of " bottom limit level " below as " scale electricity
Pole ", the total length of the scale electrode is 35mm.
The analog switch K of electrode 1 and first uniformly wrapped up by insulating materials1Output end connection, bare electrode 2 with detection electricity
Road is signally connected.
The application example employs the liquid level sensor with scale electrode, thus can be after powering plus realized during water
Auto-scaling；Difference in height between the bottom limit level and upper limit level of the application example is 120mm, full scale monitoring accuracy is reachable ±
1%, resolution ratio is up to 0.5mm；Monitoring result phase in humidifier water tank plus obtained by running water, salt solution or drinking pure water
Together.
Application examples 2
The application example monitors the height of water level of tumbling-box washing machine, is detected using described in embodiment 1 shown in circuit and Figure 10
The capacitance level gauge that capacitance level transducer is formed.
Circuit is detected as shown in fig. 6, in the circuit, standard capacitance C known to capacity1=300P, the model of single-chip microcomputer 3
N76E003, the first analog switch K1, the second analog switch K2Be model CD4066 4 path analoging switch in two-way simulation open
Close；Operational amplifier 4 be model LT1013 single supply two-way operational amplifier in all the way.
Capacitance level transducer is as shown in Figure 10, and the electrode 1 uniformly wrapped up by insulating materials is thick 0.8mm, wide 10mm
Stainless steel band, parcel electrode 1 insulating materials 1-1 be thick 0.15mm polyester material, bare electrode 2 be diameter 0.5mm not
Become rusty steel wire；In use, the electrode 1 be bent to the circular arc that chamber size matches in washing machine cylindrical water tank 6, and with circle
Cylindricality water tank arranged concentric, the arc-shaped outer surface of electrode 1 and the spacing of tank inner wall are 1mm, and the bare electrode 2 is along tank inner wall
Arrangement, its end can contact in the bottom limit level that water tank is set with the water in water tank, and electrode 1 and bare electrode 2 are by being arranged on
Buckle on water tank is fixed, and in the application example, the height of bottom limit level to water tank minimum point is 10mm.
The analog switch K of electrode 1 and first uniformly wrapped up by insulating materials1Output end connection, bare electrode 2 with detection electricity
Road is signally connected.
Due to monitored liquid level H and CxNon-linear relation, by the arc length and C of the electrode 1 of water submergedxIt is linear
Relation, thus can will be with CxThe arc length of the corresponding electrode 1 by water submerged is converted into corresponding liquid level H and calibrated.
Liquid level gauge in the application example, allow the prison between liquid level (upper limit level) in water tank bottom limit level and water tank highest
Precision reachable ± 3% is surveyed, it is to running water or identical added with the monitoring result of the running water of washing powder.
Claims (5)
1. a kind of detection circuit for monitoring the liquid level height that electrical conductivity is not zero, it is characterised in that the circuit includes single-chip microcomputer
(3), operational amplifier (4), the first analog switch (K1), the second analog switch (K2) and capacity known to standard capacitance (C1), institute
State operational amplifier (4) and connect into voltage follower, the first analog switch (K1) input and single-chip microcomputer an I/O
Mouth connection, the first analog switch (K1) output end and the second analog switch (K2) input connection, the second analog switch (K2)
Output end and capacity known to standard capacitance (C1) one end connected with the input of voltage follower, it is described first simulation open
Close (K1) and the second analog switch (K2) control terminal be connected respectively with an I/O mouth of single-chip microcomputer, the voltage follower it is defeated
Go out end to be connected with the AD mouths of single-chip microcomputer, standard capacitance (C known to the capacity1) the other end and the detection circuit signal ground
Connection.
2. the detection circuit for the liquid level height that monitoring electrical conductivity is not zero according to claim 1, it is characterised in that institute
State standard capacitance (C known to capacity1) standard capacitance (C as known to the first capacity1-1) and the second capacity known to standard capacitance
(C1-2) parallel combination forms, and is additionally arranged the 3rd analog switch (K3), the second analog switch (K2) output end and first
Standard capacitance (C known to capacity1-1) one end connected with the input of voltage follower, the 3rd analog switch (K3) input
End and the second analog switch (K2) output end connection, the 3rd analog switch (K3) output end and the second capacity known to standard
Electric capacity (C1-2) one end connection, the 3rd analog switch (K3) control terminal and single-chip microcomputer an I/O mouth connect, described first
Standard capacitance (C known to capacity1-1) and the second capacity known to standard capacitance (C1-2) the other end with the detection circuit
It is signally connected.
3. a kind of liquid level gauge for monitoring the liquid level height that electrical conductivity is not zero, it is characterised in that by claim 1 or right
It is required that the 2 detection circuits and capacitance level transducer are formed, the capacitance level transducer is by one by insulating materials
The electrode (1) uniformly wrapped up and a bare electrode (2) that can be directly contacted with liquid in the bottom limit level of monitored target setting
Composition, the electrode (1) uniformly wrapped up by insulating materials and the first analog switch (K1) output end connection, bare electrode (2) with inspection
Slowdown monitoring circuit is signally connected.
4. the liquid level gauge for the liquid level height that monitoring electrical conductivity is not zero according to claim 3, it is characterised in that electric capacity
The shape of cross section of the electrode (1) uniformly wrapped up by insulating materials and bare electrode (2) in formula liquid level sensor is circular, oval
Shape or polygon, global shape are shaft-like, banding or arcuation.
5. the liquid level gauge for the liquid level height being not zero according to the monitoring electrical conductivity of claim 3 or 4, it is characterised in that electricity
The mutual alignment relation of the electrode (1) and bare electrode (2) that are uniformly wrapped up by insulating materials in appearance formula liquid level sensor is not restricted
About.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110132320A (en) * | 2019-06-13 | 2019-08-16 | 成都祥民科技发展有限责任公司 | The method for monitoring capacitance type sensor capacitance variations |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110132320A (en) * | 2019-06-13 | 2019-08-16 | 成都祥民科技发展有限责任公司 | The method for monitoring capacitance type sensor capacitance variations |
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