CN108896131B - Level gauging unit and material level gauge in RF admittance level meter based on temperature-compensating - Google Patents
Level gauging unit and material level gauge in RF admittance level meter based on temperature-compensating Download PDFInfo
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- CN108896131B CN108896131B CN201810431128.1A CN201810431128A CN108896131B CN 108896131 B CN108896131 B CN 108896131B CN 201810431128 A CN201810431128 A CN 201810431128A CN 108896131 B CN108896131 B CN 108896131B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
- G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
- G01F23/266—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors measuring circuits therefor
Abstract
The invention discloses the level gauging units and material level gauge in a kind of RF admittance level meter based on temperature-compensating, the level gauging unit includes: the first measuring electrode, the second measuring electrode and the measuring circuit being electrically connected with the first, second measuring electrode, the lower end of first, second measuring electrode is all inserted into level material container to be measured, and upper end is electrically connected to measuring circuit；Measuring circuit includes: the Acquisition Circuit of the first frequency-selective network, the second frequency-selective network, third frequency-selective network, temperature-compensation circuit, pumping signal generation circuit, the phase shift of π/4 narrow-pulse generation circuit and the phase point amplitude signal of π/4；Pumping signal generation circuit generates sine wave exciting signal S1, and the phase shift narrow-pulse generation circuit of π/4 is electrically connected to the output end of pumping signal generation circuit, receives pumping signal S1；The phase shift narrow-pulse generation circuit of π/4 is also electrically connected to the Acquisition Circuit of the phase point amplitude signal of π/4, and Acquisition Circuit receives narrow pulse signal S4, exports the phase point amplitude signal of π/4 S5.
Description
Technical field
The present invention relates to level gauging fields, more particularly to a kind of T-type frequency-selective network auxiliary value that is based on to eliminate bridging shadow
In loud RF admittance level meter, the level gauging unit of temperature-compensating can be carried out.
Background technique
Current contact material level gauge (level switch) is widely used in field of industrial production, and principle multiplicity is various in style.
Wherein, the Level measurements device such as tuning-fork type material level gauge, capacitance level meter, radar material level gauge, mechanical material level gauge occupies absolutely
Most of market share.But there are still defects in the industrial production for these current contact material level gauges, when measured object
When material is attached on the surface of measuring electrode, error can be brought to measurement, long-term in measurement environment cannot reliably used, at
For a key factor for restricting safety in production；Or restricted application and higher cost, it makes troubles to production.
Radio frequency admittance formula material level gauge be it is a kind of grow up from capacitance level meter, anti-bridging, it is more reliable, more acurrate,
The wider array of novel article position measuring device of applicability, is the upgrading of capacitance object position technology.The meaning of so-called radio frequency admittance, admittance is
The inverse of electricity middle impedance, it is formed by resistive compositions, capacitive component, sensitive ingredients synthesis, and radio frequency, that is, high frequency is wireless
Electric wave spectrum, so radio frequency admittance can be understood as with the admittance of high frequency radio wave measurement.When instrumentation, instrument is used to sense
Two electrodes (wherein an electrode can be fill wall) and measured medium form admittance value, when level changes, admittance value corresponding change,
Circuit unit will measure admittance value and be converted into the output of level signal, realize level gauging.Frequently with following several method:
1, MCU carries out zero point detection, takes and does copped wave integral between 3 positions the π of π/4 to 7/4, is controlled and is believed by optoelectronic switch
Number；This method data point is more, and operation is complex.
2, using capacitor, resistance combination, make the value of signal phase shift π/4；Although this method circuit is simple, measurement result
Poor, testing capacitance value changes when level changes, and causes phase shift to change therewith, measurement error can be larger.
3, the impedance and capacitive reactance that capacitance sensor is calculated using MCU, are pushed away bridging capacitive reactance by radio frequency admittance principle is counter, obtain reality
Border capacitance；This method calculates complexity, and there are larger unknown errors for data.
In addition, in the industrial production, material level gauge is affected for the measurement tested person environment of practical level.Temperature change
It will cause the error of level gauging, this error is that circuit itself generates.If such as material level gauge is used in China Hainan and China
Heilungkiang, can all cause the result measured to generate great error because too high or too low for temperature, and error in the industrial production can
It has an immense impact on to the instruction of instrument, record, alarm and control.Error brought by this temperature change is in the hardware design
It must eliminate.
It is eliminated there are mainly two types of the methods that temperature influences material level gauge measurement result at present:
1, density null method: the mistake for causing the variable density of measured medium to generate measurement due to temperature change is eliminated
Difference, density null method are by increasing the circuit to Medium Measurement density, to measure the change of density, with effective density change pair
The influence of measurement error；However, this method does not eliminate influence of the circuit due to temperature change to measurement result itself；
2, Electrode treatment method: mainly by handling measuring electrode, thermal insulation material, reduction pair are wrapped up on the electrode
The influence of circuit；The method does not eliminate influence of the circuit due to temperature change to measurement result itself equally.
Summary of the invention
At actual industrial scene, bridging is always had on sensing electrode and is sticked, form false level；The bridging part sticked can
To regard the appearance being made of capacitor and resistance resistance network as.The technical problems to be solved by the present invention are: how when measuring level
It really eliminates material and is suspended on caused measurement error in measuring electrode, and keep measurement result not influenced by ambient temperature.
It is pointed out in radio frequency admittance theory, " when the bridging layer long enough real part (resistance of bridging layer bring equivalent impedance Z
It R is) equal with imaginary part (capacitive reactance X) ".It is in brief exactly that is, 45 °, to be detected because the impedance angle of adhesion substances formation is π/4
Electrode both ends add a high-frequency excitation signal (15-400KHz), while taking at the actual measurement electrode tip level signal phase point of π/4
Value can theoretically accomplish to eliminate the false level information generated on electrode by adhesion substances in this way.
In order to solve the above technical problems, the technical scheme adopted by the invention is that: by by singlechip group at circuit, choosing
The amplitude for taking out the phase point of π/4 in measured signal obtains accurate level height by carrying out A/D conversion to this amplitude；Together
When, influence of the temperature to measurement result is eliminated by established standards capacitor.Specifically,
The present invention provides the level gauging unit based on temperature-compensating in a kind of RF admittance level meter, comprising: first surveys
Measure electrode, the second measuring electrode and the measuring circuit being electrically connected with the first, second measuring electrode, first, second measurement
The lower end of electrode is all inserted into level material container to be measured, and upper end is electrically connected to the measuring circuit；Wherein,
First, second measuring electrode is equivalent to two pole plates of a capacitor respectively, between the first, second measuring electrode
Material is dielectric, using the capacitor as testing capacitance CIt surveys；
The measuring circuit include: the first frequency-selective network, the second frequency-selective network, third frequency-selective network, temperature-compensation circuit,
The Acquisition Circuit of the phase shift of pumping signal generation circuit, π/4 narrow-pulse generation circuit and the phase point amplitude signal of π/4；
The temperature-compensation circuit includes standard capacitance CMark, resistance R0 ' and analog switch K, wherein the standard capacitance
CMarkFor the capacitor of low-temperature coefficient, the analog switch K is single-pole double-throw switch (SPDT), the standard capacitance CMarkIt is in parallel with resistance R0 ',
The first end of parallel combination is connected to the first stationary contact of the analog switch K；
First frequency-selective network includes capacitor C1 and inductance L1 in parallel, and second frequency-selective network includes electricity in parallel
Hold C2 and inductance L2, the third frequency-selective network includes capacitor C3 and inductance L3 in parallel；First frequency-selective network is through resistance
R1 is electrically connected to the first output end of the pumping signal generation circuit, and second frequency-selective network is electrically connected to institute through resistance R2
The second output terminal of pumping signal generation circuit is stated, the first end of the third frequency-selective network is grounded through a resistance R3；Described
One frequency-selective network is electrically connected to second frequency-selecting through capacitor C4 and resistance R4 in parallel, again through capacitor C5 and resistance R5 in parallel
Network；If the place of electrical connection between capacitor C4, resistance R4 in parallel and capacitor C5, resistance R5 in parallel is Q1, testing capacitance CIt surveys
After in parallel with resistance R0, one end is electrically connected to Q1, and the other end is electrically connected to the second stationary contact of the analog switch K；The mark
Pseudo-capacitance CMarkQ1 is also electrically connected to the second end of resistance R0 ' parallel combination；The movable contact of the analog switch K is electrically connected to institute
The second end of third frequency-selective network is stated, if the movable contact of the analog switch K is tested point Q0, the phase point amplitude of the π/4 letter
Number Acquisition Circuit be electrically connected to tested point Q0, receive the measured signal S0 drawn from tested point Q0；
The pumping signal generation circuit is for generating sine wave exciting signal S1 and exporting；
The phase shift narrow-pulse generation circuit of the π/4 is electrically connected to the third output end of the pumping signal generation circuit, connects
Receive the sine wave exciting signal S1 issued from the pumping signal generation circuit；The phase shift of the π/4 narrow-pulse generation circuit is also
It is electrically connected to the Acquisition Circuit of the phase point amplitude signal of the π/4, the Acquisition Circuit of the phase point amplitude signal of the π/4, which receives, to be come
From the phase shift narrow-pulse generation circuit of the π/4, compared with Q0 point signal phase shift π/4 narrow pulse signal S4, export the phase of π/4
Point amplitude signal S5.
Based on the above technical solution, the present invention can also be improved as follows.
Preferably, it is equipped in the phase shift narrow-pulse generation circuit of the π/4: digital regulation resistance U1, operational amplifier U2, operation
Amplifier U3, monostable flipflop U4, resistance R6~R13, capacitor C6~C10, and the phase shift narrow-pulse generation circuit of the π/4
Power supply is DC power supply Vcc；Wherein,
The input terminal of the digital regulation resistance U1 is electrically connected to external single-chip microcontroller, ground terminal ground connection, power end electrical connection
To power Vcc, which is also grounded through capacitor C10；The W output end of the digital regulation resistance U1 is electrically connected to the operation and puts
The non-inverting input terminal of big device U2, which is also electrically connected to power Vcc through resistance R13, and is grounded through capacitor C9；The number
The L output end of potentiometer U1 is grounded；
The inverting input terminal of the operational amplifier U2 is electrically connected to the output of the operational amplifier U2 through resistance R12
End；The power end of the operational amplifier U2 is electrically connected to power Vcc, ground terminal ground connection；The output of the operational amplifier U2
End is electrically connected to the non-inverting input terminal of the operational amplifier U3 through resistance R11, again through resistance R10, wherein resistance R11 and electricity
It is grounded at electrical connection between resistance R10 through capacitor C8；
The non-inverting input terminal of the operational amplifier U3 is also electrically connected to the output of the operational amplifier U3 through resistance R7
End；The inverting input terminal of the operational amplifier U3 is grounded through resistance R9, is also electrically connected to power Vcc through resistance R8, and through electricity
Hold the output end that C7 is electrically connected to the pumping signal generation circuit, receives and issued just from the pumping signal generation circuit
String wave excitation signal S1；The power end of the operational amplifier U3 is electrically connected to power Vcc, ground terminal ground connection；The operation is put
The output end of big device U3 is electrically connected to the input terminal of the monostable flipflop U4；
The Rext terminal of the monostable flipflop U4 is electrically connected to power Vcc through resistance R6, is also electrically connected through capacitor C6
To Cext terminal；The output end of the monostable flipflop U4 exports the narrow pulse signal S4 of phase shift π/4 compared with Q0 point signal
To the Acquisition Circuit；The power end of the monostable flipflop U4 is electrically connected to power Vcc, ground terminal ground connection.
Preferably, it is equipped in the Acquisition Circuit of the phase point amplitude signal of the π/4: operational amplifier U5, operational amplifier
U6, analog switch U7, operational amplifier U8, resistance R14~R21, capacitor C11~C13, and the phase point amplitude signal of the π/4
Acquisition Circuit power supply be DC power supply Vcc；Wherein,
The non-inverting input terminal of the operational amplifier U5 is electrically connected to tested point Q0 through resistance R21, receives and comes from tested point
The measured signal S0 that Q0 is drawn；The inverting input terminal of the operational amplifier U5 is electrically connected to the output of the operational amplifier U5
End；The power end of the operational amplifier U5 is electrically connected to power Vcc, ground terminal ground connection；The output of the operational amplifier U5
End is electrically connected to the non-inverting input terminal of the operational amplifier U6 through capacitor C13, again through resistance R20；
The non-inverting input terminal of the operational amplifier U6 is also electrically connected to power Vcc through resistance R18, and connects through resistance R19
Ground；The inverting input terminal of the operational amplifier U6 is electrically connected to the output end of the operational amplifier U6 through resistance R17；It is described
The power end of operational amplifier U6 is electrically connected to power Vcc, ground terminal ground connection；The output end of the operational amplifier U6 is electrically connected
To the input terminal of the analog switch U7；
The control terminal of the analog switch U7 is electrically connected to the output end of the monostable flipflop U4, receives and believes with Q0 point
Number compare phase shift π/4 narrow pulse signal S4；The normally opened output end of the analog switch U7 is grounded through capacitor C12；The simulation
The power end of switch U7 is electrically connected to power Vcc, ground terminal ground connection；The output end of the analog switch U7 is also through resistance R16 electricity
It is connected to the non-inverting input terminal of the operational amplifier U8；
The inverting input terminal of the operational amplifier U8 is electrically connected to the operation through resistance R14 and capacitor C11 in parallel
The inverting input terminal of the output end of amplifier U8, the operational amplifier U8 is also grounded through resistance R15；The operational amplifier U8
Output end export the phase point of π/4 amplitude signal S5, be sent to external single-chip microcontroller；The power end electricity of the operational amplifier U8
It is connected to power Vcc, ground terminal ground connection.
Preferably, the digital regulation resistance U1 is MAX540IEKA-T.
Preferably, the operational amplifier U2 and/or U8 is TLV2451.
Preferably, described operational amplifier U3, U5 and/or U6 are OPA835.
Preferably, the monostable flipflop U4 is SN74LVC1G123.
Preferably, the analog switch U7 is TS5A3160DCUR.
The present invention provides a kind of RF admittance level meter, including above-mentioned level gauging unit, and,
The single-chip microcontroller being electrically connected with the level gauging unit；
For accommodating the shell of the level gauging unit and single-chip microcontroller；
It is embedded at the case surface, the display unit with the monolithic mechatronics.
Preferably, it is equipped with the communication interface for carrying out wire communication with host computer in the single-chip microcontroller, or is carried out with host computer
The communication module of wireless telecommunications.
Compared with prior art, the present invention has the following technical effect that
1, in the detection circuit of instrument and meter, the parameter of the device of inductance and capacitance characteristic can variation with temperature generation
Biggish variable quantity, the relationship between this variable quantity and temperature are nonlinear；Especially detected physical quantity belongs to electricity
When holding characteristic, this variable quantity is affected to detected physical quantity, generates a certain amount of error, this error and temperature it
Between none governed rule, can not be modified with temperature parameters；The present invention can in circuit due to inductance and capacitor
The parameter of the device of characteristic varies with temperature the variable quantity of generation, when caused detected physical quantity belongs to capacitance characteristic,
The error generated to detected physical quantity is accurately corrected；
2, by generating burst pulse at signal π/4, the i.e. 45 ° phase of measurement point, control measurement can effectively eliminate extension
Material influences measurement bring；
3, the T-type frequency-selective network in measuring circuit has filtered out the interference of the harmonic wave from all directions, turns on fundamental wave, and
And the more stable signal for selecting the phase point of required π/4, keep measurement more accurate.
Detailed description of the invention
Fig. 1 is the use state diagram of level gauging unit of the invention；
Fig. 2 is the circuit structure diagram of level gauging unit of the invention；
Fig. 3 is the natural resonance frequency and magnitude relation curve graph for causing variation by level variation；
Fig. 4 is the phase shift of π of the invention/4 narrow-pulse generation circuit structure chart；
Fig. 5 is shown as the waveform diagram of narrow pulse signal S4；
Fig. 6 is shown as the contrast effect figure of measured signal Yu the phase shift narrow pulse signal of π/4 S4；
Fig. 7 is the circuit structure diagram of the Acquisition Circuit of the phase point amplitude signal of π of the invention/4.
In the accompanying drawings, list of designations represented by each label is as follows:
100 levels material container to be measured
101 first measuring electrodes
102 second measuring electrodes
200 measuring circuits
201 first frequency-selective networks
202 second frequency-selective networks
203 third frequency-selective networks
204 pumping signal generation circuits
The phase shift narrow-pulse generation circuit of 205 π/4
The Acquisition Circuit of the phase point amplitude signal of 206 π/4
Specific embodiment
The principle and features of the present invention will be described below with reference to the accompanying drawings, and the given examples are served only to explain the present invention, and
It is non-to be used to limit the scope of the invention.
It please refers to shown in Fig. 1, is the use state diagram of level gauging unit of the invention.The level gauging list
Member includes: the first measuring electrode 101, the second measuring electrode 102 and the measuring circuit being electrically connected with the first, second measuring electrode
200, wherein in the lower end insertion level material container 100 to be measured of first, second measuring electrode, upper end is electrically connected to
The measuring circuit 200；Optionally, second measuring electrode is also possible to the metallic walls of the material container 100；
Level gauging unit of the invention measures the height of level using the first, second measuring electrode, can be equivalent to: the
One, the second measuring electrode is respectively two pole plates of a capacitor, and the material between the first, second measuring electrode is then dielectric,
Using the capacitor as testing capacitance CIt surveys, by measuring CIt surveysSize, and then obtain level height.
It is the circuit structure diagram of level gauging unit of the invention referring again to shown in Fig. 2；In Fig. 2, with electricity to be measured
Hold CIt surveysThe first, second measuring electrode is indicated, since the level of material can change, so testing capacitance CIt surveysBeing can power transformation
Hold；The measuring circuit 200 includes: the first frequency-selective network 201, the second frequency-selective network 202, third frequency-selective network 203, temperature benefit
Repay adopting for circuit, pumping signal generation circuit 204, the phase shift of π/4 narrow-pulse generation circuit 205 and the phase point amplitude signal of π/4
Collector 206, wherein
The temperature-compensation circuit includes standard capacitance CMark, resistance R0 ' and analog switch K, wherein the standard capacitance
CMarkFor the capacitor of low-temperature coefficient, such as mica capacitor, the analog switch K is single-pole double-throw switch (SPDT), the standard capacitance CMark
In parallel with resistance R0 ', the first end of parallel combination is connected to the first stationary contact of the analog switch K；
First frequency-selective network 201 includes capacitor C1 and inductance L1 in parallel, and second frequency-selective network 202 includes simultaneously
The capacitor C2 and inductance L2 of connection, the third frequency-selective network 203 include capacitor C3 and inductance L3 in parallel；The first frequency-selecting net
Network 201 is electrically connected to the first output end of the pumping signal generation circuit 204, second frequency-selective network 202 through resistance R1
It is electrically connected to the second output terminal of the pumping signal generation circuit 204 through resistance R2, the first of the third frequency-selective network 203
End is grounded through a resistance R3；First frequency-selective network 201 through in parallel capacitor C4 and resistance R4, again through capacitor C5 in parallel and
Resistance R5 is electrically connected to second frequency-selective network 202；If in parallel capacitor C4, resistance R4 and capacitor C5 in parallel, resistance R5
Between electrical connection at be Q1, testing capacitance CIt surveysAfter in parallel with resistance R0, one end is electrically connected to Q1, and the other end is electrically connected to described
The second stationary contact of analog switch K；The standard capacitance CMarkQ1 is also electrically connected to the second end of resistance R0 ' parallel combination；Institute
The movable contact for stating analog switch K is electrically connected to the second end of the third frequency-selective network 203, i.e. L3 and C3 do not connect the terminal of R3,
If the movable contact of the analog switch K is tested point Q0, the Acquisition Circuit 206 of the phase point amplitude signal of the π/4 is electrically connected to
Tested point Q0 receives the measured signal S0 drawn from tested point Q0；Three frequency-selective networks constitute T-type frequency-selecting potential-divider network knot
Structure, electrical characteristics have filtered out the harmonic wave from all directions, turn on fundamental wave, and be conducive to more steadily to select required π/
The signal of 4 phase points.
The present invention repeatedly measures testing capacitance C by control analog switch as a result,It surveysMeasured value and standard capacitance CMark's
Measured value calculates CMarkRelative measurement error, calculate C with this relative measurement errorIt surveysMeasurement error, to eliminate temperature
Cause error.For example, CMarkActual value be 1000pF, at a certain temperature, the actual value of capacitor, inductance in circuit etc. all by
Temperature influences and is changed, so that CMarkMeasured value at 1050pF, then relative measurement error is 5%；So, warm herein
Under degree, the C that measuresIt surveysMeasured value also increase 5% compared with actual value.Need to be illustrated: material itself is affected by temperature
And to CIt surveysThe influence of generation is extremely low, can be neglected；Temperature-compensating of the invention is just for component in circuit by the shadow of temperature
It rings.
When analog switch K connects the first stationary contact, that access in measuring circuit is standard capacitance CMarkWith resistance R0's ' and
Connection combination, testing capacitance CIt surveysBe disconnected with the parallel combination of resistance R0, in this case, measurement be standard capacitance value, because
It is extremely low for the temperature coefficient of standard capacitance, it can be ignored by the interference of temperature；By the measured value and standard capacitance of standard capacitance
The comparison of practical capacitance size, relative measurement error can be calculated, then the second stationary contact is connected by single-chip microcontroller control analog switch；
When analog switch K connects the second stationary contact, that access in measuring circuit is testing capacitance CIt surveysWith resistance R0's and
Connection combination, standard capacitance CMarkIt is disconnected with the parallel combination of resistance R0 ', in this case, measures testing capacitance CIt surveysMeasured value,
The relative measurement error obtained when using measurement standard capacitor is modified in data show and automatically control, obtains standard
True testing capacitance CIt surveysCapacitance；
Need to be illustrated: the natural resonance frequency of entire circuit changes with the variation of testing capacitance；Letter to be measured
Number amplitude with circuit natural resonance frequency variation in similar quadratic function shape, as shown in figure 3, it is is changed by level
Cause the natural resonance frequency and magnitude relation curve graph of variation.Known material is more, and equivalent capacity is bigger, natural resonance frequency
Relationship with capacitor isThat is, frequency reduces with the increase of capacitor.It is accurate for value, guarantee result
Uniqueness takes in Fig. 3 close to linear part as natural resonance frequency exploitation range, i.e., and f1 as shown in Figure 3~
f2；In practical applications, can according to this frequency range, in conjunction with the size of material container, i.e., testing capacitance variation range (such as
0~45000pF), design the specific size of capacitor in three frequency-selective networks, inductance and outer connecting resistance.
Further, the pumping signal generation circuit 204 is for generating sine wave exciting signal S1 and exporting, that is, excitation
Signal generating circuit is sine wave generating circuit；Sine wave generating circuit is this field circuit common, such as has Wien bridge circuit, number
Word sine-wave generator etc. can all be realized and generate this function of sine wave, as the state of the art, those skilled in the art
Member can be selected according to actual needs, and details are not described herein again.
Further, the phase shift of the π/4 narrow-pulse generation circuit 205 is electrically connected to the pumping signal generation circuit 204
Third output end receives the sine wave exciting signal S1 issued from the pumping signal generation circuit 204；The phase shift of the π/4
The Acquisition Circuit 206 that narrow-pulse generation circuit 205 is also electrically connected to the phase point amplitude signal of the π/4 (is all referred to as adopted below
Collector 206), the Acquisition Circuit 206 receive it is from the phase shift of the π/4 narrow-pulse generation circuit 205, with Q0 point signal phase
Than the narrow pulse signal S4 of phase shift π/4；Specifically,
Shown in referring to figure 4., Fig. 4 is the phase shift of π of the invention/4 narrow-pulse generation circuit structure chart；The phase shift of the π/4 is narrow
It is equipped in pulse-generating circuit: digital regulation resistance U1, operational amplifier U2, operational amplifier U3, monostable flipflop U4, resistance
R6~R13, capacitor C6~C10, and the power supply of the phase shift narrow-pulse generation circuit of the π/4 is DC power supply Vcc；Wherein,
The input terminal of the digital regulation resistance U1 is electrically connected to external single-chip microcontroller, ground terminal ground connection, power end electrical connection
To power Vcc, which is also grounded through capacitor C10；The W output end of the digital regulation resistance U1 is electrically connected to the operation and puts
The non-inverting input terminal of big device U2, which is also electrically connected to power Vcc through resistance R13, and is grounded through capacitor C9；The number
The L output end of potentiometer U1 is grounded；I.e. digital regulation resistance U1 connects with resistance R13 and is followed by between power supply and ground, among the two
Tie point is electrically connected to the non-inverting input terminal of the operational amplifier U2.The inverting input terminal of the operational amplifier U2 is through resistance
R12 is electrically connected to the output end of the operational amplifier U2；The power end of the operational amplifier U2 is electrically connected to power Vcc,
Ground terminal ground connection；Form voltage follower circuit.The output end of the operational amplifier U2 is electrically connected through resistance R11, again through resistance R10
It is connected to the non-inverting input terminal of the operational amplifier U3, wherein be electrically connected place through capacitor C8 between resistance R11 and resistance R10
Ground connection；The non-inverting input terminal of the operational amplifier U3 is also electrically connected to the output end of the operational amplifier U3 through resistance R7；
The inverting input terminal of the operational amplifier U3 is grounded through resistance R9, is also electrically connected to power Vcc through resistance R8, and through capacitor C7
It is electrically connected to the output end of the pumping signal generation circuit 204, what reception was issued from the pumping signal generation circuit 204
Sine wave exciting signal S1；The power end of the operational amplifier U3 is electrically connected to power Vcc, ground terminal ground connection；The operation
The output end of amplifier U3 is electrically connected to the input terminal of the monostable flipflop U4；The end Rext of the monostable flipflop U4
Son is electrically connected to power Vcc through resistance R6, is also electrically connected to Cext terminal through capacitor C6, since pulse signal needs to control simulation
Switch, the amplitude size of measured signal when accurately obtaining π/4, needs lesser duty ratio, and making pulse width is about 100ns,
Therefore R6 should be big resistance, and C6 should be small capacitances, such as resistance R6 selects 1k Ω, capacitor C6 to select 20pF；The monostable touching
The output end for sending out device U4 exports the narrow pulse signal S4 of phase shift π/4 compared with Q0 point signal to the Acquisition Circuit 206；The list
The power end of steady state trigger U4 is electrically connected to power Vcc, ground terminal ground connection.
Single-chip microcontroller inputs to the data that digital regulation resistance U1 and current testing capacitance match as a result, adjusts the resistance value of U1,
And then operational amplifier U2 is made to export a reference voltage signal to match with current testing capacitance, as operational amplifier U3
Reference voltage；The square-wave signal of U3 output is input at the input terminal pin 1 of monostable flipflop U4, square-wave signal S3
Failing edge monostable flipflop is triggered, make monostable flipflop output pin export narrow pulse signal；Adjust connection
Change pulse width in the capacitor C6 of monostable flipflop pin 6,7, the size of resistance R6, making pulse width is about 100ns, In
Monostable flipflop output pin exports narrow pulse signal S4, as shown in Figure 5；Obtained narrow pulse signal S4 and measured signal phase
Than having differed the phase shift of π/4, the contrast effect figure of measured signal and the phase shift narrow pulse signal of π/4 S4 is as shown in Figure 6.
Preferably, MAX540IEKA-T can be selected in the digital regulation resistance U1；
Preferably, TLV2451 can be selected in the operational amplifier U2；
Preferably, OPA835 can be selected in the operational amplifier U3；
Preferably, SN74LVC1G123 can be selected in the monostable flipflop U4.
Next, being the circuit of the Acquisition Circuit of the phase point amplitude signal of π of the invention/4 referring again to shown in Fig. 7
Structure chart；It is equipped in the Acquisition Circuit: operational amplifier U5, operational amplifier U6, analog switch U7, operational amplifier U8,
Resistance R14~R21, capacitor C11~C13, and the power supply of the Acquisition Circuit is DC power supply Vcc；Wherein,
The non-inverting input terminal of the operational amplifier U5 is electrically connected to tested point Q0 through resistance R21, receives and comes from tested point
The measured signal S0 that Q0 is drawn；The inverting input terminal of the operational amplifier U5 is electrically connected to the output of the operational amplifier U5
End；The power end of the operational amplifier U5 is electrically connected to power Vcc, ground terminal ground connection；The output of the operational amplifier U5
End is electrically connected to the non-inverting input terminal of the operational amplifier U6, the operational amplifier U6 through capacitor C13, again through resistance R20
Non-inverting input terminal be also electrically connected to power Vcc through resistance R18, and be grounded through resistance R19；The reverse phase of the operational amplifier U6
Input terminal is electrically connected to the output end of the operational amplifier U6 through resistance R17；The power end of the operational amplifier U6 is electrically connected
It is connected to power Vcc, ground terminal ground connection；The output end of the operational amplifier U6 is electrically connected to the input of the analog switch U7
End, the control terminal of the analog switch U7 are electrically connected to the output end of the monostable flipflop U4, receive and Q0 point signal phase
Than the narrow pulse signal S4 of phase shift π/4；The normally opened output end of the analog switch U7 is grounded through capacitor C12；The analog switch
The power end of U7 is electrically connected to power Vcc, ground terminal ground connection；The normally opened output end of the analog switch U7 is also through resistance R16 electricity
It is connected to the non-inverting input terminal of the operational amplifier U8；The inverting input terminal of the operational amplifier U8 is through resistance in parallel
R14 and capacitor C11 is electrically connected to the output end of the operational amplifier U8, and the inverting input terminal of the operational amplifier U8 also passes through
Resistance R15 ground connection；The output end of the operational amplifier U8 exports the phase point of π/4 amplitude signal S5, is sent to external monolithic
Machine；The power end of the operational amplifier U8 is electrically connected to power Vcc, ground terminal ground connection.
Measured signal S0 is input to input of the pin 3 of operational amplifier U5 in Fig. 7 as voltage follow as a result, to
It surveys signal S0 and is passing through primary voltage with subsequent, and be superimposed a DC potential, by being inputted again after operational amplifier U6 output
Input pin 4 to analog switch U7 is used as input signal, and the pin 6 of analog switch U7 controls foot and accesses monostable flipflop U4
The high level control analog switch U7 of the narrow pulse signal S4 of generation, burst pulse are led at the phase of the π of measured signal/4 every time
Logical, such measured signal S0 is to charge at the phase of π/4 to capacitor C12 every time, maintains the amplitude of the phase point of π/4.Above just
It is the whole process of data acquisition, data collected in this way are closer to true value.
Preferably, OPA835 all can be selected in described operational amplifier U5, U6；
Preferably, TS5A3160DCUR can be selected in the analog switch U7；
Preferably, TLV2451 can be selected in the operational amplifier U8.
Next, the phase point amplitude signal S5 of collected π/4 is carried out the analysis of data, processing by external single-chip microcontroller；
Single-chip microcontroller can also will analysis treated that data are sent to host computer, carry out further Data Analysis Services；By capacitance size
Level height is converted to, by many experiments calibration correction, obtains accurate level height.
Every time when measurement, single-chip microcontroller control analog switch first disconnects and the connection of testing capacitance, and is connected to standard capacitance
Side first measures the parameter of standard capacitance, since the parameter of standard capacitance is known, and the ginseng of standard capacitance
Amount not variation with temperature and change, the relative measurement error as brought by temperature change can be measured in this way；So
Single-chip microcontroller control analog switch disconnects the connection with standard capacitance again afterwards, and is connected to testing capacitance side, i.e., again to electricity to be measured
The parameter of appearance measures, at this moment measuring the result is that with error, then with the relative measurement as brought by temperature change
Error is modified, and can eliminate error, obtains accurate result.
In actual production, level gauging unit and external single-chip microcontroller are combined, are set in a shell,
Case surface can be embedded the display unit with monolithic mechatronics, after the analysis, processing of single-chip microcontroller progress data, by result
It is presented on display unit；If wishing to keep operation more humanized, necessary switch key etc. can also configure.
The foregoing is merely presently preferred embodiments of the present invention, is not intended to limit the invention, it is all in spirit of the invention and
Within principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.
Claims (10)
1. the level gauging unit in RF admittance level meter based on temperature-compensating, comprising: the first measuring electrode, the second measurement electricity
The lower end of pole and the measuring circuit being electrically connected with the first, second measuring electrode, first, second measuring electrode is all inserted into
In level material container to be measured, upper end is electrically connected to the measuring circuit；Wherein, respectively etc. by the first, second measuring electrode
Effect is two pole plates of a capacitor, and the material between the first, second measuring electrode is dielectric, using the capacitor as testing capacitance
CIt surveys；It is characterized in that,
The measuring circuit includes: the first frequency-selective network, the second frequency-selective network, third frequency-selective network, temperature-compensation circuit, excitation
The Acquisition Circuit of the phase shift of signal generating circuit, π/4 narrow-pulse generation circuit and the phase point amplitude signal of π/4；
The temperature-compensation circuit includes standard capacitance CMark, resistance R0 ' and analog switch K, wherein the standard capacitance CMarkFor
The capacitor of low-temperature coefficient, the analog switch K are single-pole double-throw switch (SPDT), the standard capacitance CMarkIt is in parallel with resistance R0 ', it is in parallel
Combined first end is connected to the first stationary contact of the analog switch K；
First frequency-selective network includes capacitor C1 and inductance L1 in parallel, and second frequency-selective network includes capacitor C2 in parallel
With inductance L2, the third frequency-selective network includes capacitor C3 and inductance L3 in parallel；First frequency-selective network is through resistance R1 electricity
It is connected to the first output end of the pumping signal generation circuit, second frequency-selective network is electrically connected to described sharp through resistance R2
The second output terminal of signal generating circuit is encouraged, the first end of the third frequency-selective network is grounded through a resistance R3；First choosing
Frequency network is electrically connected to the second frequency-selecting net through capacitor C4 and resistance R4 in parallel, again through capacitor C5 and resistance R5 in parallel
Network；If the place of electrical connection between capacitor C4, resistance R4 in parallel and capacitor C5, resistance R5 in parallel is Q1, testing capacitance CIt surveysWith
After resistance R0 is in parallel, one end is electrically connected to Q1, and the other end is electrically connected to the second stationary contact of the analog switch K；The standard
Capacitor CMarkQ1 is also electrically connected to the second end of resistance R0 ' parallel combination；The movable contact of the analog switch K is electrically connected to described
The second end of third frequency-selective network, if the movable contact of the analog switch K is tested point Q0, the phase point amplitude signal of the π/4
Acquisition Circuit be electrically connected to tested point Q0, receive the measured signal S0 drawn from tested point Q0；
The pumping signal generation circuit is for generating sine wave exciting signal S1 and exporting；
The phase shift narrow-pulse generation circuit of the π/4 is electrically connected to the third output end of the pumping signal generation circuit, receives and
The sine wave exciting signal S1 issued from the pumping signal generation circuit；The phase shift narrow-pulse generation circuit of the π/4 is also electrically connected
It is connected to the Acquisition Circuit of the phase point amplitude signal of the π/4, the Acquisition Circuit of the phase point amplitude signal of the π/4, which receives, comes from institute
State the phase shift narrow-pulse generation circuit of π/4, compared with Q0 point signal phase shift π/4 narrow pulse signal S4, output measured signal exist
The amplitude signal S5 of the phase point of π/4.
2. level gauging unit according to claim 1, which is characterized in that in the phase shift narrow-pulse generation circuit of the π/4
It is equipped with: digital regulation resistance U1, operational amplifier U2, operational amplifier U3, monostable flipflop U4, resistance R6~R13, capacitor C6
~C10, and the power supply of the phase shift narrow-pulse generation circuit of the π/4 is DC power supply Vcc；Wherein,
The input terminal of the digital regulation resistance U1 is electrically connected to external single-chip microcontroller, ground terminal ground connection, and power end is electrically connected to electricity
Source Vcc, the power end are also grounded through capacitor C10；The W output end of the digital regulation resistance U1 is electrically connected to the operational amplifier
The non-inverting input terminal of U2, which is also electrically connected to power Vcc through resistance R13, and is grounded through capacitor C9；The number current potential
The L output end of device U1 is grounded；
The inverting input terminal of the operational amplifier U2 is electrically connected to the output end of the operational amplifier U2 through resistance R12；Institute
The power end for stating operational amplifier U2 is electrically connected to power Vcc, ground terminal ground connection；The output end of the operational amplifier U2 is through electricity
Resistance R11, the non-inverting input terminal of the operational amplifier U3 is electrically connected to through resistance R10 again, wherein resistance R11 and resistance R10 it
Between electrical connection at be grounded through capacitor C8；
The non-inverting input terminal of the operational amplifier U3 is also electrically connected to the output end of the operational amplifier U3 through resistance R7；Institute
The inverting input terminal for stating operational amplifier U3 is grounded through resistance R9, is also electrically connected to power Vcc through resistance R8, and through capacitor C7 electricity
It is connected to the output end of the pumping signal generation circuit, the sine wave issued from the pumping signal generation circuit is received and swashs
Encourage signal S1；The power end of the operational amplifier U3 is electrically connected to power Vcc, ground terminal ground connection；The operational amplifier U3
Output end be electrically connected to the input terminal of the monostable flipflop U4；
The Rext terminal of the monostable flipflop U4 is electrically connected to power Vcc through resistance R6, is also electrically connected to through capacitor C6
Cext terminal；The output end of the monostable flipflop U4 exports the narrow pulse signal S4 of phase shift π/4 compared with Q0 point signal extremely
The Acquisition Circuit；The power end of the monostable flipflop U4 is electrically connected to power Vcc, ground terminal ground connection.
3. level gauging unit according to claim 1 or 2, which is characterized in that the phase point amplitude signal of the π/4 is adopted
It is equipped in collector: operational amplifier U5, operational amplifier U6, analog switch U7, operational amplifier U8, resistance R14~R21,
Capacitor C11~C13, and the power supply of the Acquisition Circuit of the phase point amplitude signal of the π/4 is DC power supply Vcc；Wherein,
The non-inverting input terminal of the operational amplifier U5 is electrically connected to tested point Q0 through resistance R21, receives and draws from tested point Q0
Measured signal S0 out；The inverting input terminal of the operational amplifier U5 is electrically connected to the output end of the operational amplifier U5；
The power end of the operational amplifier U5 is electrically connected to power Vcc, ground terminal ground connection；The output end of the operational amplifier U5 passes through
Capacitor C13, the non-inverting input terminal for being electrically connected to the operational amplifier U6 through resistance R20 again；
The non-inverting input terminal of the operational amplifier U6 is also electrically connected to power Vcc through resistance R18, and is grounded through resistance R19；Institute
The inverting input terminal for stating operational amplifier U6 is electrically connected to the output end of the operational amplifier U6 through resistance R17；The operation
The power end of amplifier U6 is electrically connected to power Vcc, ground terminal ground connection；The output end of the operational amplifier U6 is electrically connected to institute
State the input terminal of analog switch U7；
The control terminal of the analog switch U7 is electrically connected to the output end of the monostable flipflop U4, receives and Q0 point signal phase
Than the narrow pulse signal S4 of phase shift π/4；The normally opened output end of the analog switch U7 is grounded through capacitor C12；The analog switch
The power end of U7 is electrically connected to power Vcc, ground terminal ground connection；The normally opened output end of the analog switch U7 is also through resistance R16 electricity
It is connected to the non-inverting input terminal of the operational amplifier U8；
The inverting input terminal of the operational amplifier U8 is electrically connected to the operation amplifier through resistance R14 and capacitor C11 in parallel
The inverting input terminal of the output end of device U8, the operational amplifier U8 is also grounded through resistance R15；The operational amplifier U8's is defeated
Outlet exports the phase point of π/4 amplitude signal S5, is sent to external single-chip microcontroller；The power end of the operational amplifier U8 is electrically connected
To power Vcc, ground terminal ground connection.
4. level gauging unit according to claim 2, which is characterized in that the digital regulation resistance U1 is
MAX540IEKA-T。
5. level gauging unit according to claim 2, which is characterized in that the operational amplifier U2 and/or U8 is
TLV2451。
6. level gauging unit according to claim 2, which is characterized in that described operational amplifier U3, U5 and/or U6 are
OPA835。
7. level gauging unit according to claim 2, which is characterized in that the monostable flipflop U4 is
SN74LVC1G123。
8. level gauging unit according to claim 3, which is characterized in that the analog switch U7 is
TS5A3160DCUR。
9. a kind of RF admittance level meter, which is characterized in that including level gauging unit according to any one of claims 1 to 8,
And
The single-chip microcontroller being electrically connected with the level gauging unit；
For accommodating the shell of the level gauging unit and single-chip microcontroller；
It is embedded at the case surface, the display unit with the monolithic mechatronics.
10. RF admittance level meter according to claim 9, which is characterized in that be equipped in the single-chip microcontroller and host computer
Carry out the communication interface of wire communication, or the communication module communicated wirelessly with host computer.
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