CN110160602A - A kind of lubricating cup level measuring method of range hood - Google Patents
A kind of lubricating cup level measuring method of range hood Download PDFInfo
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- CN110160602A CN110160602A CN201810141712.3A CN201810141712A CN110160602A CN 110160602 A CN110160602 A CN 110160602A CN 201810141712 A CN201810141712 A CN 201810141712A CN 110160602 A CN110160602 A CN 110160602A
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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
- G01F23/28—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 the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/296—Acoustic waves
- G01F23/2962—Measuring transit time of reflected waves
Abstract
A kind of lubricating cup level measuring method of range hood, which is characterized in that comprise the following steps that the raw ultrasonic excitation signals of (1) main product meet following condition:(2) main control chip control analog-digital converter starts at the t=NT moment and carries out sampling processing to ultrasonic reflections signal；(3) main control chip judges whether present sample signal occurs sign mutation, if so, then performing the next step rapid；If not, recycling this step；(4) main control chip calculates transition time Δ t of the analog-digital converter when receiving jump signal；(5) liquid level is soughtThe present invention has the advantages that the problem inaccurate for receiving point initial pulse detection in conventional ultrasonic wave ranging scheme, designs completely new ultrasonic excitation signalsBy the way of phase hit, jump signal can be received in ultrasonic wave receiving end, so that the detection of receiving end signal is more simple and accurate.
Description
Technical field
The present invention relates to a kind of lubricating cup level measuring methods of range hood.
Background technique
The greasy dirt that range hood generates in use can be discharged into lubricating cup, in general, the liquid level of lubricating cup inner fluid needs
Artificial observation detection, needs in time to outwell greasy dirt to prevent from overflowing after running up to certain liquid level.In order to facilitate sight
Lubricating cup liquid level is examined, traditional range hood oil cup can use transparent plastics material mostly, but the lubricating cup of plastic material exists by force
Spend problem low, easy to aging；Also there is the lubricating cup using metal material, although intensity is high, observation lubricating cup liquid level is simultaneously inconvenient, i.e.,
Make with the presence of observation window, but be adhered on observation window using rear greasy dirt for a long time, the liquid of lubricating cup can not be seen clearly by also resulting in user
Position.
In view of the above-mentioned problems, occurring various lubricating cup liquid level automatic detection devices and detection method in the prior art, such as
A kind of Chinese invention patent " range hood oil cup oil level detecting device " of some Patent No. ZL201310653491.5 passes through
Hot type thermistor in detection circuit is heated and is detected the temperature of oil liquid to the oil liquid in lubricating cup, and then analyzes and obtain
The height of oil liquid is obtained, but the detection mode of this contact can make service life of the electronic component under oil pollution environment significantly
It reduces, to reduce detection accuracy, influences detection accuracy；For another example application No. is 201510386967.2 Chinese invention applications
" range hood oil cup guards against oil level distant warning device " discloses such a oil level detecting device, and the device is by being placed on lubricating cup
The equipment such as interior floating body detect lubricating cup and guard against liquid level, but the disadvantage of this device is that floating body long-time bubble can be reduced in greasy dirt
Service life, detection accuracy be not high.
Above-mentioned traditional contact distance measuring method will cause detection device service life and greatly reduce, be because of fume pollution
It can adapt to the adverse circumstances such as fume pollution, extend the service life of detection device, the ultrasound occurred in the prior art
It is that cost is relatively low, widely used distance measuring method in a kind of non-contact close-in measurement away from method, ultrasonic transmitter generates super
Sound wave propagates the transition time Δ t for arriving at that the receiver time experienced is ultrasonic wave by medium, in conjunction with the biography of ultrasonic wave
Speed C is broadcast, testing distance x=C × Δ t can be obtained；A but main problem existing for ultrasonic ranging method at present
Be: the starting point amplitude that ultrasonic wave receives signal is too small, so that receiving end can not obtain accurately initial signal, receives signal
Starting point detection difficult causes the error of ranging larger, and final detection result precision is low, therefore, needs to make further
Improvement.
Summary of the invention
It is more simple the technical problem to be solved by the present invention is to provide a kind of detection for above-mentioned state of the art
And the lubricating cup level measuring method of the high range hood of range accuracy.
The technical scheme of the invention to solve the technical problem is: a kind of lubricating cup level gauging side of range hood
Method, which is characterized in that the lubricating cup liquid level emasuring device include ultrasonic wave transmitting tube, digital analog converter, ultrasonic wave reception pipe,
Analog-digital converter and main control chip, the ultrasonic wave transmitting tube and ultrasonic wave reception pipe are set in same level, the oil
Cup level measuring method comprises the following steps that
(1), the main control chip control digital analog converter generates ultrasonic excitation signalsThe ultrasonic excitation signals
Meet following condition:
Wherein, the N is positive integer, and the T is harmonic period and meets ωs0T=2 π, the UmFor ultrasonic exciting
SignalMaximum voltage, the ωs0For resonance angular frequency；
(2), the main control chip control analog-digital converter starts at the t=NT moment and adopts to ultrasonic reflections signal
Sample processing；
(3), the main control chip judges whether present sample signal occurs sign mutation, if so, then performing the next step rapid；
If not, recycling this step；
(4), the main control chip calculates transition time Δ t of the analog-digital converter when receiving jump signal；
(5), liquid level is acquiredWherein, H is height of the ultrasonic wave transmitting tube apart from lubricating cup bottom surface, h
For lubricating cup liquid level, C is the aerial spread speed of ultrasonic wave.
Preferably, piezoelectric ceramic transducer, core is respectively adopted in the ultrasonic wave transmitting tube and ultrasonic wave reception pipe
Heart device is piezoelectric vibrator.
Preferably, the sample frequency f of the analog-digital converter in the step (2)samp=2NsampF, wherein the f
For ultrasonic excitation signalsFrequency and satisfactionThe NsampFor the sampling number in half of sampling period.
As further preferred, the sampling number NsampValue range is 2~16, value Nsamp=8 be best.
Preferably, the sampled signal that analog-digital converter receives in the step (2) includes that signal amplitude gradually increases
The mutation stage that big initial phase, signal amplitude are kept for the stable stabilization sub stage and signal amplitude jump.It is adopted in starting
After sample, due to not receiving ultrasonic signal at the beginning, the signal amplitude before initial phase is zero.
It is approximately sinusoidal signal that ultrasonic wave, which receives signal, sets current sample values as ad_now, current sample values it is previous
Secondary sampled value is ad_bef, the difference DELTA ad_now=ad_now-ad_bef between current adjacent sample values, before neighbouring sample
Difference DELTA ad_bef=ad_bef-ad_bef ' between value, wherein ad_bef ' is adjacent with a preceding sampled value previous again
Secondary sampled value；According to the feature of signal intensity, preferably, the sampled signal of the initial phase includes following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is all larger than；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is respectively less than；
C, before the difference maximum value Δ ad_max_now between current adjacent sample values is all larger than between adjacent sample values
Difference maximum value Δ ad_max_bef；
D, before the difference minimum value Δ ad_min_now between current adjacent sample values is all larger than between adjacent sample values
Difference minimum value Δ ad_min_bef.
Preferably, the sampled signal of the stabilization sub stage includes following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is equal to；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is equal to；
C, before the difference maximum value Δ ad_max_now between current adjacent sample values is equal between adjacent sample values
Difference maximum value Δ ad_max_bef；
D, before the difference minimum value Δ ad_min_now between current adjacent sample values is equal between adjacent sample values
Difference minimum value Δ ad_min_bef.
Preferably, the sampled signal in the mutation stage includes following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is respectively less than；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is all larger than；
C, before the difference maximum value Δ ad_max_now between current adjacent sample values is respectively less than between adjacent sample values
Difference maximum value Δ ad_max_bef；
D, before the difference minimum value Δ ad_min_now between current adjacent sample values is all larger than between adjacent sample values
Difference minimum value Δ ad_min_bef.
Since ultrasonic wave receiving end is sampled there may be certain clock jitter, jump signal sampled point is difficult directly to acquire
At the time of to signal amplitude being zero, in order to reduce the detection error of jump signal collection point, detection accuracy is further increased,
As further preferred, transition time Δ t can be acquired by the following method in the step (4):
(4.1), taking and acquiring difference is maximum value as the first two sampled point A1, A2, wherein the corresponding sampling of sampled point A1
Value is ada1Sampling point value corresponding to < 0, sampled point A1 is MAD；The corresponding sampled value of sampled point A2 is ada2> 0, sampled point
Sampling point value corresponding to A2 is MAD+1；
(4.2), time migration at the time of sampled value is 0 relative to sampled point A1 is acquired
(4.3), the time migration at the beginning of analog-digital converter starting samples relative to sampled point A1 is acquired
(4.4), the transition time is obtainedWherein, fsampFor sample frequency.
The transition time for using the above method to acquire has fully considered that signal amplitude is zero moment relative to current collection point
Time migration, it is more accurate to obtain the final transition time, and then can further improve detection accuracy.
Compared with the prior art, the advantages of the present invention are as follows: arteries and veins is originated for receiving point in conventional ultrasonic wave ranging scheme
The inaccurate problem of punching detection, designs completely new ultrasonic excitation signalsBy the way of phase hit, in ultrasonic wave receiving end
Jump signal can be received, so that the detection of receiving end signal is more simple and accurate；Traditional high-precision ultrasonic is surveyed
Away from scheme, it usually needs using calculation methods such as Fast Fourier Transform (FFT) (FFT), operand is big, the operation for main control chip
Ability is very big test, and the application only carries out plus and minus calculation, operation to the A/D conversion signal (analog-to-digital conversion signal) after sampling
Speed is fast, and the main control chip that low cost can be used is realized, and the range accuracy measured is high.
Detailed description of the invention
Fig. 1 is the lubricating cup liquid level detection device scheme of installation of the embodiment of the present invention.
Fig. 2 is the system construction drawing of the lubricating cup liquid level detection device of the embodiment of the present invention.
Fig. 3 is the flow chart of the lubricating cup level measuring method of the embodiment of the present invention.
Fig. 4 is the ultrasonic excitation signals of the embodiment of the present invention and the comparison of wave shape figure of ultrasonic wave reception signal.
Fig. 5 is that the ultrasonic wave of the embodiment of the present invention receives sampling schematic diagram of the signal within the single sampling period.
Fig. 6 is that the ultrasonic wave reception signal of the embodiment of the present invention shows from the stabilization sub stage to the waveform diagram in mutation stage and sampling
It is intended to.
Specific embodiment
The present invention will be described in further detail below with reference to the embodiments of the drawings.
The present embodiment is related to the lubricating cup liquid level emasuring device and its measurement method of a kind of range hood, the lubricating cup of the present embodiment
Liquid level emasuring device uses ultrasonic distance measurement principle, specifically, using transit time method TOF (time of flight): first
It measures ultrasonic wave and encounters barrier and return to time experienced from being emitted to, two times of sound is just obtained multiplied by the speed of ultrasonic wave
The distance between source and barrier.
It as shown in Figure 1 and Figure 2, is the lubricating cup liquid level emasuring device schematic diagram of the present embodiment, the setting of lubricating cup liquid level emasuring device
In the range hood main body being located at right above lubricating cup, lubricating cup level gauge has specifically included ultrasonic wave transmitting tube, digital-to-analogue conversion
Device, ultrasonic wave reception pipe, analog-digital converter and main control chip, wherein ultrasonic wave transmitting tube and ultrasonic wave reception pipe are respectively adopted
Piezoelectric ceramic transducer, core devices are piezoelectric vibrator；
Digital analog converter is electrically connected ultrasonic wave transmitting tube, and analog-digital converter is electrically connected ultrasonic wave reception pipe, digital analog converter
It is electrically connected main control chip with analog-digital converter, also, ultrasonic wave transmitting tube and ultrasonic wave reception pipe are set to same level
In face；Height of the ultrasonic wave transmitting tube apart from lubricating cup bottom surface is set as H, lubricating cup liquid level is h, and main control chip controls digital-to-analogue and turns
Parallel operation generates ultrasonic excitation signals, and ultrasonic wave encounters lubricating cup fluid level after air is propagated and reflects, most
The reflection signal received is sent to analog-digital converter and carries out sampling processing by whole ultrasonic wave reception pipe.
As shown in Fig. 3~Fig. 6, the lubricating cup level measuring method of the present embodiment comprises the following steps that
(1), main control chip control digital analog converter generates ultrasonic excitation signalsThe ultrasonic excitation signalsIt is full
The following condition of foot:
Wherein, N is positive integer, and T is harmonic period and meets ωs0T=2 π, UmFor ultrasonic excitation signalsMaximum
Voltage, ωs0For resonance angular frequency.
(2), main control chip control analog-digital converter starts at the t=NT moment, and the sampling module of analog-digital converter is to ultrasound
Wave reflection signal carries out sampling processing；Set the sample frequency f of analog-digital convertersamp=2NsampF, wherein f swashs for ultrasonic wave
Encourage the frequency and satisfaction of signalNsampFor the sampling number in half of sampling period, referring to Fig. 5, sampling number NsampIt takes
Being worth range is 2~16, the present embodiment preferably value Nsamp=8, i.e. the sampling number within a complete sampling period is
16.
(3), main control chip judges whether present sample signal occurs sign mutation, if so, then performing the next step rapid；Such as
It is no, then recycle this step.
(4), main control chip calculates transition time Δ t of the analog-digital converter when receiving jump signal.
(5), liquid level is acquiredWherein, H is height of the ultrasonic wave transmitting tube apart from lubricating cup bottom surface, h
For lubricating cup liquid level, C is the aerial spread speed of ultrasonic wave.
In above-mentioned steps (2), the collected ultrasonic reflections signal of analog-digital converter includes that signal amplitude is gradually increased
Initial phase, signal amplitude mutation stage for being kept for the stable stabilization sub stage and signal amplitude jump, sampled in starting
Afterwards, due to not receiving ultrasonic signal at the beginning, the signal amplitude before initial phase is zero.
According to the waveform of ultrasonic excitation signals, it is approximately sinusoidal signal that the ultrasonic wave of the present embodiment, which receives signal, setting
Current sample values are ad_now, and a preceding sampled value for current sample values is ad_bef, the difference between current adjacent sample values
Δ ad_now=ad_now-ad_bef, before the difference DELTA ad_bef=ad_bef-ad_bef ' between adjacent sample values,
In, ad_bef ' is an again preceding sampled value adjacent with a preceding sampled value；
If current sample values are equal to sampled value before and are zero, i.e. ad_now=ad_bef=0, then it represents that ultrasonic wave receives
End receives ultrasonic reflections signal not yet, and ultrasonic wave receives signal and is in front of initial phase.
Until ultrasonic wave receiving end receives initial signal, then the sampled signal of initial phase includes following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is all larger than；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is respectively less than；
C, before the difference maximum value Δ ad_max_now between current adjacent sample values is all larger than between adjacent sample values
Difference maximum value Δ ad_max_bef；
D, before the difference minimum value Δ ad_min_now between current adjacent sample values is all larger than between adjacent sample values
Difference minimum value Δ ad_min_bef.
Tetra- features of above a, b, c, d show that ultrasonic wave initially receives ultrasonic signal rising after the reflection of lubricating cup liquid level
Beginning signal, meanwhile, main control chip saves the sampled point for working as the first two sampling period.
It is stable sine wave that ultrasonic wave, which receives the signal that the signal stabilization stage receives, and the sampling of the stabilization sub stage is believed
Number include following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is equal to；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is equal to；
C, before the difference maximum value Δ ad_max_now between current adjacent sample values is equal between adjacent sample values
Difference maximum value Δ ad_max_bef；
D, before the difference minimum value Δ ad_min_now between current adjacent sample values is equal between adjacent sample values
Difference minimum value Δ ad_min_bef.
Ultrasonic wave receiving end will receive jump signal after receiving stable sine wave signal, and setting ultrasonic wave receives
The time domain of signal is expressed as r (t), ultrasonic wave receives the difference of the stabilization sub stage and mutation stage of signal are as follows: the 1. stabilization sub stage
Maximum sampled value is greater than the maximum sampled value in mutation stage, and the minimum sampled value of stabilization sub stage is less than the minimum sampling in mutation stage
Value；2. derivative is maximum when the phase that is easy to get is 0 or π for SIN function, that is to say, that the maximum value of stabilization sub stage difference is greater than prominent
The maximum value of change stage difference, the minimum value of stabilization sub stage difference are less than the minimum value of mutation stage difference.
Therefore, during transforming to the mutation stage from the stabilization sub stage, the sampled signal in the mutation stage includes following
Feature:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is respectively less than；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is all larger than；
C, before the difference maximum value Δ ad_max_now between current adjacent sample values is respectively less than between adjacent sample values
Difference maximum value Δ ad_max_bef；
D, before the difference minimum value Δ ad_min_now between current adjacent sample values is all larger than between adjacent sample values
Difference minimum value Δ ad_min_bef.
There may be certain clock jitters when in view of the sampling of ultrasonic wave receiving end, when mutation signal, sampling
Point is difficult directly to collect signal amplitude at the time of be zero, in order to reduce the detection error of jump signal collection point, into one
Step improves detection accuracy, and transition time Δ t can be acquired by the following method in step (4):
(4.1), taking and acquiring difference is maximum value as the first two sampled point A1, A2, wherein the corresponding sampling of sampled point A1
Value is ada1Sampling point value corresponding to < 0, sampled point A1 is MAD；The corresponding sampled value of sampled point A2 is ada2> 0, sampled point
Sampling point value corresponding to A2 is MAD+1；
(4.2), time migration at the time of sampled value is 0 relative to sampled point A1 is acquired
(4.3), the time migration at the beginning of analog-digital converter starting samples relative to sampled point A1 is acquired
(4.4), the transition time is obtainedWherein, fsampFor sample frequency.
Then, in conjunction with liquid level formulaAvailable lubricating cup liquid level are as follows:
The present embodiment receives that signal starting point amplitude is too small to be caused to receive for ultrasonic wave in conventional ultrasonic wave ranging scheme
The problem for holding initial pulse detection inaccurate, devises completely new ultrasonic excitation signalsUsing ultrasonic wave transmitting terminal phase hit
The mode that ultrasonic wave receiving end sampling later is opened, so that ultrasonic wave receiving end is able to detect that signal characteristic variation is apparent prominent
Thus varying signal accurately obtains transition time Δ t, to guarantee the accuracy of lubricating cup liquid level final detection result.
It is compared to traditional high-precision ultrasonic ranging scheme, needs to calculate using Fast Fourier Transform (FFT) (FFT) etc.
Method, since operand is big, the operational capability of main control chip is very big test, the main control chip of selection often higher cost；
The present embodiment then devises the ultrasonic high accuracy distance measuring method based on time domain, only carries out plus-minus fortune to the modulus signal after sampling
It calculates, operation can be realized using the main control chip of low cost, not only arithmetic speed is fast, but also the range accuracy measured is high, product
Dependable with function it is strong.
Claims (9)
1. a kind of lubricating cup level measuring method of range hood, which is characterized in that the lubricating cup liquid level emasuring device includes super
Sound wave transmitting tube, digital analog converter, ultrasonic wave reception pipe, analog-digital converter and main control chip, the ultrasonic wave transmitting tube and super
Acoustic receiver pipe is set in same level, and the lubricating cup level measuring method comprises the following steps that
(1), the main control chip control digital analog converter generates ultrasonic excitation signalsThe ultrasonic excitation signalsMeet
Following condition:
Wherein, the N is positive integer, and the T is harmonic period and meets ωs0T=2 π, the UmFor ultrasonic excitation signalsMaximum voltage, the ωs0For resonance angular frequency；
(2), the main control chip control analog-digital converter starts at the t=NT moment and carries out at sampling to ultrasonic reflections signal
Reason；
(3), the main control chip judges whether present sample signal occurs sign mutation, if so, then performing the next step rapid；Such as
It is no, then recycle this step；
(4), the main control chip calculates transition time Δ t of the analog-digital converter when receiving jump signal；
(5), liquid level is acquiredWherein, H is height of the ultrasonic wave transmitting tube apart from lubricating cup bottom surface, and h is lubricating cup
Liquid level, C are the aerial spread speed of ultrasonic wave.
2. the lubricating cup level measuring method of range hood according to claim 1, it is characterised in that: the ultrasonic wave hair
It penetrates pipe and piezoelectric ceramic transducer is respectively adopted in ultrasonic wave reception pipe.
3. the lubricating cup level measuring method of range hood according to claim 1, it is characterised in that: in the step (2)
Analog-digital converter sample frequency fsamp=2NsampF, wherein the f is ultrasonic excitation signalsFrequency and satisfactionThe NsampFor the sampling number in half of sampling period.
4. the lubricating cup level measuring method of range hood according to claim 3, it is characterised in that: the sampling number
NsampValue range is 2~16.
5. the lubricating cup level measuring method of range hood according to claim 1, it is characterised in that: in the step (2)
The sampled signal that analog-digital converter receives includes that initial phase for being gradually increased of signal amplitude, signal amplitude keep stable
The mutation stage that stabilization sub stage and signal amplitude jump.
6. the lubricating cup level measuring method of range hood according to claim 5, it is characterised in that: setting current sample values
For ad_now, a preceding sampled value for current sample values is ad_bef, the difference DELTA ad_now=between current adjacent sample values
Ad_now-ad_bef, before the difference DELTA ad_bef=ad_bef-ad_bef ' between adjacent sample values, wherein ad_bef ' is
An again preceding sampled value adjacent with a preceding sampled value；The sampled signal of the initial phase includes following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is all larger than；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is respectively less than；
C, the difference before the difference maximum value Δ ad_max_now between current adjacent sample values is all larger than between adjacent sample values
It is worth maximum value Δ ad_max_bef；
D, the difference before the difference minimum value Δ ad_min_now between current adjacent sample values is all larger than between adjacent sample values
It is worth minimum value Δ ad_min_bef.
7. the lubricating cup level measuring method of range hood according to claim 5, it is characterised in that: setting current sample values
For ad_now, a preceding sampled value for current sample values is ad_bef, the difference DELTA ad_now=between current adjacent sample values
Ad_now-ad_bef, before the difference DELTA ad_bef=ad_bef-ad_bef ' between adjacent sample values, wherein ad_bef ' is
An again preceding sampled value adjacent with a preceding sampled value；The sampled signal of the stabilization sub stage includes following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is equal to；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is equal to；
C, the difference before the difference maximum value Δ ad_max_now between current adjacent sample values is equal between adjacent sample values
It is worth maximum value Δ ad_max_bef；
D, the difference before the difference minimum value Δ ad_min_now between current adjacent sample values is equal between adjacent sample values
It is worth minimum value Δ ad_min_bef.
8. the lubricating cup level measuring method of range hood according to claim 5, it is characterised in that: setting current sample values
For ad_now, a preceding sampled value for current sample values is ad_bef, the difference DELTA ad_now=between current adjacent sample values
Ad_now-ad_bef, before the difference DELTA ad_bef=ad_bef-ad_bef ' between adjacent sample values, wherein ad_bef ' is
An again preceding sampled value adjacent with a preceding sampled value；The sampled signal in the mutation stage includes following characteristics:
A, the maximum value ad_max_bef of sampled value before the maximum value ad_max_now of current sample values is respectively less than；
B, the minimum value ad_min_bef of sampled value before the minimum value ad_min_now of current sample values is all larger than；
C, the difference before the difference maximum value Δ ad_max_now between current adjacent sample values is respectively less than between adjacent sample values
It is worth maximum value Δ ad_max_bef；
D, the difference before the difference minimum value Δ ad_min_now between current adjacent sample values is all larger than between adjacent sample values
It is worth minimum value Δ ad_min_bef.
9. the lubricating cup level measuring method of range hood according to claim 1, it is characterised in that: in the step (4)
Transition time, Δ t was acquired by the following method:
(4.1), taking and acquiring difference is maximum value as the first two sampled point A1, A2, wherein the corresponding sampled value of sampled point A1 is
ada1Sampling point value corresponding to < 0, sampled point A1 is MAD；The corresponding sampled value of sampled point A2 is ada2> 0, sampled point A2 institute
Corresponding sampling point value is MAD+1；
(4.2), time migration at the time of sampled value is 0 relative to sampled point A1 is acquired
(4.3), the time migration at the beginning of analog-digital converter starting samples relative to sampled point A1 is acquired
(4.4), the transition time is obtainedWherein, fsampFor sample frequency.
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