CN107655543A - Phase-locked capacitance liquid level meter - Google Patents
Phase-locked capacitance liquid level meter Download PDFInfo
- Publication number
- CN107655543A CN107655543A CN201610591455.4A CN201610591455A CN107655543A CN 107655543 A CN107655543 A CN 107655543A CN 201610591455 A CN201610591455 A CN 201610591455A CN 107655543 A CN107655543 A CN 107655543A
- Authority
- CN
- China
- Prior art keywords
- phase
- liquid level
- level meter
- controlled oscillator
- output end
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000007788 liquid Substances 0.000 title claims abstract description 48
- 238000005259 measurement Methods 0.000 claims abstract description 32
- 239000004973 liquid crystal related substance Substances 0.000 claims description 6
- 238000004891 communication Methods 0.000 claims description 5
- 239000002184 metal Substances 0.000 abstract description 2
- 229910052751 metal Inorganic materials 0.000 abstract description 2
- 230000009286 beneficial effect Effects 0.000 abstract 1
- 230000010355 oscillation Effects 0.000 description 15
- 239000012530 fluid Substances 0.000 description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 239000003990 capacitor Substances 0.000 description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 230000005611 electricity Effects 0.000 description 4
- 239000013078 crystal Substances 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000010453 quartz Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 241000208340 Araliaceae Species 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 235000005035 Panax pseudoginseng ssp. pseudoginseng Nutrition 0.000 description 1
- 235000003140 Panax quinquefolius Nutrition 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 235000013399 edible fruits Nutrition 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 235000008434 ginseng Nutrition 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000010349 pulsation Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
-
- 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
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
Abstract
The invention relates to a phase-locked capacitance liquid level meter. The invention comprises a capacitance test rod (1) and a phase-locked loop (7); the phase-locked loop (7) comprises a voltage-controlled oscillator (3), a phase discriminator (4) and a low-pass filter (6); one input end of the voltage-controlled oscillator (3) is connected with the capacitance test rod (1), and the output end of the voltage-controlled oscillator (3) is connected with one input end of the phase discriminator (4); the output end of the phase discriminator (4) is connected with one input end of the low-pass filter (6); one output end of the low-pass filter (6) is connected with the other input end of the voltage-controlled oscillator (3). The capacitance test rod is two concentric metal cylinders sleeved together, has a simpler structure and does not have any moving part, so the capacitance test rod works stably and reliably; the invention has the advantages that whether the power supply voltage is stable or not does not influence the measurement precision, and the invention is beneficial to realizing the power supply of the battery or working in the occasions with severe power supply conditions.
Description
Technical field
The invention belongs to test the liquid level gauge in measuring instrumentss field, in particular it relates to a kind of phase-locking type capacitive liquid
Position meter.
Background technology
Existing liquid level gauge includes float type level gauge, pressure-type liquidometer, ultrasonic level gauge etc..Float type level gauge needs
Float is placed in container, liquid level is obtained by measuring float position；Pressure-type liquidometer needs to install in container bottom
Pressure gauge, liquid level is obtained by measuring pressure；Ultrasonic level gauge needs to install ultrasonic transmitter and reception in container top
Device, liquid level is obtained by supersonic sounding.Their common drawback is that structure is more complicated, there is movable part, measurement knot in container
Fruit is not accurate enough, and service behaviour is bad at low ambient temperatures.
The content of the invention
The purpose of the present invention is in view of the shortcomings of the prior art, there is provided a kind of phase-locking type capacitance liquid level meter, has structure letter
It is single, stable and reliable in work, measurement result is accurate, the advantages that level gauging available for cryogenic liquid such as liquid nitrogen etc..
For achieving the above object, technical scheme is as follows：
The phase-locking type capacitance liquid level meter of the present invention, including capacity measurement bar 1 and phaselocked loop 7；Wherein, the phaselocked loop 7 wraps
Include voltage controlled oscillator 3, phase discriminator 4 and low pass filter 6；
The voltage controlled oscillator 3 has two inputs and an output end, one of input and capacity measurement bar 1
It is connected, its output end is connected with an input of phase discriminator 4；
The phase discriminator 4 has two inputs and an output end, its output end and an input of low pass filter 6
It is connected；One output end of the low pass filter 6 is connected with another input of voltage controlled oscillator 3.
According to the phase-locking type capacitance liquid level meter of the present invention, wherein, the phase-locking type capacitance liquid level meter can also include reference
Frequency generator 5, the reference frequency maker 5 are connected with another input of phase discriminator 4.
According to the phase-locking type capacitance liquid level meter of the present invention, wherein, the phase-locking type capacitance liquid level meter can also turn including A/D
Parallel operation, single-chip microcomputer, liquid crystal display, communication module and voltmeter it is first-class in one or more of optional components, the one or more
Optional component is connected with another output end of low pass filter 6.
The capacity measurement bar 1 of the present invention, is referred to as capacitance level transducer, is that two to be nested together are concentric
Metallic cylinder, there is certain capacitance between two.When capacity measurement bar immerses nonconducting liquid, medium between two
Dielectric constant increase so that the capacitance between two also increases.Liquid level is higher, and the part that liquid level bar is submerged is more,
Capacitance is also bigger.Therefore capacitance size just reflects the height of liquid level.
The phaselocked loop 7, for capacitance to be converted into d. c. voltage signal, including following assemblies：
Voltage controlled oscillator (VCO) 3, it is a variable-frequency oscillator, frequency of oscillation is simultaneously by liquid level bar capacitance
With input control voltage control.
Phase discriminator (PD) 4, is a phase comparator, and it compares the signal between voltage controlled oscillator and frequency reference source
Phase difference, export the DC voltage of a pulsation, average value and the approximately linear pass of aforementioned signal phase difference of this DC voltage
System.
Low pass filter 6, the pulsating dc voltage of phase discriminator output is equalized, becomes steady dc voltage.
In addition, the phase-locking type capacitance liquid level meter of the present invention, which can also include reference frequency maker 5, is used as frequency reference source,
It is the oscillator that a frequency is fixed, using quartz crystal as frequency reference, therefore its frequency precision of oscillation is very high.
The phase-locking type capacitance liquid level meter of the present invention also includes power supply, is each electricity consumption assembly power supply.
Remaining optional component includes：A/D converter, single-chip microcomputer, liquid crystal display, communication module, voltmeter are first-class.It is above-mentioned optional
Component is connected with another output end of low pass filter 6, when multiple optional components are connected with low pass filter 6 simultaneously,
The connection in series-parallel relation of optional component can be according to being specifically actually needed determination.
Compared with prior art, phase-locking type capacitance liquid level meter provided by the invention has the following technical effect that：
1st, capacity measurement bar is two concentric metal cylinders being nested together, compared with the liquid level gauges such as differential, float-type,
It is simple in construction, without any moving component, therefore it is stable and reliable in work；
2nd, insecure component that can not work or work under the low temperature such as pressure gauge, ball float need not be used, therefore can be used for
Measure the liquid level of cryogenic liquid such as liquid nitrogen, liquid oxygen etc.；
3rd, because the frequency of oscillation of frequency reference source, voltage controlled oscillator does not change with power source supplying voltage, therefore power supply
Whether voltage stabilization does not influence measurement accuracy, is advantageously implemented battery powered, can be in no AC power or in condition of power supply
Severe occasion work.
Brief description of the drawings
Fig. 1 is the phase-locking type capacitance liquid level meter schematic diagram of the present invention.
Accompanying drawing identifies
1st, capacity measurement bar 2, fluid to be measured 3, voltage controlled oscillator 4, phase discriminator
5th, reference frequency maker 6, low pass filter 7, phaselocked loop 8, the direct current signal of output
Embodiment
With reference to the accompanying drawings and detailed description, the present invention will be further described in detail.
As shown in figure 1, the phase-locking type capacitance liquid level meter of the present invention, including capacity measurement bar 1 and phaselocked loop 7；Wherein, it is described
Phaselocked loop 7 includes voltage controlled oscillator 3, phase discriminator 4 and low pass filter 6；The voltage controlled oscillator 3 have two inputs and
One output end, one of input are connected with capacity measurement bar 1, and its output end is connected with an input of phase discriminator 4；
The phase discriminator 4 has two inputs and an output end, and its output end is connected with an input of low pass filter 6；Institute
An output end of low pass filter 6 is stated with another input of voltage controlled oscillator 3 to be connected.The phase-locking type capacitance liquid level of the present invention
Meter can also include reference frequency maker 5, and the reference frequency maker 5 is connected with another input of phase discriminator 4.
The present invention phase-locking type capacitance liquid level meter can also include A/D converter, single-chip microcomputer, liquid crystal display, communication module with
One or more of optional components during voltmeter is first-class, the optional component of one or more are another defeated with low pass filter 6
Go out end to be connected.The direct current signal 8 that low pass filter 6 exports can be received and handled by optional component.
Capacity measurement bar 1 is inserted in fluid to be measured container during use and fixed, power-on can be directly from optional group
Fluid to be measured level value is read on the liquid crystal display or voltmeter head of part；Or PC is connected by communication module, read and remember on PC
Record fluid to be measured level value.
Embodiment 1
The present embodiment structure is as shown in Figure 1.Wherein, capacity measurement bar 1 grows 1.2 meters, and internal layer is the copper pipe of 10mm diameters, outside
Layer is the copper pipe of 15mm diameters, then when capacity measurement bar 1 does not immerse fluid to be measured 2, the electric capacity between inner/outer tube is 164pF；When
When capacity measurement bar 1 is totally immersed into fluid to be measured 2 (the present embodiment is the liquid nitrogen that dielectric constant is 2.28), the electricity between inner/outer tube
Appearance is changed into 375pF.When fluid to be measured 2 is immersed in the part of capacity measurement bar 1, the electric capacity between inner/outer tube between 164~375pF,
It is linear with liquid level position.
Reference frequency maker 5 coordinates 16MHz quartz crystal with 74HC4060,16MHz oscillator signal by
74HC4060 exports the square-wave signal of 500kHz fixed frequencies after 5 wheel two divided-frequencies.
Voltage controlled oscillator 3 is 74HC4046 built-in oscillator, it is configured to external capacitor 250pF, control voltage
For 2.5V when, frequency of oscillation 500kHz；When external capacitor deviates 250pF, frequency of oscillation is inversely proportional with external capacitor value；Control
During voltage deviation 2.5V, the variable quantity of frequency of oscillation is directly proportional to control voltage variable quantity, and control voltage often changes 1V, oscillation frequency
75kHz is raised and lowered in rate.
Phase discriminator 4 uses 74HC4046 built-in phase discriminator I.When two input signal phases differ 0 degree~180 degree,
Its corresponding output duty cycle is 0%~100% square wave, turns into 0V~5V DC voltage after low pass filter 6, this electricity
Pressure controls voltage controlled oscillator 3 again.
The course of work of whole phaselocked loop 7 is qualitatively described below：
When the electric capacity of capacity measurement bar 1 is exactly 250pF, the frequency of oscillation of voltage controlled oscillator 3 is 500kHz, with reference frequency
500kHz signals caused by maker 5 keep 90 degree of phase difference so that phase discriminator 4 exports the square wave of 50% dutycycle, passes through
Turn into 2.5V DC voltage after low pass filter 6, then control voltage controlled oscillator 3, whole system reaches stable state.
When the electric capacity of capacity measurement bar 1 is less than 250pF, the frequency of oscillation of voltage controlled oscillator 3 is higher than 500kHz, with reference
500kHz signals are compared caused by frequency generator 5, and its phase gradually lags so that phase discriminator 4 export duty cycle square wave by
Gradually reduce, the DC voltage after low pass filter 6 gradually reduces from 2.5V, then control voltage controlled oscillator 3 make its frequency by
Gradually reduce, untill reverting to 500kHz.Now both frequencies are equal, and phase difference is less than 90 degree, after low pass filter 6
For a DC voltage for being less than 2.5V.
Then similar when the electric capacity of capacity measurement bar 1 is more than 250pF, final low pass filter 6 exports one and is more than 2.5V
DC voltage.This DC voltage reflects the electric capacity of capacity measurement bar 1, that is, level condition.This direct current is pressed into
Row sampling, be converted to data signal and liquid level is obtained by single-chip microcomputer conversion, be then displayed on liquid crystal display, or pass through serial ports, USB
Computer is sent to Deng interface.
Embodiment 2
The same Fig. 1 of the present embodiment structure.Wherein, capacity measurement bar 1 grows 6 meters, and internal layer is the copper pipe of 20mm diameters, and outer layer is
The copper pipe of 25mm diameters, then when capacity measurement bar 1 does not immerse fluid to be measured 2, the electric capacity between inner/outer tube is 1494pF；Work as electric capacity
When reference test bar 1 is totally immersed into fluid to be measured 2 (the present embodiment is the liquid hydrogen that dielectric constant is 1.22), the electric capacity between inner/outer tube becomes
For 1823pF.When fluid to be measured 2 is immersed in the part of capacity measurement bar 1, the electric capacity between inner/outer tube between 1494~1823pF, with
Liquid level position is linear.
Reference frequency maker 5 coordinates 38kHz quartz crystal with 74HC2G04, vibration output 38kHz fixed frequencies
Square-wave signal.
The 74HC4046 built-in oscillator of voltage controlled oscillator 3, it is configured to external capacitor 1650pF, control voltage
For 2.5V when, frequency of oscillation 38kHz；When external capacitor deviates 1650pF, frequency of oscillation is inversely proportional with external capacitor value；Control
During voltage deviation 2.5V, the variable quantity of frequency of oscillation is directly proportional to control voltage variable quantity, and control voltage often changes 1V, oscillation frequency
5.8kHz is raised and lowered in rate.
Phase discriminator 4 uses 74HC4046 built-in phase discriminator I.When two input signal phases differ 0 degree~180 degree,
Its corresponding output duty cycle is 0%~100% square wave, turns into 0V~5V DC voltage after low pass filter 6, this electricity
Pressure controls voltage controlled oscillator 3 again.
The course of work of whole phaselocked loop 7 is qualitatively described below：
When the electric capacity of capacity measurement bar 1 is exactly 1650pF, the frequency of oscillation of voltage controlled oscillator 3 is 38kHz, with reference frequency
38kHz signals caused by maker 5 keep 90 degree of phase difference so that phase discriminator 4 exports the square wave of 50% dutycycle, through too low
Turn into 2.5V DC voltage after bandpass filter 6, then control voltage controlled oscillator 3, whole system reaches stable state.
When the electric capacity of capacity measurement bar 1 is less than 1650pF, the frequency of oscillation of voltage controlled oscillator 3 is higher than 38kHz, with reference
38kHz signals are compared caused by frequency generator 5, and its phase gradually lags so that the duty cycle square wave that phase discriminator 4 exports is gradual
Reduce, the DC voltage after low pass filter 6 gradually reduces from 2.5V, then controls voltage controlled oscillator 3 to make its frequency gradual
Reduce, untill reverting to 38kHz.Now both frequencies are equal, and phase difference is less than 90 degree, is after low pass filter 6
One DC voltage for being less than 2.5V.
Then similar when the electric capacity of capacity measurement bar 1 is more than 1650pF, final low pass filter 6 exports one and is more than 2.5V
DC voltage.This DC voltage reflects the electric capacity of capacity measurement bar 1, that is, level condition.
A pointer voltage gauge outfit is connected in the output end of low pass filter 6, to the measurement voltage value under different liquid levels
After demarcation, the dial of voltmeter head is pulled down, changes corresponding fluid level scale into, you can realization is read directly from gauge outfit is surveyed
The level value of amount.
It should be noted last that the above embodiments are merely illustrative of the technical solutions of the present invention and it is unrestricted.Although ginseng
The present invention is described in detail according to embodiment, it will be understood by those within the art that, to the technical side of the present invention
Case is modified or equivalent substitution, and without departure from the spirit and scope of technical solution of the present invention, it all should cover in the present invention
Right among.
Claims (6)
- A kind of 1. phase-locking type capacitance liquid level meter, it is characterised in that the phase-locking type capacitance liquid level meter include capacity measurement bar (1) and Phaselocked loop (7)；Wherein, the phaselocked loop (7) includes voltage controlled oscillator (3), phase discriminator (4) and low pass filter (6)；The voltage controlled oscillator (3) has two inputs and an output end, one of input and capacity measurement bar (1) It is connected, its output end is connected with an input of phase discriminator (4)；The phase discriminator (4) has two inputs and an output end, its output end and the input phase of low pass filter (6) Even；The output end of the low pass filter (6) is connected with another input of voltage controlled oscillator (3).
- 2. phase-locking type capacitance liquid level meter according to claim 1, it is characterised in that the phase-locking type capacitance liquid level meter also wraps Reference frequency maker (5) is included, the reference frequency maker (5) is connected with another input of phase discriminator (4).
- 3. phase-locking type capacitance liquid level meter according to claim 2, it is characterised in that the reference frequency maker (5) is The oscillator that frequency is fixed.
- 4. phase-locking type capacitance liquid level meter according to claim 1, it is characterised in that the capacity measurement bar (1) is to be enclosed on Two concentric metallic cylinders together, there is certain capacitance between two.
- 5. phase-locking type capacitance liquid level meter according to claim 1, it is characterised in that the voltage controlled oscillator (3) is variable The oscillator of frequency.
- 6. according to any described phase-locking type capacitance liquid level meters of claim 1-5, it is characterised in that the phase-locking type capacitance liquid level Meter also includes one or more of optional components in A/D converter, single-chip microcomputer, liquid crystal display, communication module and voltmeter head, described One or more of optional components are connected with another output end of low pass filter (6).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201610591455.4A CN107655543A (en) | 2016-07-25 | 2016-07-25 | Phase-locked capacitance liquid level meter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201610591455.4A CN107655543A (en) | 2016-07-25 | 2016-07-25 | Phase-locked capacitance liquid level meter |
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| Publication Number | Publication Date |
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| CN107655543A true CN107655543A (en) | 2018-02-02 |
Family
ID=61126896
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| CN201610591455.4A Pending CN107655543A (en) | 2016-07-25 | 2016-07-25 | Phase-locked capacitance liquid level meter |
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Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0587612A (en) * | 1991-09-27 | 1993-04-06 | Jiyaruko:Kk | Detector for liquid body level using pll circuit |
| CN101135584A (en) * | 2006-08-31 | 2008-03-05 | 深圳迈瑞生物医疗电子股份有限公司 | Detecting probe liquid level detector and method |
| CN101865718A (en) * | 2009-04-17 | 2010-10-20 | 深圳迈瑞生物医疗电子股份有限公司 | Liquid level detection circuit, device and calibration method thereof |
| CN102798433A (en) * | 2012-08-20 | 2012-11-28 | 张家港保税区美达电子电脑有限公司 | Capacitance-type low-temperature liquid level sensor |
| CN203323827U (en) * | 2013-07-12 | 2013-12-04 | 苏州长光华医生物医学工程有限公司 | Self-adaption liquid level detection system |
| CN105043501A (en) * | 2015-05-05 | 2015-11-11 | 苏州市职业大学 | Liquid level detecting device for low-temperature liquid nitrogen and detecting method thereof |
| CN205940707U (en) * | 2016-07-25 | 2017-02-08 | 中国科学院理化技术研究所 | Phase-locked capacitance liquid level meter |
-
2016
- 2016-07-25 CN CN201610591455.4A patent/CN107655543A/en active Pending
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0587612A (en) * | 1991-09-27 | 1993-04-06 | Jiyaruko:Kk | Detector for liquid body level using pll circuit |
| CN101135584A (en) * | 2006-08-31 | 2008-03-05 | 深圳迈瑞生物医疗电子股份有限公司 | Detecting probe liquid level detector and method |
| CN101865718A (en) * | 2009-04-17 | 2010-10-20 | 深圳迈瑞生物医疗电子股份有限公司 | Liquid level detection circuit, device and calibration method thereof |
| CN102798433A (en) * | 2012-08-20 | 2012-11-28 | 张家港保税区美达电子电脑有限公司 | Capacitance-type low-temperature liquid level sensor |
| CN203323827U (en) * | 2013-07-12 | 2013-12-04 | 苏州长光华医生物医学工程有限公司 | Self-adaption liquid level detection system |
| CN105043501A (en) * | 2015-05-05 | 2015-11-11 | 苏州市职业大学 | Liquid level detecting device for low-temperature liquid nitrogen and detecting method thereof |
| CN205940707U (en) * | 2016-07-25 | 2017-02-08 | 中国科学院理化技术研究所 | Phase-locked capacitance liquid level meter |
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