CN101586979B - Constant-flow bubble type automatic water level measurement method - Google Patents

Abstract

The invention belongs to the field of sensor measurement, and in particular relates to a method for automatically measuring water level by adopting a constant-flow bubble type water gauge, which comprises the following steps: measuring vertical height difference H of two ports of an air duct and mounting height h0 of an air exhaust; inputting a gravity acceleration g, the height difference H of the two ports of the air duct and the mounting height h0 of the air exhaust into a data acquisition device through a register; acquiring a pressure output value P0 of the constant-flow bubble type watergauge and a gas temperature T in the duct by the data acquisition device in fixed time; and acquiring a pressure output value PA of a barometer by the data acquisition device in fixed time. The inven tion provides the method more accurate than classic pressure water level relation conversion formula, and discloses that the vertical height difference of the two ports of the air duct is the main reason for influencing the measuring precision of the constant-flow bubble type water gauge, but not the difference of the gravity acceleration or water density. The method can effectively reduce the water level measurement error, and has more obvious effect particularly when the vertical height difference of the two ports of the air duct exceeds 10 meters.

Description

A kind of constant-flow bubble type automatic water level measurement method

Technical field

The invention belongs to field of sensor measurement, particularly adopt the constant-flow bubble type water level gauge to carry out the method for level measuring automatically.

Background technology

The principle of work of constant-flow bubble type water level gauge: the pressure-sensitive unit links to each other with tracheae through gas path device, and the openend of tracheae is fixed on the underwater, and when the air pressure in the gas path device and hydraulic pressure reached balance, the pressure-sensitive unit was converted to height of water level with this pressure.

Compare with traditional float type level meter, the constant-flow bubble type water level gauge have install simple, need not to build advantages such as water level well, civil engineering workload are little, small investment, the construction period is short, range is big, in automatic system of hydrological data acquisition and transmission, use more and more widely at present.

But, exist than mistake between the measured value of constant-flow bubble type water level gauge and the artificial observation value, and the big more then error of range of stage is big more in a lot of application scenarios.Generally believe that at present this error is that the acceleration of gravity at scene and the difference between water-mass density and the theoretical value cause.

Summary of the invention

The objective of the invention is to overcome home and abroad constant-flow bubble type water level gauge measuring error with the deficiency that range of stage increases, analyzed the key factor that error exists, a kind of automatic water level measurement method is provided, improved measurement accuracy effectively.

The invention provides the method that a kind of automatic water level is measured, it is characterized in that, may further comprise the steps:

1) according to the longitude and latitude and the sea level elevation of installation site, tabling look-up obtains gravity acceleration g;

2) vertical height difference H and the exhausr port of measuring the wireway two-port installed elevation h ₀

3) by putting counting apparatus gravity acceleration g, tracheae port height difference H and exhausr port are installed elevation h ₀The input data acquisition unit;

4) the pressure output value P of data acquisition unit timing acquiring constant current mode bubble water level gauge ₀With gas temperature T in the pipe;

5) the barometrical pressure output value P of data acquisition unit timing acquiring _Aa

6) data acquisition unit is according to formula (E13) calculated water head height;

7) data acquisition unit is according to elevation h is installed ₀Revise actual water level;

8) data acquisition unit is sent to central station by communication terminal with waterlevel data.

Description of drawings

Fig. 1 is an automatic water level measuring system structure.

Fig. 2 is a constant current bubble water level gauge mounting structure.

Fig. 3 is a process flow diagram of the present invention

Embodiment

Automatic water level measurement method of the present invention comprises telemetry station 1 and central station 2, as shown in Figure 1.Telemetry station is formed by putting counting apparatus 3, data acquisition unit 4, barometer 5, constant-flow bubble type water level gauge 6, communication facilities 7 and power supply 8.Central station forms 11 by communication facilities 9, computing machine 10 and power supply.

The level measuring flow process as shown in Figure 3.Data acquisition unit is according to predefined working method, the pressure output value P of timing acquiring constant current mode bubble water level gauge ₀With gas temperature T in the pipe, and barometrical pressure output value P _Aa, according to formula (E13) calculated water head height,, waterlevel data is sent to central station through communication terminal according to elevation correction actual water level, show, store and handle.

The mounting means of air bubble type water level meter as shown in Figure 2.Pressure-sensitive unit 12, nitrogen cylinder 13 and gas circuit galvanostat 14 are installed in the level measuring station 15, link to each other with the fixed protection equipment 18 that is installed in the water surface 17 belows by wireway 16.The gas circuit galvanostat can be responded to variation in water pressure, and automatic adjustments of gas flow, and the gas in the nitrogen cylinder is outwards discharged with constant pressure by wireway.One end of wireway is installed under water, and an other end links to each other with the gas circuit galvanostat, is full of nitrogen under the normal condition in the tracheae, and wireway is the pressure and the hydraulic balance of port under water.The pressure-sensitive unit links to each other with the gas circuit galvanostat, receive the instruction of data acquisition unit after, measure temperature in the wireway and air pressure and numerical value returned to data acquisition unit.

In the gas-liquid intersection 18 of tracheae underwater portion end, the intraductal atmospheric pressure of this position is the atmospheric pressure that hydraulic pressure adds this position all the time, and that the pressure-sensitive unit is measured is the pressure and the atmospheric difference P in this position of the other end 12 of tracheae ₀And send data acquisition unit.

This metering system is assumed to be prerequisite with two: the atmospheric pressure of position 12 and position 18 equates, and the gaseous tension in two place's wireways equates.In fact the elevation of station is greater than the terminal elevation of wireway under water.And gas is subjected to gravity effect, and in the vertical direction pressure is with highly successively decreasing.Therefore above-mentioned hypothesis can be brought error.

If position 12 place's atmospheric pressures are P _Aa, nitrogen pressure is P _ANThen

P _AN＝P ₀+P _Aa (E1)

If the position 17 atmospheric pressure P of place _CA, the nitrogen pressure at 18 places, position is P _CN, the depth of water (position 17 is to position 18) is h, water-mass density is ρ, gravity acceleration g.Then

P _CN＝P _CA+ρgh (E2)

A bit of nitrogen gas column in the application of differential methods analyst tracheae, the pressure differential of gas column lower end and upper end is dp, the vertical discrepancy in elevation of gas column is dz.Then

dp＝-ρ _Ngdz (E3)

Nitrogen in the tracheae can be regarded ideal gas as, according to the imperial equation of carat uncle,

$\frac{\mathrm{PV}}{T}=\frac{\mathrm{mR}}{M_N}---\left(E4\right)$

Wherein m and V get SI units

Can derive

$\frac{P}{T}=\frac{1000{\mathrm{\ρ}}_{N}R}{M_N}---\left(E5\right)$

Wherein

P: nitrogen pressure

T: nitrogen temperature

ρ _N: density of nitrogen

R: gas law constant equals 8.3145Jmol ^-1K ^-1

M _N: the nitrogen molecule amount

With formula (E5) substitution formula (E3),

$\frac{\mathrm{dp}}{P}=-\frac{M_{N}g}{1000\mathrm{RT}}\mathrm{dz}---\left(E6\right)$

Definite integral is got on both sides,

${\∫}_{p_{\mathrm{BN}}}^{p_{\mathrm{AN}}}\frac{\mathrm{dp}}{P}=-{\∫}_{h_B}^{h_A}\frac{M_{N}g}{1000\mathrm{RT}}\mathrm{dz}---\left(E7\right)$

If the tracheae two ends discrepancy in elevation is H,

$P_{\mathrm{CN}}=P_{\mathrm{AN}}{e}^{\frac{M_{N}g}{1000\mathrm{RT}}H}---\left(E8\right)$

In like manner,

$P_{\mathrm{CA}}=P_{\mathrm{Aa}}{e}^{\frac{M_{a}g}{1000\mathrm{RT}}(H-h)}---\left(E9\right)$

M wherein _aIt is the air mean molecular weight

By formula (E1), formula (E2) and formula (E9),

$P_{\mathrm{Aa}}{e}^{\frac{M_{a}g}{1000\mathrm{RT}}(H-h)}+\mathrm{\ρgh}=(P_{\mathrm{Aa}}+P_0)e^{\frac{M_{N}g}{1000\mathrm{RT}}H}---\left(E10\right)$

In the following formula, P _Aa, H, M _a, g, R, T, ρ be equal known quantity, h and P like this ₀Relation can solve by following formula.Consider in the following formula

With Be approximately equal to 0, use Maclaurin formula and launch to get (getting first order derivative)

$e^{\frac{\mathrm{Mag}}{1000\mathrm{RT}}(H-h)}\≈1+\frac{M_{a}g}{1000\mathrm{RT}}(H-h)---\left(E11\right)$

$e^{\frac{M_{N}g}{1000\mathrm{RT}}H}\≈1+\frac{M_{N}g}{1000\mathrm{RT}}H---\left(E12\right)$

Finally can draw the water level computing formula

$h=\frac{P_0(1+\frac{M_{N}g}{1000\mathrm{RT}}H)+P_{\mathrm{Aa}}\frac{(M_N-M_a)g}{1000\mathrm{RT}}H}{g(\mathrm{\ρ}-P_{\mathrm{Aa}}\frac{M_a}{1000\mathrm{RT}})}---\left(E13\right)$

As can be seen from the above equation, the parameter of actual influence level measuring value has: the density p of the vertical discrepancy in elevation H of tracheae two-port, gravity acceleration g, gas temperature T, water and the atmospheric pressure P of pressure-sensitive unit _Aa

That all constant current mode bubble water level gauges use when carrying out the conversion of pressure and water level at present is classical computing formula (E14), the level measuring value is only relevant with acceleration of gravity and water-mass density, and the acceleration of gravity of getting when carrying out conversion Calculation is normal acceleration of gravity (g=9.80665m/s ²), the density (ρ=1000Kg/m when water-mass density is 4 ℃ ³).

$h=\frac{P_0}{\mathrm{\ρg}}---\left(E14\right)$

In a plurality of constant-flow bubble type water level gauges erecting stage, particularly under the situation that the vertical discrepancy in elevation in tracheae two ends is bigger, all find the artificial observation value of water level and adopt between the automatic measurements of formula (E14) to exist than mistake, and employing has good consistance with result and the artificial observation value that formula (E13) carries out conversion Calculation, maximum error is no more than 0.01 meter, and do not have tangible correlativity with range, see Table 1.

Suppose P ₀=98066.5Pa, g=9.80665m/s ², ρ=1000Kg/m ³, nominal water level 10m with the variation of formula (E13) error of calculation with H, with the variation of formula (E14) error of calculation with g and ρ, sees Table 2.

Table 1: hydrometric station bathymetric data contrast table unit: rice

As can be seen, use the error of classical formulas (E14) to be linear growth substantially, and use (E13) formula result calculated and on-the-spot actual observation result very identical.

Table 2: different factors are to the influence of measurement error unit of contrast: rice

As seen, from the equator to the arctic, only 0.03 meter of the SEA LEVEL VARIATION that the variation of acceleration of gravity causes; Temperature variation from 0 ℃ to 20 ℃ changes the range of stage cause less than 0.02 meter by water-mass density; Much smaller more than the error that the tracheae two-port discrepancy in elevation causes.

The present invention proposes more accurate water level measurement method, and the vertical discrepancy in elevation that has disclosed the tracheae two-port is the main cause that influences constant current mode bubble water level gauge level measuring value precision.Under a lot of application scenarios, the discrepancy in elevation at tracheae two ends had all surpassed 50 meters when constant current mode bubble water level gauge was installed, and the present invention can obviously remedy the error that classical measuring method is ignored, and made measurement result more near the actual value of water level.

Claims (1)

1. a constant-flow bubble type automatic water level measurement method is characterized in that, may further comprise the steps:

1) according to the longitude and latitude and the sea level elevation of installation site, tabling look-up obtains gravity acceleration g;

2) vertical discrepancy in elevation H and the exhausr port of measuring constant current mode bubble water level gauge tracheae two ends installed elevation h ₀

3) by putting counting apparatus the vertical discrepancy in elevation H and the exhausr port at gravity acceleration g, constant current mode bubble water level gauge tracheae two ends are installed elevation h ₀The input data acquisition unit;

4) data acquisition unit timing acquiring constant current mode bubble water level gauge is measured output pressure P ₀Absolute temperature T with constant current mode bubble water level gauge erecting stage;

5) the atmospheric pressure P of data acquisition unit timing acquiring constant current mode bubble water level gauge erecting stage _Aa

6) data acquisition unit calculates the depth of water according to formula (E13);

7) data acquisition unit is according to elevation h is installed ₀Revise actual water level;

8) data acquisition unit is sent to central station by communication terminal with waterlevel data;

Wherein depth of water computing formula is:

$h=\frac{P_0(1+\frac{M_{N}g}{\mathrm{RT}}H)+P_{\mathrm{Aa}}\frac{(M_N-M_a)g}{\mathrm{RT}}H}{g(\mathrm{\ρ}-P_{\mathrm{Aa}}\frac{M_a}{\mathrm{RT}})}---\left(E13\right)$

Wherein,

H: the depth of water

P ₀: constant current mode bubble water level gauge is measured output pressure

M _N: the nitrogen molecule amount

M _a: air gas molecular weight

G: the acceleration of gravity of constant current mode bubble water level gauge erecting stage

R: gas law constant

T: the absolute temperature of constant current mode bubble water level gauge erecting stage

H: the vertical discrepancy in elevation at constant current mode bubble water level gauge tracheae two ends

P _Aa: the atmospheric pressure of constant current mode bubble water level gauge erecting stage

ρ: the density of constant current mode bubble water level gauge erecting stage water.

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