SU1434330A1 - Method of measuring liquid density - Google Patents

Abstract

The invention relates to a measurement technique, and specifically to methods for determining the density of liquid media. The purpose of the invention is to improve the accuracy and simplify the determination of the density of a liquid by the gravimetric method. The method for determining the density of a liquid is concluded in that air is blown in two cycles through a long and short measuring tubes placed in the liquid under study and a pressure compensator, and in the first stroke blows air through a compensator and a short tube, adjust the pressure in the compensator so that the difference the pressure between it and the short tube became zero; in the second stroke, air is blown through the compensator and the long tube, measuring kgg of pressure difference between them, which is used to judge the desired value. 3 il. i (L

Description

00 00

The invention relates to a measurement technique, and to methods for determining the density of liquid media.

The purpose of the invention is to improve the accuracy and simplify the determination of the density by eliminating the operations of moving the ballast pressure compensator tube and measuring its value .10

Fig, I shows a structural diagram of a pneumometric densitometer that implements the proposed method; Fig. 2 illustrates a control computing unit; FIG. 3 is a time diagram 15 of the operation of the density meter.

The method consists in that the air is blown in two cycles through a dpine and short measuring tubes, placed in the liquid under study, and a pressure compensator; moreover, in the first stroke, air is blown through the compensator and the short tube, the pressure in the compensator is adjusted so that so that the differential pressure between the compensator and the short tube becomes zero, in the second stroke air is blown through the compensator and the dp measuring tube, the differential is measured. pressure between them, at which su- 0 d t about the density of the liquid.

The method is implemented using a pneumometric densitometer,

The densitometer contains air supply unit 1, supplying positive 2 and minus 35 independent 3 independent pneumatic lines, between which differential pressure gauge 4 is connected. Positive pneumolini 2 feeds through a normally closed pneumatic valve 5. the main measuring tube b, 40, immersed in a controlled fluid to a depth of H, and through the normally open pneumatic valve 7, an additional tube 8, immersed in the fluid to a depth of And + h. Minus pneumatic 45 line 3 through a normally closed pneumatic valve 9 supplies pneumatic capacity 10 and a pneumatic throttle 11 connected in series with it, connected to the atmosphere through a normally charged JQ indoor pneumatic valve 12, Minus chamber of a differential pressure gauge A connected to minus pneumatic line 3 at the junction of pneumatic capacity 10 11, the output of the differential pressure gauge 4 is connected to the input of the control-computing unit 13, the first output of which is connected to the control inputs of pneumatic valves 5 and 7, and the second and third - from the control valve of the pneumatic valve s 9 and 12, respectively,

The control and computing unit 13 consists of a comparator 14, the first input of which is connected with the output of differential meter 4, and the second with the output of the setpoint block 15, a trigger 16 with installation inputs, the first input of which (reset input) is connected to the output of the comparator 14, and the output is connected to the control input of the pneumatic valve 12, generator 17, trigger 18 with a counting input, the input of which is connected to the output of the generator 17, and the first output to control inputs of the pneumatic valves 5 and 7, the first input of the coincidence circuit 19 and the input of the one-vibrator 20, output which is connected to the control input and pneumatic valve 9, the second input (installation) of the trigger 6, the input of the inverter 21 and the second input (reception resolution) of the register 22, the voltage converter - the frequency 23, the input of which is connected to the output of the differential pressure gauge 4, the circuits 24 and 25 coincidence, the first inputs of which associated with the first and second outputs of the trigger 18, and the third with the output of the converter 23, and the reversing counter 26, the first, second and third inputs of which (inputs Addition, Subtraction.and Reset) are respectively connected to the outputs of circuits 25, 24 and 19 match, and code - with the first input p Registry 22. Second and Third ENTRANCE. matching circuits 19 are respectively connected with the output of the inverter 21 and the output of the generator 17, and the second inputs of the matching circuits 24 and 25 are connected with the output of the inverter 27, whose input is connected to the output of the generator I7,

The method is carried out using a densitometer as follows.

In the first stroke, the main measuring tube 6 and the adjustable ballast pressure compensator, implemented in the minus pneumatic line 3 using pneumatic capacitance 10, pneumatic throttle 11 and pneumatic valves 9 and 12, achieve a zero or close to zero reading of the differential pressure meter. the reading is memorized and the pressure in the compensator is recorded for this condition.

In the second cycle, at a fixed value of pressure in the compensator, the immersion depth of the measurement is increased: the body tube - the measuring tube 8 is connected to the positive pneumole 2 and the readings of di (1) manometer 4 are recorded. The required density is proportional to the differential reading of the diffuser. meters in the second and first bars. In the i-M measurement cycle (i 1,3, 5, ...) pressure is applied to the plus chamber of the differential pressure gauge 4

R; pgH - P ,, PS; PV; ,

where p is the measurement and density; g - 9.81 m / s - acceleration of the force of tin; - pressure loss at the site

Lightning from the place of connection of the differential pressure gauge to the lower section of the bubbling tube caused by air friction against the walls of the pneumatic line and the tube in the i-M cycle;

R., is the excess air pressure caused by the surface tension forces necessary for the bubble to break from the lower end of the tube in the i-th cycle;

P is the pressure due to the velocity head of the fluid, which changes the condition for the detachment of the air bubble from the lower end of the tube in the ith cycle. Let the pressure in the compensator (in the pneumatic container 10) be equal at the time of compensation.

If the model of the static characteristic of the differential pressure gauge 4 is

W; a „+ ADR -;),

40

output signal (current, voltage, etc.);

nominal coefficients of the model; . static displacement j

conditioned by

drift zero differential pressure gauge 4; sensitivity coefficient of differential pressure gauge 4,

tact at the time of compensation CQ

output of differential pressure gauge 4 is equal to

W;

+ a; (pgH + / iP; - Р), (1)

where a. , - values of coefficients

models of static behavior in the i-th cycle.

LR; P (v; + + P

Vi

In the (i - (- l) -M cycle, pressure is applied to the plus chamber of the differential pressure gauge

R.

, v, - h) Рм, (- Г

Since the duration of the measurement cycle can always be made sufficiently short, then:

R . - R . .

(l + () A

Ps (, 4, PS;

p p

V (Ui),

The pressure values in the compensator and the coefficients of the model also cannot change during one clock cycle, therefore:

mouth

 1 + I) 9 0 (1 + n | o1

() one,

Thus, in the (i + O-M cycle, the signal at the output of the differential pressure gauge 4 is equal to

 + o

a .fngCH h) + UP, - - (2)

y; n P (2) and (1) we have

. - Y,, () From here the density is found by algorithm

about

five

0

j

Q

(3)

(four)

c

d zi.

I- 1

Ia; gh

With full compensation; Oh and the measurement algorithm takes the form

l R a; gh

The value of h is chosen from the following consideration.

For a given limit of measurement of the Pp of the differential pressure gauge 4 at the maximum measured density, the value of the pressure differential on the differential pressure measurement 4 in the second cycle should not exceed the limit of measurement.

For r rmaco in the first bar we have

R | - р, p «„, e gH + Р,, (5) in the second cycle

PI - Р рмакс 8 (И + б) -Ь UP, - р; .. R,. (6)

From here we find 1

h. (7)

Rmake ё As seen from (3) and (4), the value

The density of the monitored fluid does not depend on the working conditions of the densitometer and the drift of the differential pressure gauge, but is determined by the results of two adjacent measurement cycles and the largest h.

Thus, the determination of the current density of a liquid is made according to the results of two cycles of measurement: in the first stroke, the pneumatic fork is open, pan 5, and pneumatic valves 7 are closed; the measuring tube 6 is working; compensating the pressure differential over the differential 10 trigger 18 starts the one-shot 20j

generating a positive pulse of duration f, opening the pneumatic valve 9 at this time. During this time, the pressure in the air capacity 10 exceeds

5 the pressure in the positive chamber of the meter A, the signal at its output will have a negative sign. Comparator 14, in conjunction with block 15, is configured in such a way that it

20 is triggered when a small negative signal is turned off, a- is turned off when the signal at its input is zero, Track, body, for a time not exceeding the value of cG, comparator 14

 will work and will be located in the pump 4 and will be carried out in the minus | pneumolin 3 by regulating the pressure in the luminescence capacity lO. For this, during a short time, the pneumatic valve 9 is opened and the pneumatic valve 12 is closed. The pressure in the pneumatic capacitance 10 begins to increase and at some point exceeds the pressure in the positive chamber of the differential pressure gauge 4. The output at the ei o output becomes negative. Then the pneumatic valve 9 is closed and the pneumatic valve 12 is opened. The pressure in the tank begins to monotonously fall, so i as it discharges into the atmosphere through the pneumatic throttle 11 and the signal at the output of the differential pressure gauge 4 increases, as the output of the differential pressure gauge 4, the pneumatic valve reaches : pan 12 is closed and is being produced

information retrieval (output signal

: the differential pressure gauge may be slightly larger: shegul, since the response time of the pneumatic valves orpaHii4eHo and during the switching time the pressure in the pneumatic capacitance O can decrease)

In the second stroke, the pneumatic valve 5 is closed, and the pneumatic valve 7 is open. The junction of elements in negative pneumatic 3 remains unchanged. Since the optional tube 8 works, the pressure in the plus chamber of the differential pressure gauge increases and information is collected about the result of the second measurement cycle. Density calculation

as well as all manipulations with pneumatic valves produces a control-computing unit 13; operating as follows (see FIG. 3, where timing diagrams 28-36 illustrate operation of generator 17, trigger 18, one-shot 20, coincidence circuit 19, match circuits 24 and 25, differential pressure gauge 4, comparator 14, trigger 16) .

thin 1; The back of the pulse from the one-shot 20 trigger 16 is set to state I and opens the pneumatic valve 12

30 10 starts to discharge through the pkkommo-choke 1 into the atmosphere, the pressure in it drops, the signal at the output of the differential pressure gauge 4 increases, and when it reaches zero, the comparator p 14

35 is turned off and the switch goes to state O. The falling edge of the pulse of the comparator 14 resets the trigger 16, the pneumatic valve 12 closes - fixing such pressure in the pneumatic capacitance 10, that

40 differential meter readings are equal to or. close to zero.

The volume of pneumatic capacitance 10, the magnitude of pneumatic resistance pneumodrossel 45 1 1 J duration of pulses T, and c are chosen so that during time b the pressure in pneumocapacity JO exceeds the pressure in the positive chamber of the differential pressure gauge 4, in time T, compares to lower limits. This is easily achieved.

50

varying with and - pneumatic resistance pneumosrosle P.

Thus, by the time of the end of the pulse from the generator 17 of the initial state, the pneumatic valve 55 n / 4 shows zero or

1 7, which forms a positive pulse length T with a period T. By (the leading edge of the pulse from generator 5, trigger 7 18 is set to state 1 and opens the pneumatic valve 5, and pneumatic valve 7 closes and the tube 6 operates. On the leading edge of the pulse from the first (direct) output

thin 1; The back of the pulse from the one-shot 20 trigger 16 is set to state I and opens the pneumatic valve 12

10 begins to discharge through the pkkom-choke 1 into the atmosphere, the pressure in it drops, the signal at the output of the differential pressure gauge 4 increases, and when it reaches zero, the comparator p 14

turns off and goes to state O. The back of the pulse of the comparator 14 resets the trigger 16, the pneumatic valve 12 closes - fixing such pressure in the pneumatic capacitance 10 that

Differenometer readings are equal to or. close to zero.

The volume of pneumatic capacitance 10, the magnitude of pneumatic resistance of pneumodrossel 1 1 J duration of pulses T, and c are chosen in such a way that during time b the pressure in pneumatic capacitance JO exceeds the pressure in the positive chamber of the differential pressure gauge 4, in time T, it is easy to achieve this.

varying with and - pneumatic resistance pneumosrosle P.

Thus, by the time of the end of the pulse from the generator 17

7 is open, pneumatic valves 5, 9 and 12 are closed, triggers 16 and 18 are in the state O. Duration of cycles; equal to T and determined by the generator

close to zero value, which, converted to a frequency on the transducer 23, during the time T-T, formed by the circuit 24 coincidence.

one

enters the read out value of the sigzio counter 26.

Let the characteristic of bodies 23 be

; „T Ku.,

where f is the initial frequency corresponding to the zero signal from the differential pressure gauge;

K - sensitivity transducer.

Then, during the first measurement cycle, the number

N, f, (T - T,) (f, -.- Ku,) (T - - T,).

The second impulse from the generator 17 front edge resets the trigger 18, the pneumatic valve 5 closes and the pneumatic valve 7 opens and the tube 8 starts to work. The pressure in the positive chamber of the differential pressure gauge 4 increases, a signal appears at its output that during the time T-T generated By the matching circuit 25, it is fed to the summing input of the reversible counter 26 and is written into it in the following pulses:

N, f (T - T,) (f; + Ky, j) (T - - T,).

Thus, by the end of the second clock cycle in the reversible counter 26 there will be a number

N N - N, K (T - T,) (y - y,) K (T - T,) a, pgh, (B)

directly proportional to the measured density.

In the third clock cycle, the pulse signal from the one-shot 20 will be overwritten into register 22, and the pulse duration T-T generated by the coincidence circuit 19 will reset the reversible counter 26, and then the circuit will repeat.

Thus, in the register 22 there is always a number proportional to the density of the fluid, as determined in the previous measurement cycle.

From (8) it can be seen that the drift of zero converter 23 also does not affect the measurement result and,: by varying the value of K or T, one can always achieve the condition K (T - T,) 1 and immediately get the result in units of density.

30 V

The method) has an increased accuracy, does not depend on such influencing factors as the level of the controlled fluid, excess pressure, flow rate, air flow in the pneu- line, temperature, drift zero of the measuring transducer, pressure drop in the compensator. Densitometers that implement the proposed method can be operated for a long time in real conditions without adjustment and correction.

The positive effect of the used invention is achieved by that; that the parameters of the compensator and the pressure factor on it are not included in the measurement result and do not affect it, as a compensator you can

use not only a hydraulic valve with an adjustable piezometric. tube, but also simpler and coarser devices, for example, an adjustable throttle

sekakhtsimi valves and so forth.

At the same time, additive errors in the proposed method are compensated for by taking the difference of readings in the second and first cycles and multiplicative (the change in the sensitivity coefficient and the error in nonlinearity caused by the actual static characteristic from the adopted linear model)

weakened due to narrowing of the dynamic range of the measurement of the dF meter and enter the measurement result not directly, but weakened n times, where n is the ratio of the dynamic range of the pressure change on the tube to the limit of the differential pressure gauge.

With increasing n, the multiplicative error can be brought to a predetermined level. Therefore, there is no additional temperature error in the method (with the same basic one) and it is easier to implement, since it does not require a complex adjustable pressure compensator or a piezometric tube displacement meter is not required.

55

Claims (1)

Invention Formula The method of determining the density of a liquid, which consists in blowing air through two cycles through a long and short measuring tubes placed in the liquid under study and a pressure tester, regulating the pressure in the compensator, measuring the pressure difference in the compensator and measuring tubes, followed by determining the density that differs from In order to improve accuracy and simplify the determination, in the first stroke air is blown through From di nanometreg. C the compensator and the short tube regulate the pressure in the compensator so that the pressure drop between the sator and the short tube becomes zero, in the second stroke the air is blown through the l detector to the measuring tube, measuring the pressure density of the liquid. KpnevmokA 2 , u 7 R ueJ Tig.z