JPH1123443A - Method and equipment for measuring density of liquid in tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an equipment for measuring the density of a liquid in a tank at a low facility cost in which the density can be measured at high accuracy regardless of the liquid level with no problem even for a tank in a vessel (principally, tanker) where no apparatus can be mounted on the side wall of the tank. SOLUTION: A differential pressure detector A having pressure receiving/ acting parts 2a, 2b on two sides is provided in a measured liquid such that the pressure of the liquid acts on one pressure receiving/acting part 2a while the total buoyance being applied to a float 10 provided in the liquid acts on the other pressure receiving/acting part 2b along with the pressure of the liquid. Pressures acting on both pressure receiving/acting parts are outputted as electric signals and a bouyance action on the float is determined from the difference between both signals. Density of the liquid in the tank is measured by dividing the buoyance by the volume of the float.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for measuring the density of a liquid in a tank.

[0002]

2. Description of the Related Art In the quantitative management of liquid stored in a tank, the total weight of the stored liquid is the most important quantity, but especially in a large tank, the total weight of the liquid is directly measured. Since it is difficult to perform the measurement, it is common to separately determine the volume and density of the liquid and use the product of the two as the mass.

[0003] Usually, the volume of a liquid is obtained from the relationship between the liquid level and the volume of the liquid measured in advance using the measured value of the liquid level by a level meter. This is rarely measured due to reasons such as technical difficulty in obtaining high accuracy, and the temperature of the liquid is measured, and the correlation data between the temperature and the density of the same liquid separately measured in advance is obtained. It is often used to estimate density. However, this method can be applied to a liquid whose correlation data is known, but cannot be applied to a liquid whose correlation data is unknown.

[0004] There are the following methods for actually measuring the density of a liquid in a tank which are currently put into practical use. FIG. 7 (a),
As shown in (b), a differential pressure gauge is provided at the tank bottom, the differential pressure between the gas phase at the tank bottom and the gas phase at the top of the tank is measured, and this is divided by the liquid level value separately measured by the level meter to calculate the density. .

As shown in FIG. 8, a pressure gauge is provided at a height between the tank bottom and the tank, and a difference between the pressure at the tank bottom and the pressure at the intermediate height of the tank is obtained. A method of calculating the density by dividing by the vertical distance of the pressure part.

As shown in FIG. 9, a method is provided in which a return pipe for extracting a liquid is provided on a side wall of a tank, and a sample of the liquid in the tank is guided to a density measuring device outside the tank by a pump to determine the density.

However, each of these conventional methods has the following problems. Problems of the methods of FIGS. 7A and 7B (a) It is necessary to use a differential pressure gauge having a wide measuring range capable of measuring the differential pressure at the highest liquid level, and the accuracy is reduced when the liquid level is low. (b) In the case of a tank, such as a tank of a ship (tanker), in which a differential pressure gauge cannot be attached to the tank side wall, the installation method is as shown in Fig. 7 (b). If the condensed gas turns into a liquid and accumulates in the gas pressure receiving portion of the differential pressure gauge, a measurement error occurs due to the liquid pressure, and it is difficult to recover because the drain valve cannot be installed. (c) If the accuracy of the level data used for calculating the density is low,
Density measurement accuracy is also reduced.

Problems with the method of FIG. 8 (a) The density cannot be measured unless the pressure gauge at the middle height of the tank is immersed in the liquid. Also, as in FIGS. 7A and 7B, when the liquid level is low, the measurement accuracy decreases. (b) The cost is high because two pressure gauges are required. Problems of the method of FIG. 9 (a) Ancillary equipment such as a return pipe and a pump is required, which increases the cost. (b) In the case of a tank such as a tank of a ship (tanker), in which a return pipe cannot be attached to the tank side wall, the return pipe is disposed in the tank from the top of the tank, which further increases the equipment cost.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-precision density measurement regardless of the level of a liquid level, and to be used without problems in a tank such as a tank of a ship (mainly a tanker) in which equipment cannot be installed on a tank side wall. An object of the present invention is to provide a method and an apparatus for measuring the density of a liquid in a tank which can be performed at a low cost.

[0010]

To achieve the above object, the method of the present invention comprises:
A differential pressure detector having two pressure receiving operation parts is provided in the measurement liquid, one of the pressure reception operation parts receives the liquid pressure of the measurement liquid, and the other receives the pressure of the measurement liquid and the measurement liquid. The buoyancy acting on the float is determined by allowing the total buoyancy acting on the float to act, outputting the pressure acting on both pressure receiving operation parts as an electric signal, and determining the difference between the two signals to determine the buoyancy acting on the float. The density of the liquid in the tank was measured by dividing by the volume.

Further, in the apparatus for measuring the density of a liquid in a tank according to the present invention, a sensor device is provided in a housing provided with two pressure receiving operation portions, and a differential pressure detection for outputting pressure acting on each pressure receiving operation portion as an electric signal. The differential pressure detector is installed in the measuring liquid so that the liquid pressure of the measuring liquid acts on one of the pressure receiving operating parts of the differential pressure detector, and the other pressure receiving operating part is provided with the liquid pressure of the measuring liquid and the measuring liquid. The buoyancy of the float is applied, so that the pressure acting on both pressure receiving operation sections is output as an electric signal, and the electric signal of both pressures is calculated by an arithmetic unit to obtain the density. There are things.

[0012]

FIG. 1 shows a differential pressure detector used in the present invention.
The differential pressure detector A has a diaphragm 2 whose opposing openings (upper and lower openings) of the housing 1 are pressure receiving operating portions.
a, a sensor device for converting a force acting on the two diaphragms 2a, 2b into an electric signal in the housing. The sensor device has a structure in which strain gauges 5a and 5b are attached to both surfaces (upper and lower surfaces) of a cantilever beam 4 provided on one inner wall of the sensor box 3, and signal lines 6a and 6b are connected to each strain gauge. In addition, these signal lines are led out of the housing as one covered electric wire 6.

One end of each of actuators 7a and 7b made of a rod is attached to the inner surface of each of the diaphragms 2a and 2b, and the other end (tip) of each actuator is in contact with both surfaces of the beam. The strain amount of each surface of the beam due to the pressing force of
5b outputs as an electric signal. The sensor box 3 is held by two partition plates 8a and 8b and mounted in the housing, and the actuator is a partition plate,
It passes through each hole in the sensor box. FIG. 1 shows an example of a strain gauge type, but various types of sensors such as a capacitance type, an optical sensor type, a magnetic sensor type, and a differential transformer type can be applied to the principle and structure of the sensor.

As shown in FIG. 2, the power supplied to the sensor and the transmission of the output signal from the sensor are air-tightly connected at one end to the housing of the differential pressure detector A, and at the other end through the tank top plate. A vertical conduit 9 led out is provided, and the electric wire 6 is routed inside the conduit. Also, the signal from the strain gauge is input to a calculator (not shown), where the calculation of the expression (4) or the expression of FIG.

In the vicinity of the differential pressure detector A, a float 10 whose apparent specific gravity (value obtained by dividing weight by volume) is smaller than the liquid to be measured in the tank, and a mechanism for transmitting the float buoyancy are provided. The float buoyancy acts on one of the diaphragms of the differential pressure detector.

FIGS. 3 and 5 show specific examples of the mechanism for transmitting the float and buoyancy. FIG. 3 shows that the vertical hole (not shown) of the ear 12 of the float is fitted in the vertical guide rod 11 so that the float 10 is prevented from moving in the horizontal direction and the buoyancy of the float is reduced by the protrusion 10.
This is a method of directly adding one (lower) diaphragm 2b at (a). Reference numeral 13 in the figure denotes a guide rod mounting holder frame which is mounted on the connection flange 14a of the conduit tube 9a connected to the sensor box 3. The flange 14a of the conduit 9a is connected to the flange 14b of the branch pipe 9a of the vertical conduit 9.

FIG. 5 shows a method of transmitting the buoyancy of the float to one of the diaphragms by a link mechanism. For example,
A curved portion of an inverted L-shaped link 16 having a float 10 at an end of a horizontal portion 16a is rotatably attached to a bearing 15 provided on a flange 14a of a conduit tube 9a of the sensor box by a horizontal rotating shaft 17, and a vertical portion is provided. Projection 1 provided at the end of 16b
8 acts on one actuator 7b via the diaphragm 2b when the float rises. Reference numeral 19 in the drawing indicates a stopper that regulates the lower limit position of the float 10.

In the method shown in FIG. 3, the mechanical friction acting on the float 10 is small and the measurement accuracy is high, but the structure is slightly complicated. Conversely, the method of FIG. 5 has a simple structure, but the friction torque acting on the horizontal rotating shaft 17 of the link 16 increases in proportion to the buoyancy of the float, and is less advantageous than the method of FIG. Each system has advantages and disadvantages.

Next, the principle of density measurement by the method shown in FIG. 3 will be described. Since the forces acting on the differential pressure detector A in the method of FIG. 3 are the pressure of the liquid, the pressure of the gas phase, and the force from the float, they are as shown in FIG. In the same figure, F: buoyancy of the float S; effective area of the diaphragm Wf; weight of the float P _G ; pressure of the gas phase ρ; density of the liquid Δh; interval between two diaphragms h _A : from the upper diaphragm The liquid level.

Assuming that the output of the differential pressure detector is E _O , E _O is proportional to the difference between the forces acting on the upper and lower diaphragms. When there is no float, the force acting on the lower diaphragm is f ₁ = S ｛ρ (h _A + Δ
h) + P _G力 The force acting on the upper diaphragm is f ₂ = S (ρ · h _A + P
_G ), E _O = k (f ₁ −f ₂ ) = k · ρ · S · Δh (1) Here, k is a constant representing the sensitivity of the sensor.

When there is a float, a force by the float is applied to the lower diaphragm. Flow - Since the upward force acting on the lower diaphragm by preparative an F-W _f, flow - when there is bets (f ₁ -f ₂₎ is F
Increased by -W _f, the output E _O is given by _{E O = k (ρ · s} · Δh + F-W f) ······· (2).

On the other hand, the buoyancy F of the float is as follows: F = ρ · V (3) where V is the volume of the float. , (3) is substituted into the expression (2), and the data is arranged as follows: ρ = 1 / (V + SΔh) · (E _O / k + W _f ) (4) V, S, Delta] h, W _f is known, k is a constant representing the sensitivity of the sensor, because it is pre-determined that for each sensor, (4) the liquid from the output E _o of the differential pressure detector by formula Can be known.

If the volume V of the float is larger than S · Δh, equation (4) is approximately calculated as follows: ρ−Wf / V = E _O / Vk (5) is represented by Wf / V means the apparent specific gravity or density of the float. The calculation of the equation (4) is based on the output E of the detector.
After converting _O into a digital quantity, there is no technical difficulty if it is performed by an arithmetic unit composed of a microprocessor.

The above is a description of the system shown in FIG. 3, but the same effect is obtained in the system shown in FIG. In the case of the method shown in FIG. 5, if the diaphragm surface is perpendicular to the liquid surface and the detectors are installed so that the heights of the two diaphragms are equal, Δh in equation (1) becomes 0, and the density ρ Is obtained from the output E of the detector by the following equation. ρ−ρ _O = (ρ _max −ρ _O ) · E / E _max (6) where ρ _O is the density of the liquid at which the force applied to the diaphragm by the lever is exactly zero. ρ _max : maximum value of measurable liquid density E _max : output at liquid density ρ _max , conversion using a liquid of density ρ _max is performed, and E _max may be obtained in advance.

[0025]

The present invention has the following features as compared with the conventional method. (1) Measurement is possible if the float and differential pressure detector are immersed in the liquid, and if these are installed near the tank bottom, the density can be measured regardless of the liquid level in the tank and the measurement accuracy Is not affected by the liquid level. Further, if a plurality of density measuring devices of the present invention are installed at different heights in the tank as shown in FIG. 6, it is possible to know the density distribution of the liquid having non-uniform density.

(2) In the case of the present invention, as can be seen from the above equation (5), the output E _O of the differential pressure detector is proportional to the difference between the density of the liquid and the apparent density of the float. Therefore, if the float is manufactured so that the apparent density of the float is at the lower limit of the density measurement range, the differential pressure detector will detect the increase from the lower limit and easily obtain high accuracy. Can be Assuming now that the measurement range of the density is 0.7 to 1.2 g / cm ³ ,
If the float of this apparatus is manufactured to have an apparent density of 0.7 g / cm ³ , the differential pressure detector will have a liquid density of 0.7 g / cm ^3.
Since only the increment from / cm ³ needs to be measured, a high-resolution sensor with a narrow measurement range can be used.

On the other hand, in the conventional method shown in FIGS. 7 (a) and 7 (b), the measuring range of the differential pressure gauge is from 0 to the liquid pressure at the maximum liquid level. When the pressure is low, the pressure of the liquid to be measured is much smaller than the maximum measurable pressure, so that it is difficult to obtain high accuracy. Also, in the conventional method of FIG. 8, similarly to FIGS. 7 (a) and 7 (b), the measurement range of the pressure gauge is the liquid pressure from the liquid level 0 to the maximum liquid level. The accuracy when the position is low becomes a problem. The apparent density of the float in the present invention can be easily adjusted by adding a weight to the float.
And can be performed accurately.

(3) As is clear from FIGS. 3 and 5, the apparatus of the present invention is mounted on a vertical conduit inserted into the tank substantially vertically from the top of the tank, and a signal line from the differential pressure detector is passed through the pipe. If it is led out of the tank from the tank top, it can be easily installed in a tank such as a ship that cannot be attached from the side wall of the tank.

(4) The apparatus according to the present invention comprises one differential pressure detector,
Since it is composed of individual floats and a simple float guide mechanism, installation in the tank is not particularly complicated as compared with the conventional method, so that the equipment cost can be reduced far as compared with the conventional means. .

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a differential pressure detector in an embodiment of an apparatus according to the present invention.

FIG. 2 is a front view showing an embodiment of the device according to the present invention.

FIG. 3 is an enlarged fragmentary sectional view showing a differential pressure detector and a float in an embodiment of the apparatus according to the present invention.

FIG. 4 is a longitudinal sectional view showing a force acting on a pressure receiving operation portion of the differential pressure detector.

FIG. 5 is an enlarged fragmentary sectional view showing a differential pressure detector and a float in another embodiment of the device according to the present invention.

FIG. 6 is a front view showing still another embodiment of the device according to the present invention.

FIG. 7 is a front view showing a conventional example.

FIG. 8 is a front view showing another conventional example.

FIG. 9 is a front view showing still another conventional example.

[Explanation of symbols]

 A Differential pressure detector 1 Housing 2a, 2b Pressure receiving operation section (diaphragm) 3 Sensor box 4 Cantilever beam 5a, 5b Strain gauge 6 Insulated wire 6a, 6b Signal wire 7a, 7b Actuator 8a, 8b Partition plate 9 Vertical conduit 9a Sensor tube conduit 9b Branch pipe 10 Float 11 Guide rod 12 Float ear 13 Guide rod mounting holder frame 14a Conduit pipe connection flange 14b Branch pipe connection flange 15 Bearing 16 Link 16a Link horizontal part 16b Link Vertical part 17 Rotation axis of link 18 Projection of link 19 Stopper

Claims (2)

[Claims] 1. A differential pressure detector having two pressure receiving operation parts is provided in a measurement liquid, and one of the pressure reception operation parts has a liquid pressure of the measurement liquid,
The other pressure receiving operating part is made to apply the liquid pressure of the measuring liquid and the total buoyancy acting on the float provided in the measuring liquid, and the pressure acting on both the pressure receiving operating parts is output as an electric signal, and the difference between the two signals is output. , The buoyancy acting on the float is determined, and the buoyancy is divided by the volume of the float to determine the density of the measurement liquid. 2. A differential pressure detector, wherein a sensor device is provided in a housing having two pressure receiving operating portions, and a differential pressure detector for outputting a pressure acting on each pressure receiving operating portion as an electric signal is provided in the measurement liquid, and the differential pressure is detected. The liquid pressure of the measurement liquid acts on one of the pressure-receiving parts of the vessel, and the other pressure-receiving part receives the liquid pressure of the measurement liquid and the buoyancy of the float provided in the measurement liquid. An apparatus for measuring the density of a liquid in a tank, wherein the pressure acting on the pressure receiving operation section is output as an electric signal, and the electric signal of both pressures is calculated by an arithmetic unit to obtain the density.