JPS607211B2 - Liquid level detection part - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a liquid level detection unit that measures the liquid level by partially immersing it in liquid and using a load detector to detect changes in buoyancy based on changes in liquid level acting on an outer cylinder. It is related to.

Various types of liquid level meters are used, including, for example, a float type level meter, a pneumatic level meter, a capacitance type level meter, and an ultrasonic level meter.

Each of these level meters has advantages and disadvantages, and is selected and used as appropriate depending on the purpose and properties of the liquid. However, they generally have the disadvantages of being prone to breakdowns, unstable instructions, and time-consuming maintenance, and generally being expensive. An object of the present invention is to solve the above-mentioned problems and drawbacks, and to provide a liquid and detection unit that has a simple structure, can obtain highly accurate measurement values, and is inexpensive. A liquid level detection part that measures the liquid level by immersing a part of the part into the liquid to be measured from above, and includes a base having a mounting part for fixing the detection part to a liquid tank, and a part extending downward from the base. a vertically installed punch body, a bottomed buoyancy detection outer cylinder disposed outside the punch body, a bellows-like sealing material that does not transmit force, connecting the upper end of the outer cylinder and the base; A load detector is provided between the inner bottom of the outer cylinder and the lower end of the punch, and the liquid level is measured by detecting changes in buoyancy acting on the outer cylinder with the load detector. It is characterized by the following.

The present invention will be explained in detail based on illustrated embodiments.

As shown in FIG. 1, the embodiment of the liquid level detection unit 1 according to the present invention has a substantially cylindrical shape, the lower part of which is immersed in the liquid to be measured 2, and a load cell installed inside the liquid level detection unit 1 has a substantially cylindrical shape. An electrical output signal is transmitted to the increasing circuit 3 and an instruction circuit 4 instructs it.

The structure of this liquid level detection section 1 is shown in detail in FIG. The base 5 of the liquid level detection unit 1 has a mounting part 8 consisting of a flange for mounting, for example, to the lid 7 at the top of the liquid tank 6, and an inner cylinder 9 is provided below the base 5. A hollow outer cylinder 11 for buoyancy detection with a closed bottom portion 10 is disposed outside the inner cylinder 9 without contacting the inner cylinder 9. The bottom 10 of the outer cylinder 11 and the lower end of the inner cylinder 9 are connected by, for example, a strain gauge type load cell 12, so that the buoyant force acting on the outer cylinder 11 can be detected by the load cell 12. Further, between the open weave of the outer cylinder 11 and the base 5, a bellows-shaped rubber sealing material 13, for example, is connected to prevent the liquid 2 from entering the outer cylinder 11. No force is transmitted between the outer cylinder 11 and the base 5. Load cell 1
The electrical output of 2 passes through the inside of the inner cylinder 9 and is drawn out to the outside of the detection unit 1 and transmitted by a lead wire 14 . Therefore, if the lower part of the outer cylinder 11 of the liquid level detection unit 1 is immersed in the liquid to be measured 2 and held at a predetermined position as shown in FIG. changes, and the force is detected by the load cell 12, making it possible to measure the liquid level. To explain this principle using a mathematical formula, the force that the load cell 12 receives from the outer cylinder 11 is F, the cross-sectional area of the outer cylinder 11 is S, the length of the part of the outer cylinder 11 submerged in the liquid 2 is h, If the specific gravity of the liquid is r and the weight of the outer cylinder 11 is W, then F=rSh-VV...
[1] is established, and the length h of the submerged outer cylinder 11, that is, the liquid level h, is determined by measuring F based on formula '1} since F, r, and W are known. It is determined by

Since the electrical output of the load cell 12 is proportional to the force F' applied to the load cell 12, the relationship between the output and the liquid level is a linear equation shown by the equation {1}, which agrees extremely well with the experimental results. .

In general, the load cell 12 may be of a compression type since the force F is directed upward from below, but if the weight W of the outer cylinder 11 is larger than the buoyant force acting on the outer cylinder 11, the load cell 12
Since the force F acting on is negative and acts downward, the load cell 12 can also be of a tension type.
Furthermore, as the load detector, for example, a force balance type differential coil or the like may be used in place of the load cell. Further, when mounting the liquid level detecting section 1, there is no problem even if the liquid level detecting section 1 is directly mounted on the side wall of the liquid tank 6 using a mounting section 8' as shown in FIG. Although the inner cylinder 9 has a cylindrical body for convenience of making it easier to insert the lead wire 14, it does not necessarily have to be a cylindrical body, and may be a punch body for holding the load detector in a predetermined position. As described above, the liquid level detection section 1 according to the present invention has an extremely simple structure and can obtain highly accurate measurement values.
However, when the specific gravity of the liquid to be measured changes from y to y+Δy due to a temperature change, etc., it is impossible to avoid the intervention of an error of Δy·Sh, as is clear from the equation '1}. Therefore, for example, a temperature sensor may be attached inside the outer cylinder 11 and temperature compensation may be performed based on the coefficient of thermal expansion of the liquid 2, or a liquid such as oil may be filled in the outer cylinder 11 and the temperature sensor may be immersed therein. Similar to crushing, temperature compensation can also be performed to arithmetically correct the liquid level measurements. FIG. 4 shows a system for compensating for specific gravity changes in measured values without using a temperature sensor as described above, and a detection section 21 for specific gravity correction is installed alongside the liquid level detection section 1 according to the present invention. This detection unit 21 is connected to a load detection unit 24 in which a reference volume 22 of a fixed volume completely submerged in the measuring liquid is passed through a connecting punch 23 with a pongee diameter made of metal or the like.
It is connected to a load cell (not shown) inside, so that the buoyant force acting on the reference volume body 22 can be detected. In particular, the connecting punch 23 in this case needs to have a diameter so that the buoyancy applied to the correction load cell in the load detection section 24 hardly changes even if the liquid level changes. Note that 25 is a protection tube for protecting the reference volume body 22. The electrical output from the load cell for specific gravity correction is inputted to the calculation circuit 27 together with the output of the load cell 12 of the liquid level detection unit 1 via the increase circuit 26, and the calculation circuit 27 performs specific gravity correction calculation, which will be described later. The corrected liquid level signal is output to the indicating circuit 4. In this case, if the force applied to the correction load cell is f, the volume of the reference volume 22 is v, and the weight of the reference volume 22 including the connecting village 23 is w, then the force f applied to the load cell is f=yV -W “-{2
}.

Therefore, if we eliminate the specific gravity y from the equations {1} and [2-, we get h
=(v/S)・(F+W)/(f+w). ...[3' is required.

As is clear from this '3' formula, it is understood that by knowing F and f, the liquid level h can be accurately measured regardless of the specific gravity y. The calculation circuit 27 incorporates an electric circuit for realizing the calculation of formula (3'), and calculates the force F from the load cell 12 of the liquid level detection section 1 and the force f from the load cell of the detection section 21 for specific gravity correction. The liquid level h is calculated by inputting the liquid level h, and is output to the indicating circuit 5.As explained above, the liquid level detecting part according to the present invention has almost no moving parts, and the outer periphery that receives the buoyant force is Since measurements can be made in a nearly fixed state, there are very few failures and maintenance is easy.

In addition, the measurement principle is expressed by the {1} formula, and ``Since it is performed based on an extremely simple principle, there are few errors other than changes in specific gravity, and highly accurate measurement is possible. By providing this, the liquid level can be measured accurately even if the specific gravity changes.

[Brief explanation of the drawing]

The drawings show an embodiment of the liquid level detection section according to the present invention, and FIG. 1 is a front view showing the state of use in which it is immersed in a measuring liquid, FIG. 2 is a longitudinal sectional view thereof, and FIG. 4 is a partially cutaway side view of another mounting method, and FIG. 4 is an explanatory view showing a state in which a detection section for specific gravity correction is provided to correct the specific gravity. 1 is the liquid level detection unit, 2 is the liquid, 3 is the increase circuit, 4 is the indicator circuit, 5 is the base, 6 is the liquid tank, 8 and 8' are the mounting parts, 9
1 is the inner cylinder, 1 is the bottom, 11 is the outer cylinder, 12 is the load cell,
13 is a sealing material, 21 is a detection section for specific gravity correction, 22 is a reference volume body, and 24 is a load detection section. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. A liquid level detection part that measures the liquid level by immersing a part of the liquid into the liquid to be measured from above, and a base having a mounting part for fixing the detection part to a liquid tank; A rod hanging downward from the base, a bottomed buoyancy detection outer cylinder disposed outside the rod, and a bellows-like sealing material that does not transmit force connecting the upper end of the outer cylinder and the base. and a load detector interposed between the inner bottom of the outer cylinder and the lower end of the rod, and the load detector detects changes in buoyancy acting on the outer cylinder to measure the liquid level. A liquid level detection unit characterized in that: