JPS6018923B2 - Liquid level detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid level detection device that is safe under high pressure and has very little error.

A method of detecting the liquid level in tanks under high pressure is to use a differential pressure transmitter to detect the difference in pressure between the high pressure side and the low pressure side.

In this case, when the gas composition and temperature/pressure conditions in the tank change, the specific gravity of the gas changes accordingly, causing a considerable error between the detected liquid level and the actual liquid level. There is no liquid detection method that can follow the ever-changing temperature and pressure conditions, and currently it is being used with some errors, so there has been a desire to develop a detection device with even fewer errors. Particularly recently, as chemical plants have become more pressurized and technology has become more sophisticated, extremely precise liquid level detection has become necessary. The present invention was developed in view of these points, and includes a differential pressure transmitter using dry piping and a differential pressure transmitter using wet piping in the tank to be measured, and calculates the output signals from both differential pressure transmitters. To provide a liquid level detection device which can always perform accurate liquid level detection even when temperature and pressure conditions change by inputting the liquid into a calculation unit and calculating the output signal of the calculation unit. The configuration and the like will be explained in detail below with reference to embodiments shown in the drawings. Fig. 1 shows a liquid & detection device using dry piping, Fig. 2 shows a liquid & detection device using wet piping, and Fig. 3 shows a liquid level detection device with dry piping and wet piping according to the present invention. In these figures, a is an explanatory diagram of piping, etc., and b is a diagram of the relationship between the liquid & and the output signal of the differential pressure transmitter.

First, in the case of dry piping, tank 1 is shown in Figure 1a.
A liquid 2 is placed inside, and a gas 3 is filled above the liquid 2. The predicted highest liquid level and the predicted lowest liquid level of the tank are connected by a pipe 4A equipped with a differential pressure transmitter A on the way, and the differential pressure transmitter A connects its low pressure side L to the highest liquid level side of the pipe 4A. The high pressure side is connected to the lowest liquid level side of the pipe 4A. The side of this piping that connects to the highest liquid level is filled with gas 3, just like the inside of the tank, and is a so-called dry piping system.
Day indicates the liquid level, and HN^x indicates the highest liquid level. The differential pressure transmitter A transmits the difference in pressure at both inlets as an output signal, and the output signal is designated as a. In the dry piping system configured as described above, if the differential pressure transmitter A is adjusted to the zero point when the liquid level is zero, when the liquid & Due to the effect of the gas head, the output signal a shows a smaller value than the output signal for the true liquid &. Therefore, the relationship between the liquid & and the differential pressure across the pen pressure transmitter A is expressed by the following equation. △P=
(y, - yg) days......In the formula [1''1}, when the upper gas is loose, that is, in a vacuum state, g =
0, and if the piping outlet dimension is HN^x, the technical difference pressure △Pw^x applied to the reed pressure transmitter is calculated by substituting yg=0 into equation {1) and △PM^x=(y, -0 ) Hu^x =y, Hw^x ......[2'.

The symbols used in the above equation are as follows. △P...Differential pressure applied to the differential pressure transmitter (k9/ground) △P skin x...Maximum differential pressure of the differential pressure transmitter ([9') yl...Liquid specific weight (k9/average) yg...Gas specific weight (k9/ground)
Day...Liquid level (kite) HM^x...Output signal maximum scale (kite) {11÷
{21△P-Koyanagi: (・-Tsutomu) Diary △PM^X yIH...X Here, considering the dimensionless △P, H' and substituting it into the above formula, △P' = Table horse H' = Nishin △P'=(1-Tsu)H'....・・・．・Side The above equation '3}, that is, the relationship between the output signal and the liquid level can be expressed in a diagram as shown in FIG. 1b.

In the figure, the output signal △P' is applied to the vertical ball, and the liquid level H is applied to the machine axis.
′, the straight line 6 represents the above-mentioned glue formula. Further, a straight line 5 shows an ideal input/output relationship in which the relationship between the liquid level H' to be detected and the output signal ΔP' is expressed as ΔP';H' and is not affected by changes in the gas specific gravity yg. △P'=H' to △P'
= Playing with H ``Substituting Ryo, we get △P - day △PM^X - HM^X.

Substituting the '2} formula made by adjusting the detector range into the above formula, we get AP - day y, HM^x Kazuma^X, and △P=y, day is derived and gas specific gravity yg is not included. It is confirmed that this is an ideal input-output relational expression.

The above explanation is for dry piping, and in the case of green piping, which will be explained next, tank 1 and liquid 2 are shown in Figure 2.
, gas 3, and differential pressure transmitter B are the same in the case of dry piping.
The piping 48 connecting the expected maximum liquid level of the tank 1 and the expected highest liquid level of the tank 1 is filled with a liquid having the same specific gravity as the liquid 2 in the tank 1, and is of a so-called wet type piping system.

In this case, the high pressure side of the differential pressure transmitter B is connected to the lowest liquid level side of the pipe 4B, and the low pressure side L is connected to the highest liquid level side of the pipe 4B. Therefore, the differential pressure transmitter B is a lid pressure transmitter equipped with a bias mechanism that moves the measurement range in parallel, and the output signal of the rhombic pressure transmitter B is designated as b. In the wet piping system configured in this way, if the output signal of differential pressure transmitter B is adjusted to indicate the maximum differential pressure when the liquid level is at its highest level, when the liquid level reaches zero, the tank Due to the influence of the head of the gas 3 that has flowed inside, the output signal b will show a value larger than zero. Therefore, the relationship between the liquid level and the differential pressure across the lid pressure transmitter B is expressed by the following equation. △P=(y
l-yg) (day by day M^x) ...{41 Also, as in the case of ■ formula, △PM^x=y, HM^x
......'51 The codes used in the above formula are the above {11, '2'
The same is true for Eq.

'4'÷'5} △P (y "yg Considering and substituting into the above formula, △P' = (1-ticket) (H'-1) Small... [6] Here, range suppression corresponding to HM^x is added to differential pressure transmitter B. shall be.

When converted to differential pressure, △P=y, HM^x Considering the dimensionless amount △P' for the same machine and substituting it into the above formula, △P'
= Basic rod, etc. = Takan rod... Vine = In the {6} formula, it is sufficient to consider the positive direction movement 1 of the △P' axis.
Substituting P′-1, △P′-1=(1-Tsu)(H′-
・)△P'=(1-ticket)(H'-1)11. ．．・[7
'If the above equation {7), that is, the relationship between the output signal and the liquid level, is expressed in a diagram, it will be as shown in FIG. 2b.

As in the case of dry piping, the straight line 7 is △, the same as the straight line 5 above.
P: represents IH, and straight line 8 represents the above '71 formula. Although the cases of dry piping and wet piping have been explained above with reference to FIGS. 1 and 2, the liquid level detection device according to the present invention is equipped with the differential temperature transmitter using the dry piping and the differential pressure transmitter using the wet piping. This will be explained below with reference to FIG.

In Figure a, a tank 1 filled with a liquid 2 and a gas 3 is provided with a differential pressure transmitter A connected by a dry pipe 4A and a differential pressure transmitter B connected by a wet pipe 4B. Let the output signal of differential pressure transmitter A be a, and the output signal of differential pressure transmitter B be b. 9 is a computing unit with vertical simple computing ability; differential pressure transmitter A;
After inputting the output signals a and b of B, a preset arithmetic expression is calculated, and the liquid level is detected by reading the output signals.

Now, the relationship between the output signal of the differential pressure transmitter and the liquid level when both such dry type and wet type piping are used together is shown in Fig. 3b in a bran diagram. This figure 3D is, in other words, figure 1b
and FIG. 2b, 5 represents the mathematical formula ΔP'=y, H' as mentioned above, and 6 represents the above-mentioned glue formula ΔP'=
(1-everyone) represents H' and says,
1-ep) (H-1) represents 11. '3-type and '7}
It is clear that the lines representing both equations are parallel on the map.

As shown in the figure, take an arbitrary point 10 on the straight line 6,
Let the vertical axis coordinate of this point 10 be a. Further, a point 11 is placed on the straight line 8 at the same liquid level as the point 10, that is, the same horizontal axis coordinate, and the vertical axis coordinate of this point 11 is set as b. point 10 and point 11
The intersection point between the straight line connecting the lines and the straight line 5 is set as 12, and the vertical axis coordinate and machine axis coordinate of point 12 are the same numerical value, and this is set as c. Now, if the vertical axis coordinate of point 13, which is on the straight line 6 and whose machine axis coordinate is 1, is d, then by geometric analysis, d=1-(b
It is clear that -a)=10a-b. In addition, the machine axes at points 10, 11, and 12 are hooked to the side of the woven fabric.

This is the true liquid level that the target desires.

The true liquid level can be determined by inputting these a and b into a calculator, calculating C=value, and taking the signal.

We have explained the structure of the liquid level detection diamond which performs the following calculation and is equipped with a counter, but by changing the connection direction of differential pressure transmitter B in the device shown in Fig. There is a device that leads to one mathematical formula, so
This device will be explained below.

This device, like the device shown in Fig. 3, has a dry pipe 4A and a green pipe 4B, of which the dry pipe is completely connected to the pipe 4A side in Fig. 1, that is, Fig. 3. Since they are the same, their explanation will be omitted. FIG. 4 shows only the wet piping side of this double-dry/humidifier, corresponding to FIGS. 2 a and b, and the connection direction of the differential pressure transmitter B is different from that in FIG. The high pressure side of the differential pressure transmitter B is connected to the highest liquid level side of the pipe 4B. Therefore, the differential pressure transmitter B that is not equipped with the bias mechanism is used. In the above-mentioned Souma, the relationship between the liquid & and the differential pressure across the lid pressure transmitter B was expressed by the formula '41, but in this device, the days and HM^x are reversed, and it is expressed by the following formula. . All symbols used are as described above. △P=(y, -yg)(HN^x-H) ...[8-'8} In the formula, when there is no upper gas, that is, in a vacuum state, yg=0, and if the pipe outlet dimension is HM^x The maximum differential pressure △PM^x applied to the hair pressure transmitter is obtained by substituting yg = 0 into the m formula, △PM^X = (y, -0)HN^X = yIHMx ......{91].

'8) ÷ ■ △P (ryg force HM^x-H) d 11 △PMAX y, HN^X = (1- etc.) (1-item) Here, dimensionless △P, H' Considering and substituting into the above formula, △F'=(1-ticket)(1-H').・・・．・・・．・
In Fig. 4b, the straight line 7 is the same as in Fig. 2b, △P=
yIH', and the straight line 14 represents the above equation 00.

As is clear from the figure, this time the trouble of straight line 14 is reversed,
When the liquid level reaches the highest level, the output signal becomes zero. This device is the same as the device shown in FIG. 3 except that the connection direction of the differential pressure transmitter B is different.

FIG. 5 is a composite of FIG. 1b and FIG. 4b, and is a diagram showing the relationship between the output signal and the liquid level in the current reinstallation. In the figure, an arbitrary point 15 is placed on the straight line 6, and the vertical coordinate of this point 15 is set as a. Also, point 15 is on straight line 14.
Take the same liquid level, that is, the same point 16 on the machine axis coordinates, and let the vertical axis coordinate of this point 16 be b. The intersection point between the extension of the line connecting points 15 and 16 and the straight line 5 is designated as 17, and the vertical axis coordinate and machine axis coordinate of point 17 are the same, and this is designated as c. The vertical axis coordinate of the point 18 whose machine axis coordinate is 1 on the straight line 6 is now d
Then, it is clear from geometrical analysis that d=a+b. Also, it is a matter of time before the point 15'16'17 is on the machine seat side.

In other words, this C: is the true liquid level sought by poison.

The arithmetic unit inputs these a and b, performs arithmetic operations, and reads the output signal to determine the liquid level. Note that a normal industrial instrument signal has a base signal, and the calculation formula actually used is as follows.

Assuming that the unified signal is the 1 to WDC signal, the above a
, b, c signals are dimensionless signals, so 0<a<
1, 0 b<1, 0<c<1. The unified output signal of differential pressure transmitter A is Va, and the unified output signal of differential pressure transmitter B is Vb.
Then, when △P' = a = 0, Va = 1 (V) When △P' = a = 1, Va = 5 (V) Since there is a linear relationship between the dimensionless signal and the unified output signal, Va = K, a + K2 ...... (11
) Substituting the above conditions into equation (11), va=Kasaju・^
a: Mini...--. -. (・2) Similarly, b=
Uniformity……(13) Therefore, by substituting equations (12) and (13) here, Va
-1. ．． ．． ．． ．． ．． ．． ．． ．． (14)V
a-Vb 14 Also, by substituting <12) (13) into the arithmetic expression, Va-1... ．． 、． ．． ．． (
15) Va+Vb-2 The calculation formula actually used is (14)
and (15).

As explained above, according to the present invention, a differential pressure signal device using dry piping and a differential pressure signal device using wet piping are installed in the tank to be measured, and their output signals are input to an attached calculator for calculation and output. It is possible to detect the liquid level without any error by using an extremely simple method of reading the signal.When detecting the liquid level under high pressure, the zero point and maximum difference of the differential pressure transmitter can be detected under safe atmospheric pressure. Please adjust the pressure.
Thereafter, even if the gas composition and temperature conditions at the top of the tank change, there is no need to readjust the transmitter each time, and the liquid level can always be detected with high accuracy.

In addition, there is no need for readjustment even if the operating conditions fluctuate drastically, and the effect is extremely large in terms of work simplification and safety.

[Brief explanation of the drawing]

Figure 1a is an explanatory diagram of the piping of the liquid level detection device using dry piping, Figure 1b is a diagram of the relationship between the liquid level and the output signal of the plexus pressure transmitter, and Figure 2a is a diagram of the liquid level detection device using wet piping. FIG. 2b is also a relationship diagram between the liquid level and the output signal of the differential pressure transmitter, and FIGS. 3 to 5 are illustrations of the liquid level detection device according to the present invention. For example, Figure 3a is an explanatory diagram of the piping, etc., Figure 3b is a Kensen diagram of the relationship between liquid & and the output signal of the pen pressure transmitter, and Figure 4a is the diagram shown in Figure 3. This is an explanatory diagram of piping, etc. showing only the wet piping side of a liquid level detection device with dry and wet piping, which has a different connection direction of the differential pressure transmitter.
Figure b is a relationship diagram between the liquid level and the output signal of the differential pressure transmitter, and Figure 5 is a diagram of the relationship between the liquid level and the output signal of the differential pressure transmitter, which is a combination of Figures 1b and 4b. The relationship is Sun Kangzu. 1...Tank, 4A...Dry piping, 4
B...Wet piping, A...Differential pressure transmitter using dry piping, B...Differential pressure transmitter using wet piping,
a: Output signal of differential pressure transmitter using dry piping,
b... Output signal of differential pressure transmitter using wet piping,
9...Arithmetic unit, c...Output signal of the arithmetic unit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. The predicted highest liquid level and predicted lowest liquid level of a tank to be measured filled with liquid and its evaporated gas are connected by a pair of pipes each having a differential pressure transmitter in the middle, and Fill the pipe with gas on the highest liquid level side of the differential pressure transmitter and connect this pipe to the low pressure side of the differential pressure transmitter, and attach a bias mechanism for parallel movement of the measurement range to the differential pressure transmitter on the other pipe. Fill the highest liquid level side of this differential pressure transmitter with liquid, connect this piping to the low pressure side of the differential pressure transmitter, and input the output signals from both differential pressure transmitters to the attached calculator. , calculate the formula a/(1+a-b) that includes the input value a from the gas side differential pressure transmitter and the input value b from the liquid side differential pressure transmitter, and read the output signal of this calculator. A liquid level detection device characterized by detecting the liquid level. 2. Connect the expected maximum liquid level and expected minimum liquid level of the tank to be measured filled with liquid and its evaporated gas by a pair of pipes each equipped with a differential pressure transmitter in the middle, and connect the differential pressure transmitter on one pipe. Fill the highest liquid level side of the pipe with gas and connect this pipe to the low pressure side of the differential pressure transmitter, and fill the other pipe with liquid on the highest liquid level side of the differential pressure transmitter and connect this pipe to the differential pressure transmitter. At the same time, the output signals from both differential pressure transmitters are input to the attached calculator, and the input numerical value a from the gas side differential pressure transmitter and the input numerical value from the liquid side differential pressure transmitter are connected to the high pressure side of the device. A liquid level detection device characterized in that the liquid level is detected by calculating the formula a/(a+b) including b and reading the output signal of this arithmetic unit.