JPH0560641A - Zero point correcting method in highly accurate differential pressure measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a zero point correcting method which is effective to correct not only the movement of a zero point resulting from the temperature change, but the movement of the zero point due to the pressure applied in common to both ends of a differential pressure transducer of a highly accurate differential pressure measuring apparatus. CONSTITUTION:When a zero point is to be corrected from the measuring state of a differential pressure transducer 6 while a valve V1 of a high pressure piping 5 and a valve V3 of a low pressure piping 7 are opened, with a valve V2 of a shortcircuiting piping 8 being closed, the valve V1 of the high pressure piping 5 is closed as the valve V3 of the low pressure piping 7 is remained opened, and then the valve V2 of the shortcircuiting piping 8 is opened. As a result, the residual pressure at the high pressure side of the differential pressure transducer 6 is freed to the low pressure side. When no pressure is left between both ends of the differential pressure transducer, the valve V3 of the low pressure piping is closed to correct a zero point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-precision differential pressure measuring device used for measuring the level of a fluid in a tank, measuring the density of fluid, measuring the flow rate and velocity of fluid, and measuring atmospheric pressure. The present invention relates to an improvement in the method of correcting the zero point.

[0002]

2. Description of the Related Art When measuring the liquid level, amount, and density of a liquid contained in a tank, air is blown into the liquid by using a thin tube installed so that its tip is located in the liquid. The air purge method for measurement is widely used. An example of the air purge method will be described with reference to FIG. FIG. 1 illustrates an example of a differential pressure measuring device for measuring the liquid level of a liquid nuclear fuel substance 2 contained in a tank 1, in which two air purifying thin tubes 3, 4 is inserted. The tip of the thin tube 3 is arranged at a predetermined depth in the liquid, and its back pressure is applied to the high pressure side of the differential pressure converter 6 via the high pressure side pipe 5 having the valve V1. On the other hand, the tip of the thin tube 4 is located above the liquid level, and its back pressure is applied to the low pressure side of the differential pressure transformer 6 via the low pressure side pipe 7 having the valve V3. The high-pressure side pipe 5 and the low-pressure side pipe 7 are connected by a short-circuiting pipe 8 on the downstream side of the valves V1 and V3, and the short-circuiting pipe 8 is connected to the valve V2.
Are arranged. When measuring the differential pressure, valves V1 and V3
With the valve V2 open and the valve V2 closed, the difference in back pressure between the thin tubes 3 and 4 can be measured by a differential pressure converter.

Since the tank containing the nuclear fuel material is relatively small, the differential pressure is as small as several hundred mm to several thousand mm of water column. Also, the liquid volume of nuclear fuel material must be measured accurately,
Therefore, when measuring the base differential pressure, a high accuracy of about ± 0.2 mm water column is required. However, the differential pressure transducer used in the differential pressure measuring device is 1 when the ambient temperature changes.
The zero point moves about ± 0.2 mm of water column per ° C, and the change is added to the measured value, resulting in an error. Therefore, it is necessary to correct the zero point of the differential pressure converter.

The zero point correction of the differential pressure converter in the differential pressure measuring device of FIG. 1 has been conventionally performed in the following steps.
The relationship between the pressure change in the differential pressure changer and the open / closed state of the valve is shown in FIG.

1) In the differential pressure measuring state, the valve V1 is opened and the valve V2 is opened.
In the closed state and the valve V3 opened, the high pressure side pressure and the low pressure side pressure are applied to the high pressure side and the low pressure side of the differential pressure converter 6, respectively, and the differential pressure is measured. When measuring in this state, the zero point moves due to the temperature change, and the change amount is added to the measured value, resulting in an error.

2) Then, zero correction is started. That is, when the three valves are simultaneously opened and closed to close the valve V1, open the valve V2, and close the valve V3, both ends of the differential pressure converter 6 are short-circuited, and the zero-point output VD that has moved due to temperature change is output.
Is obtained, and this is input to the digital memory 9.

3) When a zero point correction command is given to the digital memory 9, the sign of VD is inverted and becomes -VD,
By adding this value to VD by the adder 10, the correction output 0 (= VD-VD) is obtained.

4) After correcting the zero point in this way,
Return the three valves to the open / closed state of 1) and return to the differential pressure measurement state.

[0009]

According to the above-mentioned conventional zero point correction method, the zero point movement of the differential pressure transducer due to temperature change can be effectively corrected. However, the zero point of the differential pressure converter is not moved only by the temperature change, but is also moved by the pressure commonly applied to both the high pressure side and the low pressure side of the differential pressure converter. Full scale is 10,
2,000 mm using a crystal vibration type differential pressure transducer of 000 mm water column
Taking the case of measuring the differential pressure of a 00 mm water column as an example, the zero point moves about ± 0.2 mm water column per 1 ° C. temperature change of the differential pressure transducer, and the pressure applied to both ends of the differential pressure transducer in common is 1.
A zero point moves about 0.1 to 2.5 mm water column per 000 mm water column. In the above-mentioned conventional zero point correction method in which both ends of the differential pressure converter are short-circuited to make the differential pressure zero, in the state of 3),
Between both ends of the differential pressure converter, the high pressure side (for example, 2,000 mm
An intermediate pressure (for example, 1,000 mm water column) between the water column) and the low-pressure side (for example, 0 mm water column) remains in common. Therefore, the zero point moves due to the residual pressure that is commonly applied to both ends of the differential pressure transducer, and the conventional zero point correction method that only corrects the zero point movement due to temperature change cannot achieve highly accurate and accurate zero point correction. It was

Therefore, according to the present invention, when performing the zero point correction of the differential pressure converter in the high precision differential pressure measuring device as shown in FIG. 1, not only the zero point movement caused by the temperature change but also the both ends of the differential pressure converter are performed. The object of the present invention is to provide an improved zero-point correction method capable of effectively correcting the zero-point movement due to the commonly applied pressure.

[0011]

That is, the present invention is directed to a differential pressure converter, a high pressure side pipe having a valve V1 connected to the high pressure side of the differential pressure converter, and a low pressure side of the differential pressure converter. The zero point of the high-accuracy differential pressure measuring device having the low-pressure side pipe having the valve V3 and the short-circuiting pipe having the valve V2 connecting the high-pressure side pipe and the low-pressure side pipe downstream of the valves V1 and V3 is corrected. When the zero point is corrected from the differential pressure measurement state in which the valve V1 of the high pressure side pipe and the valve V3 of the low pressure side pipe are opened and the valve V2 of the short circuit pipe is closed, the low pressure side pipe After closing the valve V1 of the high-pressure side pipe while keeping the valve V3 of the above, the valve V2 of the short-circuit pipe is opened to open the pressure remaining on the high-pressure side of the differential pressure converter to the low-pressure side, Next, close the valve V3 of the low-pressure side pipe to perform zero point correction of the differential pressure converter. It is an feature.

[0012]

Operation: At the stage of starting the zero point correction, the valve V of the low pressure side pipe
By closing the valve V1 of the high pressure side pipe while keeping 3 open, and then opening the valve V2 of the short circuit pipe, the pressure remaining on the high pressure side of the differential pressure converter is released to the low pressure side. No pressure remains between the ends of the pressure transducer. In this way, by giving a time difference to the operation of the valve, not only the zero point movement caused by the temperature change but also the zero point movement caused by the pressure applied to both ends of the differential pressure converter can be effectively corrected.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Each step of the method of zero correction according to the present invention is
With reference to the differential pressure measuring device shown in FIG. 1, a description will be made step by step so that it can be compared with the above-described conventional zero-point correction method. 2 illustrates the relationship between the pressure change of the differential pressure changer and the open / closed state of the valve in the method of the present invention, and corresponds to FIG. 3 of the conventional method.

1) In the differential pressure measuring state, the valve V1 is opened and the valve V2 is opened.
In the closed state and the valve V3 opened, the high pressure side pressure and the low pressure side pressure are applied to the high pressure side and the low pressure side of the differential pressure converter 6, respectively, and the differential pressure is measured. When measuring in this state, the zero point moves due to the temperature change, and the change amount is added to the measured value, resulting in an error.

2) Then, the zero point correction is started. That is, the valve V1 is first closed and then the valve V2 is opened.
At this stage, the valve V3 remains open, the pressure remaining on the high pressure side of the differential pressure converter 6 is released on the low pressure side, and no pressure remains between both ends of the differential pressure converter. After the pressure remaining on the high pressure side is sufficiently opened to the low pressure side, the valve V3 is closed. At this point, both ends of the differential pressure converter 6 are short-circuited,
A zero-point output VD moved by the temperature change and the pressure commonly applied to both ends of the differential pressure converter is obtained, and this is input to the digital memory 9.

3) When a zero point correction command is given to the digital memory 9, the sign of VD is inverted to become -VD,
By adding this value to VD by the adder 10, the correction output 0 (= VD-VD) is obtained.

4) After the zero point is corrected in this way,
The three valves are returned to the open / closed state of 1) in the reverse order of the above open / closed order to return to the differential pressure measurement state.

In the case of the above-mentioned measurement example in which the differential pressure of the water column of 2,000 mm is measured by using the crystal vibration type differential pressure transducer of the full scale of 10,000 mm water column, the pressure applied to both ends of the differential pressure transducer is 1, 0.1-2.5 per 000mm water column
Although a zero point movement of about mm mm of water column occurs, the zero point correction method according to the present invention can also correct the zero point movement due to the pressure commonly applied to both ends of the differential pressure transducer.

When operating each valve with a time lag, the operation of each valve can be controlled simply and reliably with a predetermined time lag by using a timer.

[0020]

As can be seen from the above description, according to the present invention, when the zero point of the differential pressure transducer is corrected, the operation of the valve has a time difference, so that not only the zero point shift caused by the temperature change but It is also possible to effectively correct the zero point movement due to the pressure applied to both ends of the differential pressure converter. As a result, it becomes possible to measure the differential pressure more accurately as compared with the conventional zero-point correction method that only corrects the zero-point movement caused by the temperature change.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a differential pressure measuring device by an air purge method.

FIG. 2 is an explanatory diagram showing the relationship between the pressure change of the differential pressure changer and the open / closed state of the valve in the zero correction method of the present invention.

FIG. 3 is an explanatory view showing a relationship between a pressure change of a differential pressure changer and a valve opening / closing state in a conventional zero-point correction method. 5 ... High-pressure side piping, 6 ... Differential pressure converter, 7 ... Low-pressure side piping, 8 ... Short-circuiting piping, V1, V2, V3 ... Valves.

Claims (2)

[Claims] 1. A high pressure side pipe having a differential pressure converter, a valve V1 connected to the high pressure side of the differential pressure converter, and a low pressure side pipe having a valve V3 connected to the low pressure side of the differential pressure converter. , Valve V1
And a method for correcting the zero point of a differential pressure measuring device, which comprises a short-circuit pipe having a valve V2 connecting the high-pressure side pipe and the low-pressure side pipe downstream of the valve V3. When the zero point is corrected from the differential pressure measurement state in which the valve V3 of the side pipe is opened and the valve V2 of the short circuit pipe is closed, the valve V3 of the high pressure side pipe is opened with the valve V3 of the low pressure side pipe being opened. After closing the valve, the pressure remaining on the high pressure side of the differential pressure converter is opened to the low pressure side by opening the valve V2 of the short circuit pipe, and then the valve V3 of the low pressure side pipe is closed to perform the zero point correction. A zero-point correction method in a high-accuracy differential pressure measuring device characterized by the above. 2. The zero-point correction method according to claim 1, wherein the opening / closing operation of each of the valves V1, V2 and V3 is controlled by a timer.