JP2003294569A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To display a filling pressure in a leak test and a leak pressure thereafter in an easily-understandable display mode to a user. <P>SOLUTION: When this pressure sensor 1 detects the filling pressure and outputs an ON signal (point A in figure 1), a PLC receiving the ON signal outputs a shift signal toward the pressure sensor 1. When receiving the shift signal, the pressure sensor 1 performs setting of the shift quantity capable of making the signal zero by using a detection pressure (for example, 100 kPa) at that time as a reference state by a shift quantity setting part 6, and simultaneously a display mode of a display part 8 is switched to a shift pressure display. Hereby, in leak detection after the point A, if a threshold set for detecting whether the shift pressure is in the range of an allowable leak quantity or not is, for example, '-20 kPa', leak determination is performed by comparison between the threshold and the shift pressure, and the shift pressure which is a variation from the reference state is displayed on the display part 8. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor suitable for leak test.

[0002]

2. Description of the Related Art For example, to inspect defects of PET bottles that are widely used as containers for mineral water,
A leak test is carried out by injecting pressurized air into the bottle to check whether or not there is a leak. A pressure sensor is used for this leak test.

FIG. 1 shows a pressure change in a leak test.
Referring to the figure, each step of the leak test will be described in time series. First, when the valve of the pressurized air source is opened, the pressure in the bottle rises, and the pressure in the bottle reaches a predetermined pressure value (predetermined value). Filling pressure) (point A). Then, the valve is closed and left for a predetermined time (To). This leaving period (To) when the valve is closed is a substantial leak test period, and the pressure in the bottle is higher than the threshold value due to leakage (leak) by the point B at which the leak test period (To) ends. If the pressure drops to a low pressure value, the bottle is treated as "NG" (defective product), because there is a hole in the bottle. Conversely, the leak test period (T
If the pressure drop in o) is slight and the pressure in the bottle is above the threshold, then the bottle is considered "no defect".

In this leak test, two independent outputs of the pressure sensor (independent two-output mode) are generally used.
Is used to detect the filling pressure with one output and to detect the leak of the bottle with the other output.

Further, the pressure sensor is provided with hysteresis as in the case of other photoelectric sensors and the like in order to stabilize the output (FIG. 2). In the figure, the solid line is the threshold value (setting value), the broken line is the hysteresis line, and the amount of this hysteresis can be arbitrarily set by the user.
Conventionally, the hysteresis line is generally provided below the set value as shown in FIGS. 2 and 3, and an ON signal is output when the detected pressure exceeds the set value, and an OFF signal is output when the detected pressure falls below the hysteresis line. (Fig. 3).

Further, this type of pressure sensor has a function of shifting a detected value by a predetermined shift amount, holds the shifted value as an internal value, or displays the shifted value and displays the shifted value as the shifted value. , It is possible to compare the magnitude with a threshold value set arbitrarily.

That is, this type of pressure sensor has the following two
One operation mode, the first operation mode that displays the value before the shift even if the reference value is shifted by the internal processing, and the second operation mode that always displays the shifted value after the shift once. And two operation modes, and one of these operation modes is selected by the user.

[0008]

In the conventional leak test using the pressure sensor, the hysteresis is provided below the threshold value with respect to the setting of the threshold value (leak detection pressure) for detecting the leak of the bottle. Therefore, in the detection of “NG (defective product)”, the output is not output when the value is below the threshold value, and the output is output only when the value is below the hysteresis line. The leak detection output was performed under different pressure conditions.

Further, since the display of the pressure sensor is fixed to the display of the detected pressure (generally gauge pressure) or the shift pressure, that display is the gauge pressure (absolute pressure) or the shift pressure which is the relative pressure. Had to monitor the pressure on either.

By the way, in the leak test, in order to know whether or not the bottle has reached a sufficient filling pressure, it is desirable to display the gauge pressure (absolute pressure), and after filling the bottle with pressurized air. It is desirable to be able to confirm how much the pressure inside the bottle has dropped due to a leak when the valve is closed and left for a predetermined time (To) (points AB).

In the conventional pressure detector, even if the operation mode of the pressure detector is changed during the leak test in order to meet such a request, the operation mode change requires a complicated operation. Also, in order to display with the shifted value, it is impossible to actually meet the above-mentioned request because the setting work of shifting the reference value to, for example, zero is required in the mode changing operation. It was

Therefore, an object of the present invention is to provide a pressure sensor capable of displaying the filling pressure in a leak test and the subsequent leak pressure in a display mode that is easy for the user to understand.

Another object of the present invention is to provide a pressure sensor that allows a user to immediately grasp the leak amount in a leak test.

[0014]

According to the present invention, such a technical problem is that in a pressure sensor equipped with a display means capable of displaying the detected pressure, the pressure at which the gas is filled in the bottle is measured by a gauge pressure. Filling pressure detection and display means for displaying on the display unit in (absolute pressure) and detecting whether or not the filling pressure has reached a predetermined filling pressure in comparison with a predetermined filling threshold value, and a gas filled in the bottle. In order to detect the leak, the detected pressure is displayed as a pressure change amount from the predetermined filling pressure, and whether the pressure change amount is within an allowable leak amount range by comparing the pressure change amount with a predetermined leak threshold value. Leak detection and display means for detecting whether or not, and after the filling pressure detection and display means completes the detection of the filling pressure, the leak detection and display means operates in place of the filling pressure detection and display means. It is achieved by providing a pressure sensor according to claim Rukoto.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the present invention, a hysteresis related to the leak threshold is preferably provided above the leak threshold. With this, when the detected pressure falls below the leak threshold value, a signal can be output from the pressure sensor in conjunction with this.

In order to stably detect the filling pressure, it is preferable to use a first threshold value which defines the upper limit value and a second threshold value which defines the lower limit value, and in this case, the lower limit value. Hysteresis associated with a second threshold that defines is preferably above the second threshold. According to this, when the detected pressure falls below the second threshold value, a signal can be output from the pressure sensor in conjunction with this.

The above and other objects of the present invention, and the effects thereof will be apparent from the following detailed description of the preferred embodiments of the present invention.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a preferred embodiment of the present invention, a pressure sensor having a display means will be described below as an example.

FIG. 4 is a block diagram of the pressure sensor of the embodiment. In the figure, the pressure sensor 1 has a pressure detection unit 2 that detects the pressure (gauge pressure) in the pressure conduit. The pressure detected by the pressure detection unit 2 is compared with a threshold value by the output determination unit 3, and the output unit 4 turns ON or O depending on the magnitude.
The FF signal is output. In the setting unit 5 for setting the threshold value, the user can set two threshold values of arbitrary values by, for example, key input, one is used for determining the filling pressure, and the other is used. Are used to detect leaks. Here, the first threshold value for detecting the filling pressure can be set by a gauge pressure (absolute pressure), and the second threshold value for detecting the leak is relative to a reference state described later. It can be set by pressure.

The pressure sensor 1 also has a shift amount setting section 6 including a memory and a shift input section 7 for receiving a shift signal from an external device such as a programmable logic controller (PLC). When the shift signal from the PLC is input to the shift input unit 7, the shift amount setting unit 6 sets a shift amount capable of converting the detected pressure (gauge pressure) to zero with reference to the state at this time. The set shift amount is stored in a memory (not shown).

The display value converter 8 generates a shift pressure by converting the gauge pressure detected by the pressure detector 2 by a set shift amount. The display unit 9 of the pressure sensor 1 can display the detected gauge pressure, and can also display the shift pressure, which is the amount of change from the reference state.

FIG. 5 is a flow chart showing the procedure of a leak test using the pressure sensor 1. First, in step S10, an object to be measured such as a PET bottle is set, and then in step S11 the valve of the pressurized air source is opened to fill the bottle with air. Then, step S12
Then, it is determined whether or not the pressure in the PET bottle has reached a predetermined filling pressure. This determination is performed by comparing the pressure (gauge pressure) detected by the pressure sensor 1 with a preset first threshold value. Referring to FIG. 1, if the first threshold value is set to 100 kPa (gauge pressure) as an example, the pressure (gauge pressure) detected by the pressure sensor 1 is 1
When it becomes 00 kPa and YES is determined in step S12, it is determined that the detection of the filling pressure is completed, and the process proceeds to the next step S13 to start the substantial leak test. This leak test is started by closing the valve of the pressurized air source by a signal from the PLC (point A in FIG. 1).

When the leak test is started, the detected pressure is compared with the threshold value for a predetermined period (To) (steps S14 and S15). That is, the pressure fluctuation during the leak test period (To) is the substantial detection area of the pressure sensor 1. Referring to FIG. 1, as an example, if the second threshold value set for detecting the leak is 80 kPa,
In step S14, the pressure detected by the pressure sensor 1 is 8
It is determined whether it is higher than 0 kPa. When the leak test period (To) has elapsed, if the detected pressure is higher than 80 kPa, the result is YES, and the process proceeds to step S16, and it is determined that there is no problem with the PET bottle to be inspected, and step S18 is performed.
Open the pressure reducing valve to release the air in the PET bottle to the outside. As shown by the phantom line in FIG. 1, the pressure in the bottle significantly decreased during the leak test period To,
When it falls below Pa (threshold value), the above step S1
If NO is determined in step 4, the process proceeds to step S17, and it is determined that the PET bottle to be inspected is a defective product in step S18.
Proceed to and finish the leak test.

In the above leak test, the valve is controlled to open and close by a PLC, but the pressure sensor 1 detects a predetermined filling pressure (100 kPa) and the pressure sensor 1 outputs ON to detect the filling pressure. When is completed,
The PLC receives this ON output and outputs a shift signal toward the pressure sensor 1.

That is, when the pressure sensor 1 detects the filling pressure and outputs an ON signal (point A in FIG. 1), this O
The PLC receiving the N signal outputs a shift signal to the pressure sensor 1. When the pressure sensor 1 receives this shift signal, the pressure detected at that time, that is, 100 kP in the example of FIG.
The shift amount setting unit 6 sets a shift amount that can be zero with a as a reference state, and the set shift amount is stored in a memory (not shown). At the same time, the display mode of the display unit 8 is switched to the shift pressure display.

As a result, in the leak detection after the point A, if the threshold value set for detecting whether the leak amount is within the allowable leak amount range is, for example, "-20 kPa", this threshold value is set. And the shift pressure are compared with each other to make a leak determination, and the display unit 8 displays the shift pressure, which is the amount of change from the reference state. That is, during the leak test period (To), when the pressure in the bottle decreases, the amount of decrease from the reference state (leaked pressure) is displayed. In the example of FIG. 1, if the bottle internal pressure (gauge pressure) is reduced from 100 kPa to 90 kPa, a shift pressure of "-10" is displayed (steps S13 to S15 in FIG. 5). By seeing this shift pressure, the degree of leakage of the bottle can be directly confirmed.

At point B, the pressure sensor 1 is synchronized with the opening of the pressure reducing valve by the signal from the PLC.
From "Shift pressure display" to "Gauge pressure (absolute pressure) display"
A signal for switching the display mode is input to. Upon receiving the display mode change signal, the pressure sensor 1 displays the pressure detected by the pressure sensor 1 in gauge pressure. As a result, after the point B, the gauge pressure of the detected pressure is displayed on the display unit 8, and the user sees the numerical value displayed on the display unit 8 to confirm that the pressure inside the bottle has returned to atmospheric pressure. Can be immediately confirmed (between steps S15 and S18 in FIG. 5).

Similarly, during steps S10 to S12, which are the steps of the leak test preparation, the pressure sensor 1 operates substantially in the "gauge pressure (absolute pressure)" operation mode. Thus, the user can immediately confirm that the pressure inside the PET bottle is rising by looking at the numerical value (gauge pressure) displayed on the display unit 8.

Next, in leak detection, the operation mode is substantially "shift pressure". Thus, the user can check how much the pressure in the PET bottle is lower than the reference pressure, that is, the degree of leak, by looking at the numerical value (leak pressure that is a relative pressure) displayed on the display unit 8. can do.

FIG. 6 is a diagram for explaining the threshold value used for the leak determination and the hysteresis related thereto. As can be seen from the figure, the threshold value for detecting the presence / absence of leak by the leak pressure (shift pressure), which means the pressure change amount from the reference state, is related to the hysteresis It is provided above. As a result, when the detected pressure falls below the leak threshold, the pressure sensor 1 outputs an ON signal. Therefore, the pressure sensor 1 operates at the same pressure as the pressure set by the user and outputs a leak detection signal.

Regarding the detection of the filling pressure, preferably,
To detect this filling pressure, it is preferable to use two thresholds that define the upper limit value and the lower limit value (FIG. 7). As a result, the filling pressure can be detected stably. Also,
More preferably, as shown in FIG. 7, it is preferable to provide hysteresis in a region sandwiched between the upper limit value and the lower limit value. That is, the first threshold value defining the upper limit has the first value below the first threshold value.
It is preferable that a hysteresis is provided and a second hysteresis is provided above the second threshold value that defines the lower limit value. According to this, the pressure sensor 1 outputs an ON / OFF signal at the detected pressure corresponding to the set first and second threshold pressure values. In this case, the PLC may output a shift signal to the pressure sensor 1 when the detected pressure crosses the second threshold value (lower limit value) from the bottom to the top, or the pressure sensor 1 may supply the filling pressure. The ON signal is output for the first time upon detection and P
The shift pressure operation mode may be switched after a predetermined time has elapsed since the shift signal was input from the LC.

The preferred embodiment of the present invention has been described above. However, the present invention is not limited to this, and for example, at the time of a leak test, the display color of the display unit 9 is changed to change the gauge pressure (absolute pressure). The display color may be switched between when () is displayed and when the shift pressure is displayed. Also, when the leak from the bottle is large and the pressure sensor 1 determines that the leak in the bottle is large and / or when the filling pressure is insufficient, the display color of the display unit 9 is switched to, for example, red. It may be possible to call the user's attention.

Further, a leak test mode for performing the above-described series of operations is prepared, and this leak test mode is added to one of the operation modes selectable by the user, and the user can perform a simple key operation (for example, pressing an operation button). It is preferable that the operation mode of the pressure sensor 1 is switched to the leak test mode and the pressure sensor 1 executes the above-described series of operations only by performing the above) for the convenience of the user.

[Brief description of drawings]

FIG. 1 is a diagram showing a pressure change in a leak test of a PET bottle, for example.

FIG. 2 is a diagram for explaining a relationship between a threshold value and hysteresis related thereto.

FIG. 3 is a diagram for explaining ON and OFF signals output by a pressure sensor in relation to a threshold value and its hysteresis.

FIG. 4 is a block diagram of a pressure sensor according to an embodiment.

FIG. 5 is a flowchart for explaining a bottle leak test operation.

FIG. 6 is a diagram for explaining a relationship between a threshold value for detecting a leak and hysteresis related thereto in the embodiment.

FIG. 7 is a diagram for explaining an upper limit value and a lower limit value set for detecting the filling pressure in the embodiment, and hysteresis associated with each of the upper limit value and the lower limit value.

[Explanation of symbols]

1 Pressure sensor 2 Pressure detection part of pressure sensor 3 Pressure sensor output judgment section 6 Pressure sensor shift amount setting section 8 Display value converter of pressure sensor 9 Pressure sensor display

Claims (4)

[Claims] 1. A pressure sensor equipped with a display means capable of displaying the detected pressure, wherein the pressure with which the gas is filled in the bottle is displayed as a gauge pressure (absolute pressure) on the display unit and a predetermined filling is performed. Filling pressure detection and display means for detecting whether or not the bottle has been filled up to a predetermined filling pressure in comparison with a threshold value, and a detection pressure for detecting a leak of gas filled in the bottle, from the predetermined filling pressure. And a leak detecting and displaying means for displaying whether or not the pressure change amount is within a range of an allowable leak amount by comparing the pressure change amount with a predetermined leak threshold value. A pressure sensor, wherein the leak detection and display means operates in place of the filling pressure detection and display means after the detection of the filling pressure by the pressure detection and display means is completed. 2. The pressure sensor according to claim 1, wherein a hysteresis related to the leak threshold value is provided above the leak threshold value. 3. The filling pressure is detected by using a first threshold value defining an upper limit value and a second threshold value defining a lower limit value. The pressure sensor according to 2. 4. The pressure sensor according to claim 3, wherein a hysteresis related to the second threshold value is provided above the second threshold value.