Liquid Level Sensor

Abstract

This liquid level sensor 1 includes: a sleeve 2 that is provided in a vertical direction; a float 3 that moves along the sleeve as a liquid level fluctuates; a resistance row 4; a plurality of grounding means 5 that are provided inside the sleeve; and a liquid level signal output means 6 that extracts, as a liquid level signal that is a signal corresponding to the liquid level, an electric signal detected between a positive electrode side end part 4a and a connection part grounded by the grounding means 5, and further includes a warning signal output means 7 that outputs a warning signal when the float 3 is located within a predetermined distance from a warning position that is a predetermined position within a movable range of the float 3. Accordingly, a compact and highly reliable liquid level sensor is achieved.

Description

[Technical Field]

[0001] The present invention relates to a liquid level sensor. [Background technology]

[0002] 2. Description of the Related Art There is known a type of liquid level sensor that converts information about the liquid level into an electrical signal.

[0003] For example, the liquid level sensor 1' according to the prior art shown in FIG. 8 has a sleeve 2 provided in the vertical direction, a float 3 that moves along the sleeve 2 in accordance with fluctuations in the liquid level, and a float 3 that moves when the float 3 approaches the sleeve 2. 3 The liquid level sensor 1' is composed of a reed switch (not shown) that is activated by the magnetic field generated by a magnet built into the tank. By providing multiple liquid level sensors 1' in the tank, it is possible to know whether the liquid level is at the upper limit, intermediate position, or lower limit position, for example.

[0004] Furthermore, for example, Patent Document 1 describes an invention for a liquid level sensor that is composed of a resistor string in which multiple resistors are connected in series and multiple reed switches that supply current to the resistor connections. In this liquid level sensor, when the reed switch closes in response to the position of a magnetic source linked to the float, current is supplied to a part of the resistor string via the connections. The resistance value of the part through which current flows changes depending on the position at which the reed switch is closed. By detecting this resistance value, the remaining amount of liquid corresponding to the resistance value can be detected. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Utility Model Application Publication No. 5-64737 Summary of the Invention [Problem to be solved by the invention]

[0006] The liquid level sensor 1' shown in Figure 8 can pinpoint whether the liquid level is at a specific position. It also has a simple structure and is highly reliable. However, it is necessary to install a number of liquid level sensors corresponding to the number of liquid levels that can be detected. Therefore, in order to increase the number of liquid levels to be detected in one device, it is necessary to install more liquid level sensors, which poses problems such as increased installation costs and a reduced volume of liquid that can be stored in the tank.

[0007] On the other hand, the liquid level sensor described in Patent Document 1 can detect the liquid level between the reed switch at the highest position and the reed switch at the lowest position as a pseudo-analog signal with an accuracy determined by the spacing between the reed switches. However, since the structure is more complex than the liquid level sensor shown in Figure 8, there is a risk of outputting an erroneous signal due to a malfunction.

[0008] The present invention has been made in view of the above-mentioned problems, and has as its object to realize a compact and highly reliable liquid level sensor. [Means for solving the problem]

[0009] The liquid level sensor according to the present invention comprises a vertically disposed sleeve, a float configured to move along the sleeve in response to fluctuations in the liquid level, a resistor string including a plurality of resistors connected in series and having both ends constantly connected to a DC power source, a plurality of grounding means provided inside the sleeve corresponding to the junctions of adjacent resistors in the resistor string, and a liquid level signal output means configured to extract, as a liquid level signal, an electrical signal corresponding to the liquid level detected between the positive end of the resistor string, which is the end connected to the positive electrode of the DC power source, and the junction grounded by the grounding means. The plurality of grounding means are configured to ground the corresponding junction when the float is located within a predetermined distance, and not ground the corresponding junction when the float is not located within the predetermined distance. In addition to the above, the liquid level sensor according to the present invention further comprises an alarm signal output means configured to output an alarm signal when the float is located within a predetermined distance from an alarm position, which is a predetermined position within the float's movable range, and not output an alarm signal when the float is not located within the predetermined distance from the alarm position.

[0010] With the above configuration, in the liquid level sensor of the present invention, when the float is positioned within a range where multiple grounding means are provided, the liquid level can be detected by the liquid level signal obtained from the resistor string, and when the float is positioned within a predetermined distance from the warning position, an alarm signal can be output by an alarm signal output means separate from the resistor string.

[0011] In a preferred embodiment of the present invention, the liquid level sensor has a positive grounding means configured to ground the positive end when the float is located within a predetermined distance from or outside the grounding means corresponding to the connection closest to the positive end of the plurality of grounding means, and / or a negative grounding means configured to ground the connection closest to the negative end when the float is located within a predetermined distance from or outside the grounding means corresponding to the connection closest to the negative end of the plurality of grounding means, which is the end of the resistor string opposite the positive end of the resistor string.With a configuration including a positive grounding means, for example, even if an abnormality occurs in the grounding means corresponding to the connection closest to the positive end and the corresponding connection cannot be grounded, the positive end is grounded by the positive grounding means when the float is located within the predetermined distance from or outside the grounding means, so that a liquid level signal corresponding to the position of the grounding means corresponding to the connection closest to the positive end can be extracted. Furthermore, with a configuration having a negative electrode grounding means, even if, for example, an abnormality occurs in the grounding means corresponding to the connection closest to the negative electrode end and the corresponding connection cannot be grounded, when the float is located within a predetermined distance from the grounding means or when the float is located outside the grounding means, the connection closest to the negative electrode end is grounded by the negative electrode grounding means, so that a liquid level signal corresponding to the position of the grounding means corresponding to the connection closest to the negative electrode end can be extracted. [Effects of the Invention]

[0012] According to the present invention, a liquid level sensor consisting of a single sleeve can detect the liquid level with high accuracy based on the liquid level signal, and can also generate a highly reliable warning signal. As a result, when the liquid level sensor according to the present invention is applied to a tank, for example, the liquid level can be accurately and reliably managed without compromising the tank's liquid storage capacity. [Brief explanation of the drawings]

[0013] [Figure 1] 10 is a schematic graph showing an example of the range of liquid levels at which each of the sensors constituting the plurality of grounding means operates and the magnitude of the liquid level signal output when each sensor operates. [Figure 2] 10 is a schematic graph showing another example of the range of liquid levels at which each of the sensors constituting the plurality of grounding means operates and the magnitude of the liquid level signal output when each sensor operates. [Figure 3] 1 is a perspective view showing an example of a resistor string and a grounding means according to the present invention; [Figure 4] 1 is a partial cross-sectional view showing an example of a liquid level sensor according to the present invention. [Figure 5] 1 is a circuit diagram showing an example of a liquid level sensor according to the present invention; [Figure 6] FIG. 10 is a circuit diagram showing another example of a liquid level sensor according to the present invention. [Figure 7] 5A to 5C are schematic diagrams showing an example of the operation of the liquid level sensor according to the present invention. [Figure 8] FIG. 1 is a partial cross-sectional view showing an example of a liquid level sensor according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description and drawings are merely examples of the preferred embodiments of the present invention, and the preferred embodiments of the present invention are not limited to the preferred embodiments shown in the following description and drawings.

[0015] The liquid level sensor 1 according to the present invention has a sleeve 2 that is provided in the vertical direction. The sleeve 2 is fixed so that its longitudinal direction coincides with the direction perpendicular to the liquid surface. At least a portion of the exterior of the sleeve 2 is in contact with the liquid, and a grounding means 5, which will be described later, is provided inside the sleeve 2. In other words, the sleeve 2 functions as a protective tube that isolates the grounding means 5, which is an electronic component that constitutes the liquid level sensor 1, from the liquid. The resistor array 4, which will be described later, may be provided inside the sleeve 2. Alternatively, the resistor array 4 may be provided outside the sleeve 2, and each of the plurality of grounding means 5 provided inside the sleeve 2 and each of the plurality of connection portions 4c of the resistor array 4 provided outside the sleeve 2 may be connected by, for example, lead wires or a flexible printed circuit board.

[0016] The sleeve 2 also functions as a guide for the float 3, which moves in accordance with fluctuations in the liquid level. In a preferred embodiment of the present invention, the float 3 has a hole with a cross-sectional shape corresponding to that of the sleeve 2, and the sleeve 2 moves up and down with the sleeve 2 inserted into the hole. The cross-sectional shape of the sleeve 2 may be circular, elliptical, or polygonal. For stable movement of the float 3, it is preferable that the cross-sectional shape of the sleeve 2 be consistent along the length of the sleeve 2.

[0017] The material constituting the sleeve 2 is preferably one that is resistant to corrosion by the liquid, such as stainless steel. As will be described later, if the float 3 is equipped with a magnet and the grounding means 5 is activated by detecting the magnetic field generated by the magnet, it is preferable to select a material constituting the sleeve 2 that is difficult to magnetize so as not to hinder the magnetic field from reaching the grounding means 5 and the movement of the sleeve 2 in the vertical direction.

[0018] The liquid level sensor 1 according to the present invention has a float 3 that moves along the sleeve 2 in response to fluctuations in the liquid level. The float 3 is configured to float on the liquid surface by buoyancy. Typically, the float 3 has a hollow structure. In the present invention, the liquid level is indirectly detected by detecting the position of the float 3. If liquid enters the interior of the float 3 (for example, the hollow portion), the positional relationship between the float 3 and the liquid surface changes, causing an error in the detection of the liquid level, so the float 3 must be configured so that liquid does not enter or exit. At least the portion of the float 3 that faces the sleeve 2 is preferably made of a material that is difficult to magnetize.

[0019] The liquid level sensor 1 according to the present invention has a resistor string 4, which is provided inside or outside the sleeve 2 and includes multiple resistors connected in series. Both ends (positive end 4a and negative end 4b) of the resistor string 4 are constantly connected to a DC power source. The positive end 4a is the end of the resistor string 4 that is connected to the positive electrode of the DC power source, and the negative end 4b is the end of the resistor string 4 opposite the positive end 4a. The resistor string 4, combined with a grounding means 5 (described later), functions to convert the position information of the float 3, i.e., the liquid level, into an electrical liquid level signal. The multiple grounding means 5 provided inside the sleeve 2 corresponding to the connection portions 4c of adjacent resistors in the resistor string 4 are preferably arranged in parallel (i.e., between the connection portions 4c and ground) in the same order as or in the reverse order of the multiple resistors along the longitudinal direction, i.e., the vertical direction, of the sleeve 2. By constantly connecting a DC power source to the resistor string 4, the liquid level signal can be constantly monitored, thereby increasing the reliability of the liquid level signal.

[0020] The resistors constituting the resistor string 4 preferably have high resistance accuracy, and if the resistor string 4 is provided inside the sleeve 2, it is preferable that they have a small installation area. For example, chip resistors can be used as such resistors. The number of resistors constituting the resistor string 4 can be appropriately selected depending on the length of the range of liquid level to be detected, the size of the resistors, the liquid level detection accuracy, and other factors. In the present invention, the wiring, lead wires, terminals, etc. that electrically connect adjacent resistors in the resistor string 4, and conductors at the same potential as these, are referred to as connection parts 4c.

[0021] The liquid level sensor 1 according to the present invention has a plurality of grounding means 5 provided inside the sleeve 2 corresponding to the connection portions 4c of adjacent resistors in the resistor string 4. The plurality of grounding means 5 are configured to ground the corresponding connection portions 4c when the float 3 is located within a predetermined distance, and not to ground the corresponding connection portions 4c when the float 3 is not located within the predetermined distance. In the present invention, the number of grounding means 5 may be equal to or less than the number of resistors included in the resistor string 4. When the number of grounding means 5 is equal to the number of resistors, the liquid level detection accuracy is highest. When the number of grounding means 5 is thinned out more than that, the liquid level detection accuracy decreases.

[0022] In the present invention, "grounding the connection part" means electrically connecting the connection part 4c to the earth of the electric circuit constituting the liquid level sensor 1. When the connection part 4c is connected to the earth, the negative electrode side end 4b of the resistor string 4, which was originally connected to the earth, and the grounded connection part 4c have the same potential, so that current does not flow through the resistor between them, and current flows only through the resistor between the positive electrode side end 4a and the grounded connection part 4c. This electric signal is output to the outside as a liquid level signal, which is a signal corresponding to the liquid level, using the liquid level signal output means 6, which will be described later.

[0023] The plurality of grounding means 5 of the liquid level sensor 1 according to the present invention grounds the corresponding connection portion 4c when the float 3 is in a nearby position. 3It may be the one closest to the float 3, or multiple adjacent ones. Specifically, it may be configured so that only the grounding means 5 closest to the float 3 is activated to ground the connection part 4c corresponding to that grounding means 5. Alternatively, it may be configured so that the second closest grounding means 5 or the second and third closest grounding means 5 are activated simultaneously with the one grounding means 5 closest to the float 3, to ground the connection parts 4c corresponding to these grounding means 5, respectively.

[0024] However, if only one grounding means 5 closest to the float 3 is configured to operate, there may be a moment when none of the grounding means 5 is operating (none of the connection parts 4c is grounded) between the time when the float 3 changes position and the time when the adjacent grounding means 5 is activated, which may result in an unpredictable jump in the liquid level signal. Therefore, it is preferable to adjust the spacing between the grounding means 5 and the strength of the magnetic field generated by the magnet (described later) to prevent such a moment from occurring, and it is more preferable to configure the ranges of float 3 positions where adjacent grounding means 5 are activated so that they partially overlap each other. In this way, the ranges of float 3 positions where adjacent grounding means 5 are activated Part of When the float 3 is positioned within the range, the plurality of grounding means 5 are simultaneously operating. In this case, the resistance of the plurality of connecting portions 4c grounded by the operating grounding means 5 is column A liquid level signal corresponding to the position of the grounding means 5 corresponding to the connection part 4c closest to the positive electrode side end 4a of the electrode 4 is output.

[0025] Figure 1 is a schematic graph showing an example of the liquid level ranges at which each of the 25 sensors S1 to S25 constituting the grounding means 5 operates and the magnitude of the liquid level signal output when each sensor operates, with the horizontal axis representing the liquid level [mm] and the vertical axis representing the magnitude [V] of the liquid level signal. As shown in the graph in Figure 1, the liquid level ranges at which each sensor operates slightly overlap with the liquid level ranges at which adjacent sensors operate. As a result, while essentially achieving a configuration in which only the grounding means 5 closest to the float 3 operates, the possibility of a moment when none of the grounding means 5 is in operation between a change in the position of the float 3 and the operation of the adjacent grounding means 5 is reduced, thereby reducing the possibility of an unpredictable jump in the liquid level signal.

[0026] The liquid level sensor 1 according to the present invention includes a liquid level signal output means 6 configured to output an electrical signal detected between a positive end 4a of the resistor string, which is the end connected to the positive electrode of the DC power supply, and a connection 4c grounded by a grounding means 5, as a liquid level signal corresponding to the liquid level. The electrical signal output as the liquid level signal between the positive end 4a and the connection 4c grounded by the grounding means 5 may be a voltage signal or a current signal. If the electrical signal output as the liquid level signal is a voltage signal, the voltage range may be, for example, 1.0 V to 5.0 V, or, depending on the application, 0.0 V to 5.0 V. If the electrical signal is a current signal, the current range may be, for example, 4 mA to 20 mA. The liquid level signal output in this manner is a pseudo-analog signal containing information about the liquid level. The liquid level can be detected by electrically processing the liquid level signal using a known method.

[0027] In the configuration of the liquid level sensor 1 according to the present invention, there is no particular limitation as to whether the grounding means 5 corresponding to the connection 4c closest to the positive electrode end 4a of the resistor string 4 and the connection 4c closest to the negative electrode end 4b are provided at the upper or lower limit of the liquid level to be detected. For example, if the grounding means 5 corresponding to the connection 4c closest to the positive electrode end 4a of the resistor string 4 is provided at the lower limit of the liquid level, the number of resistors existing between the positive electrode end 4a and the connection 4c grounded by the grounding means 5 increases as the liquid level increases. Therefore, if the DC power supply is a constant current power supply and the electrical signal extracted as the liquid level signal is a voltage signal, the higher the liquid level, the greater the intensity of the liquid level signal. Also, if the DC power supply is a constant voltage power supply and the electrical signal extracted as the liquid level signal is a current signal, the higher the liquid level, the smaller the intensity of the liquid level signal. Conversely, if the grounding means 5 corresponding to the connection 4c closest to the negative electrode end 4b of the resistor string 4 is located at the lowest limit of the liquid level, the number of resistors existing between the positive electrode end 4a and the connection 4c grounded by the grounding means 5 decreases as the liquid level increases. Therefore, if the DC power supply is a constant current power supply and the electrical signal extracted as the liquid level signal is a voltage signal, the higher the liquid level, the smaller the intensity of the liquid level signal. On the other hand, if the DC power supply is a constant voltage power supply and the electrical signal extracted as the liquid level signal is a current signal, the higher the liquid level, the larger the intensity of the liquid level signal. In either case, the obtained liquid level signal can be electrically processed and converted into liquid level information, so there is no practical problem.

[0028] Hereinafter, the behavior of the liquid level sensor when one of the sensors constituting the multiple grounding means 5 fails will be described in detail. In the following explanation, a liquid level sensor will be described in which sensors S(1), S(2), S(3) ... S(n-1) and S(n) constituting the multiple grounding means 5 corresponding to each of the connection parts 4c existing in series from the positive electrode end 4a to the negative electrode end 4b of the resistor string 4 are arranged in order from the lower limit to the upper limit of the liquid level, and only the one grounding means 5 closest to the float 3 is activated.

[0029] In the above liquid level sensor, when the sensors S(1) to S(n) constituting the grounding means 5 are all normal, the value of the output liquid level signal changes as the liquid level rises, as shown in the following Table 1. Note that "ON" in the table means that the sensor as the grounding means 5 is activated by the approach of the float 3 and the corresponding connection part 4c is grounded, and 1 to n indicate the liquid level rising from the lower limit to the upper limit and the position of the corresponding sensor.

[0030] [Table 1]

[0031] As described above, when all sensors S(1) to S(n) are normal, the sensor serving as the grounding means 5 closest to the position of the float 3 corresponding to the liquid level operates, and a liquid level signal corresponding to the position of each sensor is output.

[0032] Next, let us consider a case where the third sensor S(3) from the lower limit of the liquid level among the sensors S(1) to S(n) is constantly in the "ON" state (it operates regardless of the position of the float 3 and the corresponding connection part 4c is grounded) due to a malfunction. In this case, the value of the output liquid level signal changes as the liquid level rises, as shown in Table 2 below.

[0033] [Table 2]

[0034] As described above, when a plurality of grounding means 5 are operating simultaneously, the resistance of the plurality of connecting portions 4c grounded by the operating grounding means 5 is columnA liquid level signal corresponding to the position of the grounding means 5 corresponding to the connection part 4c closest to the positive electrode end 4a of the grounding means 5 is output. Therefore, as shown in Table 2, even if the liquid level is higher than the third sensor S(3) from the lower limit, the same liquid level signal (output 3) is output as when the liquid level is at the position of sensor S(3). However, when the liquid level is at the same position as sensor S(3) or lower than sensor S(3), the liquid level signals (output 1, output 2, and output 3) corresponding to the positions of the first, second, and third sensors S(1), S(2), and S(3) from the lower limit are correctly output, as in the normal state shown in Table 1.

[0035] Next, let us consider a case where the operating state of the third sensor S(3) from the lower limit of the liquid level is in an "indeterminate" state due to a malfunction (for example, a state where it may or may not operate or output an abnormal signal regardless of the position of the float 3). In this case, the value of the output liquid level signal changes as the liquid level rises, as shown in Table 3 below.

[0036] [Table 3]

[0037] As mentioned above, the sensor S(3) is located at the same position as the faulty sensor S(3) or at a position closer to the faulty sensor S(3). expensive When the liquid level is at this position, the operating state of sensor S(3) is "undefined," and the liquid level signal is also undefined. However, when the liquid level is at a position lower than sensor S(3), the liquid level signals (output 1 and output 2) corresponding to the positions of the first and second sensors S(1) and S(2) from the lower limit are correctly output, just as in the normal state shown in Table 1.

[0038] Next, let us consider a case where sensor S(3) is always in the "OFF" state (it does not operate regardless of the position of float 3 and the corresponding connection part 4c is not grounded) due to a malfunction. In this case, the value of the output liquid level signal changes as the liquid level rises, as shown in Table 4 below.

[0039] [Table 4]

[0040] In this case, when the float 3 is near the sensor S(3), the sensor (3) should normally be activated to the "ON" state, grounding the corresponding connection 4c and outputting the normal liquid level signal (output 3). However, due to the failure, the sensor S(3) does not enter the "ON" state and remains in the "OFF" state. Therefore, when the float 3 is near the sensor S(3), none of the grounding means 5 is activated (none of the connection 4c is grounded), and the magnitude of the liquid level signal is the maximum value that can be output by the resistor string 4. As a result, when the float 3 passes the position of the sensor S(3), the magnitude of the liquid level signal suddenly jumps, which may cause inconvenience, such as confusion for the operator. However, when the float 3 is near a sensor other than the sensor S(3), the liquid level signals (output 1, output 2, ... output n-1 and output n) corresponding to the positions of the first, second, ... n-1th and nth sensors S(1), S(2), ... S(n-1) and S(n) from the lower limit are correctly output, just as in the normal state shown in Table 1.

[0041] As explained above with reference to Tables 2 to 4, in the liquid level sensor 1 according to the present invention, even if some of the grounding means 5 fail and become unable to operate normally, the liquid level sensor does not lose all of its function, and it can detect part of the range of liquid levels to be detected in the same way as in normal times. In other words, it can be said that a liquid level sensor having such a configuration has high redundancy.

[0042] However, as shown in Table 4, if some sensors are always in the "OFF" state due to a malfunction, when the float 3 is located near that sensor, none of the grounding means 5 will be activated, causing a problem in which the magnitude of the liquid level signal suddenly jumps. This is because the liquid level sensor is configured so that only the grounding means 5 closest to the float 3 is activated. To reduce this problem, it is preferable to configure the liquid level sensor so that at least two adjacent grounding means 5 are activated corresponding to the position of the float 3.

[0043] 2 is a schematic graph showing an example of the liquid level range at which each of the sensors S1 to S25 constituting the 25 grounding means 5 operates, and the magnitude of the liquid level signal output when each sensor operates. As shown in the graph of FIG. 2, in this example, the spacing between the grounding means 5 and the strength of the magnetic field generated by the magnet provided in the float 3 are adjusted so that at least two adjacent grounding means 5 operate in accordance with the position of the float 3. Except for this point, FIG. 2 is the same graph as FIG. 1. In a liquid level sensor having such a configuration, even if sensor S(3) is always in the "OFF" state due to a malfunction as shown in Table 4, the value of the liquid level signal changes as the liquid level rises, as shown in Table 5 below.

[0044] [Table 5]

[0045] As shown in Table 5, even when float 3 is in a position where sensors S(3) and S(4) should be in the ON state at the same time, if a malfunction occurs, SBecause output (3) remains OFF, the sensor closest to the positive electrode end of the operating sensors becomes sensor S(4). Therefore, when float 3 is in that position, a liquid level signal (output 3) corresponding to the position of sensor S(3) should be output, but instead a liquid level signal (output 4) corresponding to the position of sensor S(4) is output. As a result, although the period during which the liquid level signal (output 4) corresponding to the position of sensor S(4) is output is extended, the state illustrated in Table 4, "where none of the grounding means 5 is in operation (none of the connection parts 4c is grounded)," is not reached. This reduces the risk of operator confusion caused by a sudden jump in the magnitude of the liquid level signal when float 3 passes the position of sensor S(3). In other words, a liquid level sensor with this configuration can be said to have even higher redundancy.

[0046] Next, a description will be given of the configuration relating to the reliability of the alarm function, which is a feature of the present invention. The liquid level sensor 1 according to the present invention detects the float 3 within a predetermined distance from the alarm position, which is a predetermined position within the movable range of the float 3. 3 The alarm signal output means 7 is configured to output an alarm signal when the float 3 is located outside the range where the grounding means 5 are provided, and not output an alarm signal when the float 3 is not located within a predetermined distance from the alarm position. For example, the alarm signal output means 7 may be configured to output an alarm signal when the float 3 is located outside the range where the grounding means 5 are provided. "The float 3 is located outside the range where the grounding means 5 are provided" means that the float 3 is not located within the range from the upper limit to the lower limit of the liquid level to be detected by the grounding means 5, but is located above the upper limit or below the lower limit of the liquid level. In this case, a predetermined position above the upper limit or below the lower limit of the liquid level becomes the alarm position, and the alarm signal output means 7 can output an upper limit alarm signal when the float 3 is located above the upper limit, and a lower limit alarm signal when the float 3 is located below the lower limit. In the present invention, the alarm signal output means 7 may be configured to output only either an upper limit alarm signal or a lower limit alarm signal.

[0047] In addition to or instead of the above, the warning signal output means 7 may be configured to output a warning signal when a float 3 is present at (within a predetermined distance from) a predetermined position within the range where a plurality of grounding means 5 are provided. In this case, the "predetermined position" within the range where a plurality of grounding means 5 are provided becomes the warning position, and the warning signal output means 7 can output a warning signal when a float 3 is present at (within a predetermined distance from) the warning position. In either case, one or more warning positions can be set as needed.

[0048] In the present invention, the warning signal output means 7 is provided as an independent component separate from the liquid level signal output means 6. Therefore, even if an error occurs somewhere in the liquid level signal output means 6 and the liquid level signal no longer indicates the actual liquid level, warning signals such as an upper limit warning signal and / or a lower limit warning signal can be generated normally. This improves the reliability of the liquid level sensor compared to conventional techniques that do not have an independent warning signal output means 7.

[0049] The specific configuration of the warning signal output means 7 according to the present invention is not particularly limited. Preferably, the additional grounding means 7a constituting the warning signal output means 7 can be provided outside the range in which the grounding means 5 constituting the liquid level signal output means 6 are provided, or within the range in which the float 3 can move, at a predetermined position. As described above, an upper limit warning signal can be generated by adding a grounding means 7a outside the upper limit of the liquid level, and a lower limit warning signal can be generated by adding a grounding means 7a outside the lower limit of the liquid level. Alternatively, both of these can be added. The additional grounding means 7a constituting the warning signal output means 7 can be provided in the same position as any of the multiple grounding means 5 constituting the liquid level signal output means 6, or can be inserted between adjacent grounding means 5.

[0050] It is preferable to operate these added grounding means 7a according to the same operating principle as the grounding means 5 constituting the liquid level signal output means 6, since this allows the use of a common configuration with the liquid level signal output means 6. Here, the common configuration is, for example, a magnet or a light source (described later) installed on the float 3. Alternatively, a means different from the grounding means 5 constituting the liquid level signal output means 6, such as a limit switch, may be used as the added grounding means 7a constituting the warning signal output means 7.

[0051] In a preferred embodiment of the present invention , liquid level sensor 1 When the float 3 is located within a predetermined distance from the grounding means 5 corresponding to the connection part 4c that is closest to the positive electrode side end 4a among the plurality of grounding means 5, or The relevant Grounding means 5 When the float 3 is located outside the positive electrode grounding means 8a that grounds the positive electrode end 4a and / or the grounding means 5 corresponding to the connection part 4c that is closest to the negative electrode end 4b, which is the end opposite to the positive electrode end 4a of the resistor string 4, among the plurality of grounding means 5, or when the float 3 is located within a predetermined distance from the grounding means 5The float 3 has a negative grounding means 8b configured to ground the connection 4c closest to the negative end 4b when the float 3 is located outside of the range indicated by the arrows 1 and 2. As described above, when the float 3 is located near the grounding means 5 corresponding to the connection 4c closest to the positive end 4a, all resistors constituting the resistor string 4 are bypassed, resulting in the lowest resistance value (between the positive end 4a and the negative end 4b). However, if the float 3 passes from near the grounding means 5 corresponding to the connection 4c closest to the positive end 4a to outside the range where the grounding means 5 is located, the operation of the grounding means 5 corresponding to the connection 4c closest to the positive end 4a may stop, potentially interrupting the grounding of the connection 4c. When the grounding of the resistor string 4 on the positive side is interrupted in this way, the resistance value of the resistor string 4, which had been at its lowest until then, suddenly jumps to its highest value, causing a corresponding sudden jump in the magnitude of the liquid level signal. This will cause a discrepancy between the liquid level information indicated by the liquid level signal output means 6 and the liquid level information indicated by the warning signal output means 7, causing confusion for the operator. A similar problem can also occur if an error accidentally occurs in the liquid level signal output means 6 when the float 3 is located near the grounding means 5 corresponding to the connection part 4c closest to the positive electrode end 4a or the negative electrode end 4b.

[0052] In the above-described preferred embodiment, the grounding means 5 is located near the grounding means 5 corresponding to the connection portion 4c closest to the positive electrode end 4a, or is located outside the grounding means 5. flow The position of No. 3 isIn some cases, the positive electrode grounding means 8a forcibly grounds the positive electrode end 4a of the resistor string 4. This keeps the positive electrode end 4a grounded even if the grounding means 5 corresponding to the connection 4c closest to the positive electrode end 4a stops operating, thereby preventing the above-mentioned problem from occurring. This effect can be obtained equally whether the grounding means 5 corresponding to the connection 4c closest to the positive electrode end 4a of the resistor string 4 is located at the lower limit or the upper limit of the liquid level. Furthermore, the negative electrode grounding means 8b prevents the above-mentioned problem from occurring if an error accidentally occurs in the liquid level signal output means 6 when the float 3 is located near the grounding means 5 corresponding to the connection 4c closest to the negative electrode end 4b.

[0053] In a preferred embodiment of the present invention, the warning signal output means 7 includes logic inversion means 9. Logic inversion means outputting a signal that is the opposite of the ON and OFF states of an input signal, and can be implemented, for example, by a transistor. When the warning signal output means 7 is configured with the added grounding means 7a as described above, in a configuration lacking the logic inversion means 9, the warning signal turns ON when the output signal from the added grounding means 7a is ON (i.e., when an operation is occurring in response to the approach of the float 3), and an alarm can be generated based on this. However, for example, if the wiring connecting the sensor unit 1a, which includes the multiple grounding means 5, and the control unit 1b, which supplies power to the sensor unit 1a and extracts signals from the sensor unit 1a, is broken or has a poor connection, the output signal from the added grounding means 7a turns OFF. As a result, the warning signal does not turn ON even when an alarm should be generated, and therefore the alarm is not generated.

[0054] Therefore, in a preferred embodiment of the present invention, the warning signal output means 7 is configured to logically invert the warning signal output and to generate an alarm when the warning signal is OFF. This makes it possible to turn the warning signal OFF and generate an alarm when the output signal from the added grounding means 7a is ON (i.e., when operation is occurring in response to the approach of the float 3), and turn the warning signal ON and not generate an alarm when the output signal from the added grounding means 7a is OFF (i.e., when operation is not occurring in response to the approach of the float 3). As a result, the warning signal turns OFF and an alarm is generated in both cases, when the output signal from the added grounding means 7a is ON and when an error occurs in the signal wiring, thereby achieving a fail-safe function.

[0055] The plurality of grounding means 5 in the present invention may be any means that can ground the connection portion 4c of the adjacent resistors that corresponds to the grounding means 5 located closest to the float 3. In a preferred embodiment of the present invention, the float 3 is provided with a magnet, and the grounding means 5 is activated when it detects the magnetic field generated by the magnet. death (Ground the corresponding connection 4c Shi)Ma The grounding means 5 is configured so as not to operate (i.e., not to ground the corresponding connection part) when it does not detect a magnetic field generated by the magnet. In another preferred embodiment, the grounding means 5 is configured as either a reed switch or a Hall IC. A reed switch is a mechanical switch that closes when it detects a magnetic field and opens otherwise. A Hall IC is an electric element configured with a Hall element and a switching circuit, which grounds the output terminal to earth when the Hall element detects a magnetic field and disconnects the output terminal from earth otherwise. The above-mentioned configuration including a magnet and a reed switch or a Hall IC can also be applied to the warning signal output means 7. In another preferred embodiment, the sleeve 2 and float 3 are made of a light-transmitting material, the float 3 is equipped with a light source, and the grounding means 5 is configured as a switch that operates by detecting light.

[0056] In a preferred embodiment of the present invention, the DC power supply includes a constant current circuit, and the resistance values ​​of the resistors constituting the resistor string 4 are all the same. The constant current circuit maintains the value of the current flowing through the resistor string 4 at a constant value. In this case, if a voltage signal is used as the liquid level signal, the magnitude of the voltage signal is proportional to the sum of the resistance values ​​of the resistors located between the positive end 4a of the resistor string 4 and the grounded grounding means 5. Therefore, if the resistance values ​​of all the resistors are made the same and multiple grounding means 5 are arranged at equal intervals, the magnitude of the voltage signal, which is the liquid level signal, is roughly proportional to the number of resistors between the positive end 4a of the resistor string 4 and the connection 4c of the grounded grounding means 5 that is closest to the positive end 4a. Moreover, since multiple grounding means 5 are arranged at equal intervals, a liquid level sensor with excellent linearity between the liquid level signal and the actual liquid level can be configured.

[0057] In a preferred embodiment of the present invention, the warning signal output means 7 is configured with a power supply different from the DC power supply (+Vcc) used to extract the above-mentioned liquid level signal. By configuring the warning signal output means 7 with a separate, independent power supply different from the DC power supply used for the resistor string 4, the reliability of the warning signal output means 7 can be further improved. [Example]

[0058] Next, a preferred embodiment of the present invention will be described in more detail with reference to the drawings. FIG. 3 is a perspective view showing an example of a resistor array 4 and grounding means 5 according to the present invention. In this embodiment, 25 chip resistors constituting the resistor array 4 and 25 Hall ICs constituting the grounding means 5 are alternately mounted by soldering on a long, narrow board formed by a printed wiring board. The chip resistors have an installation area of ​​0.5 mm in length and 1.0 mm in width. The Hall ICs are 3.2 mm high and arranged at a pitch of 2.5 mm in the vertical direction in FIG. 3. The Hall ICs detect magnetic fields in the vertical direction in FIG. 3. In this configuration, the pitch of the Hall ICs is limited by the size of the Hall ICs themselves and the size of the chip resistors placed between them. Of the 25 Hall ICs constituting the grounding means 5, a Hall IC is mounted above the topmost one and below the bottommost one, both of which serve as additional grounding means 7a constituting the warning signal output means 7. Two transistors are mounted above the resistor array 4 as logic inversion means 9 for logically inverting the outputs of these two Hall ICs. From the viewpoint of improving the reliability of the liquid level sensor, it is preferable that the power supply to these Hall ICs and transistors be performed by a DC power supply different from the DC power supply that is always connected to the Hall IC that constitutes the grounding means 5.

[0059] FIG. 4 is a partial cross-sectional view showing an example of a liquid level sensor 1 according to the present invention. A sleeve 2 is installed vertically within the tank, and the tip of the printed wiring board (shown in FIG. 3) is inserted and fixed inside the sleeve 2. In this example, not only the 25 Hall ICs that make up the grounding means 5 but also the 25 chip resistors that make up the resistor array 4 are installed inside the sleeve 2. The sleeve 2 is inserted into the central hole of the float 3, and the float 3 moves up and down along the sleeve 2 in response to fluctuations in the liquid level in the tank. A ring-shaped magnet (not shown) is installed inside the float 3, and the magnetic field generated by the magnet activates the grounding means 5 near the float 3 and the additional grounding means 7a. The liquid level signal and warning signal generated by the printed wiring board installed inside the sleeve 2 are output from the top of the printed wiring board and transmitted to the outside via output terminals (not shown).

[0060] FIG. 5 is a circuit diagram showing an example of a liquid level sensor according to the present invention. In this embodiment, the liquid level sensor 1 is operated by a constant current. The left half of FIG. 5 shows the circuit of the sensor unit 1a, which is configured using the printed wiring board illustrated in FIG. 3, and the right half shows the circuit of the control unit 1b, which is separated from the sensor unit 1a. The sensor unit 1a and the control unit 1b are connected by multiple wires. The sensor unit 1a includes R1, R2, ..., R(n-1), and R(n), which are n resistors connected in series and which constitute the resistor string 4 of the present invention. Resistor R1 is connected to resistor R0 via the output terminal LQout, and a total of n+1 resistors, including R0, constitute the resistor string 4. That is, in this example, of the n+1 resistors that constitute the resistor string 4, n resistors R1 to R(n) are provided inside the sleeve 2, and one resistor R0 is provided outside the sleeve 2. The positive end 4a and negative end 4b of the resistor string 4 are constantly connected to a DC power supply (+Vcc). The DC current flowing through the resistor string 4 is controlled to a constant value, for example, 1 mA, by a constant current circuit (CCC). In this embodiment, the second resistor R1 from the positive end 4a of the resistor string 4 corresponds to the lower limit of the liquid level, and the resistor R(n) closest to the negative end 4b corresponds to the upper limit of the liquid level.

[0061] S(1), ..., S(n-1), S(n) are n grounding means 5 that ground the connection parts 4c of adjacent resistors. The grounding means 5 is composed of a Hall IC and has an input electrode (+Vs), an output electrode (OUT), and a ground electrode (GND). A voltage (+Vcc) for operating the Hall IC is applied between the input electrode (+Vs) and the ground electrode (GND). Each output electrode (OUT) is connected to the connection part 4c of the resistor string 4.

[0062] The ground electrode (GND) and output electrode (OUT) of the Hall IC (S) are insulated when in an inactive state. When the Hall IC (S) senses the magnetic field generated by the magnet, it enters an active state, the resistance between the ground electrode (GND) and the output electrode (OUT) becomes almost zero, and the output electrode (OUT) is essentially grounded. In this state, no current flows through the resistor between the resistor R(n) closest to the negative electrode end 4b and the connection 4c grounded by the grounding means 5, but current flows through the resistor between the resistor R(n) closest to the positive electrode end 4a and the connection 4c closest to the positive electrode end 4a, among the connection 4c grounded by the grounding means 5. A voltage signal corresponding to this current is output as a liquid level signal to the output terminal (LQout) via the buffer amplifier (U1).

[0063] In this embodiment, n grounding means 5 are arranged so that the grounding means 5 (S(1)) corresponding to the connection 4c closest to the positive electrode end 4a is at the lower limit of the liquid level, and the grounding means 5 (S(n)) corresponding to the connection 4c closest to the negative electrode end 4b is at the upper limit of the liquid level. Furthermore, the resistance values ​​of resistors R1 to R(n) are all the same. Therefore, as the liquid level rises, the number of resistors through which current flows increases approximately linearly. In other words, a proportional relationship is established between the float position and the magnitude of the liquid level signal. The liquid level signal is generated in the range of 1.0 V to 5.0 V. To set the lower limit of the liquid level signal to 1.0 V, the resistance value of resistor R0 is set to 1 kΩ.

[0064] An additional grounding means 7a (S(L)) that constitutes the warning signal output means 7 for outputting a lower limit alarm Lout as a warning signal is provided outside the grounding means 5 (S(1)) corresponding to the connection 4c closest to the positive terminal 4a of the resistor string 4. When this additional grounding means 7a (S(L)) is activated, a current flows through the resistor RL1. This current signal is logically inverted by the transistor QL1, which serves as the logic inversion means 9, turning off the lower limit alarm Lout terminal and generating a lower limit alarm at the output terminal (LQ_Lout) via the photocoupler (PL1). The additional grounding means 7a (S(L)) is operated by a DC power supply that is common to the DC power supply (+Vcc) that drives the resistor string 4, but differs from the resistor string 4 in that it does not include a constant current circuit.

[0065] Simultaneously with the issuance of the lower limit alarm, the positive electrode grounding means 8a, which is made up of a photocoupler (PL2), is activated, and the connection point 4c between resistors R0 and R1 is grounded. As a result, the liquid level signal indicates the lower limit value of 1.0 V, regardless of the state of the grounding means 5. By transmitting the signal via a photocoupler, noise generated in the external electrical circuitry is prevented from being transmitted to the electrical circuitry that constitutes the liquid level sensor, making the operation of the liquid level sensor more stable.

[0066] An additional grounding means 7a (S(H)) constituting the warning signal output means 7 for outputting an upper limit alarm Hout as a warning signal is provided outside the grounding means 5 (S(n)) corresponding to the connection 4c closest to the negative terminal end 4b of the resistor string 4. When this additional grounding means 7a (S(H)) is activated, a current flows through the resistor RH1. This current signal is output by a transistor which is a logic inversion means 9. Ta The logic is inverted by QH1, the upper limit alarm Hout terminal is turned OFF, and an upper limit alarm is generated at the output terminal (LQ_Hout) via the photocoupler (PH1). The added grounding means 7a (S(H)) also operates using a DC power supply that is common to the DC power supply (+Vcc) that drives the resistor string 4, but does not include a constant current circuit. The warning signal output means 7 that generates the upper limit alarm is not linked to the positive grounding means 8a.

[0067] Although not shown, in a preferred embodiment of the present invention having a negative grounding means 8b, the warning signal output means 7 that generates the upper limit alarm may be linked to the negative grounding means 8b. For example, the negative grounding means 8b may be configured to operate simultaneously with the generation of the upper limit alarm, thereby grounding the connection 4c closest to the negative end 4b (the connection 4c between resistors R(n) and R(n-1)). With this configuration, even if an abnormality occurs in the grounding means 5 corresponding to the connection 4c closest to the negative end 4b and the connection 4c cannot be grounded, the connection 4c can be grounded by the negative grounding means 8b when the float is located within a predetermined distance from the grounding means 5 or when the float is located outside the grounding means 5. Therefore, a liquid level signal corresponding to the position of the grounding means 5 corresponding to the connection 4c closest to the negative end 4b can be extracted. Furthermore, the negative electrode grounding means 8b can prevent the above-mentioned problem that may occur when an error accidentally occurs in the liquid level signal output means 6 when the float 3 is located near the grounding means 5 corresponding to the connection part 4c closest to the negative electrode end 4b. In this case, the configuration of the resistor string 4 may be adjusted so that the output value of the upper limit alarm that is output when the added grounding means 7a (S(H)) constituting the warning signal output means 7 that issues the upper limit alarm is grounded matches the upper limit value (e.g., 5.0 V) of the liquid level signal.

[0068] As described above, the positive electrode grounding means 8a may also be configured so that the connection 4c closest to the positive electrode end 4a is grounded instead of the positive electrode end 4a. This configuration is preferable because it means that at least one of the multiple sensors S(1) to S(n) constituting the multiple grounding means 5 always grounds the corresponding connection 4c, regardless of the position of the float, and this ensures consistency between the logic circuit and the liquid level signal.

[0069] FIG. 6 is a circuit diagram showing another example of a liquid level sensor according to the present invention. Unlike the embodiment shown in FIG. 5, in this embodiment, the liquid level sensor 1 is driven by a constant voltage. The resistor string 4 is composed of n+1 resistors R0 to R(n) provided inside the sleeve 2, and the positive and negative ends 4a and 4b of the resistors are constantly connected to the DC power supply (+Vcc). Resistor R0 is provided as a load resistor to prevent the DC power supply (+Vcc) from shorting out when the grounding means S(1) is activated. In this embodiment, n grounding means 5 are also arranged so that the grounding means 5 (S(1)) corresponding to the connection 4c closest to the positive end 4a is at the lower limit of the liquid level, and the grounding means 5 (S(n)) corresponding to the connection 4c closest to the negative end 4b is at the upper limit of the liquid level. Therefore, as the liquid level rises, the number of resistors to which a voltage is applied increases, and the resistor string 4 The current flowing through the output terminal (LQout) decreases. In other words, the magnitude of the liquid level signal output to the output terminal (LQout) changes nonlinearly as the liquid level rises. In this embodiment, the electrical circuit is simpler than in the case of constant current drive, so the overall risk of failure and manufacturing costs can be reduced. The configuration and functions of the parts common to Figure 5 other than those mentioned above are the same as in the embodiment shown in Figure 5, so explanations will be omitted here.

[0070] FIG. 7 is a schematic diagram showing an example of the operation of the liquid-level sensor according to the present invention. This example is the example of constant current drive shown in FIG. 5. The horizontal axis of the diagram represents the float position measured from the lower limit position in mm. The vertical axis represents the liquid-level signal measured as a voltage signal in V. The liquid-level signal is adjusted so that it is 1.0 V when the float is at the lower limit position and 5.0 V when it is at the upper limit position. The liquid-level signal is shown as a fine-step graph, and it can be seen that a pseudo-analog signal with excellent linearity is output relative to the liquid level. In addition, the bottom of the diagram shows the float position when the warning signal output means 7 is activated and a lower limit alarm (L) and an upper limit alarm (H) are output as warning signals, indicated by thick lines.

[0071] In Figure 7, if some error occurs in the liquid level sensor 1 and the grounding means 5 does not operate normally when the float is at the lowest position, the liquid level signal may jump to 5.0 V as shown by the dotted line in the figure. However, in the present invention, the warning signal output means 7, which includes the added grounding means 7a, is configured with an electrical circuit different from that of the liquid level signal output means 6, so the warning signal (lower limit alarm) itself is generated normally. Furthermore, in a preferred embodiment of the present invention that has a positive grounding means 8a, when the positive grounding means 8a operates, the liquid level signal remains at 1.0 V as shown by the solid line in the figure, so the liquid level signal and the warning signal are consistent and no confusion occurs to the operator. [Explanation of symbols]

[0072] 1 Liquid level sensor 1a Sensor section 1b Control section 1' Liquid level sensor (conventional technology) 2 sleeves 3. Float 4 resistor string 4a Positive electrode end 4b Negative electrode side end 4c Connection 5 Grounding means 6 Liquid level signal output means 7. Warning signal output means 7a Additional Grounding Means 8a Positive grounding means 8b Negative grounding means 9. Logic inversion method

Claims

1. A sleeve provided in a vertical direction, a float configured to move along the sleeve as the liquid level changes; a resistor string including a plurality of resistors connected in series and having both ends constantly connected to a DC power supply; a plurality of grounding means provided inside the sleeve corresponding to the connection portions of adjacent resistors in the resistor string, the plurality of grounding means being configured to ground the corresponding connection portion when the float is located within a predetermined distance and not ground the corresponding connection portion when the float is not located within the predetermined distance; a liquid level signal output means configured to extract, as a liquid level signal corresponding to the liquid level, an electrical signal detected between a positive end of the resistor string, which is the end connected to the positive electrode of the DC power supply, and the connection part grounded by the grounding means; A liquid level sensor having an alarm signal output means configured to output an alarm signal when the float is located within a predetermined distance from an alarm position, which is a predetermined position within the movable range of the float, and not output an alarm signal when the float is not located within the predetermined distance from the alarm position, by providing additional grounding means at a predetermined position that is provided as an independent configuration separate from the liquid level signal output means and that is separate from the grounding means that constitutes the liquid level signal output means; a positive grounding means separate from the grounding means constituting the liquid level signal output means, configured to ground the positive electrode side end or the connection part closest to the positive electrode side end when the float is located within a predetermined distance from the grounding means corresponding to the connection part closest to the positive electrode side end among the plurality of grounding means or when the float is located outside the grounding means; and / or a negative grounding means separate from the grounding means constituting the liquid level signal output means, configured to ground the connection part closest to the negative electrode side end when the float is located within a predetermined distance from the grounding means corresponding to the connection part closest to the negative electrode side end, which is the end of the resistor string opposite the positive electrode side end, among the plurality of grounding means, or when the float is located outside the grounding means. The liquid level sensor further comprises:

2. The warning signal output means is provided with logic inversion means The liquid level sensor according to claim 1 .

3. the float comprises a magnet; the grounding means is configured to ground the corresponding connection part when detecting a magnetic field generated by the magnet, and not to ground the corresponding connection part when not detecting a magnetic field generated by the magnet, The warning signal output means is configured to output the warning signal when it detects the magnetic field generated by the magnet, and not to output the warning signal when it does not detect the magnetic field generated by the magnet.

3. The liquid level sensor according to claim 1 or 2.

4. The grounding means and the warning signal output means include either a reed switch or a Hall IC. The liquid level sensor according to claim 3 .

5. the DC power supply includes a constant current circuit, The resistance values ​​of the resistors constituting the resistor string are all the same.

5. A liquid level sensor according to claim 1.

6. The warning signal output means is configured by a power source different from the DC power source.

6. A liquid level sensor according to claim 1.

7. (delete)

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