JP2014077646A - Water level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water level sensor allowing output characteristics to be easily adjusted, thereby allowing the readjustment for secular variations and the change of a measurement range to be easily performed.SOLUTION: A water level sensor has a sensor body that is arranged in the water. The sensor body includes: a semiconductor pressure sensor element (pressure sensor unit) 44 that outputs an analog signal of voltage according to a water pressure; an A/D conversion unit 61 that converts an analog signal from the sensor element 44 into a digital signal; and an adjustment unit 63 that adjusts the digital signal on the basis of a predetermined output characteristic. The sensor is provided with a writing cable 21c for changing the output characteristic that is connected to the adjustment unit 63 from the outside of the sensor body.

Description

  The present invention relates to a water level sensor used by being placed in water.

  As a water level sensor, for example, a throw-in type water level sensor that is submerged in water and detects the water level is known. This water level sensor includes a pressure sensor that outputs an electrical signal corresponding to the water pressure, and an analog circuit system that processes the signal from the pressure sensor and outputs the signal to the outside. The water level can be measured by outputting an output value from the water level sensor based on preset output characteristics (output value at zero pressure, output value per unit pressure, etc.) as the water pressure increases or decreases. (For example, refer to Patent Document 1). Note that the output characteristics of the water level sensor are adjusted by turning a volume or the like provided in the analog circuit system, and after adjustment, the water level sensor is housed in the main body of the water level sensor, so that it cannot be easily operated from the outside. .

JP 2012-112924 A

  However, in this water level sensor, a pressure sensor or an analog circuit system may deteriorate or change in quality due to the passage of time or temperature, and the output value may be changed. Such fluctuations in output value require readjustment of the water level sensor because the fluctuation range cannot be predicted. In this case, it is necessary to take the water level sensor out of the water, disassemble the sensor body, turn the volume of the analog circuit system, readjust it manually to achieve the initial output characteristics, and seal the sensor body again. Therefore, it is troublesome and time consuming for the operator. Also, when the water level sensor whose measurement range is initially adjusted to the water level 0 to 10 m is changed to a water level sensor whose measurement range is the water level 0 to 8 m, the sensor body is disassembled and the volume is turned in the same manner as described above. After the adjustment, the sensor body needs to be sealed again, which is troublesome for the operator.

  In view of the circumstances as described above, the present invention provides a water level sensor that can easily adjust the output characteristics and easily perform readjustment with respect to secular change and change of the measurement range. The purpose is to do.

  In order to solve the above problems, the present invention employs the following means. A water level sensor having a sensor body disposed in water, the sensor body outputting a pressure sensor unit that outputs an analog signal related to a voltage in accordance with water pressure, and an A / A that converts the analog signal from the pressure sensor unit into a digital signal. A D conversion unit and an adjustment unit that adjusts the digital signal based on preset output characteristics, and is connected to the adjustment unit from the outside of the sensor body, and a writing cable for changing the output characteristics is provided. It is done.

  The sensor main body may include a D / A conversion unit that converts the digital signal adjusted by the adjustment unit into an analog signal and outputs the analog signal. The pressure sensor unit may be a semiconductor pressure sensor element in which a bridge circuit is configured by a piezoresistor formed on a semiconductor substrate. Further, the output characteristic may be at least one of an offset relating to an output at zero pressure and a span relating to an output per unit pressure. Further, as the output characteristics, the relationship between the pressure and the output may be corrected so as to maintain linearity. Further, the adjustment unit may separately receive a digital signal corresponding to a temperature change from the pressure sensor unit, and the output characteristic may be corrected according to the temperature change. In addition, a readout cable may be provided that is pulled out of the sensor body from the adjustment unit and takes out a digital signal from the adjustment unit.

  According to the present invention, it becomes possible to easily adjust the output characteristics of the water level sensor. Therefore, readjustment when the output characteristics fluctuate due to long-term use, and change adjustment of the measurement range are facilitated. Can be shortened and the burden on the operator can be reduced.

It is explanatory drawing which shows the use condition of the water level sensor which concerns on this invention. It is sectional drawing which shows embodiment of the water level sensor which concerns on this invention. It is a block diagram which shows an example of the circuit structure used for a water level sensor. It is a graph which shows the example of adjustment of the output characteristic of a water level sensor. It is a graph which shows the example of adjustment of the output characteristic of a water level sensor. It is a graph which shows the example of adjustment of the output characteristic of a water level sensor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the contents described below.
As shown in FIG. 1, a water level detection system 100 is electrically connected to a water level sensor 101 through a cable 20 and a throw-in type water level sensor 101 that detects the water level in a state where it is submerged in water. And a receiving device 102 that measures and displays the water level by processing the output from the device 101.

  As shown in FIG. 1, the water level sensor 101 is arranged in a suspended state in stored water 103 accumulated in, for example, a well or a borehole. It should be noted that the arrangement of the water level sensor 101 is not limited to the suspended state shown in FIG. In addition to being used for wells, etc., it can also be used for pools, water tanks, water tanks, etc. in addition to rivers, ponds and lakes. Further, the water level sensor 101 may be fixed to an anchor installed at the bottom of the water so as not to move due to the flow of water, or may be held at a predetermined position by a weight provided on the water level sensor 101.

  The water level sensor 101 detects an upper water level from the position where it is arranged, and has an individual detection range for each sensor. For example, the water level sensor 101 set to a water level 0 to 10 m span has a water level 0 m (in the atmosphere and the water pressure is 0) as a minimum value, and a case where the water pressure corresponding to the water level 10 m is detected as a maximum value. The detection range is set at a water level of 0 to 10 m. The receiving device 102 measures and displays the water level based on the detection result (analog signal) of the water level sensor 101. The receiving device 102 may have a function of transmitting / receiving a digital signal to / from the water level sensor 101. For transmission / reception of digital signals, for example, an information processing device such as a personal computer, an output device such as a display, an input device such as a keyboard, or the like is used.

As shown in FIG. 2, the water level sensor 101 includes a sensor main body 10 disposed in water, and a cable 20 that electrically connects the sensor main body 10 and the receiving device 102.
The sensor body 10 includes a case 11 that houses a detection mechanism that detects water pressure. The case 11 is formed in a cylindrical shape using a material having high pressure resistance and corrosion resistance such as stainless steel. For example, information such as a serial number of the water level sensor 101 is stamped on the outer peripheral surface of the case 11. A shrink tube 17 made of polyolefin or the like is attached to the other end side (cable 20 side) of the case 11 so as to penetrate the cable 20.

  A cap 13 is attached to the distal end side of the case 11. The cap 13 is formed in a hollow shape using a material having high pressure resistance and corrosion resistance such as stainless steel and resin, and a tapered portion 13b is formed from the central portion of the tip 13a to the side surface. The cap 13 is fixed in a state where it is fitted to the tip of the case 11 and is removable. A plurality of communication holes 13 c are provided on the side surface of the cap 13 to communicate the outside and the inside of the cap 13.

  The communication holes 13c are formed at predetermined intervals over the circumference of the side surface of the cap 13, and are formed at four locations at regular intervals in the illustrated example. Accordingly, the stored water 103 (see FIG. 1) enters the inside of the cap 13 through the communication hole 13c, so that the pressure (water pressure) is equal inside and outside the cap 13. In addition, the shape, the number, and the arrangement of the communication holes 13 c are not limited to the illustrated ones, and any one that allows water to enter the cap 13 can be applied. Further, the communication hole 13c may be provided with a filter so that foreign matter such as solid matter contained in the stored water 103 does not enter inside.

  Inside the case 11 are housed a pressure sensing unit 14, an amplifier board 15 that processes a signal from the pressure sensing part 14, and a microcomputer board 16. The pressure sensitive part 14 includes an element 41, a diaphragm 42, silicone oil 43, and a semiconductor pressure sensor element 44 as a pressure sensor part.

  The element 41 is formed in a disk shape from a highly corrosion-resistant material such as stainless steel, and is fixed in a state where its outer peripheral surface is in contact with the inner peripheral surface 11 a of the case 11. An O-ring 47 is disposed between the outer peripheral surface of the element 41 and the inner peripheral surface 11a of the case 11, and seals between the two. The element 41 blocks the internal space of the case 11 from the tip side and the cable 20 side. The element 41 includes an annular projecting portion 41a projecting toward the tip, a recess 41b in which the semiconductor pressure sensor element 44 is installed, an air release hole 41c penetrating the element 41 at the position of the recess 41b, and a lead pin 46. And a through hole 41d arranged in a penetrating state. A gap between the through hole 41d and the lead pin 46 is filled with a sealing material.

  The diaphragm 42 is formed in a disk shape from a deformable metal material such as stainless steel. The ring 9 is welded to the edge on the front end side of the diaphragm 42 over the entire circumference. The edges of the ring 9 and the diaphragm 42 are sandwiched between an annular protrusion 11b that protrudes inward from the inner peripheral surface 11a of the case 11 and an annular protrusion 41a that protrudes from the element 41 toward the distal end. Thus, the diaphragm 42 is held. Due to the diaphragm 42 and the element 41, the internal space of the case 11 is a first space K 1 on the tip side (cap 13 side) of the diaphragm 42, a second space K 2 between the diaphragm 42 and the element 41, and an element 41. And the third space K3 on the cable 20 side.

  The first space K1 is a space into which water enters through the communication hole 13c of the cap 13. Accordingly, the diaphragm 42 is deformed so as to bend toward the second space K2 according to the pressure of the water that has entered the first space K1. That is, the deformation is made by an amount corresponding to the pressure difference between the first space K1 and the second space K2.

  Silicone oil 43 is sealed in the second space K2 (between the diaphragm 42 and the element 41). The silicone oil 43 is an incompressible liquid, and transmits a pressure change caused by the deformation of the diaphragm 42 to other parts as it is. The through hole 41d of the element 41 has a gap between the lead pin 46 sealed with a sealing material, and the air release hole 41c is closed with a semiconductor pressure sensor element 44 described later. Accordingly, the silicone oil 43 does not leak into the third space K3. The silicone oil 43 covers and protects the semiconductor pressure sensor element 44.

  The semiconductor pressure sensor element 44 forms a bridge circuit 48 (see FIG. 3) by a piezoresistor (gauge resistor) formed on a semiconductor substrate such as silicon. Piezoresistors are formed on a semiconductor substrate by a diffusion method, an ion implantation method, or the like. When a stress is applied to the piezoresistors, the crystal lattice is distorted by the stress and the electrical resistivity is changed. The semiconductor pressure sensor element 44 is simply referred to as the sensor element 44 in the following description.

  The sensor element 44 is fixed to the recess 41 b of the element 41. The sensor element 44 has a diaphragm structure in which the central portion on the back surface side (fixed surface side) is thinned by etching or the like. The bridge circuit 48 described above is formed in this diaphragm structure portion. In addition, the back surface space (in the recessed portion) of the sensor element 44 communicates with the third space K3 through the air release hole 41c. The third space K3 is at atmospheric pressure by an atmospheric release pipe 23 described later.

  Accordingly, when the diaphragm 42 is deformed so as to swell into the second space K2, for example, the diaphragm structure of the sensor element 44 is also subjected to pressure by the silicone oil 43 and deforms toward the third space K3. A stress corresponding to the amount of deformation is generated in the sensor element 44, and the electrical resistivity of the piezoresistor changes in proportion to the stress. The sensor element 44 is electrically connected to the lead pin 46 through the bonding wire 45.

  The amplifier board 15 is disposed in the third space K3 while being held by the lead pins 46 protruding from the element 41. The amplifier board 15 is electrically connected to the sensor element 44 via the lead pin 46 and the bonding wire 45. The amplifier board 15 amplifies and outputs a weak signal output from the sensor element 44. A microcomputer board 16 is disposed in the third space K3 and is electrically connected to the amplifier board 15 through a plurality of wires. Instead of connecting the amplifier board 15 and the microcomputer board 16 by wiring such as a cable, the two may be connected by a plug-in type such as a socket.

  The microcomputer board 16 has a microcomputer function, and a signal from the sensor element 44 is input in a state amplified by the amplifier board 15 and performs predetermined processing. Further, the microcomputer board 16 is connected to the cable 20 and outputs the processing result to the cable 20. The cable 20 is disposed through the reduced diameter portion 12 fixed to the inner peripheral surface 11 a of the case 11 and the shrinkable tube 17 attached to the end portion of the case 11. The cable 20 includes a plurality of wires 21 (21a to 21d) electrically connected to the microcomputer board 16, and an air release pipe 23 that communicates the third space K3 in the case 11 and the outside of the case 11. These are covered with a cable cover 22. The cable cover 22 and the reduced diameter portion 12 are sealed with a sealing material 18.

  As shown in FIG. 3, a bridge circuit 48 is configured by a piezoresistor provided in the sensor element 44. The bridge circuits 48 are connected to the voltage source VCC and the ground point GND, respectively. In this configuration, the bridge circuit 48 is driven at a constant voltage, and a change in electrical resistivity of the piezoresistor is output as an analog signal as a change in voltage between the points P and Q of the bridge circuit 48. The analog signal output from the bridge circuit 48 is transmitted to the amplifier board 15 via the bonding wire 45 and the lead pin 46 as shown in FIG.

  As shown in FIG. 3, the amplifier board 15 includes an amplifier 51 such as an amplifier circuit that amplifies an analog signal, and the difference voltage (P point−Q point) generated in the bridge circuit 48 of the sensor element 44 is supplied to the amplifier 51. After being amplified at a predetermined amplification factor, the signal is output to the microcomputer board 16. This difference voltage is an analog signal related to the voltage.

  As shown in FIG. 3, the microcomputer board 16 is based on an A / D conversion unit 61 that converts an analog signal output from the amplifier board 15 into a digital signal, and the converted digital signal based on preset output characteristics. An adjustment unit 63 that adjusts; a D / A conversion unit 64 that converts the digital signal adjusted by the adjustment unit 63 into an analog signal; a current conversion circuit 65 that converts the converted analog signal into a current value and outputs the current value; Each circuit of the microcomputer board 16, the amplifier 51, and a power supply circuit 66 that supplies a predetermined voltage to the bridge circuit 48 are provided. The current conversion circuit 65 is connected to the power supply unit provided in the display device 102 or the like with the connection terminal 31 via the power supply cable 21a, and the output terminal 32 is connected to the data input unit of the display device 102 via the output cable 21b. It is connected.

  In the case of the throw-in type water level sensor 101, the length of the cable 20 may be several meters to several hundred meters because the sensor body 10 is disposed in water. Accordingly, when a voltage signal is used as an output from the sensor main body 10, inconvenience occurs due to a voltage drop or noise caused by the length of the cable 20, and therefore the output signal from the sensor main body 10 is set to a current value by the current conversion circuit 65. . However, the present invention is not limited to this, and a voltage value may be used as an output signal from the sensor body 10. In this case, the current conversion circuit 65 is unnecessary. In addition, the range of the current value output from the current conversion circuit 65 is generally set to 4 mA to 20 mA, and is a range that can be supported by many models of the receiving apparatus 102.

  Further, the microcomputer board 16 has a transmission / reception circuit 67 for inputting / outputting digital signals to / from the adjustment unit 63. In the transmission / reception circuit 67, the data input terminal 33 is connected to an output terminal of a personal computer (display device 102) or the like via a write cable 21c, and the data output terminal 34 is connected to a personal computer (display) via a read cable 21d. Device 102) and the like.

  The adjustment unit 63 includes a control device 63a such as a CPU that performs comprehensive information processing, a flash memory that stores various programs and data, an EEPROM, a storage device 63b such as a RAM, and an oscillation circuit. . The storage device 63b stores data relating to output characteristics for adjusting the digital signal sent from the A / D converter 61 to a predetermined value. Therefore, the digital signal sent from the A / D conversion unit 61 is adjusted by the control device 62 a so as to have the output characteristics stored in the storage device 63 b in advance, and the adjustment value is output to the D / A conversion unit 64. Is done.

  The water level sensor 101 has its output characteristics checked before shipping, and initial data relating to the output characteristics is stored in the storage device 63b so that an accurate value is output. The check process will be described. First, the water level sensor 101 is arranged in a pressure chamber in which the pressure is defined in advance, and a signal output via the output cable 21b at that time is monitored by the receiving device 102. Then, the adjustment amount by the adjustment unit 63 is changed from the personal computer or the like via the writing cable 21c so as to be the specified pressure, and the adjustment amount when the specified pressure is output is written in the storage device 63b.

  By performing this operation with a plurality of pressures, the adjusting unit 63b creates output characteristics obtained by linearly interpolating these data and stores them in the storage device 63b. When the water level sensor 101 is adjusted as a type having a water level of 10 m span, verification work is performed for two pressures, for example, an atmospheric pressure (pressure 0) and a pressure corresponding to the water level 10 m. In addition, the contents written from the writing cable 21c, the adjusted digital signal, and the like are output from the reading cable 21d to the input terminal 34. Therefore, it is possible to confirm the contents written from the writing cable 21c, the result thereof, etc. with a personal computer or the like.

  By the way, since the resistivity of the piezoresistor formed in the sensor element (semiconductor pressure sensor element) 44 changes greatly due to a temperature change, it is necessary to compensate for the temperature when the water level sensor 101 is used in a usage environment where the temperature changes. is there. A configuration for performing this temperature compensation will be described. As shown in FIG. 3, an electrical resistance 49 is provided between the voltage source VCC and the bridge circuit 48 so that the temperature dependency can be almost ignored as compared with the sensor element 44. That is, even if the electrical resistivity of the piezoresistor changes depending on the temperature around the sensor element 44, the electrical resistivity of the electrical resistor 49 does not change.

  A point R between the electric resistance 49 and the bridge circuit 48 is connected to an A / D converter 62 provided on the microcomputer board 16 via a wiring 52. Accordingly, the voltage value (analog signal) at the point R is converted into a digital signal by the A / D conversion unit 62 and input to the adjustment unit 63. The wiring 52 is specifically connected to the microcomputer board 16 via bonding wires and lead pins as shown in FIG. Note that an amplifier for amplifying an analog signal may be separately provided before the A / D conversion unit 62.

  Compensation data for temperature compensation is stored in the storage device 63b of the adjustment unit 63, and the control device 63a is based on a signal (digital signal corresponding to a temperature change) sent from the A / D conversion unit 62. The content to be compensated is determined from the compensation data in the storage device 63b. Then, when adjusting the signal input from the A / D conversion unit 61 to a predetermined output characteristic, the control device 63a adjusts the output characteristic after correcting the output characteristic based on the compensation content. As a result, the signal output from the water level sensor 101 (analog signal output from the current conversion circuit 65) is temperature compensated. The compensation data is measured in advance by experiments or the like and stored in the storage device 63b. However, whether or not to perform temperature compensation as described above is arbitrary.

  FIG. 4 is a graph showing an example of output characteristics stored in the storage device 63b. In FIG. 4, the horizontal axis indicates the water level (unit m), and the vertical axis indicates the current value (unit mA) output from the current conversion circuit 65.

  As shown by the solid line in FIG. 4, when the water level is 0 m (atmospheric pressure), a current of 4 mA is output, and when the water level is 10 m, a maximum current value of 20 mA is output. That is, this water level sensor 101 is used with a measurement range of water levels 0 m to 10 m. Further, when the water level is between 0 m and 10 m, the current increases at a constant rate as the water level increases. That is, the output value per unit pressure (unit water level) is a constant value (1.6 mA / m). Such a current value at a water level of 0 m (pressure 0 value) and a current value per unit pressure (span) are stored in the storage device 63b as output characteristics.

  On the other hand, the pressure sensor 14 in the water level sensor 101 may change the current value output from the water level sensor 101 as each component member changes in quality over time. For example, when the pressure 0 value is offset with respect to 4 mA as indicated by the broken line (1) in FIG. 4, or the span has changed with respect to the predetermined value (1.6 mA / m) as indicated by the broken line (2). There are cases.

  A broken line (1) is a case where the pressure 0 value is offset in a direction in which it increases with respect to 4 mA, and the span does not change. The offset may occur not only in the positive direction with respect to 4 mA but also in the negative direction with respect to 4 mA. A broken line (2) is a case where the span becomes smaller than the initial value, and there is no change in the pressure 0 value. Note that the span change is not only smaller than the initial value but also sometimes larger. In the broken line (3), the pressure 0 value is offset, and the span may be changed. As described above, when the offset occurs or the span changes, it is necessary to adjust the output characteristics because the accurate water level cannot be measured from the current value.

  The adjustment of the output characteristics is performed by correcting data relating to the output characteristics stored in advance in the storage device 63b of the adjustment unit 63 via the writing cable 21c from an external personal computer or the like. When correcting the offset, the sensor body 10 is taken out of the water and placed in the atmosphere, and the current value output from the sensor body 10 is monitored at a pressure of 0, and the value deviates from the initial 4 mA. If so, the offset amount is corrected to be canceled and the correction data is written in the storage device 63b. The correction data can be confirmed by a digital signal output from the readout cable 21d. Further, instead of monitoring the current value, a digital signal output from the reading cable 21d may be monitored.

  When the span is corrected, the sensor body 10 taken out from the water is placed in a pressure chamber set at a pressure (pressure corresponding to a water level of 10 m), for example, which is the maximum value of the measurement range. The output current value is monitored, and when the value deviates from the initial 20 mA, the current value is corrected to 20 mA and the correction data is written in the storage device 63b. Based on the correction data of 20 mA, the output characteristics are corrected so that current values of 4 mA to 20 mA are output corresponding to the water levels of 0 to 10 m. Note that the correction data relating to the span can also be confirmed from the digital signal output from the readout cable 21d as described above. Similarly, the digital signal output from the readout cable 21d may be monitored instead of monitoring the current value.

  By changing the output characteristics in this manner, the water level sensor 101 can be reused. Moreover, since such adjustment work can be performed without disassembling the sensor main body 10, it can be performed easily and in a short time for the operator. Further, there is no work of disassembling and reassembling the sensor body 10, and water leakage due to insufficient sealing during reassembly can be avoided.

  Further, since the change in pressure accompanying the change in water level is linear, an output characteristic is required so that the current value output from the sensor body 10 also changes linearly. However, due to the characteristics of the pressure-sensitive part 14 including the sensor element 44, there is a case where the change in the intermediate part is not linear (the span is not a constant value). Therefore, even when 4 mA is output at a pressure of 0 and 20 mA is output at a water level of 10 m, the current value is shifted from the initial output characteristics at an intermediate water level, and a large error is included. There is a need to.

  FIG. 5 is a graph showing the relationship between the current value output from the sensor body 10 and the water level. As in FIG. 4, in FIG. 5, the horizontal axis indicates the water level (unit m), and the vertical axis indicates the current value.

  As shown by the solid line in FIG. 5, the output current value is lower and has a downwardly convex curve as shown by the broken line with respect to the desired output characteristic having linearity. For example, at a water level of 5 m, 12 mA should be output, but α is lower than this, and since this α value is measured to be a value smaller than the water level of 5 m, the error increases. Therefore, such non-linearity correction is performed by writing the linearity correction data to the storage device 63b of the adjustment unit 63 via the write cable 21c from an external personal computer or the like. The control device 63a corrects the output characteristics based on the linearity correction data so that an appropriate current value is output.

  The linearity correction data is obtained by changing the sensor body 10 into a plurality of pressures (for example, 2 m, 5 m, etc.) in the pressure chamber, calculating a predetermined curve from the current value output at each pressure, and converting the curve into a straight line. The data is stored in the storage device 63b as data for correcting the output characteristics having characteristics. In addition, after using the water level sensor 101 for a long time, the pressure zero value and the span may be shifted and the linearity of the output characteristics may be impaired. In this case, the linearity correction data is also changed along with the adjustment of the offset or the like.

In the embodiment described above, the measurement range is used as the water level sensor 101 as a sensor having a water level of 0 m to 10 m, but this measurement range can be changed.
FIG. 6 is a graph showing an example in which the measurement range of the sensor body 10 is changed. In FIG. 6, the horizontal axis indicates the water level (unit m), and the vertical axis indicates the current value (unit mA). The dotted line in FIG. 6 shows the output characteristics with a measurement range of 0 m to 10 m. For this output characteristic, the measurement range can be changed by changing the span.

  The solid line (A) in FIG. 6 is changed so that the measurement range of the water level sensor 101 is shortened from 0 m to 10 m to 0 m to 8 m. This change is performed, for example, by placing the sensor body 10 within a pressure corresponding to a water level of 8 m and adjusting the span of the output characteristics so that 20 mA is output at this pressure. The adjusted output characteristics are stored in the storage device 63b of the adjustment unit 63 via the writing cable 21c. Therefore, the control device 62a outputs a predetermined current value in a state where the measurement range is set to 0 m to 8 m according to the adjusted output characteristics.

  Moreover, in the continuous line (B) of FIG. 6, it has changed so that the measurement range of the water level sensor 101 may be expanded from 0 m to 10 m to 0 m to 16 m. The change operation is the same as in the case of the solid line (A). As described above, the measurement range can be easily changed only by adjusting the output characteristics, and it is not necessary to prepare a plurality of types of water level sensors having different measurement ranges. In addition, in the water level sensor 101 with a measurement range of 0 m to 10 m as a reference, the measurement range can be adjusted within a range of 50% to 200%. That is, it can be arbitrarily adjusted in the range of the maximum measured water level 20 m from the water level sensor of the maximum measured water level 5 m.

  In the water level sensor 101 described above, an analog signal such as a current value is used as an output signal from the sensor body 10 and is processed by the receiving device 102 (see FIG. 1). It is also possible to use a digital signal output from. In FIG. 3, the digital signal output from the adjustment unit 63 is converted into an analog signal by the D / A conversion unit 64, and then this analog signal is converted into a current value by the current conversion circuit 65 and output. The digital signal from the unit 63 may be output from the readout cable 21d via the transmission / reception circuit 67, and this digital signal may be used. The output digital signal is input to the receiving apparatus 102, and a predetermined process is performed to display the water level and the like. When the digital signal from the adjustment unit 63 is used as described above, the D / A conversion unit 64 and the current conversion circuit 65 are not required in FIG.

  For digital signal transmission / reception, for example, serial communication such as RS-232C or RS-485 is used as a communication standard. RS-485 is used when the distance between the water level sensor 101 and the receiving device 102 is relatively long. Further, whether or not the transmission / reception circuit 67 shown in FIG. 3 has the function of performing the serial communication described above is arbitrary. In addition to the transmission / reception circuit 67, an input / output circuit or the like may be provided to perform serial communication such as RS-232C.

  Although the embodiment has been described above, the present invention is not limited to the illustrated shape and the like, and the shape and the like can be changed without departing from the functions and applications of the constituent members. For example, although the semiconductor pressure sensor element 44 is used as the pressure sensor unit, a strain gauge having a bridge circuit or the like may be used instead. In addition, although the wired writing cable 21c and the reading cable 21d are used for the connection between the transmission / reception circuit 67 and an external personal computer or the like, the present invention is not limited to this. For example, the writing cable 21c or the reading cable 21d You may connect with a personal computer etc. using wireless communication etc. from the middle. Further, the writing cable 21c and the reading cable 21d need not always be drawn to the ground and connected to a personal computer or the like, and may be left in the water. In this case, the writing cable 21c and the like may be cut short.

DESCRIPTION OF SYMBOLS 10 ... Sensor main body 14 ... Pressure sensing part 15 ... Amplifier board 16 ... Microcomputer board 20 ... Cable 21 ... Wiring 21a ... Power supply cable 21b ... Output cable 21c ... Write cable 21d ... Read cable 22 ... Cable cover 44 ... Semiconductor Pressure sensor element (pressure sensor part)
DESCRIPTION OF SYMBOLS 48 ... Bridge circuit 49 ... Electric resistance 51 ... Amplifier 52 ... Wiring 61,62 ... A / D conversion part 63 ... Adjustment part 63a ... Control apparatus 63b ... Memory | storage device 64 ... D / A conversion part 65 ... Current conversion circuit 66 ... Power supply Circuit 67 ... Transmission / reception circuit 100 ... Water level detection system 101 ... Water level sensor 102 ... Display device

Claims (7)

A water level sensor having a sensor body disposed in water,
The sensor body includes a pressure sensor unit that outputs an analog signal related to a voltage according to water pressure, an A / D conversion unit that converts an analog signal from the pressure sensor unit into a digital signal, and the digital signal is preset. An adjustment unit that adjusts based on output characteristics,
A water level sensor connected to the adjustment unit from the outside of the sensor body and provided with a writing cable for changing the output characteristics.   The water level sensor according to claim 1, wherein the sensor body includes a D / A conversion unit that converts the digital signal adjusted by the adjustment unit into an analog signal and outputs the analog signal.   3. The pressure sensor according to claim 1, wherein a semiconductor pressure sensor element in which a bridge circuit is configured by a piezoresistor formed on a semiconductor substrate is used for the pressure sensor unit.   The water level sensor according to any one of claims 1 to 3, wherein the output characteristic is at least one of an offset relating to an output at zero pressure and a span relating to an output per unit pressure. .   The water level sensor according to any one of claims 1 to 4, wherein, as the output characteristic, a relationship between pressure and output is corrected so as to maintain linearity.   6. The adjustment unit according to claim 1, wherein a digital signal corresponding to a temperature change is separately input from the pressure sensor unit, and the output characteristic is corrected according to the temperature change. The water level sensor according to one item.   The water level according to any one of claims 1 to 6, wherein a reading cable is provided from the adjusting unit to the outside of the sensor body and for taking out a digital signal from the adjusting unit. Sensor.

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