KR20020059153A - Ground water level quality monitor - Google Patents

Abstract

PURPOSE: An automatic observation apparatus for observing an underground water level and water quality of subterranean water is provided to measure accurately the underground water level and the water quality and reduce unit costs of the automatic observation apparatus. CONSTITUTION: An underground water level sensor(10) is serially connected with an electric conductivity sensor(12). A single sensor cable is commonly used in the underground water level sensor(10) and the electric conductivity sensor(12) when the underground water level sensor(10) is serially connected with the electric conductivity sensor(12). Namely, the electric conductivity sensor(12) is connected with a lower end portion of the single sensor cable and the underground water level sensor(10) is connected with a connector under the electric conductivity sensor(12). The underground water level sensor(10) has a diameter of 25mm. The length of the underground water level sensor(10) including the connector is 145mm. The underground water level sensor(10) has a measuring range of 0 to 100m and accuracy of ±4cm.

Description

Ground water level quality monitor {Ground water level quality monitor}

The present invention relates to an underground water level and an automatic water quality observer capable of automatically observing the water level and water quality of groundwater with high accuracy, and which can be supplied at low cost.

The most important measure of the three groundwater observers is groundwater level. This is because it provides various information in terms of utilization or analysis of measurement results. There are various sensors for measuring groundwater level change such as capacitive type, bubble type, and pressure type. Most water level sensors used in Korea are pressure sensors that are easy to install and use.

In FIG. 1, the capacitive water level meter is arranged in the air at the upper end and the lower part in the water according to the water depth, and the electric capacity of the water is much larger than the induction of water. It is proportional to the underwater length (h) of the double conductor (1, 2) submerged in. Therefore, after calibrating the characteristic between the capacitance and the underwater length (h), the capacitance is measured and converted into water depth.

The electrical induction and conductivity of water vary depending on the water's properties, ie its physical and chemical properties. Since the composition and temperature of water change frequently, errors occur even when the electrical resistance is precisely measured. In addition, since the change in the electrical resistance is very small, noise is easily introduced in the process of amplifying and processing the electric signal of the DC component, and the electronic circuit is complicated, so that it is difficult to use it in the real open air.

In FIG. 2, when the water pressure measuring tube 3 is installed according to the water depth, the bubble-type water gauge is filled with water in the pipe, and the position of the water surface is equal to the external water position H, ignoring the capillary phenomenon. The pressure at the bottom of the pipe is then

P = ρH

(P: hydraulic pressure, ρ: density of water, H: height from end of pipe to surface)

If the pressure gauge is installed on the upper end of the pressure measuring tube 3 and the compressed air is supplied at a pressure slightly larger than the water pressure, the water filled in the pressure measuring tube 3 is pushed out through the lower end of the tube and bubbles start to emerge. At this time, since the pressure of the hydraulic pressure measuring tube can be regarded as equal to the hydraulic pressure, the water level H can be calculated by P measured by the pressure gauge.

The advantage of this bubble level gauge is that it is not affected by the hydraulic pressure measurement even if the hydraulic pressure pipe is tilted or arbitrarily bent. As any kind of pipe, such as polyurethane tube, can be used as the pressure measuring tube, the installation cost of the hydraulic measuring tube is greatly reduced, and the repair of the hydraulic measuring tube is not necessary.

Bubble level gauges also need a small pneumatic or compressed air tank, such as nitrogen, to blow the air in the tube. Small air compressors can be operated with batteries when the depth of measurement is small (10-20m), but deep water level measurement of about 100m has the disadvantage of requiring AC power or a large capacity battery. .

Although the bubble level sensor was developed and used earlier than the pressure level sensor, the strain gauge has a disadvantage in that its characteristics change significantly according to the temperature change. Therefore, the bubble level gauge installed on the ground has a large error in temperature change in winter and summer. In the end, pressure gauges became preferred under the assumption that the groundwater temperature was almost constant.

In Fig. 3, the pressure level gauge has an advantage that the ease of setting and the setting error are small since the pressure sensor 4 has good precision and linear output.

As shown in the figure, the pressure sensor 4 is fixedly installed in the water by using the hydraulic pressure measurement principle, the power is supplied to the pressure sensor 4, and the cable is connected to the measuring instrument side by using a cable wire that transmits the sensor output signal. will be. The pressure applied to the pressure sensor 4 is the sum of the hydraulic pressure ρH and the atmospheric pressure Pa acting on the water surface.

P = ρH + Pa

H = (P-Pa) / ρ

(P: hydraulic pressure, Pa: atmospheric pressure)

Pressure level sensor has the advantage of easy installation and wider range of measurement than other level sensors. However, at least one time of the year should be characterized, which is difficult to maintain in that the pressure sensor installed in the water must be inspected from atmospheric pressure to the measuring range and then returned to its original position.

In addition, special cables with tubes inserted in the cable should be used to compensate for atmospheric pressure. This cable is expensive. Therefore, the initial installation cost is excessive. In addition, if the cable is damaged during installation or external impact, the cable may not be cut and the whole must be replaced.

In addition, the float type is a water level meter of a method of capturing the movement of the float operating in accordance with the change of the water surface, a method of changing the float movement into an electrical signal. In addition, the ultrasonic method is a method of converting the time interval from the transmitting side to receiving the echo reflected from the liquid surface to the depth of water by emitting ultrasonic waves on the liquid surface.

Table 1. Comparison table by level measurement method (1)

Type of sensor Usage Measuring range (m) Measurement principle Price (KRW million) Accuracy of the measurement Pressure Long-term observation 0-100 Measure the water pressure on the water surface and the reference surface with a pressure gauge 3 to 10 Difference occurrence ± 0.5% according to model Pumping test 0-100 7-10 Accurate ± 0.1% or less Bubble type Long-term observation 0-50 Blow the compressor to convert pressure measurement to water level 7-10 Relatively accurate ± 0.1% or less Tension Long-term observation 0 to 20 Convert mass change by buoyancy to water level 2 to 4 Relatively accurate ± 0.1% or less Sonic Long-term observation 0 to 20 Sound distance measurement from reference point to water surface 2 to 4 Relatively accurate ± 0.01% or less Float Long-term observation 0-10 Float on the surface to measure changes in the surface 0.8 Accurate ± 1%

Table 2. Comparison table by level measurement method (2)

Sensor type By use Disadvantages At the time of purchase Etc Pressure Long-term observation High accuracy, price varies with accuracy Correction function for pressure change Can operate with small battery Pumping test High price, accurate Bubble type Long-term observation Inability to measure rapid water level changes Bubble generation method according to installation place Need gas cylinder for bubble generation Tension Long-term observation Low measuring range Long life with small battery Sonic Long-term observation Low measuring range Small measuring range suitable for hydrologic measurement Float Long-term observation Small measuring depth 1 month use 1.5V battery

There are two types of sensors. All measuring sensors are integrated in one probe and one measuring sensor in one probe.

In the early years of groundwater observing equipment, it was necessary to have a measuring instrument for all items to be measured when observing groundwater at the site as a separate observer. In order to solve this inconvenience, it was necessary to record the measurement data in the field without any storage device by attaching several measuring sensors to one probe. It can be automatically saved and transferred to a computer for further analysis. Table 2 compares the advantages and disadvantages of the integral type and the separate type.

Table 2. Comparison table of integrated sensor and detachable sensor

division Advantages Disadvantages Integrated * Maintenance is economical * Individually replaceable in case of sensor failure * Installation is simple and easy because only one cable is required for sensor and data processing device Data can be obtained. * Low price. * Sensor lifting before teaching some sensors. * Measurement data are not available during replacement time. * The entire sensor is often replaced, resulting in excessive maintenance and repair costs. Detachable * More advanced type. * Use of single cable, easy maintenance. * Easy installation. * Replace only defective sensor. * Low maintenance cost. * Separate cables for each sensor type are required. * Installation is complicated and inconvenient because multiple cables are connected from the well to the data processing device.

In the above table, the integrated type is more advanced than the separate type, and when the sensor is lifted for failure or sensor replacement, the old sensor is inevitable, so it is impossible to measure during the lifting, data cannot be obtained, and data may be missing. It is a disadvantage.

Separate cable should be installed in several strands, so in the case of high-depth installation, the cables should be bundled together to prevent twisting. Therefore, even if it is a separate type, it is equally necessary to lift all the old sensors for the maintenance or maintenance of the sensor.

In this respect, the integrated type is more efficient in terms of management than the separate type, in which several sensors are installed in the observation well and several cables are installed, and it is possible to prevent the trouble of installing cables for each sensor type, and is convenient for maintenance. Therefore, it is judged that the integrated sensor is more suitable.

As a result of investigating the type of groundwater autonomous sensor, the one-piece type and the separate type have advantages and disadvantages, so they should be selected carefully considering the purpose of use, site conditions and water quality. For example, in case of using it as a long-term observation network, it is advantageous to consider an integrated type in consideration of the post management. In the pumping test and groundwater development, the groundwater level is of primary importance, so only the level should be measured accurately. In this case, a separate type that can measure only the water level is more advantageous to the user in the field than the all-in-one type.

The reason why the integrated type is preferred to the separate type is that the integrated type is cheaper in price than the separate type in the sensor appearance. The main reason for the price difference is the cable cost. Although the difference depends on the accuracy and accuracy of the sensor and the capability of the data processing device, the longer the cable length of the observer, the larger the cost difference if the cable for each sensor type is purchased separately.

In this respect, the one-piece type is much more advantageous than the separate type considering the price. When considering only maintenance aspects, the separate type is more economical. Long-term observation network, groundwater observation network The groundwater observer for seawater penetration survey is all integrated. However, there are more than a few dozen repairs and replacements of existing observers in existing networks. Given this frequency of maintenance, the integral type is not necessarily advantageous over the separate type. In view of the long-term use of the observation network, a separate type may be advantageous.

As such, the one-piece type and the separate type have advantages and disadvantages, and a need arises to develop a water gauge that can take advantage of both types.

The present invention provides an automatic groundwater level observer capable of improving the measurement accuracy of groundwater level and water quality, and at low cost.

In order to achieve the above object, the present invention provides an underground water level and water quality automatic observer that connects an electric conductivity sensor to a lower end of a single sensor cable and connects a water level sensor to a connector under the electric conductivity.

The conductivity sensor satisfies the temperature compensation circuit, a circuit board containing two items as one substrate, and a measurement range of 0 to 10,000 µS / cm and -5 to 50 ° C.

The water level sensor has a diameter of 25 mm, a length of 145 mm including a connector, a measurement range of 0 to 100 m, and an accuracy of ± 4 cm.

In addition, the sensor cable is a lightweight and high-strength cable, the groundwater automatic observation device is equipped with a noise canceling circuit, the pressure sensor is protected by a protective film, and completely waterproof with rubber rings and silicone resin to withstand water pressure of 10 atm, ANSI Observed by a data logger with an operating program written in C.

1 is a conceptual diagram of a capacitive water level meter

2 is a conceptual diagram of a bubble-type water gauge

3 is a conceptual diagram of a pressure gauge

4 is a block diagram of the groundwater level and water quality automatic observer according to the present invention

5 is a configuration diagram of the primary water level sensor

6 is a structural diagram of a pressure sensor used in the water level sensor

7 is a configuration diagram of the secondary water level sensor

8 is a circuit diagram of the same

9 is a current-voltage signal conversion circuit diagram for connecting to an ADC.

10 is a sensor signal processing flowchart

11 is a noise diagram of the water level sensor by the motor

12 is a noise removing circuit diagram

13 is a facial expression curve of the water level sensor

14 is a circuit diagram of an electrical conductivity sensor

15 is a facial expression curve of the conductivity sensor

16 is a power control diagram of a data logger

17 is a graph of power consumption change of the data logger

18 is a digital value graph for the sensor output signal (mA)

19 is a key layout diagram of a data logger

20 is a graph showing the water level change of the groundwater well measured by the groundwater automatic observer of the present invention

21 is a graph of the change in electrical conductivity

<Explanation of symbols for the main parts of the drawings>

10: water level sensor 12: electrical conductivity sensor

20: 1st level sensor 21,31: Pressure sensor

22,32: circuit board 23,33: protective film

30: 2nd water level sensor

A technical feature of the present invention provides an underground water quality automatic observer in which one or more cables are configured to be shared by two or more sensors.

That is, as shown in FIG. 4A, the water level sensor 10 and the electric conductivity sensor 12 are connected in series to form a type of integrated water meter configured to share a single cable 14. This mixed water gauge is suitable for long-term observation networks and seawater penetration.

4B illustrates a case in which only the conductivity sensor 12 is connected, and FIG. 4C illustrates only the water level sensor 10. These are detachable. When developing a water pump or groundwater well, only the water level sensor 10 is connected as shown in FIG. 5B, and only the electric conductivity sensor 12 is connected as shown in FIG. 5A when only electrical conductivity is measured.

The most common form is pressure. In fact, when used as a long-term observation network calibrated about once every six months, you can get a fairly accurate measurement. In long-term observation networks or seawater penetration networks, it is not necessary to install a sensor with a wide measuring range of less than 10m. However, in pumping or well development, the instantaneous water level change can be up to 100m, even within one minute. Therefore, it is most preferable to use a pressure type with a wide measurement range and a fast reaction rate.

The present invention is a pressure level sensor. The pressure level sensor is more suitable than any measurement method in view of convenience and ease, but it is expensive. Therefore, the present invention is to be converted to a low-cost type in consideration of the economical pressure level sensor.

The primary water level sensor 20 was manufactured in a separate type before being manufactured in a mixed type. As a kind of preliminary experimental step, we checked the necessary matters before manufacturing the mixed level sensor such as whether the connection part leaked by water pressure and the accuracy of sensor output. That is, in FIG. 5, the primary water level sensor 20 was designed and manufactured with a diameter of 48 mm and a length of 210 mm. A signal amplification circuit board 22 and a pressure sensor (21. Model: L-100, made in Germany) were used for the measurement range of 0 to 50 m.

In FIG. 6, a bridge circuit composed of a strain gauge is embedded inside the secondary water level sensor 20. Supply the input voltage DC 24V and output minute voltage signal by changing the resistance of strain gauge by water pressure. The output voltage signal was converted into a 4-20mA current signal and connected to the ADC in the data logger. The mixed water level sensor thus constructed was lowered to a depth of 50m in the groundwater well, and the output voltage was measured. The facial expression curve was prepared.

The primary water level sensor 20 can be installed in a hole without a submersible pump installed, but cannot be installed in a minimum diameter of 54 mm (N standard) of the observation hole. In the primary water level sensor 20, a 10-mm diameter, 5-wire wire was used for the sensor cable. If the first level sensor 20 with a cable weight of 3.8kg and a total length of 20m is 100m, the cable should be 110m, so the sensor cable weighs approximately 21kg. If the water level is 100m during the pumping test, the sensor cable will be stretched to 1.2kg and 19kg. Therefore, in order to prevent the sensor cable from growing, the sensor and the cable should be made small and light.

The first water level sensor 20 was completely waterproof using rubber rings and silicone resins. Therefore, the secondary water level sensor 30 was made as light as possible in the minimum diameter. The material used was stainless steel (316L). The diameter was 25 mm and the length was 145 mm including the connecting portion. The minimum diameter of the observation hole was 54mm.

When the first and second water level sensors 20 and 30 are installed, the pressure sensor may be destroyed by the foreign matter on the surface of the water immediately in contact with the water surface. The primary water level sensor 20 is subjected to water pressure to the side as shown in Figure 7 so as not to be damaged by foreign matters when installed. In addition, the protective film 23 for the pressure sensor is covered with the sensor so as to facilitate the cleaning of the sensor.

The circuit of the secondary water level sensor 30 was designed as shown in FIG. 8 by supplementing the circuit of the primary water level sensor 20. Since the diameter of the secondary water level sensor 30 is 25mm and the inner diameter is only 20mm, the sensor circuit board is made of 20 × 28mm, and the same pressure sensor (31.L-100, made in Germany) used in the primary water level sensor 20 is made. ) Was used. Signal output from four output terminals (sensor output +, sensor output-, sensor input +, sensor input-) of pressure sensor composed of bridge circuit was processed and processed to output 4 ~ 20mA to DC 12V. Therefore, only two lines are needed to connect to the water level sensor using a sensor cable. The 4-20 mA current signal output from the sensor was converted into a 1-5 V signal using a 250 kΩ resistor as shown in FIG.

The signal output from the pressure sensor 31 composed of the bridge circuit was processed into the necessary signal in the order of FIG. In the process of processing the output signal, the same signal is not output due to the error of the sensor and the component. Therefore, before creating the facial expression curve corresponding to each sensor, the sensor test should be performed so that 4-20mA is output in the measurement range 0-100m. Forced injection using compressed air to control sensor output signal. Thus, the expression level for each level sensor (20, 30) was prepared by obtaining the water level and the digital value by putting it in an actual well while adjusting the output signal in hardware.

Accuracy is a term used to indicate how close a measurement is from a meter to its true value. The accuracy of the instrument is the percentage error of the measurement as a percentage of the error defined by

Accuracy = (Measure-True) / True × 100

For example, if the accuracy of the water level sensor that can be measured up to 100m is ± 1% FS (full scale), the difference between the water level measured by the water level sensors 20 and 30 and the actual water level is within 1m of improvement.

Precision is a term used to mean how close to the average the measured value obtained repeatedly under the same conditions is defined as follows.

Accuracy = (measured value-measured value) / measured value × 100

For example, if the value of the 100m level measured five times with a water gauge is 104, 103, 105, 103, 105m, the average value is 104m, the maximum deviation is ± 1m. Therefore, the accuracy of this instrument is calculated to be ± 1%. The accuracy of the sensor can be improved by calibration but cannot exceed its precision.

As such, precision is an important specification of the sensor. In particular, the wells that are used as groundwater observation networks are mostly used in wells that have underwater pumps installed rather than dedicated wells for groundwater observation. Since the water level sensors 20 and 30 are operated by weak electric signals, they are sensitive to noise by the motor. When the water level sensors 20 and 30 are installed in the well and the motor is operated, the measurement data can be confirmed that the noise is affected as shown in FIG. 11.

At 47.58m, the variation of the measured value is 47.48 ~ 47.81m and the accuracy is 0.34%. Thus, a noise removing circuit as shown in FIG. 11 is added. As a result, the digital signal is 47.53 to 47.61m in terms of ± 1.5 level and water level, and the accuracy is improved to 0.1%.

The pressure level gauge according to the present invention converts an analog signal output according to the depth into a digital value and then prepares an expression curve. At this time, the relationship between the measured value and the measured value is mostly drawn in the form of a quadratic function curve. This quadratic function is used to convert the water level value.

Y = aX ² + bX + c

Here, Y value is depth and X value is digital value. If these values are exact quadratic curves, a perfect water gauge is possible, but usually not so, the closest curve must be found. In order to represent the value of Y as a depth, the constants a, b, and c of the selected proximity curve must be determined. Here, give a margin of error of ± 2-5% and calculate a constant value that fits the nearest curve. The constant value calculated in this way is referred to as a approximation value in the sensor manual, b as a scale value and c as an offset value.

These values vary from sensor to sensor. This is because the compact pressure sensor is so sensitive that the sensitivity is different. Therefore, three constants are found through repeated experiments for each sensor, and the sensitivity of pressure is different for each sensor, so the level measurement accuracy and measurement range (range within tolerance) vary slightly.

The expression curve of the relationship between the digital value measured using four water level sensors according to the present invention and the actual water level is shown in FIG. 13. As shown in this facial expression curve, since the relationship between the water level and the digital value is not a curve but a linear equation, the following linear relationship is obtained.

Y = aX + b

Where Y is the actual level value and X is the digital value measured by the data logger. A, b and correlation coefficient R of the water level sensors 20 and 30 are shown in Table 4.

Table 4. Constants and Correlation Coefficients for Water Level Sensors

Water level sensor a constant Correlation coefficient a b R One 0.0319 -24.11 One 2 0.032 -24.676 0.9999 3 0.0324 -24.82 One 4 0.0319 -24.181 One

When power is supplied from one electrode in water, the strength of the signal reaching the other electrode depends on the amount of electrolyte material. The conductivity sensor is for measuring this, and the conductivity is converted to the magnitude of resistance caused by electrolyte in water. Since electrical conductivity is greatly influenced by temperature, there is a temperature sensor inside the sensor. Unlike the temperature sensor, the electrical signal converted primarily from the conductivity sensor is very weak and is affected by the measurement environment or lifespan, and thus it is often necessary to calibrate.

The principle of measurement is that a constant voltage is applied to the two electrodes in the solution and a current flows. At this time, the magnitude of the current is proportional to the intensity of the ion. In other words, electrical conductivity and correlation are established. At this time, the resistance is measured and converted into electrical conductivity. The electrical resistance (R) is as shown below.

R (Ω) = ρL / A

Where p is the resistivity (Ωcm), L is the distance between two electrodes (cm), and A is the cross-sectional area. The electrical conductivity (L) is as shown below.

L = 1 / R = A / lK

The electrical conductivity is expressed as the inverse of the electrical resistance or mho, but currently uses the international unit S (simens). K (= 1 / ρ) is the non-conductivity (mho / cm). If the same measuring system is used, the cell size is constant, so the distance and cross-sectional area between the two electrodes can be ignored. Therefore, the measurement result is expressed as the conductivity value (μmhos / cm) of the sample by multiplying the conductivity value (mho) of the sample by the cell constant (cm ^-1 ). In international units, mS / m, dS / m, or μS / cm. Here, 1S = 1mhos and 1μS = 1μmhos.

The conductivity changes with water temperature, and the higher the water temperature, the easier the energization becomes and the higher the value. Therefore, it is not possible to compare the measured values with each other unless a certain reference temperature is set. The reference temperature is 25 ° C and on average 1 ° C, the electrical conductivity increases by about 2%. For example, assuming that the difference between the water temperature T at the site and 25 ° C is Δt (T-25) ° C, the correction equation can be expressed as follows.

K ₂₅ = K _t (1 + 0.02 * △ t)

The conductivity meter is equipped with its own temperature compensation circuit at 25 ℃, so there is no need for temperature compensation.

The electrical conductivity ranges from 0.5-5 μS / cm for distilled water, 5.0-30 μS / cm for precipitation, 3-2,000μS / cm for freshwater and groundwater, 45,000-55,000 μS / cm for seawater, and 100,000 for brine. μS / cm or more.

The conductivity sensor is 25mm in diameter and manufactured to 400mm including the connector, and the connectors are attached to both terminals of the conductivity sensor in consideration of the case of using with the water level sensors 20 and 30 and the case of using the conductivity alone. . 14 is an electrical conductivity circuit diagram. The circuit board is manufactured in 240mm x 15mm size so that it can be installed inside the sensor.

In addition, it is divided into two parts to facilitate the repair and replacement of the conductivity sensor. The upper part is equipped with electrodes only and completely waterproofed with silicone resin, and no separate electric circuit is installed. As a result, there is little chance of failure at the top. In the lower part, a conductive circuit board is mounted. External shock or electrical damage is mainly caused in the circuit part, so it is designed to replace the circuit board easily in case of a failure.

As is well known, the facial expression curve of the electric conductivity sensor was obtained from the relationship with the digital value outputted by putting the sensor in the electric conductivity value. As shown in FIG. 15, the facial expression curve of the electric conductivity was 0.9979, which was lower than that of the water level sensors 20 and 30, but it was judged to be satisfactory. Therefore, it may be sufficiently improved by modifying the measurement range or modifying the circuit in the future.

The sensor cable is a line connecting the probe installed with the sensor and the data processing device. The length of the cable required depends on the depth of installation of the probe. Probes may also vary from site to site, as they must be installed taking into account the depth and level of wells. Therefore, considering the extra length in the measurement range (0-100m), it was basically 110m.

The cable must be able to withstand the tension applied based on the probe's maximum depth of installation of 100 m, and the change in cable length within the calibration period (6 months) must satisfy the ± 2 cm error range of the groundwater level. . In addition, it must be resistant to shock, less shrinkage or expansion by temperature, and fully waterproof. In particular, it should be coated with Teflon or polyurethane resin, which has no reactivity with chemicals dissolved in groundwater.

In the primary water level sensor 20, a general commercial cable was used. The reactivity with the groundwater could not be confirmed because it was not used for a long time, but the weight at 110m is difficult to carry at 21kg, and there is no possibility of increasing the cable when used as a long-term observation network because there is no iron core inside.

The sensor cable was a cable with a high tensile force containing 6 strands and a wire. As a result of tension measurement, it was found to be possible up to 100kgf. The tension was sufficient given that the total weight of the sensor and cable weight was 7.5 kg. The cover of the sensor was made of polyurethane which is not reactive with chemicals dissolved in groundwater.

Data loggers with data storage in groundwater networks are essential. The storage capacity in the data logger should have sufficient memory in consideration of the intermittent transfer of data to the notebook. In particular, groundwater observation networks are installed on site, so power consumption becomes a very important factor. If the power consumption is large, not only high-capacity batteries need to be installed, but also need to be replaced frequently. Therefore, a data logger with sufficient memory and low power consumption is needed.

The functions of the data logger are data measurement, storage and transmission. These functions are handled by small CPUs that perform only simple functions. A general processor uses various connection elements that are measurement and control devices. This ensures that the data logger as well as the power consumption are not large. The ultra-low power and compact data loggers were built using the ADuc812, a single-chip processor with ROM, RAM, CPU, I / O, ADC, and timer. The ADuc812 has eight channels of 12-bit ADC, which is sufficient to use the groundwater auto observer. Built-in 2 wire serial I / O, RS232C communication method. Therefore, if you connect to RS232C port of notebook without having to write a separate communication program, CPU is automatically recognized and can communicate.

Based on the data logger manufactured by ADuc812 CPU, a second data logger consisting of CPU, S-RAM, power switch and terminal was manufactured. The size of the secondary data logger is 145 × 45mm, which is smaller than the general controller. Basic specifications of the secondary data logger are as follows.

-Power consumption: 50mA in operation, 0.005mA or less in sleep mode

-Secure flash memory for writing and writing user programs

-32K S-RAM to store and analyze continuously measured data

-8 channels of 12 bit ADC

-2 channels of communication port (serial port) (for modem, laptop connection)

Built-in RTC (Real Time Controller)

-2 × 16 LCD Board Control Function

-Control switch setting function with button switch

Power Supply: DC 12V

-Size: 45W × 125D × 15H (mm)

Groundwater autonomous system used as long-term observation network uses AC power, solar cell or external battery because power consumption is high by using data processing device and modem. If AC power is not available due to site conditions, solar cells should be installed, but external batteries are inevitable in areas where installation is difficult due to high price. If you use an external battery, the period of use is about 1 month, so it needs to be replaced frequently. do. If no external battery or solar cell is installed, the internal battery must be available for at least three months.

When the data logger was manufactured, a kind of power sleep mode was applied instead of the low power IC. As shown in FIG. 16, the external timer (RTC-72421) is used to operate the CPU during measurement and the CPU operates the relay to supply power to the sensor. After the measurement is completed, the CPU turns off the sensor and goes to sleep itself. As shown in FIG. 17, the data logger consumes about 50 mA of power when measured, but when it is not measured, the power supplied to the data logger is cut off to enter the sleep mode. In sleep mode, only the external timer clock is activated, reducing power consumption to 0.005mA. For example, a measurement interval of 1 minute and a measurement time of 5 seconds consume 50 mA for 5 seconds and 0.005 mA for 55 seconds. By applying the same method as shown in <Table 5>, 12V, 1.9Ah small battery can be used for a long time.

Table 5. Battery Life of Data Loggers

Measuring interval Average power consumption Available period 1 minute 4.17 mA 20 days 1 hours 0.07 mA 1,140 days Battery used: 12V, 1.9Ah

The groundwater level and water quality were measured, and the measurement results were displayed on LCD or a program for data transmission was written in ANSI C language. The operation program consists of initialization of groundwater automatic observer, sensor measurement, power saving mode, LCD display and notebook data transmission and reception.

Communicating with a laptop or modem allows the input of system control parameters or the reception of stored data. Control variable input command is shown in <Table 6>.

Table 6. Control Variable Commands and Usage

Control Variable Input Command Input method Command Description time time hh: mm: ss Reset and reset system clock date date yy / mm / dd Initializing and resetting the system date list list Download stored data mclr mclr Delete saved data intv intv mm Enter measurement time interval (minutes) auto auto c c = 1: enable data storage mode (enable) c = 0: disable maxc maxc ch aa Maximum measuring range of input terminal (ch: channel, mm: maximum value) minc minc ch ii Minimum measuring range of input terminal (ch: channel, mm: minimum value) maxe maxe ch aa Digital value at the maximum measurement range of the input terminal mine mine ch ii Digital value at minimum input range of input terminal vpar vpar ch Variable output corresponding to input terminal

The ADC resolution of groundwater autonomous detectors is 12-bit and can convert analog signals into digital signals from a minimum of "0" to a maximum of "4095". FIG. 18 shows the relationship between the digital values output from the observer and the forced increase from 0 mA to 20 mA external to channel 1. FIG. Theoretically, when 0mA is connected, the digital value should be "0", and at 20mA, 4095 should be output.

But at 1mA, the difference is 192, 20mA to 3,922. Therefore, even though the sensor is output exactly linearly, the difference may be due to the error of the component itself such as resistance. In the present invention, ignoring the error of the data logger itself, input the actual value and the digital value within the measurement range of the sensor to obtain the first linear equation (expression curve) was added to the program.

In addition, one of the four analog channels connected to the ADC of the groundwater automatic observer is a water level sensor, a channel 2 electric conductivity sensor, and a channel 3 temperature sensor. Since there is a case to use, since the expression of the sensor connected to the input terminal is different, a program must be written to input a unique value corresponding to the sensor. In this case, the linear linear equation is obtained programmatically by inputting the digital value of the measuring range of each sensor, ignoring the error of the data logger itself.

The actual input variables associated with the sensor are approximations, standard values, and offset values. This value should be determined after comparing the sensor with the actual level and the measured value from the observer under various conditions. The data logger's operating program is also required to calculate the error for each channel of the data so that it can be accurately measured no matter which channel the sensor with its unique parameters is connected to.

In the absence of a laptop, the keypad can be used in the field to input and control LCD parameters for the system. That is, it adds operation functions such as time setting through LCD, measurement time interval setting, sensor calibration and current data check.

As shown in FIG. 19, five keys, such as a power up, reset, up, down, and enter keys, are installed in the data logger. The description of these keys is shown in <Table 7>.

Table 7. Key functions for the data logger

division Key Description Power up Transition from sleep mode to active state Up, Down Display input variables and reset variable values sequentially Enter Check input variable and variable value Reset System initialization

The groundwater automatic observation device of the present invention was installed in the groundwater well that is used for the apartment complex living water and measured for 10 days. This groundwater well was open to local residents for a limited time only in the morning and evening.

20 and 21, it was possible to check the ground water use time and the water level change, and the natural water level was measured 10 days after the start time and 10 days with a manual water level meter compared the accuracy of the sensor was about 7cm error. Since there was an error in the cable length at the time of installation, the error of the sensor itself is considered to be small. As a result of measuring the conductivity with measuring equipment, it was measured within ± 10μS / cm, and the conductivity sensor of the observer was also measured relatively accurately.

As described above, the ground water level automatic observation device of the present invention can measure three items in one probe in an integrated manner when used as an observation network, and one item in a separate manner when used for pumping test and development. It is convenient because we can measure bay.

In addition, the groundwater level and the electrical conductivity can be measured quickly and accurately with high accuracy, and it is also possible to provide an underground water level and an automatic water quality observer that can be supplied at low cost.

Claims (5)

Groundwater level and water quality automatic observer, characterized in that the conductivity sensor is connected to the bottom of the single sensor cable, and the water level sensor is connected to the connector under the conductivity. The groundwater sensor according to claim 1, wherein the conductivity sensor satisfies a temperature compensation circuit, a circuit board containing two items as one substrate, and a measurement range of 0 to 10,000 µS / cm and -5 to 50 ° C. Water level and quality automatic observer. The groundwater level and water quality automatic observer according to claim 1, wherein the water level sensor has a diameter of 25 mm, a length of 145 mm including a connector, a measuring range of 0 to 100 m, and an accuracy of ± 4 cm. The groundwater level and water quality automatic observer according to claim 1, wherein the sensor cable is made of a light weight and high tensile cable. According to claim 1 to 4, wherein the ground water level and water quality automatic observation device is equipped with a noise removing circuit, the pressure sensor is protected by a protective film, and is completely waterproofed with a rubber ring and silicone resin to withstand water pressure of 10 atm. , Automatic groundwater level and water quality observer, characterized in that the observation by the data logger having an operating program written in ANSI C language.