JP2006126030A - Liquid level sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level sensor capable of detecting a liquid level continuously to enhance precision. <P>SOLUTION: This level sensor is layered with a heater part 16 for elevating a temperature of a thermistor 15, an insulation layer 17, an electrode 18 opposed to the thermistor 15, and the thermistor 15 in this order, on an insulating substrate 14. The thermistor 15 has a gas temperature detecting thermistor 19 contacting with only gas, a liquid temperature detecting thermistor 20 contacting with only a liquid, and a liquid level detecting thermistor 21 contacting with both the gas and the liquid around a liquid face as a boundary, and is formed by coupling the liquid temperature detecting thermistor 20 with the gas temperature detecting thermistor 19 in an end part of the liquid level detecting thermistor 21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid level sensor for detecting a liquid level.

  A conventional liquid level sensor will be described with reference to the drawings.

  FIG. 9 is a front view of a conventional liquid level sensor, and FIG. 10 is an enlarged front view in which a portion A of the liquid level sensor in use is enlarged.

  In FIG. 9, reference numeral 1 denotes an insulating substrate, and this insulating substrate 1 is erected substantially perpendicular to the longitudinal direction, and a power electrode 2, an intermediate electrode 3, and a GND electrode are positioned on one side of the insulating substrate 1. 4 are provided in parallel. A plurality of thermistors 6 are provided on one side surface of the insulating substrate 1 from the upper side to the lower side so that one end of the GND electrode 4 is electrically connected via the first circuit pattern 5. The thermistor 6 has a characteristic that its resistance value rapidly decreases as the temperature rises. In addition, a plurality of fixed resistors 7 are provided on one side surface of the insulating substrate 1 at the same height as the thermistor 6, and one end of each of the fixed resistors 7 is connected to the power source via the second circuit pattern 8. The electrode 2 is electrically connected. Further, a plurality of third circuit patterns 9 are provided on one side surface of the insulating substrate 1, and the other end of the thermistor 6 and the other end of the fixed resistor 7 are electrically connected by the third circuit pattern 9. is doing.

  The liquid level sensor is used, for example, by standing substantially vertically inside a container storing liquid, or standing substantially vertically outside a container storing liquid such as an infusion bag. When standing, it may be bonded with an adhesive or embedded in the container itself.

  A DC voltage is applied between the power supply electrode 2 and the GND electrode 4. In this case, the thermistor 6 located above the liquid level generates heat when energized, and the thermistor 6 located below the liquid level is cooled by the liquid. Since the thermistor 6 has a characteristic that the resistance value rapidly decreases as the temperature rises, the resistance value of the thermistor 6 located above the liquid level is sufficiently higher than the resistance value of the thermistor 6 located below the liquid level. Small value. That is, the current flowing through the thermistor 6 positioned above the liquid level is sufficiently larger than the current flowing through the thermistor 6 positioned below the liquid level.

  Therefore, when an ammeter is connected in series to the power supply electrode 2 and the GND electrode 4, the current flowing between the power supply electrode 2 and the GND electrode 4 increases according to the number of thermistors 6 located on the liquid surface. Therefore, it is possible to know the height of the liquid level.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP 62-102120 A

  In the above configuration, since the plurality of thermistors 6 are provided sequentially from the upper side to the lower side, the liquid level of the liquid 10 is located between the thermistors 6 adjacent to each other as shown in FIG. The change of can no longer be detected. That is, there is a problem that the output signal cannot be continuously changed according to the change in the liquid level, and the liquid level cannot be detected with high accuracy.

  The present invention solves the above-described problems, and an object of the present invention is to provide a liquid level sensor that continuously detects the liquid level and improves accuracy.

  In order to achieve the above object, the present invention includes a substrate, a thermistor disposed on the substrate, and an electrode disposed on the substrate so as to face the thermistor, and the thermistor is for detecting a gas temperature contacting only a gas. The thermistor for detecting the liquid temperature in contact with only the liquid, and the thermistor for detecting the liquid level in contact with both the gas and the liquid with the liquid surface as a boundary, and the thermistor for detecting the liquid level. In this configuration, the thermistor for detecting the liquid temperature and the thermistor for detecting the gas temperature are coupled to the end portion, and a heater unit for raising the temperature of the thermistor is provided.

  With the above configuration, since the liquid level sensor continuously detects the liquid level, it can continuously detect the liquid level with high accuracy according to the change in the liquid level. Moreover, since the heater part for heating up a thermistor is provided, the sensitivity of each thermistor can be improved and the precision as a liquid level sensor can be improved.

  Hereinafter, the invention described in all claims of the present invention will be described using embodiments with reference to the drawings.

  1 is a block diagram of a liquid level detection system according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of a liquid level sensor used in the liquid level detection system, and FIG. 3 is a partially transparent plan view of the liquid level sensor. It is.

  1 to 3, a liquid level detection system according to an embodiment of the present invention includes a liquid level sensor that detects a liquid level. The liquid level sensor continuously detects and detects the liquid level. A transmission / reception system that transmits the liquid level as liquid level information from the liquid level sensor and receives the liquid level information from the liquid level sensor is provided. The transmission / reception system transmits the liquid level information detected by the liquid level sensor to the display device 11 by wireless or wired to display it as visual information, or transmits it to the acoustic device to generate sound as sound information. Is. When wireless is used, the wireless transmission unit 12 and the wireless reception unit 13 are used in combination, and the liquid level information is transmitted through the wireless transmission unit 12, received through the wireless reception unit 13, and connected to the wireless reception unit 13. It is displayed on the display device 11 and the acoustic device, and sounds are generated.

  The liquid level sensor used in this liquid level detection system includes an insulating substrate 14, a heater unit 16 for raising the temperature of the thermistor 15, an insulating layer 17, an electrode 18 electrically connected to the thermistor 15, and the thermistor 15 in this order. Laminated.

  Here, consider a case where a liquid level sensor is attached to, for example, an infusion bag (not shown) to detect an infusion bag (not shown) liquid level.

  This thermistor 15 includes a gas temperature detection thermistor 19 that contacts only gas via the medium of the drip bag (not shown) and a liquid temperature detection that contacts only liquid via the medium of the drip bag (not shown). And a liquid level detection thermistor 21 that contacts both the gas and the liquid at the boundary of the liquid level, and is connected to the liquid temperature detection thermistor 20 at one end of the end of the liquid level detection thermistor 21. The other end is connected to the thermistor 19 for detecting the gas temperature.

  The liquid level sensor includes a calculation unit 22 that calculates a resistance value or a resistance value change rate of each thermistor 15 (a change rate at which the resistance value changes from a reference temperature), and a resistance value or a resistance value change rate of each thermistor 15. Is connected to a processing circuit 23 having a calculation unit 22 for calculating the liquid level. These processing circuits 23 can be constituted by a microcomputer.

  Further, the processing circuit 23 is provided with a constant current source 24 as power supply means to each thermistor 15 and a heater control section 25 as control means for the heater section 16. The output signal composed of the signal is converted into the output signal composed of the analog signal by the three DACs 26. Further, the gas temperature detecting thermistor 19, the liquid temperature detecting thermistor 20, and the liquid level detecting thermistor 21 are each electrically connected in series by an output signal composed of a digital signal of the DAC 26 in the processing circuit 23. The current values of the two constant current sources 24 are set to predetermined values.

  The processing circuit 23 is provided with three amplifiers 27, which amplify output signals from the gas temperature detecting thermistor 19, the liquid temperature detecting thermistor 20, and the liquid level detecting thermistor 21. The three amplifiers 27 are each provided with an ADC 28, and the ADC 28 converts the output signal of the amplifier 27 into an output signal composed of a digital signal.

  The amount of heat generated by the heater section 16 is controlled by the difference or ratio between the resistance value of the gas temperature detection thermistor 19 and the resistance value of the liquid temperature detection thermistor 20, or the resistance value change rate difference or ratio. is doing.

  Here, the detection of the liquid level by the liquid level sensor will be described.

  The liquid level is for detecting the liquid level based on the difference in resistance value between the thermistor 19 for gas temperature detection and the thermistor 20 for liquid temperature detection or the difference in the resistance value change rate (change rate at which the resistance value changes from the reference temperature). The resistance level or the resistance value change rate of the thermistor 21 is compared to detect the liquid level continuously.

  This is because, if the resistance value or the resistance value change rate of the gas temperature detection thermistor 19 and the liquid temperature detection thermistor 20 are known, the heat dissipation constants of the gas and the liquid are different. The detection principle is that the position of the liquid level in the liquid level detection thermistor 21 is uniquely determined by the value or the resistance value change rate.

  Specific detection principles include the following, for example.

  4 is a perspective view corresponding to the thermistor 19 for detecting the gas temperature, FIG. 5 is a perspective view corresponding to the thermistor 20 for detecting the liquid temperature, and FIG. 6 is a perspective view corresponding to the thermistor 21 for detecting the liquid level.

4 to 6, the resistivity at the reference temperature is ρ ₀ , the resistivity of the gas temperature detecting thermistor 19 at the time of temperature rise is ρ _A, and the resistivity of the liquid temperature detecting thermistor 20 is ρ _B. .

When the length of the gas temperature detection thermistor 19 is L _A , the width is W _A , and the thickness is t _A , the resistance value R _{A0 at the} reference temperature and the resistance value R _A when the temperature rises are as follows. .

R _A0 = ρ ₀ W _A / L _A t _A (Expression 1)
R _A = ρ _A W _A / L _A t _A (Formula 2)
Further, the length of the liquid temperature detecting thermistor and L _B, and the width W _B, when the thickness and t _B, and the resistance value R _B0 at the reference temperature, the resistance value R _B at temperature rise as follows is there.

R _B0 = ρ ₀ W _B / L _B t _B (Formula 3)
R _B = ρ _B W _B / L _B t _B (Formula 4)
The length of the thermistor for detecting the liquid level is L _X , the width is W _X , the thickness is t _X , the length on the gas side is (L _X -X), and the length on the liquid side is bordered on the liquid level. When X is X, the resistance value R _X at the time of temperature rise is as follows.

R _X = (ρ _A ρ _B W _X / t _X ) / {ρ _A X + ρ _B (L _X −X)}
At this time, X / L _X is as follows.

X / L _X = {ρ _A ρ _B W _X / (t _X L _X ) −R _X ρ _B } / R _X
Here, since R _XA = ρ _A W _X / L _X t _X , substituting this, it is as follows.

X / L _X = (1-R _XA / R _X ) / (1-ρ _A / ρ _B ) (Formula 5)
Further, from the above (Formula 1) and (Formula 2),
ρ _A = ρ ₀ (R _A / R _A0 ) (Expression 6)
Similarly, from (Equation 3) and (Equation 4) above,
ρ _B = ρ ₀ (R _B / R _B0 ) (Expression 7)
That is, ρ _B / ρ _A = (R _B / R _B0 ) / (R _A / R _A0 ) (Equation 8)
Further, in R _XA / R _X = (R _XA / R _X0 ) / (R _X / R _X0 ), R _XA / R _X0 is as follows.

R _XA / R _X0 = (ρ _A W _X / L _X t _X ) / (ρ ₀ W _X / L _X t _X )
That is, R _XA / R _X0 = ρ _A / ρ ₀ = R _A / R _A0
Therefore, (Equation 5) can be modified as follows.

X / L _X = {1- (R _A / R _A0 ) / (R _X / R _X0 )} / {1- (R _A / R _A0 ) / (R _B / R _B0 )}
Therefore, if the rate of change from each resistance value R _X0 , R _A0, and R _B0 at ρ ₀ is known, X / L _X can be obtained.

  Examples of means for obtaining the rate of change of the resistance value include the following.

  The resistance value change rate of each thermistor 15 is calculated based on the difference in potential at the connection between each thermistor 15 and the constant current source 24 before and after the energization of the heater unit 16, and the liquid level is calculated. .

In FIG. _{7, V X = A {(} V cc -iR) -V S} + V S
That, R = {(1-A ) V S + AV cc -V X} / iA
As for R, V _R and V _X , _assuming that the initial states are R ₀ , V _R0 and V _X0 , R ₀ , V _R0 and V _X0 are as follows.

V _X0 = A {(V _cc −iR ₀ ) −V _S } + V _S
R ₀ = {(1-A) V _S + AV _cc −V _X0 } / iA (Equation 9)
When a state in which R is changed to R ₁ and V _R1 and V _X1, relations of R ₁ and V _R1 and V _X1 is as follows.

R ₁ = {(1-A) V _S + AV _cc −V _X1 } / iA (Equation 10)
From (Formula 1) and (Formula 2), R ₁ / R ₀ is as follows.

_{R 1 / R 0 = {(} 1-A) V S + AV cc -V X1} / {(1-A) V S + AV cc -V X0} ···
(Formula 11)
That is, even if the constant current value i is not known, if V _X0 is known, the rate of change of R can be obtained.

  FIG. 7 is an equivalent circuit diagram similar to the portion B in FIG. 1. If the above detection principle is applied to the present invention, the resistance value change rate of each thermistor 15 can be obtained.

FIG. 8A shows the temperature and resistance characteristics of R _A , R _B , and R _X , and FIG. 8B shows the temperature and resistance value change rate of R _A , R _B , and R _X. However, if R _A , R _B , and R _X are formed of the same thermistor material, the resistance value change rate due to temperature change shows the same characteristics as shown by the dotted line. Actually, as indicated by the solid line due to manufacturing variations, R _A , R _B , and R _X may produce different temperature characteristics. As a result, an error occurs in the calculation result of the liquid level. Therefore, the calculation may be performed by setting a correction value for correcting the sensitivity variation with respect to the temperature.

  For example, the following is a specific correction principle.

_A correction coefficient is introduced to match the sensitivity of R _A and R _B to temperature with R _X.

First, the initial resistance values of R _A , R _B , and R _X are R _A0 , R _B0 , and R _X0, with the temperature before energizing the heater unit 16 being the reference temperature T0.

Next, the resistance values of R _A , R _B , and R _X at the time when the temperature rises to an arbitrary temperature T1 after energization of the heater section 16 are R _A1 , R _B1 , and R _X1 . At this time, if the coefficient for correcting the sensitivity to the temperature of R _A to the sensitivity to the temperature of R _X is K _A , it is expressed as K _A (R _A1 −R _A0 ) / R _A0 = (R _X1 −R _X0 ) / R _X0. Can do. Therefore, K _A = (R _X1 / R _X0 -1) / (R _A1 -R _A0 -1). Similarly the K _B = the sensitivity to temperature coefficient for correcting the temperature sensitivity of R _X and _{K B (R X1 / R X0} -1) / (R B1 / R B0 -1) of R _B. In order to reflect this correction coefficient on the calculation result of the resistance value change rate, assuming that the correction coefficient is K, R ₁ / R ₀ = K [{(1-A) V _S + AV _cc −V _{X1} / {(1-A} ) V S + AV cc -V X0} -1] +1 ··· ( formula 12)
May be used. By performing this correction, the sensitivity variation of each thermistor 15 can be reduced, so that the liquid level can be detected with high accuracy.

Further, when the resistance value of each thermistor 15 varies greatly due to manufacturing variations, the value obtained by multiplying the constant current i by the constant current source and the thermistor resistance R exceeds the power supply voltage _Vcc (iR> _Vcc ). Therefore, the resistance value or the resistance value change rate cannot be detected. In order to avoid such a state, a function of adjusting the current value of the constant current source from the microcomputer via the DAC 26 so that the potential of the connection portion of each heater 15 and the constant current source 26 in the initial state becomes a predetermined potential. It may be provided.

  According to the above configuration, since the liquid level sensor continuously detects the liquid level, it can detect the liquid level continuously and accurately according to the change in the liquid level.

  In addition, since a transmission / reception system for transmitting and receiving the detected liquid level as liquid level information from the liquid level sensor is provided, the liquid level information can be detected at a location away from the liquid level sensor.

  In particular, the liquid level sensor is based on a difference in resistance value between the gas temperature detection thermistor 19 and the liquid temperature detection thermistor 20 or a difference in resistance value change rate, and the resistance value or resistance value change of the liquid level detection thermistor 21. Since the rates are compared, the liquid level can be detected continuously.

  At this time, since the heater section 16 for raising the temperature of the thermistor 15 is provided, the sensitivity of each thermistor 15 can be improved and the accuracy as a liquid level sensor can be improved.

  The amount of heat generated by the heater 16 is controlled by the difference or ratio between the resistance value of the gas temperature detection thermistor 19 and the resistance value of the liquid temperature detection thermistor 20, or controlled by the difference or ratio of the resistance value change rate. Since the heater control unit 25 is provided, the accuracy can be further improved.

  Further, a processing circuit 23 having a calculation unit 22 for calculating the resistance value or resistance value change rate of each thermistor 15 and a calculation unit 22 for calculating the liquid level from the resistance value or resistance value change rate of each thermistor 15 is connected. Since the constant current source 24 is provided in the processing circuit 23 as power supply means to each thermistor 15, the calculation can be performed relatively easily.

  The liquid level sensor has a liquid temperature detection thermistor 20 and a gas temperature detection thermistor 19 connected to the end of the liquid level detection thermistor 21 and a heater unit 16 for raising the temperature of the thermistor 15 to provide an insulating property. Since the heater part 16, the insulating layer 17, the electrode 18 electrically connected to the thermistor 15, and the thermistor 15 are laminated on the substrate 14 in this order, they can be easily formed.

  The liquid level change rate is continuously detected based on the liquid level information, and the liquid level change rate information of the detected liquid level change rate is transmitted from the liquid level sensor as the liquid level information. A transmission / reception system for receiving the liquid level information may be provided.

  In this case, the change speed of the liquid level can be confirmed.

  Also, based on the liquid level information, when the liquid level falls or rises below a predetermined value, a system for warning is provided as warning information, or the liquid level change rate falls below the predetermined change rate based on the liquid level change rate information. A system that warns as warning information when it rises may be provided.

  In particular, the warning system as described above is effective when these liquid level detection systems are used for medical purposes. For example, if a liquid level sensor is installed in a medical infusion bag and a warning is given when the amount of liquid level or the rate of change of the liquid level falls or rises below a predetermined value, the drug is injected from the infusion bag. Medical reliability can be improved for patients who are treated.

  In this warning system, even if there is no medical staff near the patient, the warning information is transmitted to the medical staff, and the medical staff can receive the warning information by a terminal or the like.

  As described above, the present invention can be used for various purposes as a liquid level sensor for detecting the liquid level.

The block diagram of the liquid level detection system in one embodiment of the present invention Disassembled perspective view of a liquid level sensor used in the same liquid level detection system Partial perspective plan view of the same level sensor Perspective view corresponding to thermistor for gas temperature detection Perspective view corresponding to thermistor for detecting liquid temperature Perspective view equivalent to a thermistor for liquid level detection Equivalent circuit diagram similar to part B in FIG. Waveform diagram showing the rate of change and ratio of resistance value for each thermistor temperature Front view of conventional liquid level sensor The enlarged front view which expanded the A section of the same level sensor at the time of use

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Display apparatus 12 Wireless transmission part 13 Wireless reception part 14 Board | substrate 15 Thermistor 16 Heater part 17 Insulating layer 18 Electrode 19 Thermistor for gas temperature detection 20 Thermistor for liquid temperature detection 21 Thermistor for liquid level detection 22 Calculation part 23 Processing circuit 24 Constant current Source 25 Heater controller

Claims (11)

A substrate, a thermistor disposed on the substrate, and an electrode provided on the substrate and electrically connected to the thermistor, wherein the thermistor is in contact with only a gas through a heat conducting medium. The thermistor of the above, the thermistor for liquid temperature detection that contacts only the liquid through a medium that conducts heat, and the liquid level detection that contacts both the gas and the liquid via a medium that conducts heat across the liquid surface And a thermistor for detecting the liquid temperature and the thermistor for detecting the gas temperature are coupled to the end of the thermistor for detecting the liquid level, and a heater part for raising the temperature of the thermistor to the substrate. Liquid level sensor provided. 2. The liquid level sensor according to claim 1, further comprising a transmission means for transmitting the liquid level information detected by the thermistor. The liquid level sensor according to claim 1, further comprising: a transmitting means for detecting the liquid level change rate based on the liquid level information detected by the thermistor and transmitting the detected liquid level change rate as the liquid level change rate information. The liquid level sensor according to claim 1, further comprising a transmission means for transmitting warning information when the liquid level falls or rises below a predetermined value based on the liquid level information detected by the thermistor. The liquid level change rate is detected based on the liquid level information detected by the thermistor, and the detected liquid level change rate is used as the liquid level change rate information. Based on the liquid level change rate information, the liquid level is determined from a predetermined change rate. The liquid level sensor according to claim 1, wherein warning information is transmitted when the pressure drops or rises. The liquid level sensor has a liquid level boundary between a thermistor for detecting a gas temperature that contacts only the gas via a medium that conducts heat, and a thermistor for detecting a liquid temperature that contacts only the liquid via a medium that conducts heat. A thermistor for detecting a liquid level that is in contact with both a gas and a liquid via a medium that conducts heat, and a difference in resistance value between the thermistor for detecting a gas temperature and the thermistor for detecting a liquid temperature, or a resistance. The liquid level sensor according to claim 1, wherein the liquid level is detected by comparing a resistance value or a resistance value change rate of the thermistor for liquid level detection based on a difference in value change rate. A heater unit for raising the temperature of the thermistor is provided, and the amount of heat generated by the heater unit is controlled by the difference or ratio between the resistance value of the thermistor for gas temperature detection and the resistance value of the thermistor for liquid temperature detection. Or the liquid level sensor of Claim 6 which provided the heater control part controlled by the difference or ratio of resistance value change rate. The liquid level sensor is provided with a processing circuit having a calculation unit that calculates a resistance value or a resistance value change rate of the thermistor and a calculation unit that calculates a liquid level from the resistance value or the resistance value change rate of the thermistor, The liquid level sensor according to claim 6, wherein a constant current source is provided in the processing circuit as power supply means to the thermistor. A heater part for raising the temperature of the thermistor is provided, and the resistance value change rate of the thermistor is based on the difference in potential of the connection part between the thermistor and the constant current source before and after energization of the heater part. The liquid level sensor according to claim 8, further comprising an arithmetic unit that calculates the liquid level. A heater unit for raising the temperature of the thermistor is provided, and the thermistor is based on the resistance value of the thermistor and the potential of the connecting part between the thermistor and the constant current source before and after energization of the heater unit. The liquid level sensor according to claim 8, further comprising a calculation unit that sets a correction value for correcting the sensitivity variation with respect to the temperature. A heater unit for raising the temperature of the thermistor is provided, and before the energization of the heater unit, the resistance value of the thermistor and the potential of the connection part of the thermistor and the constant current source become predetermined values. The current value of the constant current source is adjusted as described above, and the resistance value of the thermistor, the potential of the connection portion between the thermistor and the constant current source, and the heater section after the energization to the heater section. The liquid level sensor according to claim 8, further comprising a calculation unit that sets a correction value for correcting a sensitivity variation with respect to the temperature of the thermistor based on the predetermined value before energization.

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