JP4093099B2 - Liquid leak detection device - Google Patents

Description

[0001]
[Field of the Invention]
The present invention relates to a liquid leak detection device for detecting a liquid leak, which is used in analytical equipment such as a liquid chromatograph and industrial equipment.
[0002]
[Prior art]
As a liquid leakage detection method, there are a method for detecting electrical conductivity, a method for detecting a change in refractive index, and a method for detecting a change in the amount of heat dissipation (thermal resistance). The method of detecting electrical conductivity has the advantage that the device is simple and has high sensitivity, but liquids with low electrical conductivity cannot be detected. Sensitivity decreases due to contamination and corrosion of the electrode for measuring electrical conductivity. There are also disadvantages. In the method of detecting the refractive index, there is no restriction on the detectable liquid, but there is a disadvantage that the apparatus becomes complicated. The method for detecting the change in the amount of heat dissipation has no limitation on the detectable liquid and the apparatus is relatively simple, but has the disadvantage that the sensor output changes at the ambient temperature.
[0003]
FIG. 4 shows the basic principle of the heat dissipation amount detection type liquid leakage detection device. The temperature sensor 41 such as a thermistor is given a weak amount of heat and is kept at a higher temperature than the ambient temperature. Although the output voltage of the temperature sensor 41 varies depending on the temperature, the reference voltage obtained by the zero point storage mechanism 45 is compared with the comparator 43. If the amount of heat given to the temperature sensor 41 is Q (W), the thermal resistance to the ambient when the sensor is air is Ra (° C / W), and the ambient temperature is T0 (° C), the temperature of the temperature sensor 41 is the amount of heat. A certain equilibrium temperature is reached with thermal resistance. If the equilibrium temperature is Ta (° C) when the ambient is air, the temperature of the temperature sensor is expressed by equation (1).
Ta = T0 + Q · Ra (1)
This temperature Ta is stored in the zero point storage mechanism 45 as a reference value storage value. Here, when the surroundings of the temperature sensor 41 are in contact with the liquid, the liquid generally has a smaller thermal resistance than the air, so that the thermal resistance with respect to the surroundings decreases. When the thermal resistance in the wetted state changes to Rb (° C./W), the temperature of the temperature sensor 41 at this time changes to T1 in the equation (2).
T1 = T0 + Q · Rb (2)
Therefore, a temperature difference of ΔT in the equation (3) occurs when the surroundings of the temperature sensor 41 are air.
ΔT = T1-Ta = Q (Rb-Ra) (3)
The temperature sensor 41 can be used as a liquid leak detector by comparing Ta and T1 stored in the zero point storage mechanism 45 using the comparator 43 and detecting this temperature difference ΔT. That is, when the sensor output when the surroundings of the temperature sensor 41 is air is stored as the reference value storage value, the value obtained by subtracting the reference value from the current sensor output value is monitored, and the liquid is touched due to liquid leakage or the like If the value changes by a certain amount, it is considered that there is a liquid leak. Here, the temperature difference is detected, but the same operation is performed even if other measured values correlated with temperature, such as resistance of the thermistor, are detected.
[0004]
Although prior art literature information related to the thermal radiation amount detection type liquid leak detection device was investigated, it was not found.
[0005]
[Problems to be solved by the invention]
In the heat dissipation amount detection type liquid leakage detection device, in the method as described above, when the temperature sensor 41 is surrounded by air, the reference value is measured and stored, and used as a comparison reference value when the periphery becomes liquid. However, this presupposes that the ambient temperature T0 at the time of storing the reference value and at the time of measurement does not change. Actually, the ambient temperature changes, and recalculating equation (3) in consideration of this, when the ambient temperature at the time of storing the reference value is T0a and the ambient temperature at the time of measurement is T0I, the temperature sensor ambient is liquid. The temperature difference ΔT in the temperature sensor 41 when the surroundings are air is expressed by equation (4).
ΔT = (T0I + Q · Rb) − (T0a + Q · Ra) = (T0I−T0a) + Q (Rb−Ra) (4)
That is, not only when the liquid is detected, but also when the ambient temperature changes, the measured temperature of the temperature sensor 41 changes. When such a sensor is used as a liquid leakage sensor, when there is a temperature change, a malfunction occurs in which the liquid leakage is reported even though there is no actual liquid leakage, or the liquid leakage cannot be detected.
[0006]
The following methods can be considered as means for solving such problems. First, the amount of heat given to the temperature sensor is increased so that the temperature change (T0I-T0a) around the temperature sensor can be ignored. This method is easy to implement, but has the disadvantage that it cannot be used for flammable liquids because the temperature of the temperature sensor portion becomes high. Next, there is a method of correcting the temperature change by measuring the ambient temperature of the temperature sensor. In this method, the influence of the temperature change around the temperature sensor can be corrected with high accuracy without increasing the temperature of the temperature sensor, but another temperature sensor for measuring the temperature change around the temperature sensor is required. .
[0007]
In a device such as a liquid chromatograph using an organic solvent, the sensor temperature cannot be increased so much, and a method of absorbing a temperature change by temperature correction is effective. However, equation (4) assumes that the amount of heat Q does not change when the reference value is stored and when measured, but in general, the amount of heat changes as the ambient temperature changes. When this is taken into account and the equation (4) is corrected, it is expressed as the following equation (5).
ΔT = (T0I + Qb · Rb) − (T0a + Qa · Ra) = (T0I−T0a) + Qb · Rb−Qa · Ra (5)
From this, it can be seen that correction is difficult simply by measuring the temperature around the temperature sensor.
[0008]
The present invention has been made to solve the above problem, and an object of the present invention is to provide a liquid leakage sensor that operates normally even if the ambient temperature of the sensor changes.
[0009]
[Means for Solving the Problems]
In order to solve the above problem, the liquid leakage sensor of the present invention is a liquid leakage sensor in which the amount of heat dissipated from a temperature sensor heated or self-heated to a temperature higher than the ambient temperature changes depending on the presence or absence of liquid, and the change is measured by measuring this change. In a liquid leak detection device for detecting a leak, a temperature sensor and means for measuring an ambient temperature of the temperature sensor, a means for supplying a constant amount of heat to the temperature sensor, and a temperature and temperature sensor measured by the temperature sensor The means for measuring the ambient temperature has a means for measuring the difference from the temperature measured. Examples of the temperature sensor include a thermistor, a thermocouple, and a platinum resistor. As a means for supplying a constant amount of heat to the temperature sensor, for example, a power setting unit for setting the amount of heat to be supplied, a power monitor for measuring the amount of heat to be supplied, and a difference between a set value in the power setting unit and a measured value from the power monitor. There are combinations with power controllers that operate to eliminate.
[0010]
Equation (4) can be transformed and expressed as (4 ′).
Q (Rb−Ra) = ΔT− (T0I−T0a) (4 ′)
By subtracting the temperature T0a of the temperature sensor at the time of storing the reference value stored at the time of calibration from the temperature T0I of the current temperature sensor, ΔT of the equation (4 ′) is obtained. Similarly, the current temperature of the ambient temperature of the temperature sensor From (4 '), (T0I-T0a) is obtained by subtracting the reference value of the ambient temperature stored at the time of calibration. From these, Q (Rb-Ra) can be obtained. Since the quantity of heat Q is controlled to be a constant value, Q (Rb-Ra) is proportional to the change in thermal resistance of the temperature sensor when the surrounding is liquid and when the surrounding is air. By comparing with, liquid leakage can be detected.
[0011]
The liquid leakage sensor of the present invention is a liquid leakage sensor that detects the liquid leakage by measuring the change in the amount of heat dissipated from the temperature sensor that is heated to a temperature higher than the ambient temperature or self-heating. The detection device has a temperature sensor and a means for measuring the ambient temperature of the temperature sensor, has a means for measuring the amount of heat supplied to the temperature sensor, and further measures the temperature measured by the temperature sensor and the ambient temperature of the temperature sensor. It has a means to measure the difference with the temperature which a means measures. Examples of means for measuring the amount of heat supplied to the temperature sensor include a power monitor.
[0012]
From equation (1), the thermal resistance of the temperature sensor can be obtained as in equation (6), where Q is the amount of heat and T0 is the ambient temperature.
R = (T1-T0) / Q (° C./W) (6)
Since the amount of heat Q is obtained by means for measuring the amount of heat, by obtaining the difference between the thermal resistance when no liquid leakage occurs and the current thermal resistance, a change in thermal resistance can be obtained, and liquid leakage can be detected.
[0013]
The liquid leakage sensor of the present invention is a liquid leakage sensor that detects the liquid leakage by measuring the change in the amount of heat dissipated from the temperature sensor that is heated to a temperature higher than the ambient temperature or self-heating. The detection device has a temperature sensor and a means for measuring the ambient temperature of the temperature sensor, has a means for maintaining a constant temperature difference between the temperature sensor and the ambient temperature, and further measures the temperature measured by the temperature sensor and the surroundings of the temperature sensor. The means for measuring temperature has means for measuring a difference from the temperature to be measured. As means for keeping the temperature difference between the temperature sensor and the ambient temperature constant, for example, two temperature detectors for measuring the temperature difference between the temperature sensor and the ambient temperature, a temperature setting device for setting the temperature difference in advance, There is a combination with a heater drive circuit that controls the heater that supplies heat to the temperature sensor so as to eliminate the difference between the actual temperature difference and the set temperature difference.
[0014]
By measuring the amount of heat dissipated using the fact that the amount of heat necessary to keep the temperature of the temperature sensor constant is equal to the amount of heat dissipated, it is possible to detect liquid leakage independent of the ambient temperature. Equation (2) can be transformed into Equation (2 ′).
T1−T0 = Q · Rb (2 ′)
Here, assuming that the temperature difference between the temperature sensor and the ambient temperature is a constant value ΔTs, (2 ′) is expressed as shown in Equation (7).
ΔTs = Q · RB
Rb = ΔTs / Q (7)
That is, the thermal resistance Rb of the temperature sensor can be measured by measuring the amount of heat (electric power) supplied to the temperature sensor. From this value, by subtracting the thermal resistance Ra stored at the time of calibration when the surroundings of the temperature sensor is air, a change in thermal resistance can be obtained, and a liquid leak can be detected by comparing this with a certain threshold value.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A block diagram of an embodiment of the liquid leak detector of the present invention is shown in FIG. The liquid leak detector of the present invention includes a liquid leak detection temperature sensor 1, an ambient temperature measurement temperature sensor 2, a liquid leak detection temperature sensor reference temperature storage mechanism 4, and an ambient temperature measurement temperature sensor reference temperature storage mechanism. 5, comparators 7, 8, 10, heater 12, current amplifier 13, power monitor 14, power setting unit 15, and power controller 16. The liquid leak detection temperature sensor 1 and the ambient temperature measurement temperature sensor 2 are thermistors.
[0016]
The liquid leak detection temperature sensor 1 is supplied with a heat quantity Q from a heater 12. The heater 12 is always supplied with constant power input to the power setting unit 15 by the power monitor 14 and the power controller 16, and the heat quantity Q is always constant. By subtracting the reference value stored in the liquid leak detection temperature sensor reference temperature storage mechanism 4 at the time of calibration with the comparator 7 from the liquid leak detection temperature sensor 1, ΔT in the equation (4 ′) is obtained. By subtracting the reference value stored in the ambient temperature measurement temperature sensor reference temperature storage mechanism 5 by the comparator 8 from the temperature measurement temperature sensor 2, (T0I-T0a) in the equation (4 ′) is obtained. From these, Q (Rb−Ra) can be obtained using the comparator 10. Since the amount of heat Q is controlled to be a constant value, Q (Rb−Ra) is proportional to the change in thermal resistance of the liquid leak detection temperature sensor 1 when the surrounding is liquid and the surrounding is air. By comparing this with the criterion, liquid leakage can be detected.
[0017]
FIG. 2 shows a block diagram of the second embodiment of the present invention. In this embodiment, the liquid leak detection temperature sensor 1, the ambient temperature measurement temperature sensor 2, the thermal resistance reference value storage mechanism 23, the comparators 25 and 29, the thermal resistance measurement instrument 27, the heater 12 and the power monitor. 14.
[0018]
The liquid leakage detection device of this embodiment detects liquid leakage by directly obtaining the thermal resistance of the temperature sensor 1 for liquid leakage detection using equation (6). The liquid leak detection temperature sensor 1 is supplied with a heat quantity Q from a heater 12. The amount of heat Q may vary, but the value is always measured by the power monitor 14. A temperature difference (T1-T0) between the temperature sensor 1 for detecting liquid leakage and the temperature sensor 2 for measuring ambient temperature is obtained from the comparator 25, and this is calculated from the power obtained by the power monitor 14 in the thermal resistance measuring device 27. Since the thermal resistance Rb to the surroundings of the temperature sensor 1 for detecting liquid leakage can be directly calculated by dividing by the amount of heat Q, the liquid leakage stored in the thermal resistance reference value storage mechanism 23 at the time of calibration has not occurred. The comparator 29 compares the thermal resistance Ra and the current thermal resistance Rb. Since the thermal resistance when the surroundings are air is larger than the thermal resistance when the surroundings are filled with liquid, for example, if the Rb is reduced by 50% from Ra, the liquid leakage is detected by determining that the liquid leakage is considered. Can do.
[0019]
The configuration of the power monitor 14 is shown in FIG. The power monitor 14 includes a resistor 51, a thermistor 53, and a voltmeter 55. The resistor 51 has a resistance value R. The thermistor 53 is pulled up by the resistor 51 at the voltage Vcc, and the thermistor voltage Vth at that time is monitored by the voltmeter 55. In this circuit, the current Ith in the thermistor 53 is expressed by eight equations.
Ith = (Vcc−Vth) / R (8)
Accordingly, the heat generation power Pth of the thermistor 53 is obtained by the following equation (9).
Pth = Ith · Vth = Vth (Vcc−Vth) / R (9)
Since Vcc and R are predetermined values, the heat generation power Pth can always be monitored by measuring Vth with the voltmeter 55.
[0020]
FIG. 3 shows a block diagram of a third embodiment of the present invention. In this embodiment, the liquid leak detection temperature sensor 1, the ambient temperature measurement temperature sensor 2, the heater 12, the heater drive circuit 35, the temperature setting device 33, the power monitor 14, the thermal resistance measurement device 27, The comparator 30, 31, 39 and the thermal resistance reference value storage mechanism 23 are configured.
[0021]
The liquid leak detection apparatus of this embodiment is a thermal resistance of the liquid leak detection temperature sensor 1 by keeping the temperature difference between the liquid leak detection temperature sensor 1 and the ambient temperature measurement temperature sensor 2 constant according to equation (7). Thus, leakage of liquid can be detected. The temperature sensor 1 for detecting liquid leakage is supplied with a heat quantity Q by a heater 12 and is kept at a temperature higher than the ambient temperature. The temperature difference ΔTs between the liquid leak detection temperature sensor 1 and the ambient temperature measurement temperature sensor 2 is constantly measured by the comparator 30. The temperature setter 33 is preset with a temperature difference between the temperature sensor 1 for detecting liquid leakage and the temperature sensor 2 for measuring the ambient temperature, and is measured by the comparator 30 with the value set in the temperature setter 33. The difference from ΔTs is measured by the comparator 31. The signal from the comparator 31 is transmitted to the heater drive circuit 35 so that the temperature difference ΔTs between the liquid leak detection temperature sensor 1 and the ambient temperature measurement temperature sensor 2 always matches the temperature set in the temperature setter 33. Controlled. Further, the amount of heat Q supplied to the heater 12 is measured by the power monitor 14, and using this amount of heat Q and the temperature difference ΔTs between the temperature sensor 1 for detecting liquid leakage and the temperature sensor 2 for measuring ambient temperature (7) The thermal resistance of the liquid leak detection temperature sensor 1 is calculated by the thermal resistance measuring device 27 according to the equation. The comparator 39 compares the thermal resistance Ra stored in the thermal resistance reference value storage mechanism 23 at the time of calibration with no liquid leakage and the current thermal resistance Rb. For example, the liquid leakage can be detected by determining that the liquid leakage is considered when Rb is reduced by 50% from Ra.
[0022]
As mentioned above, although the Example of this invention was described, this invention is not limited to the said Example, A various change can be made within the range of the summary of this invention described in the claim. . For example, in the above embodiment, the liquid leakage is detected by measuring the thermal resistance of the temperature sensor 1 for detecting liquid leakage, but it is also possible to detect the liquid leakage by measuring the thermal conductivity. In this case, since the thermal conductivity when the surrounding is air is smaller than the thermal conductivity when the surrounding is filled with liquid, for example, when Rb reaches 150% of Ra, it is considered that the liquid leaks. It can be carried out.
[0023]
【The invention's effect】
According to the present invention, since the ambient temperature of the liquid leak detection temperature sensor is measured and the amount of heat supplied to the liquid leak detection temperature sensor is kept constant, the liquid leak can be accurately detected even if the ambient temperature changes. Can be detected. In addition, by measuring the ambient temperature of the liquid leak detection temperature sensor and directly measuring the amount of heat supplied to the liquid leak detection temperature sensor, it is possible to accurately detect the liquid leak even if the ambient temperature changes. It is said. In addition, by measuring the ambient temperature of the liquid leak detection temperature sensor and keeping the difference between the liquid leak detection temperature sensor and the ambient temperature constant, it is possible to accurately detect the liquid leak even if the ambient temperature changes. It is said.
[Brief description of the drawings]
FIG. 1 is a block diagram of an embodiment of a liquid leakage detection apparatus of the present invention.
FIG. 2 is a block diagram of a second embodiment of the liquid leakage detection apparatus of the present invention.
FIG. 3 is a block diagram of a third embodiment of the liquid leakage detection apparatus of the present invention.
FIG. 4 is a basic principle diagram of a conventional heat dissipation amount detection type liquid leakage detection device.
FIG. 5 is a configuration diagram of a power monitor.
[Explanation of symbols]
1 --- Temperature sensor for detecting liquid leakage 2 --- Temperature sensor for measuring ambient temperature 4 --- Temperature sensor for detecting liquid leakage Reference temperature storage mechanism 5 --- Temperature sensor for detecting ambient temperature Reference temperature storage mechanism 7 8, 10 --- Comparator 12 --- Heater 13 --- Current amplifier 14 --- Power monitor 15 --- Power setting device 16 --- Power controller

Claims (3)

A temperature sensor that is heated to a temperature higher than the ambient temperature or that self-heats;
An ambient temperature measurement sensor for measuring the ambient temperature of the temperature sensor;
Heat supply means for supplying a constant amount of heat to the temperature sensor;
Reference temperature storage means for storing the temperature measured by the temperature sensor during calibration;
Ambient reference temperature storage means for storing the temperature measured by the ambient temperature measurement sensor at the time of calibration,
The difference between the current temperature measured by the temperature sensor and the temperature stored in the reference temperature storage means, and the difference between the current temperature measured by the ambient temperature measurement sensor and the temperature stored in the ambient reference temperature storage means A liquid leakage detection device that calculates a change in thermal resistance from the amount of heat supplied from the heat supply means. A temperature sensor that is heated to a temperature higher than the ambient temperature or that self-heats;
An ambient temperature measurement sensor for measuring the ambient temperature of the temperature sensor;
A calorie measuring means for measuring the calorie supplied to the temperature sensor;
A thermal resistance measuring means for calculating a thermal resistance by dividing a difference between a current temperature measured by the temperature sensor and a temperature measured by the ambient temperature measuring sensor by a calorific value measured by the calorimetric measuring means;
Thermal resistance reference value storage means for storing the thermal resistance measured by the thermal resistance measurement means during calibration,
A liquid leak detection apparatus, wherein a change in thermal resistance is calculated from a difference between a current thermal resistance measured by the thermal resistance measurement means and a thermal resistance stored in the thermal resistance reference value storage means. A temperature sensor that is heated to a temperature higher than the ambient temperature or that self-heats;
An ambient temperature measurement sensor for measuring the ambient temperature of the temperature sensor;
Temperature difference setting means for setting a temperature difference between the temperature sensor and the ambient temperature measurement sensor;
Means for supplying heat to the temperature sensor so as to maintain a temperature difference determined by the temperature difference setting means;
A calorie measuring means for measuring the calorie supplied to the temperature sensor;
Thermal resistance measuring means for calculating thermal resistance from the temperature difference set in the temperature difference setting means and the amount of heat measured by the calorie measuring means;
Thermal resistance reference value storage means for storing the thermal resistance measured by the thermal resistance measurement means during calibration,
A liquid leak detection apparatus, wherein a change in thermal resistance is calculated from a difference between a current thermal resistance measured by the thermal resistance measurement means and a thermal resistance stored in the thermal resistance reference value storage means.

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