Liquid Quality Evaluating Apparatus

Abstract

This is an electrical apparatus for rapidly determining the quality of a liquid such as automotive brake fluid by comparing its boiling point with a predetermined reference value. Liquid to be tested is heated to its boiling point in a first vessel having a nozzle opening into a second vessel so as to transfer liquid when boiled from the first to the second vessel. Temperature rise to a predetermined value in the first vessel produces one signal and the presence of boiled liquid in the second vessel produces a second signal. Comparison of the time of occurrence of the two signals indicates the relation of the boiling point of the sample to the predetermined reference value.

Description

BACKGROUND OF THE INVENTION

This invention relates to a liquid quality evaluating apparatus for evaluating the quality of any liquid such as a brake fluid for automobiles.

Recent tendency has been towards using a brake fluid as high in boiling point as possible so as to enhance brake performance. In general, however, the higher the initial boiling point, the greater the drop of the boiling point due to its hygroscopic property and the degeneration of the brake fluid due to its hygroscopicity now presents a problem. As is known the brake fluid decreases in boiling point with an increase in the percentage of contained water. On the other hand brake fluid reaches a high temperature at the time of brake operation, particularly when a greater amount of braking force such as on a steep downhill road is required. If the brake fluid reaches its boiling point during the time of brake operation, what is called "a vapor lock phenomenon" occurs with the result that the braking force is lowered to an extreme extent, presenting a possible greater peril under which an unexpected traffic accident can take place. It is necessary, therefore, to exchange the degenerated brake fluid reaching a certain water content for a new one. The necessity for exchange has heretofore been determined by judging the frequency of uses without resort to checking the quality of a used brake fluid, or by sampling the brake fluid and chemically analyzing its constituents. In the former case however, a still usable brake fluid may be discarded with the attendant uneconomical result, since no checking is made as to the usability of the brake fluid. Furthermore, even a relatively fresh brake fluid or one left unused, when placed in moist or humid environments such as in a rainy season, reaches more than a certain water content (usually 3 percent) than expected, and its use is still continued without the knowledge that its has become dangerous. In the latter case, a relatively intricate chemical analysis, as well as a relatively long period of time, is required with the attendant disadvantages.

A liquid, in general, to say nothing of a brake fluid for automobiles, when an impurity is included therein, shows the property that its boiling point varies.

Accordingly the object of this invention is to provide a liquid quality evaluating apparatus capable of determining in a relatively simple way and in a short period of time whether any sample liquid is good or bad, by electrically detecting whether or not its boiling point exceeds a predetermined temperature level.

SUMMARY OF THE INVENTION

A liquid quality evaluating apparatus according to a preferred embodiment of this invention comprises: a sealed vessel made of a heat conductive material contained therein a predetermined amount of sample liquid and provided with a nozzle projecting in an integral fashion from a predetermined side wall thereof so that a section of the nozzle is at least higher in level than the upper surface of the sample liquid contained within the sealed vessel; a heating source including a heater disposed in proximity with the sealed vessel and a power source connected across the heater; another vessel made of an electric conductive material into which the sample liquid boiled through the heating of the heating source is forced through the nozzle; a needle-like electrode whose one end is arranged within the second-mentioned vessel in a manner to be in contact with the boiled sample liquid; a conduction current detecting circuit having an active circuit element whose input electrode is connected to a bias power source including the second-mentioned vessel, the boiled sample liquid poured into this vessel, the needle-like electrode and a first D.C. power source and whose output electrode is connected via an excitation coil with a core to the first D.C. source; a rotatable metal piece of a magnetic conductive material provided in proximity to the core of the conduction current detecting circuit and adapted to be electromagnetically attracted with its one end as a fulcrum when the conduction current detecting circuit is actuated; a temperature indicating meter continuously indicating the temperature variation of the sample liquid within the first mentioned vessel and constituting a bridge circuit constructed of three resistors and a heat responsive resistance element partly received in the first-mentioned vessel in a manner to be dipped in the sample liquid, a second D.C. power source connected acorss the paired input terminals of the bridge circuit and a temperature indicating meter consisting of a conventional D.C. galvanometer connected across the paired output terminals of the bridge circuit; and means for locking the deflection of the pointer of the temperature indicating meter by the metal piece at the moment the metal piece is attracted to the core of the conduction current detecting circuit.

According to the liquid quality evaluating apparatus so constructed the temperature indicating meter can continuously detect the temperature variation of the sample liquid within the first-mentioned vessel which is heated by the heating source, and is adapted to lock the deflection of the temperature indicating meter pointer in a position representative of a boiling point of the sample liquid at the moment it is boiled. Therefore, if the boiling temperature range of a fresh reference liquid the same as the sample liquid is preliminarily known, a temperature indicated by the locked pointer on the temperature indicating meter makes the ready evaluation of the quality of the sample liquid according to whether said indicated temperature falls within the preset boiling temperature range of the reference liquid.

A liquid quality evaluation apparatus according to another embodiment of this invention uses, in place of the metal piece of the first embodiment of this invention, a first normally closed contact and first normally open circuit both driven by the excitation coil included in the conduction current detecting circuit. There is also used, in place of a temperature indicating meter as shown in the first embodiment of this invention, a liquid temperature detecting circuit consisting of means for detecting the variation of the resistance of the heat sensitive resistance element as the variation of an amount of electric current, a D.C. amplifier for amplifying the variation of the amount of electric current so detected by said means, a Schmidt circuit connected to the D.C. amplifier, and an excitation circuit coupled to the Schmidt circuit and having an excitation coil connected between the output terminal thereof and a D.C. source so as to drive a second normally open contact and second normally closed contact. A first series circuit consisting of the first normally closed contact, the second normally opened circuit and a first lamp and a second series circuit consisting of the first normally open contact, the second normally closed contact and a second lamp are connected in parallel between both the terminals of the D.C. power source. With the liquid quality evaluating apparatus so constructed, when the conduction current detecting circuit is rendered conductive earlier than the liquid temperature detecting circuit, the second lamp is lighted earlier than the first lamp. On the contrary, when the liquid temperature detecting circuit is rendered conductive earlier than the conduction current detecting circuit, the first lamp is lighted earlier than the second lamp. A liquid, in general, exhibits the property that when any inpurity is contained therein its boiling point is raised or dropped with an increase of the impurity content.

Therefore, if a threshold voltage level of the Schmidt circuit in the liquid temperature detecting circuit is preset at the level representative of a temperature corresponding to a temperature immediately below a lower boiling point limit of a fresh reference liquid the same as the sample liquid i.e. a reference liquid whose impurity content is below a predetermined value, or at the level representative of a temperature corresponding to a temperature immediately above a upper boiling point limit thereof, then whether the sample liquid is good or bad can be determined by knowing which of the first and second lamps is lighted first.

The above-mentioned first and second series circuits can be replaced by a series circuit of a lamp and a normally open contact closed by the excitation coil of the conduction current detecting circuit and a series circuit of a lamp and a normally open contact closed by the excitation coil of the liquid temperature detecting circuit.

A liquid quality evaluating apparatus according to further embodiment of this invention comprises a vessel made of a heat conductive and electroconductive material into which a suitable amount of sample liquid is poured; a heating source having a heater arranged in proximity to the vessel and a power source connected across the ends of the heater; a needle-like electrode whose one end is arranged within the vessel in a manner to be in contact with the sample liquid; a current conduction path consisting of the needle-like electrode, the sample liquid, the vessel, a D.C. power source and a resistor; a Schmidt circuit receptive to a voltage drop appearing across the resistor in the current conduction path when the sample liquid is heated, through the vessel by the heating source, to a preset temperature corresponding to a temperature immediately below the lower boiling point limit of a fresh reference liquid the same as the sample liquid, or to a temperature immediately above the upper boiling point limit thereof; and a counter coupled to the Schmidt circuit.

With the liquid quality evaluating apparatus so constructed, if no boiling occurs when the sample liquid is heated to the aforesaid predetermined temperature, the input voltage level of the Schmidt circuit is substantially constant and the count number of the counter is 1 or 0. On the other hand, if boiling takes place, the sample liquid forms bubbles corresponding to the impurity content therein, and corresponding pulsating signals are applied to the Schmidt circuit. Therefore, if the threshold voltage of the Schmidt circuit is so preset that binary coded signals corresponding to the number of the pulsating signals from the Schmidt circuit are driven, the number of the binary coded signals are counted by the counter, and whether the sample liquid is good or bad can be evaluated according to the number of counts involved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing one embodiment of a liquid quality evaluating apparatus according to this invention;

FIG. 2 is a practical circuit diagram of the conduction current detecting circuit of FIG. 1;

FIG. 3 is a practical circuit diagram of the liquid temperature detecting circuit of FIG. 1;

FIG. 4 is a schematic block diagram showing one modification of the embodiment of FIG. 1;

FIG. 5 is a schematic block diagram showing another embodiment of a liquid quality evaluating apparatus according to this invention;

FIG. 6 is an enlarged front view showing the dial plate portion of a temperature indicating meter of FIG. 5;

FIG. 7 is an enlarged sectional view illustrating a preferred example of the cover for the heating vessel shown in FIGS. 1, 4 and 5;

FIG. 8 shows a schematic block diagram showing further embodiment of a liquid quality evaluating apparatus according to this invention; and

FIGS. 9A and 9B respectively show input and output waveforms of the Schmidt circuit in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic block diagram of one embodiment of this invention. In the figure, reference numeral 11 denotes a heating vessel made of a heat conducting material such as copper, the vessel 11 having a sufficient capacity to hold about 0.6cc of liquid and an upper opening measuring about 10mm in diameter and presenting a substantially U-shaped longitudinal cross section placed in the heating vessel 11 is about 0.5cc of an automobile brake fluid 12 to be evaluated. Then, a sealing cover 13 is placed on the top of the vessel 11. From a side wall of the heating vessel 11, for example, from the lower side wall thereof as shown in the figure, a nozzle 15 having an inner diameter of about 2mm projects in an integral fashion. A section of the nozzle is at a higher level than the upper surface 14 of the brake fluid 12 in the vessel. At the bottom of the heating vessel a heater 18 is disposed in series with a temperature adjusting variable resistor 17. The brake fluid 12 within the heating vessel 11 can thus be heated to about 100.degree.-300.degree.C by an appropriate power source 16 When the brake fluid 12 within the heating vessel 11 boils, it is rapidly forced through the open end of the nozzle 15 (due to vapor pressure of the boiled brake within the sealed vessel 11) into another vessel 19 made of a electroconductive material such as brass having substantially the same capacity and configuration as the heating vessel 11. Within the vessel 19 there is disposed a needle-like electrode 20 one end of which is permitted to contact the boiled brake fluid. The other end of the electrode 20 is connected to a positive terminal 22 of a D.C. power source 21 of about 12 volts and integrally secured through an insulating material 23 such as porcelain to the vessel 19, the negative terminal of the D.C. source 21 being connected to ground. The positive terminal 22 of the D.C. source 21 is connected to the vessel 19 through a conduction current detection circuit 25 (as will be later described with reference to FIG. 2) to the output terminal of which is connected an excitation coil 24. The conduction current detecting circuit 25 is normally open circuited, but when the brake fluid 12 within the heating vessel 11 is boiled and forced into the vessel 19, a current conduction path is established with respect to the D.C. power source 22 through the electrode 20, the boiled brake fluid 12, the vessel 19 and the conduction current detecting circuit 25, thereby causing excitation of the coil 23. To electrically detect the temperature variation of the brake fluid 12 within the heating vessel 11, there is received in a fluid-tight fashion in the heating vessel 11 a heat responsive resistance element 26. This could be a metal-coated thermistor one end of which contacts the brake fluid 12 within the heating vessel. Connected to the heat responsive resistance element 26 is a liquid temperature detecting circuit 28, as will later be described with reference to FIG. 3. The output terminal of circuit 28 is connected an excitation coil 27. The excitation coil 24 controls the opening and closing of a second normally open contact Y2 and second normally closed contact X2. As an electric assembly 29 for evaluating the quality of the sample brake fluid 12 contained within the heating vessel 11 there are provided a first series circuit 291 consisting of the first normally closed contact X1, a first lamp L1 and the second normally open contact Y2, and a second series circuit 292 consisting of the first normally open contact Y1, a second lamp L2 and the second normally closed contact X2. These series circuits 291 and 292 are connected in parallel between both the terminals of the D.C. power source 21.

FIG. 2 shows a practical circuit diagram illustrating the conduction current detection circuit 25 of FIG. 1 consisting of a Darlington circuit including a transistor TR1 whose base is connected to the vessel 19 and a transistor TR2 whose base is connected to the emitter of the transistor TR1. The excitation coil 24 is connected between the collector of the transistor TR2 and the positive terminal 22 of the D.C. power source 21. The collector of the transistor TR1 is connected via a resistor R1 to the terminal 22 of the D.C. power source, and the emitter of the transistor TR2 is connected to ground.

FIG. 3 is a practical circuit diagram showing the liquid temperature detection circuit 28 of FIG. 1 which comprises a variable current path 32 which is a series circuit consisting of a resistor R11, the aforesaid heat responsive resistance element 26 and a D.C. power source 31 whose negative pole is connected to ground. A series circuit 35 consists of a variable resistor VR and a resistor R12 series connected via a D.C. amplifier 34 between ground and a common connection 33 of the resistor R11 to the heat responsive resistance element 26. A Schmidt circuit 37 includes a transistor TR11 whose base is connected to a common junction 36 of the variable resistor VR and the resistor R12. The emitter is connected to ground via a resistor R13 and the collector is connected via a resistor R14 to the positive terminal 22 of the D.C. power source 21. A transistor TR12 has its emitter connected in common to the emitter of the transistor TR11, and the base is connected via a resistor R15 to the collector of the transistor TR11 and is connected to ground via a resistor R16 and the collector is connected via a resistor R17 to the terminal 22 of the D.C. power source 21. A driver circuit 38 includes a transistor TR13 whose base is connected via a resistor R18 to the collector of the transistor TR12; the emitter is directly connected to ground; and the collector is connected via the excitation coil 27 to the terminal 22 of the D.C. power source 21.

When the percentage of contained water of an automobile brake fluid in general is more than 3 percent, its boiling point is substantially decreased. The results of experiments made by the inventors reveal that when its boiling point is below about 150.degree.C it is necessary to exchange it for a fresh brake fluid and that a good brake fluid with a water content of below 3 percent has a boiling point in the temperature range of about 160.degree.-200.degree.C. The resistance of the heat responsive resistance element 26 is varied as the sample brake fluid 12 within the heating vessel 11 is heated by the heater 18. This causes the electric current flowing from the D.C. power source 31 to the variable current path 32 to be varied with a corresponding variation in the input voltage of the D.C. amplifier 34 appearing across the resistor R11.

Accordingly, the threshold voltage level of the Schmidt circuit 37 is preset, by adjusting the variable resistor VR in the series circuit 35, at a voltage level representing a boiling point of, for example, about 150.degree.C at which level it is possible to evaluate the quality of the brake fluid.

According to the liquid quality evaluating apparatus so constructed, when the conduction current detection circuit 25 is rendered conductive before the liquid temperature detection circuit 28, the first normally open contact Y1 is closed before the second normally open contact Y2. As a result, the second lamp L2 included in the second series circuit 292 of the liquid quality evaluating assembly 29 is lighted before the first lamp L1 included in the first series circuit 291. The sample brake fluid 12 within the heating vessel 11 is thus proved unfit for further use as brake fluid and replacement is necessary. On the other hand, when the liquid temperature detection circuit 28 is rendered conductive before the conduction current detection circuit 25 the second normally open contact Y2 is closed before the first normally open contact Y1 and the first lamp L1 is lighted before the second lamp L2. This indicates that the sample brake fluid 12 is still usable.

FIG. 4 is a schematic block diagram showing a further modification of the embodiment of FIG. 1. This modification is substantially the same as the embodiment of FIG. 1 except that the first normally closed contact X1 in the first series circuit 291 and the second normally closed contact X2 in the second series circuit 292 have been eliminated. It will be evident that this modified embodiment can be put to practice in the same way as the embodiment of FIG. 1 with substantially the same result.

FIG. 5 is a schematic block diagram showing another embodiment of a liquid quality evaluating apparatus according to this invention.

This embodiment uses, in place of the liquid temperature detection circuit 28, a liquid temperature detection circuit 281 including a bridge circuit 42 constituted by the heat responsive resistance element 26 and three resistors R21, R22 and R23. A D.C. source 41 of about 1.5 volts is connected across one pair of terminals of the bridge circuit 42; and a temperature indicating meter 43 consisting of a conventional D.C. galvanometer, such as a movable solenoid type is connected between the opposite pair of output terminals of the bridge circuit 42. With the liquid temperature detection circuit 281 so designed, when the resistors R22 and R23 are preset to be equal in resistance value to each other and the resistor R21 is preset to be equal in resistance to that of the heat responsive resistance element 26 under a normal ambient temperature (about 20.degree.-25.degree.C), then no output appears, at that temperature. When the brake fluid 12 within the heating vessel 11 is gradually heated by the heater 18, the resistance of the heat responsive resistance element 26 is increased. As a result, a corresponding output voltage appears between the output terminals of the bridge circuit 42. The temperature rise of the brake fluid causes the resistance of the heat responsive resistance element 26 to rise causing the pointer 44 of the temperature indicating meter 43 to be deflected, to represent a temperature variation. Also, with the embodiment of FIG. 5, in place of the sample liquid quality evaluating assemblies utilizing two lamps as in FIGS. 1 and 4, an arrangement is used so that when the excitation coil 24 is actuated, a metal piece 46 made of a magnetic conductive material whose one end is rotatable around a fulcrum 45 is electromagnetically attracted to cause the tip of the pointer 44 of the temperature indicating meter 43 to be locked.

According to the liquid quality evaluating apparatus so designed, when the pointer 44 is deflected, and locked of a temperature a position representative at below about 150.degree.C on the indicating meter 43 as shown in FIG. 6, the brake fluid 12 should be exchanged. Where the pointer is locked within a boiling temperature range of about 150.degree.-170.degree.C a warning "ATT" is the meter indication. When the pointer 44 is locked at a position of about 170.degree.C, the meter indication is "GOOD". As a result, it is possible to indicate the quality of the brake fluid with a high accuracy and with a simpler structure than the embodiment of FIG. 1.

FIG. 7 show a preferred embodiment of the sealed cover 13 used to close the heating vessel 11 shown in FIGS. 1, 4 and 5. The seal covering 131 of this example has a capillary bore 51 of, for example, about 0.5mm provided substantially at its center. When the brake fluid 12 within the heating vessel 11 is boiled rapidly through the nozzle 15 into the vessel 19 due to vapor pressure of the boiled brake fluid as well as capillary action, the bore of the seal covering serves to facilitate the passage of a gas or air, but prevent the passage of fluid therethrough. It is desirable that the seal covering 131 having the bore 51 be made of a heat insulating material 52 such as teflon, but it is difficult to provide in teflon, a bore as small as 0.5mm in diameter and usually 1mm is the smallest. As shown in the figure however, on the upper portion of the teflon 52 an auxiliary brass covering 53 is provided having a bore 512 with a diammeter of about 0.5mm.

FIG. 8 is a schematic block diagram showing a further embodiment of a liquid quality evaluating apparatus.

With this embodiment use is made of a heating vessel 61 made of an electric and heat conductive material, such as copper, whose longitudinal cross section is substantially U-shaped. Disposed within the vessel 62 is a needle-like electrode 62 one end of which is spaced apart about 1mm from the inner bottom surface of the vessel 62. The other end of the electrode 62 is supported, in an integral fashion through an electrical insulating material 63 such as porcelain, on the heating vessel 61 and is connected to the vessel 61 through a resistor R31 and a D.C. power source 64 of about 6 volts with the polarity indicated. Across the terminals of the resistor R31 a counter 66 is connected through a Schmidt circuit 65. Below the heating vessel 61 is a heating source 70 including a heater 67 and a power source 69 connected, through a temperature adjusting element consisting of a variable resistor 68, across the terminals of the heater 67. In the figure reference numeral 71 denotes a coupling capacitor. After the vessel 61 is heated to the boiling temperature of an automobile brake fluid having a water content of about 3 percent for example, 150.degree.C, a sample brake fluid 73 of about 0.01-0.03cc is dropped within the heating vessel 61 by a spout 72 in a manner to be in contact with the needle-like electrode 62. This establishes a current conduction path 74 consisting of the heating vessel 61, the fluid 73, the needle-like electrode 62, the resistor 31 and the D.C. power source 64. In this case, when the temperature of the heating vessel 61 is below the boiling point of the brake fluid 73; the sample brake fluid is not boiled and a constant voltage Vo of about -6 volts substantially equal to a voltage of the D.C. power source 64 as shown in FIG. 9A is applied to the Schmidt circuit 65. When, on the other hand, the temperature of the heating vessel 61 is higher than the boiling point of the sample corresponding to a water content of more than 3 percent; then, the sample boils, and bubbles substantially proportional to the water content of the brake fluid are produced. Then, a corresponding pulsating signals e1, e2, e3 . . . as shown in FIG. 9A are impressed on the Schmidt circuit 65 across the terminals of the resistor R31 included in the current conduction path 74. These pulsating signals are such that their maximum and minimum values are varied within the range of the positive voltage (0 volt) and the negative voltage (-6 volts) of the D.C. power source 64. Therefore, if the threshold voltage level S of the Schmidt circuit 65 is preset to a voltage level (the result of experiments has revealed that about - 2 to -3 volts are suitable) capable of individually detecting each of the pulsating signals e1, e2, e3 . . . , then pulse signals p1, p2, p3 - - - corresponding to the bubbles produced are driven, as shown in FIG. 9B, from the output terminal of the Schmidt circuit 65. The number of pulse signals is counted by the counter 66. When the count reaches a predetermined value, for example, 3, then the brake fluid is evaluated as "bad" and when the count is less than 3, the brake fluid is evaluated as "good".

It will be understood that the liquid quality evaluating apparatus according to this invention can be applied not only to an automobile brake fluid, but also any other liquid whose impurity content and boiling point can beforehand be obtained, since they provide a ready evaluation of the quality of the liquid.

While preferred embodiments have been disclosed herein, applicants claim the benefit of a full range of equivalents within the scope of the appended claims.

Claims

What we claim is:

1. Apparatus for determining whether the boiling point of hygroscopic liquid such as automotive brake fluid is at least above or below a reference temperature comprising:

a first substantially closed vessel made of heat conductive material for containing a predetermined sample of liquid to be tested, said vessel being provided with a nozzle projecting from a side wall, said nozzle having at least a portion higher than the level of the sample liquid within said vessel;

means for controlled heating of said vessel;

a second vessel made of electrically conductive material, positioned to receive said sample liquid when forced through said nozzle by boiling in said first vessel;

a needle-like electrode having one end disposed within said second vessel so as to be in contact with the boiled sample liquid therein;

a current detection circuit forming a closed path through at least the boiled sample liquid within said second vessel and saie needle-like electrode for producing an output signal in response to contact of the boiled sample with said electrode;

means for providing a different signal whenever the temperature of liquid in said first vessel reaches a reference temperature; and

indicating means responsive to said signals to indicate at least whether the boiling point of said sample liquid is above or below a reference temperature.

2. Apparatus as defined by claim 1 in which said vessels are substantially U-shaped in cross-section and said first vessel includes a cover having a capillary bore extending completely therethrough said bore having an inside diameter of about 0.5mm.

3. Apparatus as defined by claim 1 in which said means for controlled heating of said first vessel includes an electrically resistive heating element connected in series with a variable resistor and a power source.

4. Apparatus as defined in claim 1 wherein said current detection circuit comprises:

an active circuit means having input and output electrodes;

said second vessel;

the boiled sample liquid in said second vessel;

said needle-like electrode;

a DC power source;

an excitation coil;

said input electrode being connected to said source and said output electrode being connected through said excitation coil to said source; and wherein said liquid temperature detection circuit comprises:

a variable current path formed by a series circuit including a second DC power source, a heat responsive resistance element in said first vessel and a resistor;

a DC amplifier having its input connected to said series circuit between said heat responsive resistive element and said resistor;

a Schmidt circuit coupled to the output of said DC amplifier and having a preset threshold voltage level indicative of a boiling point substantially representing a boundary between good and bad qualities of the same type of liquid as the sample liquid on the test;

a driver circuit having its input coupled to the output of said Schmidt circuit;

a second excitation coil connected between the output of said driver circuit and said second DC source;

and wherein said indicating means includes a first normally open lamp circuit arranged to be closed when said second excitation coil is energized and a second normally open lamp circuit arranged to be closed when the other of said excitation coils is energized.

5. Apparatus as defined by claim 1 wherein said current detection circuit comprises:

an active circuit element means having input and output electrodes;

said second mentioned vessels;

the boiled liquid in said second vessel;

said needle-like electtode;

a first DC power source;

an excitation coil;

said input electrode being connected to said first DC source and said output electrode being connected through said excitation coil to said source;

and wherein said liquid temperature detection circuit comprises:

a bridge circuit one leg of which is a heat responsive resistence element in said first vessel;

a second DC source connected across one pair of terminals of said bridge circuit;

and wherein said indicating means comprises:

a temperature indicating DC galvanometer connected across the opposite pair of terminals of said bridge; and

means responsive to energization of said excitation coil for locking the pointer of said galvanometer.

6. Apparatus for determining whether the boiling point of a hydroscopic liquid such as automotive brake fluid is at least above or below a reference temperature comprising:

a heating vessel formed of a material both electrically and heat conductive;

a needle-like electrode having one end disposed in proximity to the inner bottom of said vessel;

a heating source for said vessel including a heater and a power source coupled to said heater;

a current conduction path including said vessel, a sample liquid poured into said vessel, said needle-like electrode, a resistor connected to the opposite end of said needle-like electrode and a DC power source connected between said vessel and said resistor;

a Schmidt circuit having its input terminals connected across said resistor and having a preset threshold voltage level; and

a counter coupled to the output of said Schmidt circuit to count a number of output pulse signals therefrom.