Abstract: A system for detecting the level of fluid in a fluid containing vessel. The system includes a device for applying energy to a selected location on the vessel. A sensor in proximity to the location detects the energy level at the location during first and second intervals. A memory device stores data representative of the energy detected by the sensor at each interval, and a logic circuit compares the amount of energy of the first interval to that of the second. Data corresponding to the level of fluid in the vessel may be displayed locally or signaled to remote data receiving and display devices, as appropriate.

Abstract: An apparatus in the field of power transmission, the apparatus includes a superconducting component or another component to be cooled, in a cryostat. A vacuum switch is provided in order to prevent heat being introduced into the cryostat by means of thermal conduction through the electricity cable of the component in the event of an electricity failure. This vacuum switch is integrated in a bushing in the electricity cable, so that its vacuum completes the thermal insulation of the cryostat.

Abstract: The present invention deals with determining the level of fluid in a container. Typically, a beverage container containing a liquid will absorb heat energy from the surrounding environment at a greater rate than a gaseous component in the headspace of the beverage container. Thus, as the liquid is drawn from a beverage container a greater headspace results. If a thermometric measuring device is employed along the height of the beverage container the volume may be determined by observing the difference in the temperature along the height of the beverage container. In practice, a beer keg may exhibit a difference of as much as 9 degrees Fahrenheit on the exterior surface of the beer keg when measured at the headspace as opposed to the area alp where the liquid is present in the beverage container.

Abstract: The invention concerns a microwave level measuring device for measuring of material levels in containers, suitable for operation at extreme container conditions, comprising high temperatures, high pressures, and/or chemically aggressive substances.

Abstract: An electrical current is passed through a thermistor to raise its temperature above the temperature of oil flowing in pulses past the thermistor. A change is measured in the temperature of the thermistor occurring with respect to one or more of the pulses. A level of oil flow is determined corresponding to the measured change in temperature. A signal is issued based on the determined flow level.

Abstract: An improved liquid level sensor is disclosed which provides a reliable and simple device for accurately determining the level of a liquid within a vessel. The sensor of the present invention utilizes a plurality of thermocouples grouped in pairs with the pairs being spaced along a line extending generally in the direction in which the liquid level may vary. A first thermocouple of each pair is located in relatively close thermal proximity to an electrically powered heater and the second of each pair of thermocouples is spaced away from the heater. The thermocouples are connected in series and produce a signal directly indicative of the level of the liquid along the sensor. Additionally, a pressure sensing circuit may also be incorporated with the liquid level sensor.

Abstract: A sensor for determining the level and temperature of a liquid, in particular in a motor vehicle, has an elongate housing (1), in which all the components required for temperature measurement and level measurement are accommodated. This housing (1) consists of two half shells (2, 3) which rest one on the other and of which one half shell (3) has all the components required for level measurement and the wiring and resistance wire (21) necessary for this purpose and the other half shell (2) has all the components required for temperature measurement and the wiring necessary for this purpose.

Abstract: A liquid level sensor used for determining liquid levels in a sealed container includes a heat source bonded to the container, a first temperature sensor mounted on the container adjacent the heat source, and a second temperature sensor mounted on the container spaced from the heat source. The temperatures at the first and second temperature sensors are sensed while the heat source is operating, and the differential in the temperatures is measured and used to control power to the heater. Changes in the differential in temperature between the first and second temperature sensors indicates when the heat conductivity between the first and second temperature sensors changes, due to presence or absence of a liquid in the container at the level of the temperature sensors.

Abstract: A liquid level sensor 10 includes spaced apart first and second temperature sensor 12, 14 and a heater 16 which is closer to the first temperature sensor 12 than the second temperature sensor 14. A temperature difference sensing circuit 18 provides an indication of the difference between the temperature sensed by the first and second sensor 12, 14 and more particularly the indication as to when this difference is above a threshold level. The sensors 12 and 14 and heater 16 are disposed within an elongated tube 22 made from a thermally conductive material with sensor 12 and heater 16 a distal end 26 of the tube and the temperature sensor 14 near a proximal end 28. The tube 22 is typically disposed horizontally within a sump. Temperature sensor 14 provides an indication of ambient temperature. Sensor 12 provides an indication of the temperature near the heater 16.

Abstract: An ullage meter is designed to be made up of a coating or film attached to the surface of a tank for holding compressed gas. This is used normally when the tank is warm as is the case right after the tank is pressured with gas. The coating includes materials which change in appearance when various specific temperatures are reached. The changed appearance allows numbers to be seen which tell the observer how much pressure will be lost after the warm tank has cooled to some specific temperature. This loss is an ullage.

Abstract: A humidifier including a reservoir adapted for retaining liquid and an evaporative media supported in adsorbing contact with the liquid. A reservoir temperature sensor detects a temperature within the reservoir at a low liquid level and provides a reservoir temperature signal indicative thereof. An air inlet temperature sensor detects a temperature of air upstream from the evaporative media and provides an air inlet temperature signal indicative thereof. An air outlet temperature sensor detects a temperature of air downstream from the evaporative media and provides an air outlet temperature signal indicative thereof. A controller determines an operating condition of the humidifier based upon at least one of the reservoir temperature signal, the air inlet temperature signal, and the air outlet temperature signal.

Abstract: An improved liquid level sensor is disclosed which provides a reliable and simple device for accurately determining the level of a liquid within a vessel. The sensor of the present invention utilizes a plurality of thermocouples grouped in pairs with the pairs being spaced along a line extending generally in the direction in which the liquid level may vary. A first thermocouple of each pair is located in relatively close thermal proximity to an electrically powered heater and the second of each pair of thermocouples is spaced away from the heater. The thermocouples are connected in series and produce a signal directly indicative of the level of the liquid along the sensor. Additionally, a pressure sensing circuit may also be incorporated with the liquid level sensor.

Abstract: The invention relates to a method for monitoring the refrigerant filling level of a refrigerating system, in particular a motor vehicle air-conditioning system, with a compressor subdividing the refrigerant circuit into a high-pressure side and a low-pressure side. The evaporator temperature is determined at the evaporator at short time intervals by means of an evaporator temperature sensor. According to the invention, there is provision for a time meter, t, to be activated when the evaporator temperature exceeds a predetermined threshold temperature.

Abstract: The present invention deals with determining the level of fluid in a container. Typically, a beverage container containing a liquid will absorb heat energy from the surrounding environment at a greater rate than a gaseous component in the headspace of the beverage container. Thus, as the liquid is drawn from a beverage container a greater headspace results. If a thermometric measuring device is employed along the height of the beverage container the volume may be determined by observing the difference in the temperature along the height of the beverage container. In practice, a beer keg may exhibit a difference of as much as 9 degrees Fahrenheit on the exterior surface of the beer keg when measured at the headspace as opposed to the area where the liquid is present in the beverage container.

Abstract: A liquid level sensor is used on a sealed container comprises a heat source bonded to the container, a first temperature sensor mounted on the container adjacent the heat source, and a second temperature sensor mounted on the container spaced from the heat source. The temperatures at the first and second temperature sensors are sensed while the heat source is operating, and the differential in the temperatures is measured and used to control power to the heater. Changes in the differential in temperature between the first and second temperature sensors indicates when the heat conductivity between the first and second temperature sensors changes, due to presence or absence of a liquid in the container at the level of the temperature sensors.

Abstract: Apparatus and a method of operating any structural configuration of a heater and array of temperature sensors to measure with high accuracy, the level of stratified liquids like water and oil or water and gasoline and non-stratified liquids, liquid temperature, and other liquid properties and detect ice formation on aircraft surfaces. Thin and narrow strips of dissimilar material will be used for the heater, array of temperature sensors, mount, and coating. The connecting wires to and from the apparatus will be from the same material. Simultaneous measurements from all the temperature sensors, before and after heat is applied, will be used to generate accurate temperature profiles for the entire configuration and not just from two adjacent temperature sensors. Different features of the temperature profiles will determine accurately the liquid level, liquid temperature and other liquid properties. Apparatus of the invention may also be used to detect ice formation.

Abstract: A sensor for determining the level and/or temperature of a liquid, in particular in a motor vehicle, has an elongate housing (1), in which all the components required for temperature measurement and level measurement are accommodated. This housing (1) consists of two half shells (2, 3) which rest one on the other and of which one half shell (3) has all the components required for level measurement and the wiring and resistance wire (21) necessary for this purpose and the other half shell (2) has all the components required for temperature measurement and the wiring necessary for this purpose.

Abstract: The liquid level detector system of the present invention comprises a heater thermally coupled to the interior of the vessel. A linear sensor, having a vertical longitudinal axis, is located in proximity to the heater such that discrete elevations of the interior of the vessel are thermally coupled to corresponding longitudinal portions of the sensor. The correspondence is incrementally continuous such that the elevations corresponding to the portions of the sensor increase from one to the other end of the sensor. The sensor may be actuated resulting in a resistance measurement indicative of the temperature detected by it. The vertical dimension of the sensor is sufficiently large such that the resistance measurement will vary in proportion to the longitudinal portion of the sensor thermally coupled to the liquid. The sensor generates an electrical signal defining a temperature signal indicative of the resistance measurement and thereby the temperature detected by the sensor.

Abstract: A method and an apparatus are proposed for determining and/or monitoring the quantity and quality of a fluid in which a lowering of the boiling temperature is symptomatic of a deterioration in quality. For this, the filling level and the condition of the fluid—in particular a hygroscopic fluid—are determined successively one after the other by a single sensor of a measuring instrument.

Abstract: A limit-level sensor (3) has a resistance element (4) which has an electric resistance which suddenly varies a transition temperature which lies above the maximum liquid temperature. The resistance element (4) is first of all heated by electric current. Thereupon, the electric resistance of the resistance element (4) is measured. When the resistance element (4) is covered with liquid (2), the heat generated by the electric current is led away so that the temperature of the resistance element (4) is less than its transition temperature. If the resistance element (4) is not covered by liquid (2), this heat is scarcely led away, so that the temperature of the resistance element (4) remains above the transition temperature.

Abstract: A cholesteric liquid crystal fluid level indicator that determines the level of a cooled liquid, such as beer, in a closed, opaque keg when placed in thermal contact with the exterior surface of the keg, by producing a color change that is a function of the liquid temperature when the liquid is within a predetermined temperature range, the indicator comprises a multiple level strip having a top transparent layer, liquid crystal layer, a black background layer and an attachment layer employing a protected adhesive on its bottom surface for removably attaching the strip to the keg, the instant invention employs a heat conducting adhesive on the attachment layer and for securing certain layers in the strip, such as the liquid crystal layer.

Abstract: A limit-level sensor for measuring level of a liquid has a resistance element which has an electric resistance which suddenly varies a transition temperature which lies above the maximum liquid temperature. The resistance element is first heated by electric current. Thereupon, the electric resistance of the resistance element is measured. When the resistance element is covered with liquid, the heat generated by the electric current is led away so that the temperature of the resistance element is less than its transition temperature. If the resistance element is not covered by liquid, this heat is scarcely led away, so that the temperature of the resistance element remains above the transition temperature.

Abstract: An electrically resistive fluid level sensor and system for sensing fluid levels in a container, for example washing machine basins, and for closing a supply of fluid to the container when the fluid level in the container reaches a specified level. The system includes generally fluid level resistive element portions disposed in the container and electrically connectable by fluid therein, and an input signal source, electrically coupled to the fluid level resistive element portions, whereby an output signal across the fluid level resistive element portions is proportional to the fluid level. Temperature resistive element portions are preferably disposed in the container and connected in series between the input signal source and the fluid level resistive element portions to substantially cancel any thermal effects on fluid level sensing and control.

Abstract: A sensor for determining the location of the surface of liquid in a container, includes: a hollow tubular stainless steel probe inserted into said container, said probe having one portion arranged above the surface of the liquid and having another portion submerged in the liquid; a first thermocouple operatively arranged within the probe to sense the temperature above the liquid surface; a second thermocouple operatively arranged within the probe to sense the temperature of said liquid at a point beneath the liquid surface; a resistance wire operatively arranged within the probe; a current source operatively arranged to apply a constant-current to the ends of the wire; and an ohmmeter for measuring the electrical resistance of the wire according to the equation: RT=ƒ[kaTaHh+kwTwH(1−h)] where RT is the resistance of the wire, ƒ is the symbol for “a function of”, ka is a constant for the probe first portion, Ta is the temperature sensed by the first temperatur

Abstract: Disclosed is a toner residual quantity detecting apparatus for detecting a residual quantity of toners in a developing unit. This toner residual quantity detecting apparatus has a temperature sensor, provided in the bottom of the developing unit, for generating an output proportional to a detected temperature and a detecting circuit for detecting the toner residual quantity from the output of the temperature sensor. This temperature sensor detects a difference between temperatures when covered with the toners and when not covered with the toners, thereby detecting the toner residual quantity.

Abstract: A fluid level detector according to the invention comprises a substrate formed of a heat-insulative material and one or more thermoresistive sensor elements located on the substrate that is adapted to be immersed in a fluid. A current source is connected to the sensor element for producing a current through the sensor element during a predetermined time period. The current heats the sensor element and causes a change in voltage across the sensor element at least during the time period. The amount of change in voltage during the time period is reflective of the fluid level, since the fluid serves as a heat sink for the sensor element. The voltage is measured across the sensor element and a voltage slope is determined. The determined voltage slope is indicative of fluid level.

Abstract: It is aimed to present a liquid level detector that can be assembled by simply stacking component parts one upon another, without using any soldering work at all. In the liquid level detector, a thermistor (7) is placed on an electrode (2a) of element holder (2) and is pressed by an electrode (3a) of a terminal (3), a coil spring (4) is inserted around the terminal (3) for the electrode (3a) to press the thermistor (7). An insulator (5), with which a terminal member (6) is calked together in advance, is placed to a fitting portion (2c) of the element holder (2), and then the entire assembly is inserted from the opening into a metal case (1), so that the opening is closed with the insulator (5) calked by a fitting portion (1a) of case (1) and the fitting portion (2c) of element holder (2) aligned to an indention (5c) of insulator (5).

Abstract: Apparatus and a method of operating any structural configuration of a heater and array of temperature sensors to measure with high accuracy, the level of stratified liquids like water and oil or water and gasoline and non-stratified liquids, liquid temperature, other liquid properties and detect ice formation on aircraft surfaces. Thin and narrow strips of dissimilar material will be used for the heater, array of temperature sensors, mount, and coating. The connecting wires to and from the apparatus will be from the same material. Simultaneous measurements from all the temperature sensors, before and after heat is applied, will be used to generate accurate temperature profiles for the entire configuration and not just from two adjacent temperature sensors. Different features of the temperature profiles will determine accurately the liquid level, liquid temperature and other liquid properties. Apparatus of the invention may also be used to detect ice-formation.

Abstract: By referencing either liquid volume or liquid pressure to liquid temperature, either in an implicit way and mechanically or in a non-implicit way and metronomically, the development of an electrical fault or loss of liquid can be detected. The present invention is based on the principle that any deviation from the relation between temperature and volume of a liquid, or, by implication, temperature and pressure in that liquid--the latter relation being applicable to closed systems only--is indicative either of an electrical fault in the transformer or of liquid loss from the transformer.

Abstract: A liquid level indicator has a transparent vessel for retaining hot water therein and a thermo-sensitive tape (thermo-tape) attached at a side wall of the vessel with the sensing side of the thermo-tape facing the side wall of the vessel. The thermo-tape first exhibits black, then turns white after the hot water is poured into the vessel. When the thermo-tape is pressed against a partially filled liquid container, the thermo-tape turns black at one side of a boundary and turns white at the other side of the boundary that defines the liquid/gas interface in the container. This occurs because the liquid in the container cools the thermo-tape more rapidly than the gas in the container does. The boundary is observed through the walls of the transparent vessel and the hot water to detect the liquid level within the container.

Abstract: A steam generator with automatic supply having a level sensor arranged in a zone of a vessel located at a set threshold level, the sensor measuring the temperature and comparing it with a reference temperature, in order to establish whether a liquid reaches the threshold level, and an adjustment means acting in relation to the steam tapping operations so that the sensor temperature varies in relation to the level of liquid over a variation range, wherein the reference temperature remains within the variation range.

Abstract: A measurement chamber (18) having an upper and a lower region is at substantially the same elevation as a horizontal pipe (12) having a top region and a bottom region. An equalization line (14) fluidly connects the top region of the pipe (12) to the upper region of measurement chamber (18). A sample line (16) fluidly connects the bottom region of pipe (12) to the lower region of the measurement chamber (18). Heat junction thermocouples (22) generate a signal indicative of the level of fluid in the measurement chamber (12) which is equal to the level of fluid in the pipe (12). The signal is transmitted to a remote location by line (24).

Abstract: A monitoring apparatus is provided for use in cryogenic storage tanks. The monitoring apparatus is a combination cap and monitoring system. The monitoring system includes a sensor which is submerged in liquid nitrogen, a circuit for detecting changes in resistance of the sensor should the liquid nitrogen level fall to or below a selected level, and an audio output device which generates an audible alarm if the liquid nitrogen falls to or below the selected level.

Abstract: An improved cooler with level sensor for measuring variation in the liquid refrigerant level of a refrigerant within the cooler, comprises a cooler shell for holding the refrigerant, heat exchanger tubes for carrying the liquid to be cooled, and a liquid refrigerant level sensor comprising a probe extending to a point above the heat exchanger tubes, one or more thermistors; and a heating element. When the probe is totally within the vapor refrigerant above the heat exchanger tubes, the heater raises the temperature of the thermistors above the saturation temperature of the refrigerant. As the liquid refrigerant level begins to rise, the liquid refrigerant comes in contact with the outside of the probe. Since the heat transfer coefficient of the liquid refrigerant is significantly higher than that of the vapor refrigerant, the probe in that area is quickly cooled to the saturation temperature.

Abstract: A fluid level sensor. The sensor comprises a housing; a chamber enclosed by the housing; a liquid port in a lower area of the housing operable to connect the chamber to a lower, liquid containing area of a heat exchanger; and a gas port located in an upper area of the housing and operable to connect the chamber to an upper, vapor containing area of a heat exchanger. The sensor includes first and second apertures in the housing; and cooling conduit passing through the chamber and through the first and second apertures and operable to cool the chamber. There is at least one sensor located in the chamber and adapted to sense a temperature of fluid in the chamber.

Abstract: Apparatus and a method of operating any structural configuration of a heater and array of thermocouples to measure with high accuracy, the level of stratified liquids like water and oil or water and gasoline and non-stratified liquids, liquid temperature, and other liquid properties. Simultaneous measurements from all the temperature sensors, before and after heat is applied, will be used to generate accurate temperature profiles for the entire configuration and not just from two adjacent temperature sensors. Different features of the temperature profiles will determine accurately the liquid level, and other liquid properties.

Abstract: A process and a system for operating a level sensor, particularly for measuring amounts of liquid in motor vehicles, employs a plurality of heatable thermistors wherein a number of the thermistors are covered by liquid depending on the level of the liquid, and are cooled below a breakpoint temperature of the thermistors. The total resistance of the thermistors, which may be connected with further resistors, changes discontinuously as a function of the liquid level. At least one thermistor is located above the maximum possible level. The temperature of the thermistors is increased to such an extent by a feeding of electrical heating power that all thermistors which are above the existing level exceed their breakpoint temperatures, whereupon the total resistance is measured.

Abstract: Disclosed is an indicator (15, 35) for determining the level of contents in an opaque, plastic container (10, 30, 40). The container (10, 30, 40) is filled with a solid chemical (11), such as a detergent. A spray of warm or hot water (19) impinges upon the eroding surface (16) of the solid chemical (11) to produce a chemical solution. The container (10, 30, 40) is provided with a thermo-chromatic strip (15, 35) or thermo-chromatic surface (41) for detecting the level of solid chemical (11) within the plastic capsule (10). A method of manufacturing the dispensing container (10, 30, 40) is also disclosed.

Abstract: Provided is a self-calibrating system which self-calibrates for operation regardless of the particular reservoir or expansion tank, which further detects when a hydraulic fluid system adapted to a turf care machine has developed a leak and which warns the machine operator of such a leak before an appreciable amount of hydraulic fluid is allowed to leak from the system. The system includes a reservoir for holding a quantity of hydraulic fluid. The reservoir is connected via a connecting tube or hose located at the upper-most portion of the reservoir and connected to an expansion tank mounted substantially adjacent to the reservoir. The expansion tank includes a fitting having an elongated tube extending down into the expansion tank. The end of this tube is maintained substantially below the level of hydraulic fluid in the expansion tank during operation of the turf care machine to which it is attached.

Abstract: Differential outputs produced by twin thermoresistive sensors are used to determine the level and flow of a medium. Separate constant current sources supply power to each sensor so that one constant current source supplies sufficient current to cause significant self-heating of the sensor (hot sensor) and the other constant current source supplies relatively little current with insignificant self-heating of its corresponding sensor (cold sensor). Resistive changes in the sensors produced by level and flow changes of the medium produce measurable voltage changes, thereby providing a convenient parameter by which to determine level or flow. Level or flow is determined by dividing the difference in the voltages across the hot and cold sensors by the voltage across the cold sensor.

Abstract: An apparatus for controlling level of cryogenic liquid in a vessel includes a transfer duct to a pressure supply tank. Pressure pulses are applied to the tank at one rate when the level is below a primary sensor in the vessel, and at a lower rate when the level is above the sensor, so as to compensate for intrinsic declination of the level. At startup a constant pressure is applied to the tank until the level reaches a lower sensor, and a relief valve over the tank is opened when the level overshoots to an upper sensor. Turbulence in the vessel is reduced by a pair of coaxial baffles at the liquid inlet to the vessel, and by a housing with tubular extensions enveloping the sensors.

Abstract: A fluid leak detector mechanism having a main fluid tank, an expansion tank for receiving fluid therefrom as the fluid becomes heated and expands, and a sensing chamber operatively coupled with the main tank. A signalling mechanism signals to an operator when the level of fluid in the sensing chamber has dropped significantly to alert the operator of the presence of a leak. An oil return valve is operatively coupled between the main tank and the expansion tank and has an open position that allows fluid to flow back to the main tank from the expansion tank and a closed position that blocks oil from flowing from the expansion tank to the main tank. A temperature sensor senses the temperature of fluid. A control mechanism shifts the oil return valve to its open position when the temperature sensor detects a significant drop in fluid temperature, thereby allowing the fluid levels to be reset with changes in fluid temperature.

Abstract: A level detector for detecting a level of a liquid is provided with an elongated probe having opposed proximal and distal ends. In use, the distal end of the elongated probe is submerged beneath the level of the liquid with an unwetted length of the elongated probe located above the level of the liquid. A thermal conductor or an electrical heater is provided for maintaining a temperature difference between the proximal end of the elongated probe and the liquid so that at an intermediate location of the elongated probe, located above the level of the liquid, the temperature will be dependent upon the unwetted length of the elongated probe. A thermocouple or the like can be provided for generating a signal referable to the temperature at the intermediate location and the level of the liquid can thereby be correlated with such signal.

Abstract: A liquid filling method and in particular a lens material liquid filling method suitable for manufacturing a plastic lens. A thermal sensing portion (2a) of a temperature sensor (2) is set and kept to a temperature different from that of a liquid (3). The liquid (3) is poured into a vessel (8), a change of an output from the temperature sensor (2) is detected when the surface of the liquid (3) comes into contact with the thermal sensing portion (2a) by temperature detecting means (5), and control means (6) determines that the liquid surface has reached a desired level and sends a pouring stop command to a pouring mechanism (7) to complete the filling of the liquid.

Abstract: A safety device for heated sensors. A signal representing a threshold voltage is compared with a signal from the sensor representing sensor temperature. If the latter is greater than the threshold signal, a switch is opened to remove power from the means for heating the sensor. The normal state of the switch is closed, so after cooling, heat is again applied to the sensor.

Abstract: Method and arrangement for detecting the level of a liquid cryogen having a predetermined boiling point and which is being held in a container relative to the bottom of the container. The arrangement includes a container which receives the liquid cryogen and a longitudinal extending sensing member having a length extending from the bottom of the container to a level that is greater than any depth experienced for the liquid cryogen. The sensing member is vertically disposed in the container with one end in contact with the bottom of the container and the other end extending out of the liquid cryogen. The sensing member is composed of a high temperature superconductor material having a critical temperature that is higher than the predetermined boiling point of a selected cryogen. An electrical current is passed through the sensing member and the voltage drop across the sensing member is measured.

Abstract: A transistor and integrated circuit-free remotely indicating status device for holding tanks for recreational vehicles and pleasure boats contains no moving parts, is resistant to corrosion, and is inexpensively and simply manufactured and installed. In one embodiment, common LED indicating devices may be alternatively toggled between water tank and waste tank sensor circuits.

Abstract: An apparatus and method for continuously monitoring the liquid nitrogen level a liquid nitrogen container and automatically refilling liquid nitrogen from a liquid nitrogen reservoir when the liquid nitrogen in the container falls below a predetermined level. The apparatus comprises a liquid nitrogen level sensing element, which contains a superconducting material, such as a YbaCuO type superconductiing material, disposed on a non-conducting substrate, such as magnesium oxide. The superconducting material is selected such that it has a critical temperature approximately equal to the boiling point temperature of liquid nitrogen. The superconducting material is placed near the predetermined level and, under normal conditions, the superconducting material exhibits zero or near zero resistance.

Abstract: A hydraulic fluid lead detection system which self-calibrates for operation regardless of the particular reservoir or expansion tank. A reservoir stores a quantity of hydraulic fluid and is connected via a connecting tube or hose located at the upper-most portion of the reservoir and connected to an expansion tank mounted substantially adjacent to the reservoir. An elongated tube extends down into the expansion tank. The end of this tube is maintained substantially below the level of hydraulic fluid in the expansion tank during operation of the turf care machine. During operation, the hydraulic fluid expands with rising temperatures, and the connecting tube communicates the expanding fluid to the expansion tank. A float type fluid level sensor measures the level of hydraulic fluid within the expansion tank and outputs an electronic signal corresponding to the fluid level in the expansion tank to the microcomputer based monitoring unit, which also senses the fluid temperature.

Abstract: A tank (18) forms a chamber having an upper and lower region. The tank (18) is in even elevation with a horizontal pipe (12) having a top region and a bottom region. An upper connecting pipe (14) fluidly connects the top region of the pipe (12) to the upper region of tank (18). A lower connecting pipe (16) fluidly connects the bottom region of pipe (12) to the lower region of the tank (18). Heat junction thermocouples (22) generate a signal indicative of water in the pipe (12). The signal is transmitted to a remote location by line (24).