Abstract: An all electronic, no moving parts, low cost, warning system, quickly and reliably alerts operator of malfunctions in levels, temperatures and pressures on trucks, farm implements, autos, boats, aircrafts, machinery, etc., which if not immediately attended to, may cause costly damage or even loss of life. Specifically gives aural and visual warning for: Low brake-fluid level, low transmission-fluid level, low engine-oil level, low differential-oil level, low coolant level, even low windshield-washer-fluid level, low fuel level, engine overtemperature, engine oil-pressure loss, loss of vacuum for power-brake assist, etc., in any single function, combination or extension, as pertaining to a particular truck, farm implement, auto, boat, aircraft, or similar machinery, all this being done by means of all-electronic parts, resulting into high reliability.

Abstract: An early warning system detects the failure of a marine cooling system by monitoring a resistance ground signal generated by a sensing element inserted into the cooling system. An alarm is given upon the detection of an increased resistance value of the resistance ground signal due to cessation or a severe reduction of water flow through the cooling system and hence contacting the sensing element. The sensing element is preferably inserted into the exhaust system portion of a marine engine cooling system and a detection circuit is connected to the sensing element. An alarm signal is generated by the detection circuit if insufficient water flow is present to maintain a low resistance value for the resistance ground signal generated by the sensing element. Such low resistance signal is maintained either by the electrical conduction of the water or the cooling effects of the water on the sensing element.

Abstract: In a circuit arrangement for the electrothermal measurement of level with a resistance sensor (1) which can be fed by a source of constant current (3), a flow-of-operation control (12) for timed operation of the circuit arrangement in scanning periods is provided. By the flow-of-operation control the resistance sensor is heated periodically, namely only during a heating time (t.sub.0 to t.sub.1) at the start of a scanning period. By the flow-of-operation control the compensation voltage is, in this connection, detected by the resistance sensor and provisionally stored. At the end of the heating time another detection is effected, this time of the measurement voltage. By dividing the measurement voltage by the compensation voltage a value which is analogous to the level of a fluid surrounding the resistance sensor is formed. This value contains practically no disturbing variables.

Abstract: A fluid level sensor utilizes thick film thermistors in a four-thermistor bridge configuration. The bridge is heated by a heater to sense the presence or absence of fluid at a particular level with respect to the thermistors. Upon energizing the bridge with a power source, the middle leads thereof are monitored for voltage separation and polarity. An indicator circuit indicates when one or more of the thermistors is submerged in the fluid. The heater influences the temperature of the thermistors to a greater or lesser extent depending upon whether or not they are submerged. Detectable changes in voltages across the bridge are accordingly produced.

Abstract: Double-junction thermocouple sensors located at axially spaced measurement zones within an elongated probe are interconnected in series to produce a combined output from differential signals generated by the sensors in response to unequal heating of the junctions. Axial heat flow between measurement zones is controlled to modify the combined output in a corrective direction with respect to a linear function of liquid level between the measurement zones.

Abstract: An electrically operated oil level gauge is composed of a flexible elongate bar whose one end section is provided with an oil level sensing element such as a thermistor. Additionally, a flexible elongate printed-wiring film is adhered on the surface of the flexible elongate bar so as to electrically connect the sensing element with a lead wire through which an electric current is supplied to the sensing element, thereby rendering the oil level gauge axially flexible while effectively preventing lead wire troubles.

Abstract: A thermal liquid level measuring system including a heat sensor with a sheathed heating resistor and a measuring resistor. Power is supplied to the heating resistor in a series of pulses. The measuring resistor is connected to two filters which extract the a.c. and d.c. components from the measuring signal. A temperature measuring device determines the difference in temperature of the liquid and the gas above the liquid. A computer receives signals from the filters and the temperature measuring device to determine the level of the liquid and its temperature.

Abstract: At the point or points in a vessel (1) at which the liquid or agitated charge level is to be monitored, a heat stream is fed into or out of the interior of the vessel (1) via a heat-conducting element (2) which is in thermal contact with the interior of the vessel (1) on the one hand and with a heat source or cold source (4) on the other hand. In order to indicate the level, the change in the heat stream when the liquid or agitated charge comes into contact with the elements (2) is determined by measuring the temperature of the element in the region of contact by means of a temperature sensor (5).

Abstract: A pair of PTC elements, preferably of the barium titanate variety, are mounted in a container to sense liquid level, for example oil level in an engine crankcase. The elements have the same resistance, mass and switching point but different thermal loss coefficients which have one value in air and another in liquid. In one embodiment, the elements are both positioned at the set liquid level and are electrically energized at the same moment. When the elements are in liquid, one of them will heat to the switch point before the other and change to a much higher resistance. When the elements are in air, the other element reaches the switch point first. When the elements are connected in series across a power source, the switching causes the circuit to latch in that state even though the liquid level condition changes. The junction of the elements provides a convenient signal output indicating liquid level. In a second embodiment, one PTC element is at the set liquid level and the other is in air above that level.

Abstract: A liquid level sensor includes a sensor coil co-axially positioned within a heater coil. Preferably, the sensor is coiled on a core of thin-walled stainless steel tubing to minimize the thermal conductivity along the axis thereof. The probe provides a continuous measurement of the level of a liquid due to the difference in thermal conductivity between the vapor and the liquid within the reservoir.

Abstract: Low oil level in an engine crankcase is detected immediately after the ignition switch is turned on by a circuit including the ignition switch, an oil level sensor and a coolant temperature sensor wherein a control circuit generates an output if a low oil level signal is present when the ignition switch is turned on. An enabling circuit allows an output only if the ignition switch has been turned off for a sufficient time period to allow oil drain back to the crankcase. A time delay circuit responsive to coolant temperature and the ignition switch prevents a control circuit output after the ignition switch is turned off for a short period when the temperature is high and a long period when the temperature is low.

Abstract: A low level indicator for a heated fluid in a container such as for use in indicating the glue level in a tank in a hot melt glue application. A thermistor probe is positioned at the mid-level of the container and senses the level of the heater fluid based upon sensing fluid contact with the probe. A light or alarm is activated when the heated fluid level falls below the probe, permitting of cooling the probe. The light or alarm is only activated when the probe becomes cooler subsequent to a time at which the probe was immersed in the fluid and properly heated. This conditional activation prevents continued low level alarm indications when the container is refilled with material at a temperature lower than that of the heated fluid.

Abstract: In a liquid level sensing apparatus having a stillwell in a liquid-holding tank disposed around the sensing device, a bubble shield is provided to interdict the upward flow of bubbles to the stillwell to protect the sensor from contact with bubbles or foreign matter which could result in a false reading.

Abstract: A device for measuring the level of a liquid, comprising a high temperature coefficient sensor immersed in the liquid, a detection circuit connected to the sensor for delivering a voltage indicative of the level of liquid, a memory circuit to which said voltage is applied, a saw-tooth signal generator circuit and, a comparator. The output signals of the memory circuit and of the saw-tooth signal circuit are coupled to input terminals of the comparator, and a display galvanometer is connected to the output of said comparator.

Abstract: A bearing assembly includes a lubricated bearing and a thermistor mounted in or adjacent the lubricant flow path through to or from the bearing. The thermistor is in heat exchange relationship with the lubricant and is connected in an electrical circuit so as to operate in the self heating mode to respond to a deleterious change in the flow of lubricant along the path. The rate of flow of lubricant determines the rate of dispersion of heat from the thermistor and thereby determines the temperature of the thermistor.

Abstract: An autoreferencing liquid level sensing apparatus and method determines the presence of a liquid by observation of the convective cooling rate of a heated temperature sensor. The temperature measured by the temperature sensor is compared with an adapting temperature reference whose initial value is determined from the initial measured temperature and whose value increases during the heating at a rate proportional to the rate of heating of the temperature sensor and the initial temperature. This comparison enables discrimination of whether the convective cooling rate of the temperature sensor is above or below a predetermined level. Because the rate of convective cooling depends in large part on the thermal capacity of the fluid surrounding the sensor, the convective cooling rate determination allows discrimination of whether the temperature sensor is surrounded by a gas or a liquid, or surrounded by one of two immiscible liquids having differing thermal properties.

Abstract: This invention generally pertains to a device for electrically detecting a liquid level such as water, oil and so on, which is suitably used for an automatic operating apparatus for a pump, or for a liquid level warning device. The device of the invention comprises an electric heater disposed flush with a liquid level to be detected, a heater temperature detector to electrically detect a heater temperature to generate a heater temperature signal, and an environment temperature detector to electrically detect an environment temperature to generate an environment temperature signal. In one aspect of the invention, there is further provided a reference signal generator to generate a reference signal depending on the range of the environment temperatures at which the liquid level is to be detected, and a comparative circuit to electrically compare a difference between the heater temperature signal and the environment temperature signal to generate a level signal.

Abstract: A device (1) for sensing the presence of a dielectric liquid at a predetermined level in a tank is described. The main feature of device (1) is that it comprises a first and a second bimetallic strip (23, 44) disposed facing each other and a resistor (48) disposed in proximity to said second strip (14) at a level in said tank equal to said predetermined level.

Abstract: Fluid level detection means utilizing a thermally conductive element in the general shape of a cone, in one embodiment, in direct contact with fluid whose level is to be detected. A portion of the element, excluding the apex, is directly heated. A thermal sensor is bonded to the apex. When the fluid depletes such that the apex is exposed to air, the temperature in the immediate vicinity of the apex rises to a new point of equilibrium. The sensor converts this elevated temperature into a signal recognized by electronic circuitry as a flow fluid level. This signal may subsequently be used to provide visual or audible alarm.

Abstract: A wet-niche type lamp for providing underwater illumination in a swimming pool or the like includes an over-temperature protection circuit which interrupts the supply of electrical energy to the lamp when the level of the cooling water surrounding the lamp drops below a predetermined level. The circuit includes thermistor mounted in an heat exchange relationship with the surrounding water so that heat energy generated in the thermistor, as a consequence of the current flow through it, is normally transferred to the surrounding water. Should the level of the surrounding water drop below that of the thermistor, the thermistor heat energy quickly evaporates any remaining water film on the exterior surface of the thermistor to allow its temperature to rise. The control circuit, in response to the temperature increase, interrupts the flow of electrical energy to the lamp to prevent over-temperature operation.

Abstract: A level indicator comprises a tubular probe immersed in the liquid to a depth defining the minimum liquid level in the reservoir. The probe communicates with a gas-filled chamber with a heating resistor therein. A warning member is connected to the gas-filled chamber to indicate that the level of the liquid reaches a minimum as indicated by no pressure increase occurring in said chamber.

Abstract: An amplifier system includes an operational amplifier having a reference applied to one input terminal. A voltage above or below the reference voltage is applied to the other input terminal by way of an interface circuit. The interface circuit adapts the input for use with a switch or, alternatively, the interface may be disabled to permit use of a variable resistor input such as a thermistor. The output of the operational amplifier may be a switching circuit. The amplifier system is adapted for use in a fluid level system to permit the alternate use of a switch type or thermistor level sensor.

Abstract: A liquid level detecting apparatus comprises a thermistor adapted to generate heat by current flowing therethrough, wherein the liquid level is sensed by detecting a current value at the thermistor which varies in dependence on a variation in temperature of the thermistor, which temperature in turn varies in dependence on whether the thermistor is immersed in the liquid or exposed to air. A relay coil is provided in series to the thermistor and disposed within a casing together with the latter so that the variation in temperature of the liquid may be transmitted to the relay coil, wherein the variation in the current value at the thermistor caused by the temperature variation of liquid is corrected by the variation of the resistance of the relay coil.

Abstract: Detecting different fluids, such as oil at the surface of water, by a heated monitoring element exposed for contact with the fluid, the element having a resistance characteristic that changes as a function of temperature, in preferred embodiments being the mere filament of a light bulb. One system employs circuitry for periodically applying a pulse of electrical heating current to the monitoring element, to heat and produce a change in its electrical resistance, and output circuitry responsive to change in electrical resistance to indicate the nature of the fluid. In another system the resistance of the monitoring element is controlled by comparison to a constant reference, the heating current required serving to indicate the nature: e.g. oil, water or air, of the fluid contacting the element.