Limit-level sensor and method of determining the undershooting or overshooting of an intended level of liquid in a container

A method for determining whether an intended level of liquid in a container is exceeded or not reached, the method comprising steps of:

• locating a resistance element within an intended level of the liquid, wherein electrical resistance of the resistance element changes with increase in temperature upon a heating of the resistance element by an electric current;
• enclosing the resistance element within a housing which extends in longitudinal direction into the liquid, a portion of said housing defining a cage which encloses said resistance element;
• extending a bar transversely across the housing for fixing the resistance element against oscillation and spaced apart from elements of said cage, a spacing between element of the cage and the resistance element inhibiting dissipation of heat of the resistance element via the elements of the cage;
• leading wires from the bar to he resistance element, a first of the wires being disposed alongside a second of the wires;
• clamping the wires by means of the bar in a fixed position relative to the housing;
• and
• measuring the electric resistance by feeding as much electrical energy via the wires to the resistance element upon a heating of the resistance element as is necessary in order to exceed a transition temperature of the resistance element present in air for an abrupt change in the electrical resistance.

A method for determining whether an intended level of liquid in a container is exceeded or not reached, the method comprising steps of:

• locating a resistance element within the liquid at an intended level of the liquid, the resistance of the resistance element being characterized by a transition temperature, wherein electrical resistance of the resistance element changes with increase in temperature upon a heating of the resistance element by an electric current;
• providing a housing for supporting the resistance element in the liquid, the housing terminating in a cage which encloses the resistance element;
• spacing elements of the cage away from the resistance element to allow for flow of liquid between the resistance element and elements of the cage, a spacing between the elements of the cage and the resistance element via the elements of the cage;
• extending a bar transversely across the housing for fixing the resistance element against oscillation and spaced apart from elements of said cage;
• leading wires from the bar to the resistance element, a first of the wires being disposed alongside a second of the wires;
• clamping the wires by means of the bar in fixed position relative to the housing;
• heating the resistance element and liquid adhering to the resistance element by application of electric current to the resistance element, the heating reducing viscosity of the liquid to facilitate flow of the liquid past the resistance element;
• and
• measuring the electric resistance by feeding as much electrical energy to the resistance element upon a heating of the resistance element as is necessary in order to exceed a transition temperature of the resistance element present in air for an abrupt change in the electrical resistance.

A limit-level sensor for determining whether an intended level of liquid in a container is not reached or is exceeded, the sensor comprising:

• a resistance element for receiving an electric current, the resistance element changing its electric resistance upon an increase in temperature;
• a cage enclosing the resistance element, wherein elements of the cage are spaced apart from the resistance element for flow of the liquid past the resistance element, a spacing between the elements of the cage and the resistance element inhibiting dissipation of heat of the resistance element via the elements of the cage;
• a bar extending across the cage;
• connecting wires leading from the bar to the resistance element, a first of the connecting wires being disposed alongside a second of the connecting wires
• a measurement unit connected by the wires to the resistance element for measuring the electric resistance;
• wherein the resistance element is to be located entirely within a liquid of an intended level, and the electric resistance varies abruptly above a transition temperature of the resistance element, the transition temperature lying above a maximum temperature of the liquid;
• and
• wherein a heating of the resistance element with electric current supplied by the connecting wires serves to heat liquid adhering to the resistance element for reducing viscosity of the liquid to facilitate flow of the liquid past the resistance element, and the connecting wires are clamped by means for the bar in a fixed position relative to the housing.