Device for electric monitoring of the level of a liquid in a container

In a device for electric monitoring of the level of a liquid present in a container, with a temperature-dependent resistance probe which is immersed in the liquid the level of which is to be monitored, a source of constant current connectable to the resistance probe, the current controlled by a timer, with means, controlled by the timer, for detecting and storing an initial voltage drop on the resistance probe at an initial time and a measurement voltage at a defined time after the connection of the source of constant current, and means for evaluating these voltages by subtraction of the measurement voltage from the initial voltage in order to form a display voltage which corresponds to the level, the improvement further comprising

• means for compensating for an influence of the change in level of the liquid, due to thermal expansion as a function of its initial temperature, on the display voltage, and
• means for compensating for different heat transfers from the resistance probe to the liquid as a function of the initial temperature, wherein
• a microprocessor means constitutes said means for compensating for the influence of the change in level of the liquid due to thermal expansion and said means for compensating for different heat transfers from the resistance probe to the liquid as a function of the initial temperature, said further device further comprising
• an analog/digital converter connecting said microprocessor means with the resistance probe, and wherein
• said microprocessor means includes means for storing therein at least characteristic curves of dependency of the uncorrected display voltage on the initial temperature for maximum and minimal filling quantities, and
• said microprocessor means provides for the calculating of a corrected display voltage from the initial temperature and the original display voltage.

In a device for electric monitoring of the level of a liquid present in a container, with a temperature-dependent resistance probe which is immersed in the liquid the level of which is to be monitored, a source of constant current connectable to the resistance probe, the current controlled by a timer;

• with means, controlled by the timer, for detecting and storing an initial voltage drop on the resistance probe at an initial time and a measurement voltage at a defined time after the connection of the source of constant current, and means for evaluating these voltages by subtraction of the measurement voltage from the initial voltage in order to form a display voltage which corresponds to the level, the improvement further comprising
• means for compensating for an influence of the change in level of the liquid, due to thermal expansion as a function of its initial temperature, on the display voltage, and
• means for compensating for different heat transfers from the resistance probe to the liquid as a function of the initial temperature, wherein
• said means for compensating for the influence of the change in level of the liquid due to thermal expansion is a resistance probe, and wherein
• said resistance probe comprises a resistance wire having an upper vertical section with a resistance length small compared with the length of the wire, and a lower vertical section with a resistance wire length large compared with the length of the wire.