Abstract: In a circuit for electrothermal measurement of level compensated for ambient temperature which has a switched source of constant current (2) for a resistance probe (1), a first variable formed from an initial voltage U.sub.0 on the resistance probe at the start of a heating period is compared by a comparator (14) with a second variable formed from a heating voltage U.sub.1 at the end of a heating period. One of these two variables, in this case the first variable, is formed in accordance with a time integral and used as basis for the comparison with the other variable. For the formation of the integral, a resistor (10) and a capacitor (9) are components of an integrator whose input can be coupled to the resistance probe (1) via a first sample and hold member (4, 5) for the initial voltage U.sub.0. The output of the integrator is connected to a first input (13) of a comparator (14).

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: In a device for electrically monitoring the level of a liquid present in a container, a plurality of temperature-dependent resistance probes (n-1, n, n+1) are arranged at different heights in the container, they being adapted to be connected one after the other to a source of constant current (5) under the control of a program control device. For the evaluation of the voltage at one resistance probe (for example n+1) connected at the time to the source of constant current (5), a differentiator (6) is provided as well as a comparator (7), which is arranged behind the former and is and acted on by a threshold voltage and is connected to circuitry for forming a display signal. The circuitry comprises counter (4, 19) which counts the number of resistance probes (n-1, n, n+1) whose voltage differential is above the threshold voltage after connection to the source of constant current (5).

Abstract: A device for the capacitive measurement of a level of filling having a measurement capacitor which dips into the fluids to be measured in accordance with the filling level thereof, and a unit for forming an electric value corresponding to the filling level and a unit for compensating for different dielectric constants of fluids which comprise a compensation capacitor dipping into the fluid. A circuit forms an electric value corresponding to the filling level and compensates the different dielectric constants of the fluid such that only the imaginary part of the complex conductance of the measurement capacitor and of the compensation capacitor enters into the electric value, but not the real part thereof in each case.