Device for continuous level measurement in liquids, by means of a chain of series- or parallel-connected, temperature-dependent resistors, which are heated by an electrical current

摘要

A device is described for level measurement in liquids, which uses the immersion depth of a resistor strip with a positive-temperature-coefficient behaviour (Figure 3) or with a negative-temperature-coefficient behaviour (Figure 4) for the level measurement. The resistor strips are, in this case, heated directly by an electric current. The portion of the resistor which is immersed is held at the temperature of the cooling liquid; the part which is not immersed has a significantly higher temperature than the immersed part, because of its electrical heating and the far poorer cooling effect of the surrounding gas (vapour of the liquid itself or air). In this case, in the case of positive-temperature-coefficient material, the partial resistance (Figure 1) increases in the non-immersed part, in the case of negative-temperature-coefficient material, the partial resistance (Figure 3) decreases in the non-immersed part. If the resistance Ro is known in the case of a fully immersed measuring element, the immersion depth can be determined by a comparison of Ro and the actual resistance. <IMAGE>