Laboratory systems for measuring short-term changes in water levels.

In hydraulics, one is often involved with measurements of small amplitude and relatively fast changing water levels. Different types of instruments are now being used, among which the resistance types are of common usage. However, the nonlinearity of the output signal and the variation in the conductivity of the fluid are two types of problems commonly encountered with these systems. In a first step, the linear variation of the resistivity as a function of the immersion depth of the probes is verified. Then, the shape of electrodes is determined in order to make the output voltage a linear function of the immersion depth. Also a system is proposed to obtain a linear output voltage for parallel electrodes. In a second step, an electronic system has been developed and tested in order to compensate for the variation in conductivity of the fluid being measured. The use of a reference probe in such a system gives a linear output voltage which is constant even through the conductivity of the fluid is changed during testing.