Auswerteschaltung zur Ermittlung komplexer Impedanzen, Vorrichtung zur Messung komplexer Impedanzen und Verwendung der Vorrichtung

NOVELTY - The circuit to evaluate complex impedances has a voltage supply with a frequency generator (8) to give digital signals, a 1:2 frequency divider (9), and a unit (10) to give two alternating voltage signals with a 90 deg. phase shift with the first frequency. The phase shift remains during a frequency variation. DETAILED DESCRIPTION - The frequency generator (8) gives a signal of twice the first frequency and a scanning ratio of 50%, or four times the first frequency where the voltage supply has a second 1:2 frequency divider. The unit (10) to give two alternating voltage signals is a D-flip-flop. The signals from the amplifier and the phase shifted signals are combined to give two output signals to show the real and imaginary parts of the impedance, using a half-wave or full-wave rectifier. A deep pass filter is in front of the current supply. The links between the sensor and amplifier are shrouded. The amplifier has a buffer amplifier with an amplification factor of V=1. The outer lead of the shrouding is linked to the buffer amplifier output. The amplifier has connections for positive and negative supply voltages, each with a resistance connection to the supply voltage. A voltage stabilizer is linked to the amplifier output. One or more sensors each have two electrodes to register the complex impedance. A signal converter switches the input of the evaluation circuit between the separate sensors. The electrodes are covered with a thin insulation layer of silicon carbide, in comparison to the gap between the electrodes, which has high chemical stability in a layer thickness of 0.2-2.0 mu m. The sensor is a surface wave sensor, with capacitative electrodes, and the assembly can register other measured values. The sensor can be fitted with interdigital electrodes on the substrate of the surface wave sensor, where one is the interdigital electrodes of a pair of measurement electrodes. USE - The apparatus is for measurement of fluid characteristics, the aging o f lubricant oil, the moisture content in soil, to measure ion concentrations, to determine the water content in liquids with low dielectric values, to determine the water content in alcohol or oil and vice versa, to register the water content in brake fluid, to measure the composition of milk, the time point of concrete hardening, to measure the contamination of soil by oil or acids, to identify acids and lyes in water and measure their concentration, and the like. ADVANTAGE - The circuit gives a constant phase shift even during temp. changes and frequency alterations without any complex phase smoothing systems.