Capacitance transducer of particulate material permeability with compensation of temperature

摘要

The basic component of a capacitance transducer of particulate material permeability according to the present invention, is a measuring capacitor (1) with two plates (17) and (18) and a space created between these plates (17) and (18) for passage of a measured/sensed material (2) therethrough. The measuring capacitor (1) id connected via a measuring circuit first resistor (3) to the output of an oscillator (4) with constant frequency forming thus therewith a measuring divider (13) having its output connected with a measuring circuit rectifier (5). Depending on the amount of material (2) passing through the measuring capacitor (1), the permittivity of air and material ratio changes, and due to this change, impedance of the measuring capacitor (1) and thus output voltage of the measuring divider (13) forming a part thereof changes, too. A temperature compensation circuit consists of a compensation circuit second resistor (6) connected to the constant frequency oscillator (4), a compensation circuit capacitor (7) forming along with the compensation circuit second resistor (6) a voltage divider (14) having its output connected to a compensation circuit rectifier (8). The measuring circuit rectifier (5) and the compensation circuit rectifier (8) generate voltages of opposite polarity, and are connected via a third resistor (9), a fourth resistor (10) and a resetting resistance trimmer (11) to an amplifier (12). As changes of temperature result identical changes in voltage in both the circuits, but of opposite polarity, the temperature dependence is eliminated and at the voltage output (15), there is only a voltage, which is dependent on the amount of the measured/sensed material (2) passing through the measuring capacitor (1).