A unknown value of capacitance is determined by the repeated transfer of quantities of charge from a potential store in amounts proportional to the value of the unknown capacitance. Transfer is accomplished during at least two distinct periods of a measurement cycle so that capacitance may be expressed as a ratio of a known and an unknown capacitance in order to eliminate certain circuit related errors.

A capacitance detector comprises switches for charging and discharging a sensing part, an integrator constituted by a condenser and an operational amplifier for integrating a charging current or a discharging current which is generated according to the charging and discharging the sensing part, a switch for charging an output voltage of the operational amplifier and for feedbacking an electric charge to the integrator, and a condenser. The capacitance detector can be provided by the operational amplifier having a low response performance and a small output current and no hold sample circuit, thereby a circuit scale of the capacitance type sensor can be made small.

A method and apparatus for measuring an unknown capacitance using a known reference capacitance, wherein a first electrode of the unknown capacitance is connected to ground. The apparatus includes a first device for precharging the unknown capacitance to a first predetermined potential; a second device for selectively charging a first electrode of the reference capacitance to the same potential as the second electrode of the unknown capacitance, without changing the potential on the second electrode of the unknown capacitance; a first switch for selectively electrically connecting the first electrode of the reference capacitance to the second electrode of the unknown capacitance; a third device for switching the potential on the second electrode of the reference capacitance between a first predetermined value and a second predetermined value; a comparator for comparing the potential on the second electrode of the unknown capacitance to a reference voltage; and a sequencer responsive to the output from the comparator and designed to control the second device, the first switch, and the third device, and for counting the number of times these devices are used. The number of times these devices are used in a particular measuring operation according to the present method, is indicative of the unknown capacitance.

A circuit and method for measuring the capacitance of a circuit element. A reference capacitor, a voltage source, and a switching circuit are arranged such that the circuit element and the reference capacitor are alternately charged and discharged from the voltage source at the same frequency, the charging of the circuit element being synchronized with either the charging or the discharging of the reference capacitor. Currents of the circuit element and the reference capacitor, for example the discharge currents, are supplied to a reservoir capacitor circuit and compared to provide a measure of the difference between the capacitances of the circuit element and the reference capacitor. The comparison is made by monitoring the feedback current necessary to maintain the charge of the reservoir capacitor circuit substantially constant.

A process and apparatus are disclosed for continuously determining the moisture content of a spoilable grain product which is moved along a processing line as a product stream and passed, at least in part, downwardly through a measuring section of a housing in accordance with the process, a pourable average of the product stream is created continuously within the measuring section, and the product moisture content of this product average is measured electrically on a continuous basis. In accordance with the device, the measuring housing has a capacitor as a continuous-flow measuring section and a device for continuously controlling the creation of a pourable product average.