Patent ID: 7129713
Filing Date: 2006-10-31
Classification: G01N

Abstract:
1. A moisture sensing apparatus, comprising: an oscillator having an output for supplying an AC signal; a sensor having a sensor pad, a driven ring around the pad and connected to the oscillator output, and a ground plate around the ring; and a precision rectifier connected to the sensor for rectifying a signal from the sensor to form a DC signal that is proportional to the moisture content, the precision rectifier comprising: an operational amplifier having one input connected to the pad, another input, and an output, the operational amplifier being operative to obtain a difference between input signals; a first diode connected to the output of the operational amplifier and in a feedback loop between the operational amplifier output and the other input of the operational amplifier to nullify variations in the rectified signal that are due to temperature induced variations of diode parameters, the first diode having an output for supplying a rectified signal that is a monotonic function of moisture content of material that is in contact with the sensor; and a second diode connected between the output and the other input of the operational amplifier for reducing output errors.