Patent ID: 7151381
Filing Date: 2006-12-19
Classification: A01C

Abstract:
1. A meter for measuring the dielectric constant of a particulate material to be tested, the meter comprising: a housing; a test circuit within the housing; a test cell for containing a sample of the particulate material to be tested; the test cell being arranged to be mounted on the housing and so as to be connected into the test circuit; the test cell including two electrodes in the test cell for receiving the sample of particulate material to be tested as a dielectric between the electrodes, such that the capacitance of the test cell is a function of the dielectric constant of the sample of particulate material; the test circuit including a manually adjustable variable standard capacitor which is manually adjustable by an operator by a first manual control on the housing; an indicator on the housing coupled to the variable standard capacitor for displaying a value indicative of a capacitance setting of the variable standard capacitor; the test circuit including a manually adjustable trimming capacitor which is manually adjustable by an operator by a second manual control on the housing; the test circuit including a calibrating capacitor; the test circuit including only a single oscillator for generating a single oscillator output at a frequency which is varied in dependence on a capacitance of the test cell; the single oscillator including a tuned circuit for varying the frequency of the oscillator output, the tuned circuit including capacitors defined by: a frequency monitor for comparing the single output frequency of the single oscillator with a selected frequency; a display for displaying a frequency difference value representing a difference between the single output frequency of the oscillator and the selected frequency; the test circuit including a manually operable switch; the switch being actuable to a calibrate mode in which the calibrating capacitor, the trimming capacitor, the variable standard capacitor and the test cell when empty of the sample are connected in the circuit to allow setting of the variable standard capacitor to a predetermined capacitance setting as displayed on the indicator and to allow adjustment of the trimming capacitor to effect tuning of the frequency of the tuned circuit to the selected frequency; the switch being actuable to an operate mode in which the calibrating capacitor is disconnected from the circuit, and in which the trimming capacitor, the variable standard capacitor and the test cell when filled with the sample are connected in the circuit to allow setting of the variable standard capacitor to an indicated capacitance setting as displayed on the indicator to effect tuning of the frequency of the tuned circuit to the selected frequency; wherein the display is a digital display arranged to display the frequency difference value as zero when the output frequency of the oscillator equals the selected frequency, and to display the frequency difference value as a positive value when the output frequency of the oscillator is greater than the selected frequency and to display the frequency difference value as a negative value when the output frequency of the oscillator is less than the selected frequency.