US 4,788,488 A · Continuous condition sensing system

Abstract

A probe developing an admittance with a material whose condition is to be continuously measured is capacitively coupled with a variable frequency oscillator, preferably one having a digital output stage, for generating a variable frequency signal having a period varying with the admittance developed at the probe. Both the oscillator input and output are capacitively coupled to the probe. In a preferred embodiment, a set point circuit including a plurality of resistors coupled in parallel with the oscillator output and a plurality of switches coupled in parallel with the probe conductor and each with a different one of the resistor, provides easy circuit adjustment for use of the system with a variety of materials. A preferred digital circuit employing a pair of flip flops, fixed timer and one shot generate a fixed period variable duration duty cycle digital voltage level signal for transmission, if desired, or for conversion into a variable current signal.

Claims6

Dependent claims

A system for continuously measuring a varying condition of a material comprising:

a source of a material condition generating a variable voltage signal;
oscillator means responsive to the source for generating an oscillating signal having a period varying with the variable voltage signal;
a plurality of resistor means each having an end coupled to the oscillator means output for passing said oscillating signal through one or more separate resistances coupled to the oscillator means;
and
an equal plurality of switches each having an end coupled to the source and a remaining end coupled with a remaining end of a different one of the plurality of resistor means for selectively coupling one or more of said plurality of resistor means with the source.

2 more elements

Dependencies are inferred from the claim text.

Continuous condition sensing system

Life of this patent

Continuous condition sensing system

Life of this patent

Abstract

Claims6