Continuous condition sensing system

Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters

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73304C, 324611, 324671, G01R 2726

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active

049509985

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.

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Robertshaw Controls Company, Product Specification Model 157A, Level-Tel Transmitter Model 157A.

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