Two-wire compensated level measuring instrument
First Claim
1. A circuit for performing division of first and second signals, comprising:
- integrator circuit means;
means for supplying said integrator circuit means with a first predetermined initial condition Vi ;
means for controlling operation of said integrator circuit means to integrate a first signal VR, defining a first integrated signal, until a second predetermined signal value is reached;
means for measurement of the time T required for said integration;
means for thereafter supplying said integrator means with a second signal VL ;
means for controlling operation of said integrator means to integrate said second signal, defining a second integrated signal, for an equal length of time T;
said integrator at the end of said equal length of time of integration containing an output value Eo (T); and
means for outputting a signal proportional to the ratio of the difference between said output value Eo (T) and said second predetermined value to the difference between said second predetermined value and said first predetermined initial condition Vi, equal to the ratio of said second integrated signal to said first integrated signal VL /VR l.
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Accused Products
Abstract
An improved system for generating a signal representative of the level of a material having a dielectric constant within a vessel is disclosed. The system features use of a first probe for generating a signal indicative of the dielectric constant of the material which is divided into a signal varying with the level of the material whereby a compensated level signal irrespective of the actual dielectric constant is measured. In a preferred embodiment, a single integrator is used to perform the division operation whereby inaccuracies due to component variation including long-term drift are eliminated. The instrument is disclosed as functioning in a two-wire instrument system having low power requirements, permitting use of conventional signal limits. Means for calibrating the instrument in a fail-safe manner such that the operator is assured of proper calibration are disclosed, as is means whereby bridge circuits used to measure in the capacitance measurements supplied to the division circuit are both supplied by a single oscillator means, again increasing reliability and accuracy of the system.
74 Citations
13 Claims
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1. A circuit for performing division of first and second signals, comprising:
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integrator circuit means; means for supplying said integrator circuit means with a first predetermined initial condition Vi ; means for controlling operation of said integrator circuit means to integrate a first signal VR, defining a first integrated signal, until a second predetermined signal value is reached; means for measurement of the time T required for said integration; means for thereafter supplying said integrator means with a second signal VL ; means for controlling operation of said integrator means to integrate said second signal, defining a second integrated signal, for an equal length of time T; said integrator at the end of said equal length of time of integration containing an output value Eo (T); and means for outputting a signal proportional to the ratio of the difference between said output value Eo (T) and said second predetermined value to the difference between said second predetermined value and said first predetermined initial condition Vi, equal to the ratio of said second integrated signal to said first integrated signal VL /VR l. - View Dependent Claims (2, 3, 4)
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5. Method of dividing the value of a first signal VL by the value of a second signal VR comprising the steps of:
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storing an initial condition Vi in an integrator circuit means; applying said second signal VR to said integrator circuit means; measuring a first time period T equal to the time taken for said initial condition VR to said integrator circuit means to reach a predetermined second value; applying said first signal VL to said integrator circuit means for a second time period equal to said first time period T; and providing an indication of a content of said integrator circuit means after said second time period has passed, whereby the ratio of the difference between the contents of the integrator circuit means Eo (T) and the predetermined second value to the difference between the predetermined second value and the predetermined initial condition Vi, is the ratio of the first signal to the second signal Vi /VR. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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12. Apparatus for generating a signal representative of the level of materials in a vessel and transmitting said signal over two electrical conductors to remotely-located means for responding to said signal, wherein said remotely-located means also supplies power over said two conductors to said apparatus for generating the signal, comprising means for dividing a first signal indicative of the dielectric constant of the material the level of which is to be measured into a second signal varying with the level of said material, whereby the ratio of said first and second signals is a third signal representative of the level of said material irrespective of its dielectric constant, wherein said means for dividing comprises:
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means for supplying an initial condition to integrator means; means for supplying said first signal to said integrator means, thus modifying said initial condition at a rate dependent on the magnitude of said first signal; means for measuring the time T taken for said initial condition modified in said integrator to be varied to reach a predetermined value; means for supplying said second signal to said integrator means for modifying its output; means for controlling the time said second signal is supplied to said integrator such that said time is equal to the time T taken for said predetermined value to be reached; and means for outputting a signal indicative of the ratio of the change in the output of said integrator while said second signal was supplied to said integrator to the change in the output of said integrator while said first signal was supplied to said integrator, said ratio being equal to the quotient of said first and second signals. - View Dependent Claims (13)
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Specification