Resistive liquid level/temperature sensor and transmitter
First Claim
1. A method for measuring the levels of first and second liquids in a container wherein the first liquid lies below the second liquid, said method comprising the steps of:
- locating a plurality of resistors that are interconnected to one another in electrical series inside a probe such that said resistors extend longitudinally through said probe;
dipping the probe into the liquids to be measured so that said plurality of series connected resistors extends from at least the top of the second liquid to the bottom of the first liquid;
creating a first current path through a first number of said plurality of series connected resistors which lie between the bottom of the container and the interface of the first and second liquids;
creating a second current path through a second number of said plurality of series connected resistors which lie between the top of the container and the top of the second liquid;
measuring the total resistance of said first number of said plurality of resistors within said first current path; and
measuring the total resistance of said second number of said plurality of resistors within said second current path.
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Abstract
A resistive liquid level/temperature sensor and transmitter including low voltage impedance measurement circuitry to convert three impedance values into indications of the temperature and the levels of two different liquids (e.g., oil and water) located within a storage tank. A resistive chain network including a plurality of series connected resistors and a corresponding plurality of reed switches extend longitudinally through a liquid level sensing probe that is dipped into the liquids in the tank. A pair of magnetic floats having different specific gravities surround the probe and rise to the two fluid levels. The magnetic floats close adjacent reed switches which create first and second current paths through the resistive chain network. The impedances of the first and second current paths are measured to provide an indication of the liquid levels. A resistive temperature device carried by the probe provides an indication of temperature.
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Citations
25 Claims
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1. A method for measuring the levels of first and second liquids in a container wherein the first liquid lies below the second liquid, said method comprising the steps of:
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locating a plurality of resistors that are interconnected to one another in electrical series inside a probe such that said resistors extend longitudinally through said probe; dipping the probe into the liquids to be measured so that said plurality of series connected resistors extends from at least the top of the second liquid to the bottom of the first liquid; creating a first current path through a first number of said plurality of series connected resistors which lie between the bottom of the container and the interface of the first and second liquids; creating a second current path through a second number of said plurality of series connected resistors which lie between the top of the container and the top of the second liquid; measuring the total resistance of said first number of said plurality of resistors within said first current path; and measuring the total resistance of said second number of said plurality of resistors within said second current path. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for measuring the levels of first and second liquids in a container wherein the second liquid lies above the first liquid, said method comprising the steps of:
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connecting a plurality of resistors in electrical series; connecting a plurality of magnetic force-responsive normally-open switches to respective ones of said plurality of resistors; locating said pluralities of series connected resistors and normally-open switches inside a probe so as to extend longitudinally therethrough, such that a first end of said series connected resistors lies adjacent the bottom of the probe and the opposite end of said series connected resistors lies adjacent the top of said probe; dipping said probe into the liquids to be measured; coupling first and second magnetic force generators to said probe such that said first magnetic force generator has a first specific gravity corresponding to the specific gravity of the first liquid and the second magnetic force generator has a second specific gravity corresponding to the specific gravity of the second liquid whereby said first and second magnetic force generators rise to the levels of the first and second liquids in the container so as to close respective first and second ones of said plurality of magnetic force-responsive normally-open switches lying in proximity to said force generators and thereby create a first current path starting from the first end of said plurality of series connected resistors and running upwardly relative to said probe through said first switch and a first number of said plurality of series connected resistors corresponding to the height of the first liquid and a second current path starting from the opposite end of said plurality of series connected resistors and running downwardly relative to said probe through said second switch and a second number of said plurality of series connected resistors corresponding to the height of the second liquid lying above the first liquid; and measuring the total resistance of each of said first and second current paths created when said first and second magnetic force-responsive switches are closed. - View Dependent Claims (12, 13, 14, 15, 16, 17)
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18. A liquid level sensor for indicating the levels of first and second liquids in a container, wherein the second liquid lies above the first liquid, said sensor comprising:
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a liquid probe; a plurality of magnetic force-responsive normally-open switches connected to respective ones of a plurality of resistors which are connected in electrical series to form a resistor chain network having first and opposite ends, said pluralities of series connected resistors and normally-open switches being located inside said probe and extending longitudinally therethrough; a first magnetic float having a first specific gravity surrounding the probe and sliding therealong to the first liquid level when said probe is dipped into the first and second liquids in the container; and a second magnetic float having a second specific gravity surrounding the probe, said second magnetic float lying above said first magnetic float and sliding along said probe to the second liquid level when said probe is dipped into the first and second liquids in the container, said first and second magnetic floats closing respective first and second ones of said plurality of magnetic force-responsive normally-open switches lying in proximity to said first and second magnetic floats to thereby create a first current path extending from a voltage supply to the first end of said series connected resistor chain network and running through said first magnetic force-responsive switch and a first number of said plurality of series connected resistors corresponding to the height of the first liquid and a second current path extending from said voltage supply to the opposite end of said series connected resistor chain network and running through said second magnetic force-responsive switch and a second number of said plurality of series connected resistors corresponding to the height of the second liquid above the first liquid, wherein the total resistance of each of said first and second current paths being indicative of the levels of the first and second liquids in the container. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25)
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Specification