Programmable controller
AssigneeBeckman Instruments, Inc.
InventorJames R. Brown
Life of this patent
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Abstract
There is disclosed a circuit for generating an error voltage which is proportional to the difference between a desired value of a physical parameter and the actual value of the physical parameter. The circuit operates by alternately switching the current from a source through a fixed reference resistor and a variable resistor, the resistance value of which changes as a function of the physical parameter to be controlled. The current is switched between the two resistors so that the average voltage generated across the variable resistor would be equal to the average voltage generated across the fixed resistor if the physical parameter had the desired value. By determining the difference between the average voltages across the resistors, the error voltage can be generated for controlling the physical parameter.
Claims9
A programmable controller for generating a signal for controlling the value of a physical parameter comprising:
- a fixed reference resistor;
- a variable resistor, the resistance value of which changes as a function of the value of said physical parameter;
- a source of current;
- means for switching said current alternately through said fixed and variable resistors;
- means for controlling said switching means to adjust the relative times said current is conducted through said resistors, said relative times being a function of a desired value of said physical parameter;
- and
- means for determining the difference between the average voltages across said resistors and for generating a control signal proportional thereto.
A circuit for generating an output as a function of the difference between the actual resistance of a first resistance element and a desired resistance of said first resistance element comprising:
- first and second resistance elements;
- a source of current;
- means for alternately conducting said current through said first and second resistance elements;
- means for controlling said conducting means to adjust the relative times said current is conducted through said resistance elements so that the average voltage generated across said resistance elements will be equal if said actual resistance of said first resistance element equals said desired resistance of said first resistance element;
- and
- means for generating said output as a function of the difference between the average voltages across said resistance elements.
Dependencies are inferred from the claim text.