Thermocouple vacuum gauge
AssigneeVarian Associates, Inc.
InventorJohn F. Zettler
Life of this patent
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Abstract
A thermocouple pressure gauging system for measuring partial vacuum is provided which uses time multiplexing to alternately heat the thermocouple to constant temperature and then measure the EMF from thermocouple with heating current off. A signal proportional to pressure is derived from the heating duty cycle. The pressure signal is in turn used to derive a reference signal which is compared to the EMF from the thermocouple to control the heating of the thermocouple.
Claims8
A system for deriving an electrical signal which is proportional to pressure at partial vacuum comprising:
- a thermocouple in a partial vacuum;
- servomechanism means for time-multiplexing a pulsed heating current to said thermocouple with a voltage signal from said thermocouple, said servomechanism generating timing signals;
- means for generating a signal proportional to the pressure from a duty cycle of said timing signals;
- means for generating a reference signal from said signal proportional to pressure, said reference signal being used with said voltage signal from said thermocouple to generate heating current pulses;
- and
- power supply means connected to said system.
A method of operating a thermocouple gauge in partial vacuum comprising the steps of alternately providing a heating current to a thermocouple junction and then measuring a thermally generated EMF from said thermocouple junction with said heating current off, generating a signal proportional to pressure from a duty cycle of said heating current, generating a reference signal from said signal proportional to pressure, and generating heating current pulses from said thermally generated EMF and said reference signal.
Dependencies are inferred from the claim text.