Measuring and testing – Gas analysis – By vibration
Patent
1977-03-14
1977-12-20
Ruehl, Charles A.
Measuring and testing
Gas analysis
By vibration
73 231, 324130, G01N 2518
Patent
active
040634477
ABSTRACT:
A bridge circuit having reference and measurement thermistors in respective adjacent arms is automatically readjusted to off-set any long term drift of the thermistors. The readjustment of the bridge circuit is performed between normal measurement operations using a bridge output error signal produced by the drift of the thermistors. The output signal of the bridge circuit is also applied to a comparator circuit to produce a polarity characterized output signal in response to the relative magnitude between the bridge output signal and a fixed reference signal. This characterized output signal is used to control the counting direction of an up/down counter. A source of fixed frequency pulses is connected to the input of the up/down counter during a sample window time between the measurement operations to change the count stored in the counter in accordance with the direction of counting as determined by the output signal from the comparator. The count stored in the counter, in turn, is applied to a digital to analog converter to produce an analog control signal corresponding to the digital stored count. This analog output signal is applied as a drive signal to adjustable current sources in adjacent arms of the bridge circuit to control the current through the reference and measurement thermistors whereby to offset the drift of these thermistors.
REFERENCES:
patent: 3577075 (1951-05-01), Krygeris
patent: 3590628 (1971-07-01), Orr
patent: 3784912 (1974-01-01), Van Aken
patent: 3937062 (1976-02-01), Rhodes, Jr.
Burton Lockwood D.
Halista Mitchell J.
Honeywell Inc.
Marhoefer Laurence J.
Ruehl Charles A.
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