Dynamic current drive method for powering thermal conductivity d

Details Dynamic current drive method for powering thermal conductivity d Dynamic current drive method for powering thermal conductivity d

1982-02-26

1984-07-24

Kreitman, Stephen A.

Measuring and testing

Gas analysis

By vibration

G01N 2536

Patent

active

044611668

ABSTRACT:
A gas stream detection apparatus having a balanced resistive bridge network enclosed within a housing and an electronic power supply for driving the bridge network. The power supply includes a voltage source feeding a voltage-to-current converter with two differential inputs, a current sensing resistor between the converter and bridge, twin feedback paths to the differential inputs, and a large source resistance connected to the voltage source and in parallel with a smaller source resistance, each connected to separate differential inputs. The resistance R of two bridge filaments increase by .DELTA.R when exposed to high sample gas concentration causing variations in a current I supplied to the bridge. As .DELTA.R increases, a bridge output voltage E.sub.O decreases. The dependence of current I on .DELTA.R depends on circuit parameters. The difference between the source resistances permits the voltage source to be non-constant and load dependent. The source output polarity opposes the feedback polarity and under steady state a fixed current I exists. When sample concentration increases, the feedback input decreases causing current I to increase which restores detector sensitivity and provides a linear output voltage response E.sub.O.

REFERENCES:
patent: 3864959 (1975-02-01), MacDonald
patent: 4000454 (1976-12-01), Brakl
patent: 4057755 (1977-11-01), Piesche

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