Honeywell International Inc.

Darryl J Wrest

Donald S Foreman

Russell D Braunling

Russ A Braunling

A system for monitoring corrosion in metal by comparing a test sample exposed to a corrosion causing environment and a reference sample exposed to a protected environment. An AC voltage source generates a square wave signal oscillating between ground and voltage Vcc and a filter is positioned to filter the signal to produce a sine wave with no second harmonic component. A voltage-driven current source and inverting amplifier produce a current referenced to 0.5 Vcc to provide an AC current from the drive voltage driven sinusoidally and symmetrically above and below 0.5 Vcc. A transformer steps up the AC current and thereafter transmits the current through the samples to an amplifier for amplifying the current to provide outputs in a ratio representing the degree of corrosion of the reference sample. The system can operate in situ for on site measurement and uses relatively low current to permit long operation.

Corrosion monitoring system

A micropower apparatus and method for milliohm resistance detection includes a drive circuit and a monitoring circuit. The drive circuit includes a step up current transformer that is driven by a square wave oscillator via a low pass filter and voltage-driven current source. The drive circuit drives a series arranged test coupon and reference coupon, the latter being exposed to the elements. The coupons are Kelvin connected to the monitoring circuit, which includes a pair of low noise, low offset pre-amplifiers, a pair of post amplifiers connected to outputs of the pair of pre-amplifiers, a pair of full wave rectifiers connected to outputs of the pair of post amplifiers, and a pair of low pass filters connected to the outputs of the pair of full-wave rectifiers. Resistance values of the test and reference coupons can accordingly be monitored ratiometrically to determine a state of a selected environment by, for example, detecting changes in electrical resistance due to corrosion of the test coupon.

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O'Fallon, MO, United States of America

Darryl J Wrest