Monitoring apparatus for measuring particles suspended in liquid and for measuring the opacity of the liquid

摘要

This invention relates to a portable monitoring apparatus for detecting wear particles which may be suspended in a liquid such as the lubricating oil of turbine engines and for detecting changes in the opacity of the oil. The oil sensor which may be inserted directly into the lubrication system of the engine consists of a sensor assembly having a chamber or U-shaped channel into which the oil flows. A light emitting, solid state lamp and a first photodiode are positioned on opposite sides of the channel or chamber so that the photodiode measures the attenuation of the light passing through the oil. A second photodiode is placed at a 90 DEG angle to the light beam to measure light scattered by wear particles suspended in the oil. The signals from the two photodiodes are processed and displayed to provide an indication of the degree of attenuation of the light beam due to changes in opacity and of the magnitude of the scattered light which is a measure of the amount of wear debris in the oil. The opacity of the oil is measured without directly sensing the degree of light attenuation. That is, illumination of the scatter field of view and of the first photodiode is kept constant by varying the light emission from the lamp through a closed loop control system. The change in the lamp supply voltage necessary to maintain illumination level constant is thus a measure of the light attenuation due to changes in opacity. Furthermore, by maintaining a constant illumination level in the scatter field of view, errors in the scatter output indication are avoided. That is, in the absence of a constant light level in the scatter field of view, the amount of light scattered by a given concentration of particles varies with the opacity of the oil. As opacity increases, attenuation increases and the scattered light decreases. This results in decreased output from the scatter photodiode giving an erroneous indication that there has been a reduction in the particle concentration whereas the actual reduction of the output from scatter photodiode is due to the darkening color of the oil. By maintaining constant illumination in the scatter field of view through a closed control loop which varies the light output of the lamp, an accurate measurement of the particle concentration is made possible by eliminating errors which are brought about by changes in the opacity of the oil.