Best sensor for my application

Apr 01, 2005 1 Replies
G

I want to measure the distance a glass hydrometer bulb drops over time in a solution of suspended solids. This distance is only about 4 inches. Since I can not modify the hydrometer bulb dramatically I thought I could add a drop of metallic paint on the top tip. Then I want to measure the distance from a fixed point to the top of the bulb/metallic paint. My resolution needs to be about 1 mm. I am looking to collect the data with some type of acquisition system.



What is the best type of sensor that could measure the vertical distance assuming the bulb might float form side to side about 1 inch max?



Thanks


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B

I wonder if you could constrain the hydrometer to stay on-axis and use an LVDT (Linear Variable Differential Transformer). This is a standard way of measuring linear displacements, consisting of an iron core that moves in a tube with a winding on each end. An AC excitation signal is coupled between the windings, with the percent of coupling proportional to the core displacement.

In your application, you'd have to allow for the weight of the core affecting the hydrometer depth, but this should be pretty straightforward. This isn't as elegant as the massless optical approach, but has the advantage that you might be able to do it with an off-the-shelf sensor.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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