Best sensor for my application

[gtslabs]

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

 

[Bob Masta]

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

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
www.daqarta.com