Measuring Pressure based on an Image

Imagine you would like to measure the pressure at the bottom of a liquid reservoir tank. However, the only access one has to the tank is a viewing window. This could be due to many different reasons, perhaps the liquid is highly corrosive and no pressure sensor could be installed. A very simple method is to use a camera and the principle of hydrostatic pressure. 
In this experimental study the software LabView was used for image processing and data acquisition while colored water was used as the liquid inside a transparent reservoir. In essence, the user defines a viewing area inside the viewing domain of the camera (green rectangle on the image). The computer software finds the “edge” of the liquid at the top (red line on the image). One can calibrate the image to correlate the apparent height of liquid in the camera (pixel height) to the real height of the liquid. Once this correlation is performed, one can find the pressure at the bottom of the tank by using the hydrostatic pressure equation for the given liquid inside the tank. Since the hydrostatic pressure equation is linear with height, one can directly correlate the apparent height of the liquid in the camera to pressure for a given substance. Note that in the picture the measured pressure at the bottom of the reservoir with a pressure transducer (0.1465 psi) and the measured pressure with the image (0.1447 psi) only differ by approximately 1.2%. Also it is important to say that for the image processing to work properly, a high color contrast between the liquid and background is desired. Working with images is very fun and there are a lot of things one can do with them, finding pressures is just one example.

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