Level-sensing Theory of Pressure Sensor

Liquid-level monitoring plays an important role in today’s automotive, oil, water, pressure, and gas industries, to name a few. For example, pumping oil into a storage tank requires liquid-level monitoring to prevent spillage. Draining liquid out of a silo into bottles also requires liquid level monitoring for volume control.

This article will explain how to automate a liquid monitoring system using a pressure sensor. Since obtaining the pressure is just one vital piece of the information, how to convert the sensor’s output voltage into the liquid’s height using an analog-to-digital converter (ADC) will also be explained.

Details of the pressure sensor, ADC connections, system calibration and calculations, as well as an example application, are available to guide designers through the development phase.

Level-Sensing Theory

The height of liquid in a container can be measured using a pressure sensor. Placed at the top of the container, the pressure sensor is connected to an open-ended tube that is submerged in the container. The amount of water in the container exerts a proportional amount of pressure on the sensor via the trapped air in the tube. At its output, the sensor produces a pressure equivalent voltage. Essentially, the pressure sensor is a Wheatstone Bridge. Changes to the pressure on the bridge are analogous to the changes in the value of the bridge’s resistors, R.

Liquid-level monitoring systems require the use of pressure sensors to measure the pressure, and thus the height, of the liquid. Since the sensor’s output voltage is meaningless to the average users, an ADC is needed to convert the analog voltage to a digital language in which a computer’s software can mathematically compute the height of the liquid. As illustrated in the example application, the ATO pressure sensor reference board is ideal for many pressure-sensor applications.

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