• This signal is provided as input to the machine, electronic circuit, or computer called the controller.

• The controller performs the human task of assessing the measurement and providing the output signals, u and v, to adjust the valve setting through the actuator connected to the valve by means of a mechanical connection.

• If automatic control is applied to processes designed to control the value of a variable at a fixed stage, it is called process control.

• The sound waves are directed to the free surface of the liquid from the ultrasound transmitter.

• These waves are reflected from the surface of the liquid and are received by the receiver.

• In this technique, the differences in the liquid level are measured very precisely by measuring the total time taken by the wave to travel to the liquid and then back to the receiver. (Technical time travel)

• The longer these periods fly, the farther away is the liquid surface, which is a measure / indication of the depth of the liquid.

• It takes a high degree of expertise and skill to work because the actual instrument is costly.

Measuring the state of a fluid ( liquid or gas) that is determined by the force that the fluid will exert on a unit area while resting

The difference between the two forces, is known as the gauge pressure

The differential pressure is indicated by the difference in the level between the two liquid columns and is calculated as the difference in the level multiplied by the density of the liquid

The lower pressure is ambient pressure, the total or absolute pressure is the sum of the sensor and ambient pressures.

The differential pressure is measured as the difference h between the high-pressure reading and the low-pressure reading, multiplied by the density of the liquid in the tube

The coiled tube, flattened into the cross-section shown and attached to a fixed block, is opened to the pressurized fluid