How Does a DP Cell Work?

••• grafvision/iStock/GettyImages

Measuring the pressure exerted by a column, or head, of liquid in a vessel is one of the oldest and most common methods of measuring liquid level. The advent of “smart” dp or dP cells, or transmitters, means renewed interest in this tried-and-tested technique of measuring differential pressure.


A typical dp cell works by applying differential pressure to either side of a metal diaphragm immersed in non-conducting oil. The movement of the diaphragm changes the electrical capacitance--the ratio of charge to potential difference--of the cell and, in turn, the electric output signal.

Closed Vessel

If the pressure in a closed vessel changes, the change applies equally to both sides of a dp cell. A dp cell responds only to changes in differential pressure--the difference in pressure between two points--so it remains unaffected by a change in static pressure. It therefore responds only to change in the liquid level.

Open Vessel

In an open vessel--one that is not under pressure or a vacuum--the vessel is connected to a dp cell on the high-pressure side via a pipe. The low-pressure side is left open to the atmosphere.

Related Articles

Why Do Chloroplasts Move in Elodea?
Instruments Used for Measuring Air Pressure
How to Convert mm Hg to in Hg
Why Do Chloroplasts Move in Elodea?
Living Cell Characteristics
How Do Piezoresistive Pressure Sensors Work?
What Is an Instrument Which Measures the Pressure of...
Differences Between Body Cells & Neurons
What Happens to Cells Due to a Sodium Imbalance?
How to Convert CV to GPM
What Three Things Help Push Blood Through Veins?
How to Calculate PSI
How to Calculate Ohms
Anatomy & Physiology of a Synapse's Structure
How to Calculate the Volume of Water to Fill a Rectangular...
The Structure of a Eukaryotic Cell
The Definition of a Convection Cell
How to Make a Working Heart Model
What Is a Manometer?
How to Read a Pressure Temperature Chart