Pressure Cells: Types, Working Principle, & Applications

Credits: Encardio-Rite

Geotechnical instrumentation and monitoring is a vast field that encompasses several instruments such as piezometers, load cells, strain gauges, tiltmeters, survey markers, etc.

Pressure cells are one of those geotechnical instruments that are designed to monitor stress or pressure on concrete structures, retaining walls, abutments, embankments, buildings, tunnel linings, etc.

An integral part of Geotechnical Monitoring & Instrumentation, pressure cells find their application in multiple arenas. They are also available in different shapes, sizes, and types, allowing it a wide range of implementation.

If you’re curious about what is a pressure cell, its type and other technical details, keep reading to know more!

What is a pressure cell?

Before we move forward with the technicalities, let’s first understand the pressure cell definition.

A pressure cell is a type of sensor that converts stress or pressure into a measurable and readable electrical unit. The pressure cell is fundamentally used to measure total stress in various geotechnical construction fields.

The vibrating wire pressure cells are based on vibrating wire technology. Encardio-Rite currently deals with six different types of pressure cells.

Let’s take a closer look at how pressure cells are employed in the geotechnical field.

How is a pressure cell used in the geotechnical field?

The rock/soil formation is completely dependent on the rock/soil type, stress history, shear, and normal stress levels, boundary and drainage conditions, and several environmental effects.The precise assessment of stress and changes that occur in foundation soil/rock formations is of great importance for safe engineering design.

While constructing the large civil engineering projects like tall buildings, dams, underground tunnels, etc., measurement of stress plays a vital role.

The types of stress can be categorized as:

1. Measurement of total stress at a point within a soil mass/foundation rock/concrete structure.
2. Measurement of contact stress against the face of a structural element.

The vibrating wire pressure cells are much reliable and faster than all the other types as they are capable of taking readings electrically as the frequency output is almost immune to external noise. The cable from the pressure sensor is connected to the readout unit or data logger and is protected against any possible damage during construction to give all-around reliable data.

Out of all the available pressure cells, the Encardio-Rite vibrating wire pressure cell (or stress cell) is considered rugged, reliable, and accurate.Also it can tolerate wet wiring conditions common in geotechnical applications and is capable of transmission of signals to long distances.

The applications of pressure cells (stress cells) are as below-

1. Pressure cells are designed to monitor radial and tangential stresses in shotcrete tunnel linings, underground excavations, unlined caverns, foundations.
2. Pressure Cells are used to assess the adequacy of the shotcrete lining.
3. They are used to monitor mine backfill.
4. To measure the orientation and magnitude of total pressure and stress distribution within dam embankments and the interface of soil and concrete.
5. To determine contact pressure on retaining and diaphragm walls, piers, and abutments.

What is the working principle of a pressure cell?

A pressure sensor converts the stress or applied pressure into measurable electrical output.

Pressure can be defined as the applied force per unit area that a fluid exerts on its surroundings. The pressure is given by:

Pressure (P) = Force (F)/Area (A)

The pressure transducers consist of a sensor with a constant area and respond to the force applied by fluid pressure. The force applied tends to deflect the diaphragm inside the pressure cell. The deflection of the diaphragm is calculated and converted into readable electrical output by the data loggers or readout units.

What Are the Different Types of Pressure Cells?

Encardio-Rite has different Models of Pressure Cells which include:

1. Model EPS-30V-C Concrete Pressure Cell
2. Model EPS-30V-I Soil and Rock-Concrete Interface Pressure Cell
3. Model EPS-30V-J Jack Out Pressure Cell
4. Model EPS-30V-S Earth Pressure Cell
5. Model ESC-30V Shotcrete-Concrete Stress Cell

Model EPS-30V-Series Earth and Concrete Pressure Cells

The Encardio-Rite earth and concrete pressure cell primarily consist of a flexible and circular flat capsule constructed from two stainless steel discs. These stainless steel discs are welded around the periphery and connected to a specially designed Encardio-rite pressure transducer incorporating the latest vibrating wire technology.

The vibrating wire technology allows for remote and digital readout. The pressure cell has inherently high sensitivity and it is not necessary to produce a large strain on the area being monitored for the measurement of stress. Encardio-Rite offers three types of Model EPS-30V-Series pressure cells:

Model EPS-30V-S Earth Pressure Cell — Suffix ‘S’: for use in soil, earth or rock fills

The Model EPS-30V-S Earth Pressure Cell is 200 mm Φ x 7 mm thick. It consists of two stainless steel diaphragm plates welded around the periphery. The pressure pad is connected to the vibrating wire pressure sensor through a 6 mm dia x 165 mm long stainless tube. The narrow cavity inside the pressure pad and the tube is filled with fluid .

Model EPS-30V-C Concrete Pressure Cell — Suffix ‘C’: for use in concrete

The Model EPS-30V-C Concrete pressure capsule is similar to EPS-30V-S. For applications in which the concrete pressure cell is embedded in concrete, a 600 mm long pinch tube is welded to the transducer.

Once the concrete is cured, due to cooling the shrinkage of the capsule is created which creates a gap between the concrete and cell which prevents the transmission of pressure on the cell. Thus to fill the gap, a pinch tube is squeezed to push the fluid to inflate the cell and develop a positive pressure on it.

Here’s a video for more information on Model EPS-30V-C Concrete Pressure Cell:

Model EPS-30V-I Soil and Rock-Concrete Interface Pressure Cell — Suffix ‘I’: for use at concrete and soil interface

The Model EPS-30V-I Soil and Rock-Concrete Interface Pressure Cell is similar to the above except that it is 200 mm Φ x 10 mm thick and the diaphragm on one of the sides is rigid.

Watch out the video below to know more about Model EPS-30V-I Soil and rock concrete interface pressure cell.

Working Principle of Model EPS-30V-Series Earth and Concrete Pressure Cells

The pressure applied by the earth or concrete acts on the cell and is transmitted through the fluid in the stress capsule to an integral diaphragm, which forms the part of the pressure transducer.

| Read More: Strain Gauge: Principle, Types, Features and Applications |

The change in pressure causes the diaphragm to deflect, thus altering the tension of the wire. Any change in the tension of the wire affects its resonant frequency of vibration, which is related to the pressure acting on the cell.

The resonant frequency with which the wire vibrates can be accurately measured. Encardio-Rite Model EDI-51V VW readout unit will be used for manual reading, ESDL-30 or EDAS-10 data acquisition system are available for online monitoring pressure at the site.

Data can also be transmitted over long distances to remote data acquisition system Model ESDL-30 or EDAS-10.

Specifications of Model EPS-30V-Series Earth and Concrete Pressure Cells

The pressure cell essentially consists of a flat circular capsule and a pressure transducer connected to each other by a 6 mm Φ x 165 mm long stainless steel tube. To understand the pressure transducer working principle, you can check out our blogs …[Continue reading]