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Gage or Absolute? How to Determine Which Pressure Transmitter to Use for Your Application

Pressure measurement is found in multiple applications for process monitoring, process control, maintaining safety of the equipment, personnel, factory, and environment. Each pressure application is unique and requires the proper equipment to deliver optimal performance, customer satisfaction, and plant safety.

There are multiple applications in which a gage and absolute Pressure transmitter can be used. Some applications include measuring static line pressure in pipes or vessels and tubing and casing in upstream oil and gas.

Gage and absolute transmitters come in two forms, in-line and coplanar. In-line transmitters have a single isolating diaphragm, are the lightest weight, have a compact design, and easy installation. The coplanar design features two isolating diaphragms on a single plane where the low side isolator is vented to the atmosphere.

The gage pressure transmitter takes a pressure measurement referenced to the atmosphere and the absolute pressure transmitter measurement references a full vacuum (0 psia).

Some examples of gage and absolute pressure transmitters are the Rosemount 2088 Gage and Absolute Pressure Transmitter and Rosemount 3051 Coplanar Pressure Transmitter. The coplanar transmitter measures differential pressure between the high side isolating diaphragm and the low side isolating diaphragm in a gage pressure device. The absolute pressure version has only a high side isolating diaphragm with the low side referenced to a sealed vacuum.

                                                       

Rosemount 2088 Gage and Absolute Pressure Transmitter                    Rosemount 3051 Coplanar Pressure Transmitter

While the applications for gage and absolute pressure transmitters vary from customer to customer, it is important to know in which application a gage or absolute pressure transmitter would work best.

Determine When to Use a Gage or Absolute Pressure Transmitter

Determining when to use a gage or absolute pressure transmitter for your application depends on the requirements. In applications where a vacuum is present, an absolute pressure transmitter is often the ideal choice. In applications that require a reference to atmospheric pressure, a gage pressure transmitter would be the best fit.

One example of an absolute pressure application is in black liquor evaporators operation. During the evaporation, water vapor is separated from the liquor. Multiple evaporators are used to concentrate the liquor and as the pressure decreases through each stage of the evaporator. Through each stage of the evaporation process, absolute pressure measurement provides the best accuracy with which to control the static pressure. Operators can optimize steam economy by eliminating the impact of atmospheric pressure variation on their static pressure measurement.

An example of a gage pressure application is monitoring pipelines and vessels for plant and factory safety. Pressure ratings for flanges and vessels are commonly expressed in terms of gage pressure. A gage pressure reading allows for a direct comparison to published design specifications of process equipment.

In summary, gage and absolute pressure transmitters are a great solution to monitor processes and understanding the specifications of each can help get the right product for the application. To learn more about Rosemount Pressure transmitters, visit our website.