Absolute Pressure Measurement for Difficult Process Conditions

The EJXC81A and EJAC81E are Yokogawa absolute pressure diaphragm seal systems consisting of an absolute pressure transmitter and a single diaphragm seal.

The diaphragm seal separates the process medium from the transmitter sensing assembly. This makes the system particularly useful when direct pressure connection could expose the transmitter to corrosive, viscous, toxic, high-temperature, or clogging media.

The system can be configured with Yokogawa EJX310A or EJA310E absolute pressure transmitters, allowing customers to select the transmitter performance level required for the application.

Why Use a Diaphragm Seal?

A conventional pressure transmitter may not be suitable when the process fluid can damage the sensing assembly or block the impulse connection.

A diaphragm seal creates a physical barrier between the process fluid and the transmitter. The process pressure is transferred through the diaphragm and fill system while keeping the transmitter isolated from the process medium.

This is particularly useful for:

• High-temperature fluids
• Low-temperature fluids
• Highly corrosive media
• High-viscosity fluids
• Toxic fluids
• Media containing solids or materials that may clog impulse piping

EJXC81A vs. EJAC81E

Both systems are designed for absolute pressure measurement with a remote-mounted diaphragm seal, but their measurement ranges differ.

EJXC81A

Available measurement spans include:

• M: 2.7 to 130 kPa abs
• A: 0.035 to 3.5 MPa abs
• B: 0.16 to 16 MPa abs with flush seal
• B: 0.16 to 7 MPa abs with extended seal

EJAC81E

Available measurement spans include:

• M: 3.4 to 130 kPa abs
• A: 0.06 to 3.5 MPa abs
• B: 0.46 to 16 MPa abs with flush seal
• B: 0.46 to 7 MPa abs with extended seal

The appropriate model and transmitter configuration should be selected according to the required pressure range and process conditions.

Key Features

• Absolute pressure diaphragm seal system
• Single diaphragm seal configuration
• Suitable for high and low temperature fluids
• Suitable for corrosive and high-viscosity media
• Helps prevent impulse piping clogging
• Suitable for toxic process fluids
• High-vacuum capability
• Fast response: 200 ms
• Compatible with EJX310A and EJA310E absolute pressure transmitters
• Flush and extended diaphragm seal configurations
• Multiple process connection sizes
• Remote-mount flanged seal options
• Inner diaphragm adapter and flange connection options
• Multiple pressure ranges for different applications

Diaphragm Seal and Process Connection Options

The system provides several process connection configurations to match different installation requirements.

Flush Flanged Seal

Available sizes:

• 1.5 in (40 mm)
• 2 in (50 mm)
• 3 in (80 mm)

Extended Flanged Seal

Available sizes:

• 3 in (80 mm)
• 4 in (100 mm)

Inner Diaphragm Seal

Adapter and flange connection options are available in:

• 1/2 in (15 mm)
• 3/4 in (20 mm)
• 1 in (25 mm)

Typical Applications

The EJXC81A and EJAC81E are suitable for applications where conventional pressure connections are difficult to use, including:

• Chemical processing
• Oil and gas
• Power generation
• High-temperature process systems
• Corrosive chemical processes
• High-viscosity fluids
• Toxic media handling
• Processes with clogging media
• Vacuum and low-pressure applications
• Critical storage and process equipment

Frequently Asked Questions

What is the Yokogawa EJXC81A EJAC81E?

The EJXC81A and EJAC81E are absolute pressure diaphragm seal systems. They combine an absolute pressure transmitter with a single diaphragm seal to measure process pressure while isolating the transmitter from the process medium.

Is EJXC81A EJAC81E a pressure transmitter?

Not by itself. It is a diaphragm seal system designed to be used with an absolute pressure transmitter.

The Yokogawa system is compatible with EJX310A and EJA310E absolute pressure transmitters.

Why do I need a diaphragm seal?

A diaphragm seal is useful when the process medium is too hot, cold, corrosive, viscous, toxic, or prone to clogging for a conventional pressure connection.

It isolates the transmitter from the process while allowing pressure to be transferred for measurement.

What is the difference between EJXC81A and EJAC81E?

The main difference is their available measurement span.

EJXC81A covers different pressure ranges from EJAC81E, particularly for the M, A, and B capsule configurations. The correct selection depends on the required absolute pressure range and process conditions.

Which transmitter can be used with EJXC81A or EJAC81E?

Yokogawa specifies EJX310A and EJA310E absolute pressure transmitters as applicable transmitters for this diaphragm seal system.

Can the system measure high-temperature fluids?

Yes. The diaphragm seal system is designed for applications involving high- and low-temperature fluids, where direct connection of a pressure transmitter may be unsuitable.

Can it be used with corrosive or high-viscosity media?

Yes. The diaphragm seal system is specifically designed for highly corrosive and high-viscosity fluids, as well as other difficult process media.

Can it be used when the process connection tends to clog?

Yes. One of its intended applications is for fluids that may cause clogging of impulse piping, particularly under low-temperature conditions.

What is the response time?

The EJXC81A/EJAC81E diaphragm seal system has a specified response time of approximately 200 ms.

What is the difference between flush and extended diaphragm seals?

A flush diaphragm seal places the diaphragm closer to the process connection and is commonly selected where the process connection geometry allows it.

An extended diaphragm seal provides additional insertion length and can be selected when the process connection or vessel geometry requires the diaphragm to extend further into the process connection.

The correct configuration depends on the vessel, nozzle, process medium, and installation requirements.

Can the system be used for vacuum measurement?

Yes. Yokogawa specifically identifies the system for high-vacuum applications, with absolute pressure measurement ranges extending down to very low absolute pressures.

How should I select EJXC81A or EJAC81E?

Selection should consider:

• Required absolute pressure range
• Process temperature
• Process medium
• Corrosiveness and viscosity
• Potential for impulse-line clogging
• Required diaphragm seal type
• Process connection size
• Transmitter model
• Installation geometry

For a complete configuration, the transmitter model, diaphragm seal type, process connection, and process conditions should be checked together.