Wireless Gauge Pressure Measurement with Remote Diaphragm Seals
The Yokogawa EJX438B is a wireless gauge pressure transmitter designed for applications where a conventional direct-mounted pressure transmitter is not the best choice.
Its remote diaphragm seal system separates the process medium from the pressure-sensing assembly. The diaphragm seals are connected to the transmitter through capillaries containing fill fluid, allowing the transmitter to be installed away from the direct process connection.
At the same time, the EJX438B uses ISA100.11a wireless communication and internal batteries. This eliminates the need for conventional signal wiring to the transmitter and can simplify installation at remote or difficult-to-wire measurement points.
Why Use Remote Diaphragm Seals?
A direct pressure connection is not always suitable for the process.
Remote diaphragm seals can be valuable when the process involves:
- High or low process temperatures
- Corrosive process media
- Highly viscous liquids
- Media that may clog impulse piping
- Process fluids that should not directly enter the pressure-sensing system
- Difficult or remote process connections
- Applications requiring the transmitter to be positioned away from the vessel or process line
The diaphragm seal acts as a barrier between the process and the transmitter's sensing system, while the capillary transfers the pressure through the fill fluid.
The Advantage of Wireless Installation
The EJX438B does not simply add wireless communication to a conventional pressure transmitter. Its combination of wireless communication and remote diaphragm seals can solve two installation problems at the same time.
The remote seal provides process isolation, while ISA100.11a wireless communication reduces the requirement for conventional signal cabling.
This can be particularly useful for:
- Existing plant retrofit
- Distributed tank monitoring
- Remote process equipment
- Plant expansion
- Measurement points where cable installation is difficult
- Applications where long signal cable routes would increase installation work
Yokogawa's application examples include chemical plants, gas wells, water treatment plants, tank monitoring and other distributed measurement applications.
Key Features
- Wireless gauge pressure transmitter with remote diaphragm seals
- Remote diaphragm seals connected through fill-fluid capillaries
- ISA100.11a wireless communication
- Internal battery-powered operation
- Wireless transmission of process variables and setting parameters
- Long-life battery design using two high-capacity lithium-thionyl chloride batteries
- Wireless process-value update interval selectable from 0.5 second to 60 minutes
- Infrared communication for wireless network configuration and parameter setting
- Suitable for liquid, gas, and steam applications
- Suitable for pressure, liquid level, density, and flow measurement
- Flush and extended diaphragm seal configurations available
- Designed for applications where direct process connection is unsuitable
Remote Diaphragm Seal Configurations
The EJX438B can be configured with different remote diaphragm seal arrangements according to the process connection and installation requirements.
Yokogawa provides engineering drawings for extended diaphragm seals, flush seals with a ring, and flush seals without a ring. This allows the seal configuration to be selected according to the vessel, process connection and characteristics of the measured medium.
The correct seal configuration is important because diaphragm material, seal geometry, capillary length, fill fluid and process temperature can all affect the final measurement system.
Wireless Communication and Update Time
The EJX438B uses the ISA100.11a industrial wireless communication protocol.
The measured process value can be published wirelessly at selectable intervals from 0.5 second to 60 minutes. This allows the update rate to be selected according to the dynamics of the process and the required monitoring frequency.
The transmitter can also communicate setting parameters wirelessly. Infrared communication is used for wireless network configuration and parameter setting, helping simplify commissioning.
Long-Life Battery Design
The EJX438B uses an ultra-low-current design with two high-capacity lithium-thionyl chloride batteries.
This battery-powered architecture eliminates the need for conventional wired power in the applicable configuration and supports long-term wireless operation. Actual battery life depends on update interval, network conditions, operating environment and configuration.
Typical Applications
Chemical Process Measurement
Remote diaphragm seals can help protect the sensing system when corrosive, viscous or otherwise difficult process media are being measured.
Tank Level Measurement
The EJX438B can be used for differential pressure-based liquid level measurement when the remote diaphragm seal arrangement is appropriate for the tank and process conditions. Yokogawa also lists liquid level measurement among the applications of the EJX438B/EJX118B diaphragm-sealed wireless transmitters.
High-Temperature or Challenging Media
Remote diaphragm seals allow the transmitter's sensing assembly to be separated from direct process contact, making this configuration useful where process temperature or medium characteristics make direct mounting unsuitable.
High-Viscosity or Clogging Media
When conventional impulse piping is susceptible to blockage because of viscous, crystallizing or otherwise difficult media, a suitable diaphragm seal arrangement can provide a more appropriate measurement interface.
Remote and Distributed Monitoring
Wireless communication makes the EJX438B suitable for measurement points distributed across a plant, tank farm or other large facility where installing new signal cables would be difficult.
Frequently Asked Questions
What is the Yokogawa EJX438B used for?
The EJX438B is a wireless gauge pressure transmitter with remote diaphragm seals. It can be used for pressure, liquid level, density and flow measurement of liquids, gases and steam.
Why does the EJX438B use remote diaphragm seals?
The remote diaphragm seals isolate the process medium from the transmitter's pressure-sensing assembly.
This is useful when the process is corrosive, viscous, high-temperature, difficult to connect directly, or otherwise unsuitable for a conventional pressure connection.
What is the difference between EJX438B and EJX430B?
Both are wireless gauge pressure transmitters in the EJX-B series.
The main difference is the process interface:
EJX430B is a standard wireless gauge pressure transmitter, while EJX438B adds a remote diaphragm seal system for applications requiring process isolation or remote process connection.
What is the difference between EJX438B and EJX118B?
The two models share the same remote diaphragm seal concept and wireless platform, but their pressure measurement type is different.
EJX438B measures gauge pressure, while EJX118B is a differential pressure transmitter with remote diaphragm seals. Yokogawa lists both models for liquid, gas and steam flow, liquid level, density and pressure measurement.
Is the EJX438B wireless?
Yes. The EJX438B uses ISA100.11a wireless communication and internal batteries. It can transmit process variables and setting parameters through the wireless network.
Does the EJX438B require signal cables?
The transmitter does not require conventional signal cabling for wireless process-value transmission.
A compatible ISA100 wireless infrastructure is still required for the complete measurement system.
How fast can the EJX438B update its measurement?
The wireless process-value publication interval can be selected from 0.5 second to 60 minutes.
What types of diaphragm seals are available?
Yokogawa provides flush and extended diaphragm seal configurations, including flush designs with or without a ring. The appropriate configuration depends on the process connection, vessel design, medium and installation requirements.
Can the EJX438B be used for tank level measurement?
Yes. Yokogawa identifies liquid level measurement as an application for the EJX438B diaphragm-sealed wireless transmitter. The remote seal configuration can be particularly useful when the transmitter needs to be isolated from the process or positioned away from the vessel connection.
Can the EJX438B measure flow?
Yes. Yokogawa states that the EJX438B can be used for liquid, gas and steam flow measurement. A suitable primary flow element and correctly configured pressure measurement system are required for the application.
When should I choose a remote diaphragm seal instead of a direct pressure connection?
A remote diaphragm seal is worth considering when direct process connection could expose the sensing system to unsuitable temperature, corrosive or viscous media, or when impulse piping could be difficult to maintain.
The final selection should consider process temperature, pressure, medium properties, diaphragm material, fill fluid, capillary length and process connection.
Is the EJX438B suitable for retrofit projects?
Yes. The wireless architecture can reduce the need for new signal cabling, while the remote diaphragm seal provides flexibility for challenging process connections. This combination can be particularly useful when adding pressure or level measurement points to an existing plant. Yokogawa documents wireless applications in chemical plants, water treatment, tank monitoring and other industrial facilities.
