One Transmitter for Multiple Process Measurements
The Yokogawa EJX910A is designed for applications where flow measurement depends on more than differential pressure alone.
It simultaneously measures differential pressure, static pressure, and process temperature. The measured values can then be used by its onboard flow computer to calculate fully compensated mass flow, making the EJX910A a practical alternative to building a flow measurement system from separate pressure, temperature, and flow calculation components.
How Does the EJX910A Work?
For a typical differential-pressure flow measurement system, the primary element creates a differential pressure across the pipe. The EJX910A measures this differential pressure together with static pressure and process temperature.
Its flow calculation function then uses these measurements and programmed process and primary-element information to calculate the flow rate.
The flow calculation can dynamically compensate factors including:
- Discharge coefficient
- Primary device bore
- Upstream internal pipe diameter
- Gas expansion factor
- Density
- Viscosity
This dynamic compensation helps maintain a more accurate flow calculation as process conditions change.
Mass Flow or Multi-Sensing — Which Version?
The EJX910A is available in Mass Flow and Multi-Sensing versions.
The Mass Flow Version is intended for applications where the transmitter performs compensated mass flow calculation. Yokogawa specifies mass flow accuracy of up to ±1.0% and provides pulse/contact output options.
The Multi-Sensing Version focuses on providing multiple process measurements, with differential pressure accuracy of ±0.04% and static pressure accuracy of ±0.1%.
This distinction is important when selecting an EJX910A: the required output and flow calculation function should be confirmed during configuration.
DPharp Digital Sensor Technology
The EJX910A uses Yokogawa's DPharp single-crystal silicon resonant sensor technology.
The sensor provides a direct digital signal, eliminating the need for an analog-to-digital conversion stage and supporting the transmitter's high-performance measurement architecture.
Dynamic Compensation for Flow Measurement
One of the major advantages of the EJX910A is that the flow calculation is not based only on a fixed set of flow factors.
The transmitter can dynamically compensate important parameters used in mass flow calculation. This is particularly valuable for gas and steam flow applications where pressure, temperature, density, and other process conditions influence the calculated flow rate.
Long-Term Stability
The EJX-A series is specified with ±0.1% of URL per 15 years long-term stability under the stated operating conditions.
For flow measurement applications, this can help reduce the frequency of calibration checks and associated maintenance work over the operating life of the transmitter.
Communication Options
The EJX910A supports several communication architectures depending on configuration:
- HART
- FOUNDATION Fieldbus
- RS485 Modbus
The HART version supports HART 5 or HART 7 selection and can provide simultaneous 4–20 mA and pulse outputs.
The FOUNDATION Fieldbus version provides multiple function blocks and can cyclically display multiple process values.
The RS485 Modbus version is particularly useful for transferring multi-sensing data to flow computers and can communicate with up to 32 transmitters in a multidrop configuration.
Key Features
- Multivariable measurement of differential pressure, static pressure, and process temperature
- Onboard flow computer
- Fully compensated mass flow calculation
- DPharp single-crystal silicon resonant sensor
- Dynamic compensation of flow calculation factors
- Available in Mass Flow and Multi-Sensing versions
- ±1.0% mass flow rate accuracy for the Mass Flow version
- ±0.04% differential pressure accuracy for the Multi-Sensing version
- ±0.1% static pressure accuracy for the Multi-Sensing version
- HART, FOUNDATION Fieldbus, and RS485 Modbus options
- Advanced diagnostics
- Long-term stability of ±0.1% URL per 15 years for EJX-A series applications
Typical Applications
The EJX910A is particularly suited to differential-pressure-based flow measurement where pressure and temperature compensation are important.
Typical applications include:
- Gas flow measurement
- Steam flow measurement
- Process gas monitoring
- Chemical and specialty chemical processes
- Oil and gas facilities
- Energy and utility systems
- DP flow measurement using orifice plates
- Nozzle and Venturi flow measurement
- Averaging pitot tube applications
- Low-flow sampling and carrier gas measurement
Yokogawa also provides an application example using the EJX910A with a Micro-Orifice for ultralow flow measurement of samples and carrier gases.
FAQ
What is the EJX910A?
The EJX910A is a multivariable transmitter that measures differential pressure, static pressure, and process temperature. With its onboard flow computer, it can also calculate fully compensated mass flow.
Is the EJX910A a flowmeter?
It can perform mass flow calculation, but it is more accurately described as a multivariable pressure transmitter with an onboard flow computer.
It is normally used together with a primary differential-pressure flow element such as an orifice plate, nozzle, Venturi, or averaging pitot tube. The primary element creates the differential pressure, while the EJX910A measures the required process variables and calculates the flow.
What does the EJX910A measure?
The EJX910A can measure:
- Differential pressure
- Static pressure
- Process temperature
The Mass Flow version can use these measurements to calculate compensated mass flow.
What is the difference between the EJX910A Mass Flow and Multi-Sensing versions?
The Mass Flow Version is designed to calculate compensated mass flow and provides mass flow output functions.
The Multi-Sensing Version is intended to provide multiple process measurements such as DP, static pressure, and temperature to an external system such as a flow computer or RTU.
The correct version depends on whether the flow calculation is required inside the transmitter or externally.
Does the EJX910A require a separate flow computer?
Not necessarily.
When configured as the Mass Flow Version, the EJX910A has an onboard flow computer that uses the measured process variables and programmed flow parameters to calculate compensated mass flow.
What primary elements can be used with the EJX910A?
The EJX910A can be used with differential-pressure primary elements including orifice plates, nozzles, Venturi tubes, and averaging pitot tubes, depending on the application and configuration.
Can the EJX910A measure steam flow?
Yes. The EJX910A can be used for DP-based steam flow measurement, with the transmitter using pressure and temperature information for flow calculation and compensation.
For saturated steam applications, Yokogawa also documents a saturated steam mode in HART 7 revisions 12 or later, allowing steam temperature to be calculated from static pressure using the IAPWS-IF97 steam table.
Can the EJX910A measure gas flow?
Yes. Gas flow is one of the key applications for the multivariable architecture because pressure and temperature variations can affect density and therefore the calculated mass flow. The EJX910A can dynamically compensate relevant flow factors as part of its flow calculation.
What communication protocols are available?
Depending on the configuration, the EJX910A is available with HART, FOUNDATION Fieldbus, or RS485 Modbus communication.
What is the difference between the EJX910A and EJX930A?
Both are Yokogawa multivariable transmitters designed to measure differential pressure, static pressure, and process temperature and perform compensated flow calculations.
The EJX930A is specifically designed for high-static-pressure applications, while the EJX910A is the general multivariable model.
Why use an EJX910A instead of separate DP, pressure, temperature, and flow calculation devices?
The main advantage is system integration.
The EJX910A combines multiple measurements and flow calculation functions in one transmitter, potentially reducing the number of separate devices, simplifying signal integration, and reducing installation requirements. Yokogawa positions the multivariable architecture as a way to improve operational efficiency and reduce installation costs.
Is the EJX910A suitable for low-flow measurement?
Yes. Yokogawa specifically documents an EJX910A application with a Micro-Orifice for ultralow flow measurement of samples and carrier gases, allowing technicians to access readings remotely instead of performing frequent manual rounds.
