Yokogawa Pressure Transmitter Selection Guide

Define the Pressure Measurement Type

Gauge Pressure

Gauge pressure compares process pressure with local atmospheric pressure. Typical applications include line pressure, pump discharge, open-tank level and vessel blanket pressure. If the process variable is intentionally referenced to atmosphere, a gauge transmitter is usually the appropriate starting point. Tomarok’s EJA530E is one example of an in-line Yokogawa gauge transmitter in the existing catalog.

Absolute Pressure

Absolute pressure is referenced to a vacuum rather than to the local atmosphere. It is used when atmospheric variation must not influence the measurement, such as certain vacuum, distillation, gas or scientific process applications. An absolute-pressure requirement should be stated clearly on the datasheet because it cannot be replaced by gauge measurement through a simple configuration change.

Differential Pressure

Differential pressure measures the difference between a high-pressure and a low-pressure point. It is widely used for closed-tank level, filter condition, density and flow measurement with a primary element. Yokogawa’s differential pressure transmitters include standard, high-static, draft-range, flange-mounted, remote-seal and digital remote-sensor configurations. The differential pressure transmitter guide on Tomarok provides more background on the measurement principle and common applications.

Define Range, Static Pressure and Required Performance

A pressure transmitter should be sized around the real operating window. Provide the minimum, normal and maximum expected pressure as well as the design pressure. For differential-pressure applications, also provide the line or static pressure because a very small DP may be measured on top of a high process pressure. High-static applications may require a dedicated transmitter such as an EJA130E or EJX130A rather than a standard DP model. The required accuracy should be tied to the process objective, not selected as the highest value available by default.

At the family level, Yokogawa currently positions EJA-E as its proven standard-performance series and EJX-A as its high-performance series. Yokogawa lists up to ±0.040% accuracy and up to 100:1 range ability for EJA-E, compared with up to ±0.025% and 200:1 for EJX-A. The EJA vs EJX comparison should therefore be made after the measurement range and performance target are known.

Review the Process Medium and Wetted Materials

The transmitter must be compatible with the process fluid. Water, clean gas and many utility services can often use conventional process interfaces, but acids, caustics, solvents, sour service, viscous products, hygienic media or slurries may require different diaphragm and flange materials. The material specification should consider corrosion, permeation, hydrogen effects, cleaning requirements and plant material standards. Do not assume stainless steel is suitable simply because it is the default option on another service.

Decide Whether a Diaphragm Seal Is Required

A diaphragm seal can isolate the sensing element from a hot, corrosive, viscous, crystallizing, sanitary or difficult process medium. Remote seals can also move the transmitter away from an inaccessible or high-temperature process connection. The trade-off is that the seal system introduces additional engineering variables: diaphragm size and material, capillary length, fill-fluid properties, ambient temperature, elevation difference and response time. A diaphragm-seal system should therefore be engineered as a complete measurement assembly. Tomarok’s diaphragm seal pressure transmitter guide covers these design considerations in more detail.

Select Mounting and Process Connection

Traditional-mount transmitters, in-line gauge transmitters, flange-mounted DP level transmitters and remote-seal assemblies solve different installation problems. For brownfield work, record the existing process connection, manifold arrangement, center-to-center dimensions, flange rating and available space. A technically suitable transmitter can still create unnecessary field modification if its mechanical interface has not been checked. For new projects, the piping and instrumentation specification should define the connection standard before the model code is finalized.

Choose Communication and Control-System Interface

The output must fit the plant architecture. Depending on the model, Yokogawa pressure transmitters are available with conventional 4-20 mA and digital communication options such as HART, BRAIN, FOUNDATION Fieldbus or PROFIBUS PA. Yokogawa also offers ISA100.11a wireless pressure transmitters for applications where additional wiring is difficult or where a wireless architecture is already established. Wireless should be selected as part of a plant communication strategy, not solely to avoid cable installation.

Define Safety, Hazardous-Area and Environmental Requirements

Hazardous-area classification, ambient temperature, ingress protection, vibration, electrical entry and functional-safety requirements can change the model and option code. The required approval must be verified for the exact country and installation. If the transmitter is part of a safety instrumented function, the project’s functional-safety design and proof-test requirements should be addressed separately from normal process-control accuracy.