Replacing obsolete analog nuclear pressure transmitters: alternatives to Rosemount, Ametek, Foxboro, ABB, and Bailey 

The obsolescence of instrumentation and control (I&C) systems is inevitable. It begins as soon as the facility is commissioned and worsens as the facility ages. The International Atomic Energy Agency (IAEA) notes that the aging of I&C systems can reduce safety margins and increase operating costs, and that obsolescence further complicates the situation as spare parts become difficult to source—an issue it documents in its guide to managing the aging and obsolescence of I&C systems.

For a pressure transmitter, several factors compound one another:

• Scarcity of spare parts. Stocks run down, and the price of remaining parts rises.
• Loss of manufacturer support. When a supplier drops a product line, expertise and documentation become difficult to obtain.
• Loss of skills. Specialists able to work on older technologies are becoming harder to find and retain.
• The pressure associated with extending service life. Programs extending beyond 40 years require long-term management of aging—a challenge that the IRSN places at the heart of its approach to managing the aging of sensitive components.

These factors come at a cost that is often underestimated. Premiums for replacement parts and support for legacy systems, reverse-engineering costs when the original supplier discontinues a product line, and the development of equivalents for outdated designs: a linear projection of current expenses underestimates the actual future burden.

A useful benchmark on volume: a nuclear unit typically relies on 400 to 600 pressure and differential pressure transmitters. At that scale, a widely deployed reference becomes an availability risk, not a one-off replacement.

Finally, there is a schedule constraint that no one can shorten. Nuclear-grade sensors must be ordered well in advance, and the windows for installation are determined by reactor outages, which are planned years in advance. A decision delayed by one quarter can result in a postponement of several years—or in an exception that will need to be justified.

Fuji Electric France supports this type of challenge, from plants under construction to facilities undergoing refurbishment and decommissioning projects —see our instrumentation solutions for the nuclear industry.

Certain families appear regularly in obsolescence files, because they were deployed in large numbers between the 1970s and the 1990s:

• Rosemount 1150 Series — 1151, 1152, 1153, 1154 — and Rosemount 1451
• Ametek / Gulton-Statham
• Foxboro N-E11 and N-E13
• ABB Bailey 8000 and ABB 600T
• SMAR LD301
• Legacy Weed / Ultra models

This list is there to identify the tags worth examining, not to draw conclusions. The status of any given reference rests with the original manufacturer, and with them alone: a range may be fully discontinued, partly discontinued model by model, or simply moved into a maintenance phase with no further development. Fuji Electric does not comment on the lifecycle status of other manufacturers' products.

Where to verify the actual status of a reference ?

This is the step most often skipped, and the one that avoids the most unnecessary expenditure.

Three levels of reliability, from highest to lowest. The manufacturer’s official end-of-sales notices, including the latest order dates, are considered authoritative. Next come the manufacturer’s product pages and product lifecycle guides. Finally, there are catalogs from distributors, surplus dealers, and third-party marketing materials, whose obsolescence statements are unverifiable and sometimes inaccurate—none of which are sufficient to justify a technical modification.

Two caveats should be noted regarding this ranking.

Inclusion in the catalog does not prove that a product is currently in production. A product line may remain listed—with a technical data sheet to support it—even though production has ceased and only the listing remains. The only reliable proof is a written commitment from the supplier regarding availability and lead time for the exact configuration of your part number.

Manufacturers think in terms of phases, not in black-and-white terms. Several manufacturers publish a four-stage lifecycle model—active, maintenance, limited support, obsolete—each of which involves a different level of service. This gradation provides you with a sense of timing: a product in the maintenance phase does not require immediate action, while one in the limited support phase requires planning. This is precisely what makes it possible to spread out replacements over several unit outages rather than having to handle everything at once.

There is no universally correct answer. Both technologies have their place, and the choice is made tag by tag.

Sticking with analog technology is justified when continuity is paramount: simple architecture, proven reliability, direct maintenance, and no embedded firmware. Analog technology minimizes changes to operating procedures and qualification dossiers, and reduces exposure to cybersecurity requirements and software-induced common-cause failures. It is often the most cost-effective option in terms of total cost for non-safety-related applications. Our analogue nuclear pressure transmitters certified to RCC-E meet this need.

Going digital is justified when the application derives a real benefit from it: a need for on-board diagnostics, remote configuration via a HART- pressure transmitter , superior accuracy or rangeability, integration into a modernized control architecture, or when the retrofit project already calls for a broader overhaul of the control and command system.

However, we must also address the challenges that digital technology brings: cybersecurity requirements, long-term firmware management, accounting for common-cause software failures, team training, revised procedures, potential licensing impacts, and shorter product lifecycles. The IAEA also emphasizes that while digital modernization offers benefits in terms of diagnostics and monitoring, it must be carried out as part of a well-managed strategy.

So the right question is not “analog or digital?” in absolute terms, but rather: Which technology is best suited for this specific application, given its safety class, its environment, and the impact on the entire life cycle?

When faced with an obsolete pressure transmitter , there are four possible courses of action. These are not mutually exclusive; a mixed fleet often combines several of them.

1. Repair or refurbish existing equipment. Buys time in the short term. It does not resolve the underlying obsolescence and depends on parts availability.
2. Surplus stock or lifetime buy. Purchasing in one go the volume needed for the remaining operating life. Useful, but it ties up capital and requires qualified storage.
3. Premium qualified transmitter. Appropriate for the most demanding applications — safety-related duties, severe environments. Sometimes over-specified, and expensive, on tags that do not require it.
4. Functionally equivalent alternative. Selecting a new, properly qualified transmitter whose characteristics match the tag: analogue to preserve continuity, or digital where the application justifies it. This route limits engineering change and over-qualification, provided the equivalency is documented.

An obsolete reference ultimately requires the identification and qualification of an alternative solution—its deployment can be planned for the medium term, but it cannot be postponed indefinitely. Temporarily extending the operation of existing equipment is permissible only if such an extension is based on a risk analysis, a documented spare parts strategy, and a qualified replacement plan. In the absence of these elements—and particularly the availability of spare parts—postponement is not a safe option.

A replacement is never chosen on the model number alone. The points to check, tag by tag:

• Measurement type: differential (DP), gauge (GP), or absolute (AP)
• Calibrated range (scale range) and actual calibration points
• Output signal: 4–20 mA
• Process connection and electrical connection
• Envelope dimensions and mounting bracket compatibility
• Environmental conditions: temperature, seismic resistance, radiation exposure
• Security class: security-related, non-security-related, security-critical
• Accuracy, drift, response time
• Quality documentation and equivalency support
• Lifecycle and long-term availability

Which qualification standards apply?

The nuclear qualification of a pressure transmitter is based on several standards, the selection of which depends on the country of operation, the type of reactor, and the safety class of the reference:

• RCC-E — the French standard for the design of electrical and I&C equipment, with its K1, K2, and K3 qualification levels and the associated seismic performance requirements (TAS). This is the framework used by EDF.
• IEEE 323 and IEEE 344 —U.S. standards for the environmental and seismic qualification of Class 1E electrical equipment, widely used internationally.
• KTA 3505 — a German standard issued by the Nuclear Safety Commission, dedicated to the type testing of safety-critical I&C sensors and transmitters.
• IEC 60780 / IEC 62671, ISO 19443 — Qualification of safety-critical electrical equipment; quality requirements for the nuclear industry.

The applicable standard must be identified as soon as the benchmark is analyzed: a sensor qualified under a given framework is not automatically acceptable in another regulatory context.

For markers that serve a safety function, these criteria are supplemented by specific requirements, detailed in our article on 6 Essential Criteria for Ensuring a Safety Function with a pressure transmitter..

What decision path should you follow?

Always in this order: (1) identify the tag and verify the actual status of the reference, (2) analyse the application, (3) determine the risk class, (4) choose the replacement route, (5) assemble the evidence package, (6) select the supplier. Short-cutting status verification or application analysis is the leading source of error.

⚠️ Do not replace based solely on the part number
Two sensors from the same family may differ in their measurement range, configuration, connections, materials, mounting, and qualification level. The decision must be based on the complete model code, the data sheet, the nameplate, and the application requirements.

What does a replacement really cost?

The purchase price is only part of the cost. You must also factor in engineering modifications, qualification, the impact on unit shutdowns, and maintenance. In many cases, engineering modifications and the qualification documentation cost more than the components themselves. This is the decisive argument in favor of a well-chosen equivalent: it minimizes engineering changes, requalification, and the impact on documentation.

What evidence should you gather before deciding?

For each item: technical data sheet and complete model code; proof of life-cycle status issued by the manufacturer, and a written commitment regarding availability and lead time; qualification file (RCC-E, IEEE, KTA, as applicable); seismic and radiological safety; electromagnetic compatibility; quality assurance and traceability; long-term availability data; supply chain resilience; operational references in comparable environments.

This package protects safety and budget alike. It heads off the unwelcome surprises that arise during requalification, when they cost the most.

These transmitters, including diaphragm seals pressure transmitters, also cover level measurement via hydrostatic pressure and flow measurement via differential pressure with a primary element. The differential- pressure transmitters line forms the core of the products affected by obsolescence. The associated accessories—2-, 3-, or 5-way manifolds, nuclear-grade electrical connectors, mounting brackets, high-pressure/low-pressure switches, and displays—facilitate integration into an existing installation.

Qualifications: RCC-E (NC) compliance, 2019 edition, including seismic performance (TAS); K3-A/1E and K3-ad/1E qualifications; component seismic spectrum up to 35 g, TID 50 kGy irradiation qualification with integrity up to 65 kGy, performance maintained under accident conditions (LOCA, high temperatures), ANFL-qualified electronics per IEC 62671, SIL2 / SIL3 in accordance with IEC 61508 and 61511, EDF and Framatome qualifications (QN100 / QN200 / QN300), and quality systems compliant with ISO 19443, ISO 9001, and ISO 14001.

Fuji Electric does not promise a universal “plug-and-play” replacement and does not claim equivalence without evidence. The process involves a technical review on a component-by-component basis, with qualified alternatives proposed when documentation permits. Details on part numbers and connections can be found in our nuclear pressure transmitters range.

You do not need a complete file to begin the analysis. One reference, a tag list or a datasheet is enough.

Send us your part number, tag list, or technical data sheet. Our experts will provide you with an initial technical assessment: what actually needs to be replaced, what can be planned, key considerations, the information you’ll need to gather, and the simplest approach for your situation—analog equivalent, controlled digital migration, or a custom solution. All of this before you commit to a consultation or a modification.

Would you rather start on your own? Check out our catalog of replacements for obsolete pressure transmitters to help guide your internal analysis.