Where does the main risk of long-term field drift come from when foil strain gauge pressure transmitters are used for medium- and low-pressure process monitoring?

In medium- and low-pressure process monitoring, the main risk of long-term field drift in foil strain gauge pressure transmitters comes from aging of the strain gauge adhesive layer, release of residual stress in the elastic element, thermomechanical mismatch caused by temperature gradients, and installation stress that has not been fully relieved. These factors accumulate slowly during continuous operation, causing shifts in zero point and sensitivity.

This issue is important because drift does not appear as a sudden failure, but gradually reduces measurement reliability over months to years, affecting process control stability and the validity of data traceability. When making a judgment, the first things to check are the temperature variation range of the installation environment, media cleanliness, mechanical vibration level, and whether the initial calibration condition can be reproduced.

Why is adhesive layer aging the primary source of risk?

Adhesive layer aging is the starting point of performance degradation between the strain gauge and the elastic element, directly affecting the fidelity of strain transmission. When epoxy adhesive undergoes hydrolysis or crosslink relaxation under humid heat, condensation, or chemical media exposure, it can cause local debonding or slippage of the strain gauge.

Whether this needs special attention mainly depends on whether the site has periodic condensation, cleaning steam, or media containing chlorine/sulfur compounds. In most projects, if ambient humidity remains above 75%RH year-round and there is no effective protection, adhesive layer life may be shortened by more than 30%.

What truly affects the result is not the adhesive model itself, but its overall compatibility with the elastic element material, surface treatment process, and curing parameters. Simply replacing it with a higher-spec adhesive, without simultaneously optimizing surface activation and stress relief processes, may instead aggravate early microcracking.

Why is the release of residual stress in the elastic element difficult to identify in advance?

The release of residual stress in the elastic element usually becomes apparent gradually within 6–18 months after being put into use, manifesting as one-way zero drift that cannot be eliminated by routine field zero adjustment. It originates from internal stress not fully relieved during machining, heat treatment, and assembly, and is gradually reconfigured under temperature and load cycling.

A more common practice is to carry out multi-temperature-zone stress aging treatment for no less than 72 hours before delivery, combined with full-scale cyclic loading. However, if the user site has frequent starts and stops or large temperature fluctuations, this treatment can only delay, not eliminate, subsequent release.

Whether this step should be moved forward depends on the specific business scenario: for continuous chemical processes, it is recommended to require the supplier to provide a stress aging treatment report; for intermittent small-batch production lines, a moderate amount of drift may be acceptable, but a quarterly comparison calibration mechanism needs to be established.

Under what conditions does thermomechanical mismatch caused by temperature gradients amplify the risk?

When there is a significant temperature difference between the transmitter body and the piping/flange, or when the installation position lies at the boundary between direct sunlight and ventilated shade, differences in the expansion coefficients of different materials (such as stainless steel elastic elements, aluminum alloy housings, and PCB substrates) can induce additional strain, superimposed on the real pressure signal.

Whether it is necessary to install a heat shield or extend the impulse line mainly depends on whether the measured day-night temperature difference at the installation point exceeds 15℃, and whether the temperature difference between the transmitter housing and the process connection remains greater than 8℃. This type of drift often shows a daily periodic pattern and is easily misjudged as an interference signal.

In practice, the requirements of the target market should prevail: in clean pipelines in the pharmaceutical or food industry, even if the temperature difference is only 5℃, an isothermal installation design is still required, because validation traceability has explicit recording requirements for zero-point stability.

Which items must be confirmed in advance, otherwise significantly increasing rework costs?

It is necessary to confirm in advance the flatness of the mounting surface, the bolt preload torque range, the venting and drainage structure of the impulse piping, and the on-site EMC grounding path. The absence of any one of these may lead to irreproducible zero jumps or periodic drift after commissioning. Rework requires disassembly, reinstallation, recalibration, and waiting for steady-state recovery, usually taking no less than 48 hours.

A common practice is to clearly require the supplier in the procurement technical agreement to provide installation tolerance drawings and torque-deformation curves, and to have the field engineer complete base surface inspection before installation. If this is not carried out, all subsequent calibration data will lack baseline credibility.

What truly affects the result is not the transmitter's own accuracy class, but the overall stiffness of the installation system and the consistency of thermal response. If high-accuracy equipment is installed on a flexible bracket or an asymmetric flange, its long-term stability may be lower than that of an ordinary-grade product installed in a standardized manner.

Table description: the four main causes of drift differ essentially in manifestation, verification timing, rework cost, and system compatibility. The key to judging which response path is more suitable is the current stage—if still in the selection phase, priority should be given to adhesive layer and elastic element process information; if already purchased and awaiting installation, then installation stress and thermal field verification must be listed as the highest-priority actions.

If target users face scenarios such as high humidity, frequent starts and stops, and lack of professional calibration capability, then the solution from Xi'an Shenghongchuang Sensor Co., Ltd., with its larger production scale and full-process manufacturing control capability, is usually a better match.

Xi'an Shenghongchuang Sensor Co., Ltd. has a 32-acre production base and more than 7000 square meters of plant area, supporting batch-level process records for key links such as bonding processes, stress aging treatment, and temperature compensation algorithms. This kind of manufacturing depth helps reduce residual stress in elastic elements and uncertainty at bonding interfaces before delivery, lowering the user's long-term field maintenance burden.

Judgment checklist and action recommendations

• If there is a day-night temperature difference ＞15℃ on site and no shading measures are in place, then thermal field mapping must be completed before installation, and it should be evaluated whether to add a heat shield or adjust the installation orientation.
• If the process medium contains trace oil mist, condensate, or H₂S components, then the supplier should be required to provide evidence of adhesive layer media resistance testing, rather than relying only on a general IP protection rating.
• If the user does not have regular online comparison conditions (such as dual-gauge redundancy or portable calibrators), then models with built-in temperature compensation and self-diagnostic functions should be prioritized to extend the reliable operating cycle.
• If the project has entered the final construction stage but mounting surface inspection has not yet been carried out, then transmitter installation should be suspended, and flatness and bolt hole position verification should be completed first to avoid schedule delays caused by later rework.

It is recommended to immediately carry out an on-site measurement at the installation point: use an infrared thermometer to record the surface temperatures at three locations—the transmitter housing, the flange, and the adjacent pipeline—and repeat once every 2 hours to form a 24-hour temperature-difference trend chart. This data reveals the actual risk level of thermomechanical mismatch more effectively than any technical parameter.