Understanding and Testing Temperature Offset in Pressure Transmitters

Why temperature-Induced offset can compromise your critical measurements

In high-temperature industrial processes, accurate pressure measurement is not just about selecting quality instrumentation, it is about understanding how extreme thermal conditions affect measurement integrity. When process temperatures exceed 300°F (150°C), even the most precise pressure transmitters can experience significant drift, sometimes reaching several psi per 100°F. For industries where safety, efficiency, and product quality depend on reliable data, this thermal-induced offset represents a critical challenge that demands attention during both system design and ongoing operation.

The physics behind temperature offset

Pressure transmitters equipped with remote seal assemblies are engineered to isolate sensitive electronic components from harsh process conditions: corrosive media, extreme temperatures, viscous fluids, and contamination. This isolation is achieved through a sealed system consisting of:

• A flexible sensing diaphragm that interfaces directly with the process

• An incompressible fill fluid (typically silicone oil or sodium-potassium alloy/NaK) that transmits pressure

• A capillary tube connecting the remote seal to the transmitter body

• A pressure sensing element (strain gauge, piezoresistive transducer, or capacitance cell)

While this design effectively protects the electronics, it introduces a thermal sensitivity that must be understood and managed.

The thermal expansion mechanism

As ambient or process temperatures increase, the fill fluid undergoes volumetric expansion according to its coefficient of thermal expansion. Because the system is sealed and the capillary and seal assemblies are relatively rigid compared to the fluid, this expansion translates directly into increased internal pressure. This additional head pressure is superimposed on the actual process pressure being measured, manifesting as a positive offset at the sensing element.

Key contributing factors

The magnitude of temperature-induced offset depends on several interdependent variables:

Fill Fluid Properties: Different fill fluids exhibit varying thermal expansion characteristics. Silicone oils typically have expansion coefficients around 0.001/°C, while high-temperature fluids like NaK may differ significantly. The selection of fill fluid must balance thermal performance, temperature range, chemical compatibility, and safety considerations.

Total Fill Volume: Larger seal cavities and longer capillaries contain more fill fluid, resulting in greater absolute volumetric expansion for a given temperature change.

Temperature Range and Gradients: The temperature differential between calibration conditions and operating conditions directly impacts offset magnitude. Additionally, thermal gradients along the capillary length, where portions are exposed to different ambient temperatures, can create complex, non-linear error profiles.

Capillary Geometry and Routing: Capillary diameter, wall thickness, and material properties affect both the fill volume and the system's thermal response time. Routing decisions such as exposure to direct sunlight, proximity to hot equipment, or passage through temperature-controlled areas significantly influence measurement accuracy.

Real-world Impact: when accuracy matters most

Oil and Gas Production

In wellhead monitoring and separator control, pressure measurements guide critical decisions about flow rates, safety shutdowns, and custody transfer. A 2-3 psi error induced by thermal offset can trigger unnecessary alarms, cause premature equipment shutdowns, or mask actual process upsets.

Chemical Processing

Reactor pressure control relies on precise measurements to maintain safe operating envelopes and optimize yield. Temperature-induced errors can compromise batch consistency, reduce product quality, or create hazardous conditions in exothermic reactions.

Power Generation

Steam system monitoring, turbine control, and boiler management all depend on accurate pressure data across wide temperature ranges. Thermal offset can impact efficiency calculations, maintenance scheduling, and regulatory compliance reporting.

Refining Operations

Distillation column control, catalytic cracker monitoring, and product separation all require precise differential pressure measurements. Uncorrected thermal errors can reduce throughput, increase energy consumption, and affect product specifications.

Our testing capability

At Creative Engineers, we have invested in specialized testing infrastructure to help our clients understand exactly how their pressure instrumentation will perform under actual operating conditions.

Our testing facility features a precision-controlled furnace capable of:

• Temperature range: Ambient to 600°C (1112°F)

• Configuration options: Single seal or differential seal assemblies

• Controlled environment: Stable temperature profiles with minimal gradients

• Comparative testing: Multiple instruments or configurations simultaneously

• Documentation: Complete thermal characterization curves and offset data

Get started

Contact our instrumentation specialists to discuss your high-temperature pressure measurement requirements. We'll help you understand the thermal performance of your instruments and engineer solutions that deliver reliable data when it matters most.