— A Practical Guide for Engineers, EPCs, and Plant Operators

In steel smelting, chemical production, engine testing, power generation, and countless other industrial processes, high temperatures are not an exception—they are the norm. As a critical process control instrument, the pressure transmitter's ability to operate stably and accurately under such harsh conditions directly impacts production safety and efficiency-22.

Selecting the right pressure transmitter for high-temperature applications is not just about finding a device that can survive the heat. It is about ensuring measurement accuracy, process safety, and long-term reliability in environments where a single failure can mean costly downtime or a safety incident.

1. Why High Temperatures Are a Problem for Pressure Transmitters

High temperatures affect pressure transmitters in multiple ways, compromising both accuracy and reliability-22:

The key principle: The transmitter body must be kept at near-ambient temperature. Most electronic transmitters are suitable for ambient conditions up to approximately 85°C-11. Once process media temperatures exceed approximately 100°C (220°F), you need to start considering protective solutions-. Your job is to bridge the gap between the hot process and the cool transmitter.

2. Critical Selection Parameters

2.1 Temperature Range: Know Both Numbers

When selecting a high-temperature pressure transmitter, you must consider two separate temperature specifications-1:

The transmitter's "operating temperature range" and "process media temperature range" must both have upper limits higher than the maximum field temperature-. Different high-temperature pressure transmitters offer different temperature compensation ranges, so selection should be based on the specific operating temperature-1. When reviewing specifications, pay close attention to the "temperature effect" or "temperature coefficient" (TC Zero, TC Span)指标—it directly reflects the instrument's compensation performance-22.

2.2 Pressure Range

The first step in selecting any pressure transmitter is determining the measurement range--1. The range should be based on the actual application to ensure full coverage of expected pressure variations--7:

• Too small: The transmitter may be damaged by overpressure-1

• Too large: Measurement accuracy may be reduced-1

A good rule of thumb is to select a range that places your normal working pressure at approximately 70% of the transmitter's full scale-28.

2.3 Accuracy Class

Higher accuracy classes deliver more precise measurements—but at a higher cost-1. Common industrial accuracy classes include 0.1%, 0.2%, and 0.5%-1-7:

Note: Accuracy specifications may vary by country. For example, European standards often specify accuracy over the least linear portion of the range (0–10% and 90–99% of measurement range), while Chinese and US standards typically specify accuracy in the linear portion (10–90% of measurement range). A European 1% accuracy rating is roughly equivalent to a Chinese 0.5% rating-28.

2.4 Wetted Materials

The materials used in the transmitter directly affect corrosion resistance and service life-1-7:

Key consideration: If your media is corrosive to 316L stainless steel, you should use a chemical seal (diaphragm seal) to protect the transmitter from direct contact with the media-28. This not only enables pressure measurement but also effectively isolates the transmitter from corrosive media, extending its service life-28.

2.5 Output Signal

High-temperature pressure transmitters are available with various output signal types-1-7:

Select the appropriate output signal based on the requirements of downstream equipment. The 4–20 mA output is the most common two-wire configuration-28.

3. Four Ways to Handle High Process Temperatures

When your process media temperature exceeds the transmitter's limit, you have four primary options:

3.1 Remote Seal (Diaphragm Seal) System

How it works: A remote diaphragm seal is connected to the transmitter via a capillary tube filled with silicone oil. The seal isolates the transmitter from the hot process media, transmitting only pressure--22.

Best for: Viscous, corrosive, or extremely hot media where the transmitter cannot be mounted near the process.

Considerations:

• Remote seals are the most common and effective way to protect instruments from corrosive substances-

• The seal acts as a physical barrier between the transmitter and the process media-

• For high-temperature media (200–400°C), the filling liquid needs to have high-temperature resistance-

Tiankang offering: Tiankang remote seal pressure and differential pressure transmitters are available with high-temperature silicone oil filling, suitable for process temperatures up to 400°C.

3.2 Temperature Stand-Off (Cooling Element / Condensing Loop)

How it works: A short length of tubing (impulse line) between the process connection and the transmitter dissipates heat into the atmosphere before it reaches the transmitter-2.

Best for: Applications where a special high-temperature transmitter would be expensive and a stand-off provides sufficient cooling.

How effective is it? Impulse lines act as cooling fins, effectively reducing temperatures by approximately 150°F (65°C) per foot in common ambient conditions-11. The chart below shows typical stand-off lengths for different media temperatures-2:

A 6-inch length of 1/4" OD 303 stainless steel tubing can protect a transmitter from an 1100°F (593°C) pressure media-2.

Key recommendations-11:

• While some distance is recommended, too much distance can dampen dynamic response-

• Each impulse line should lead to a dead end—sustained flow of hot medium negates any cooling advantage-11

• If the pipe is insulated, the transmitter should generally not be insulated-11

• For lengths up to 50 feet: 1/4" to 3/8" for water/steam/dry gas; 1/2" to 1" for wet gases/oil/viscous and dirty liquids-11

• When multiple impulse lines exist for the same measurement point, run lines together to maintain equivalent temperatures-11

3.3 Cooling Fins and Heat Sinks

How it works: Heat dissipation fins or cooling elements increase the surface area for natural convection cooling-22. By assembling different lengths of散热片 (heat sinks), transmitters can measure media temperatures up to higher levels-.

Best for: Moderate high-temperature applications where the transmitter is mounted near but not directly on the hot process.

Considerations:

• Install using mounting brackets or radiators to increase air contact area and promote natural convection cooling-22

• Different lengths of heat sinks allow measurement of media temperatures up to higher levels-

3.4 Water Cooling Jacket

How it works: A water jacket surrounds the transmitter or sensor, circulating cooling water to maintain a safe operating temperature.

Best for: Extreme high-temperature applications where air cooling is insufficient.

4. Installation Best Practices for High-Temperature Applications

Proper installation is essential for accurate and reliable pressure measurement-1-7.

4.1 Location Selection-1-7

4.2 Process Connection-1

• Install pressure transmitters on pipelines or vessels using threaded or flanged connections-1

• For threaded connections, proper sealing is essential to prevent media leakage—use sealant or gaskets-1

• Ensure the pressure port properly aligns with the port on the pipeline or vessel-1

4.3 Electrical Connection-1

• Make electrical connections strictly according to the wiring diagram; pay close attention to power supply polarity and voltage-1

• Ensure good insulation to prevent short circuits or electrical leakage-1

• Use cable conduits or protective tubing-1

4.4 External Heat Protection-22

5. Maintenance in High-Temperature Environments

Instruments operating in high temperatures require more frequent maintenance and calibration-22:

• Visual inspections: Check for signs of overheating (discoloured paint, warped surfaces) and seal integrity-22

• Shortened calibration intervals: Adjust calibration frequency based on service severity-22

• Performance tracking: Maintain detailed operating records to track long-term performance changes-22

• Proactive replacement: Replace components before they fail, based on service life data

6. Why Choose Anhui Tiankang for High-Temperature Pressure Measurement?

Anhui Tiankang (Group) Co., Ltd. has been manufacturing industrial instruments for nearly five decades. Our high-temperature pressure measurement solutions are trusted by major oil and gas companies, chemical plants, and power generation facilities worldwide.

Product portfolio for high-temperature applications:

Core advantages:

• Temperature compensation: Full-range compensation, ensuring minimal thermal error across the operating range

• Wide material selection: 316L SS, Hastelloy C-276, Monel, Inconel, tantalum

• Multiple cooling solutions: Remote seals, cooling stand-offs, heat sinks, and condensing loops

• Complete certifications: CCC Ex, ATEX, IECEx, SIL2/SIL3, CCS marine

• Proven track record: Long-term supplier to CNPC, Sinopec, CNOOC, and international EPC projects

7. Conclusion

Selecting pressure transmitters for high-temperature process applications requires a systematic approach:

1. Define the temperatures – Process media temperature and ambient temperature. Check both the "operating temperature range" and "process media temperature range" specifications-

2. Define the pressure – Normal operating pressure, maximum pressure, and potential spikes. Select a range where normal working pressure is approximately 70% of full scale-28

3. Select the cooling method – Remote seal, temperature stand-off, cooling fins, or water cooling

4. Choose the right materials – Match wetted materials to the media and temperature. Consider chemical seals if the media is corrosive to 316L stainless steel-28

5. Verify accuracy and compensation – Check temperature coefficients and compensation ranges; understand the total possible error (static accuracy + thermal error)-2

6. Install correctly – Location, connection, and heat protection—ensure impulse lines are properly sized and configured-11

7. Maintain proactively – Regular inspection, calibration, and performance tracking-22

Remember: The transmitter body must stay cool—your job is to bridge the gap between the hot process and the cool transmitter. With proper selection, installation, and maintenance, your pressure transmitter will deliver reliable, accurate measurements for years to come.

Contact Us

For high-temperature pressure transmitter selection advice, technical documentation, or project quotations, please contact:

Yin Shuangjie
International Sales Manager
📧 Email: [email protected]
📱 WhatsApp / Zalo: +86 17856068126
🌐 Website: http://www.tiankang-global.com/

Anhui Tiankang – Your partner for reliable high-temperature pressure measurement solutions.