High Temperature Differential Pressure Transducers for Steam, Hot Oil & Furnace ΔP

In specialized applications such as power generation, high-temperature reactors, and metallurgical smelting, process pressure measurement often faces extreme conditions of “high temperature” + “differential pressure,” with the temperature of the measured medium reaching 300℃~600℃. Differential pressure measurement of high-temperature media can be used in important processes such as flow calculation, liquid level monitoring, and differential pressure alarms, Even used for density measurement. Sino-Inst’s high-temperature differential pressure transmitter is specifically designed for high-temperature media, integrating a high-temperature isolation device, a high-precision differential pressure sensor, and a stainless steel structure to achieve differential pressure measurement of high-temperature media.

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What Is a High Temperature Differential Pressure Transducer?

High-temperature differential pressure transmitters are a type of differential pressure transmitter specifically designed for measuring high-temperature media (liquids, gases, and steam). Conventional differential pressure transmitters can directly measure media temperatures ranging from -20°C to 100°C. For media temperatures exceeding 100°C, a custom-designed high-temperature differential pressure transmitter is required. Compared to conventional differential pressure transmitters, high-temperature differential pressure transmitters primarily achieve high-temperature isolation and protection through methods such as heat sinks, capillary transmission, and high-temperature medium filling. They are compatible with media temperatures up to 600°C.

Featured High Temperature Differential Pressure Transducers

SI-3151LT Flange Mount Pressure Level Transmitter

Flange-mount diaphragm, medium temperature -40 to +304°C. Range 4 kPa to 10 MPa, 4-20 mA + HART. Diaphragm in 316L / Hastelloy C-276 / Monel / Tantalum. For hot-oil tanks, reactors, viscous-media level.

SI-804DP Small Differential Pressure Sensor

Compact DP sensor with custom medium temperature up to 600°C (-196°C also available). Range -0.1 to 10 MPa, accuracy 0.2 / 0.3 / 0.5%, zero drift ±0.03% FS/°C. Output 4-20 mA / 0-5 V / RS485. IP65.

9051 Multivariable Transmitter

Integrated DP + static pressure + process temperature with automatic compensation. 100:1 turndown, 0.04% / 0.075% / 0.1% accuracy. 4-20 mA + HART + RS485 + LoRa output.

SI-3151DP Capacitive DP Transmitter

Classic capacitive DP transmitter. Range 0.1 kPa to 41 MPa, accuracy 0.1% / 0.25% / 0.5%. With remote diaphragm seals it extends to 400°C process. 4-20 mA output, dIIBT4 / iaIICT6.

SI-8051DG Monocrystalline Silicon DP Transducer

Monocrystalline silicon DP transducer. Range -0.1 to 10 MPa, accuracy 0.075% FS. 316L stainless steel housing, 4-20 mA + HART, IP65. For precision-critical DP applications.

SI-3151 DLT Differential Pressure Level Transmitter

DP level transmitter with silicone-oil fill. Range 4 kPa to 10 MPa, accuracy ≤(0.0029r + 0.071)%. Process temperature -40 to +100°C. 4-20 mA + HART, Ex iaIICT6, IP67.

Operating Principle: Differential Pressure at High Temperature

Differential pressure transmitters measure the pressure difference ΔP = P_high − P_low between two measurement points of the same medium, outputting a 4-20 mA HART or RS485 Modbus signal. The sensing element is a capacitive or silicon piezoresistive diaphragm filled with silicone oil on both sides. This design resists high-temperature corrosion while accurately capturing the pressure difference between the two measurement points.

When the process temperature exceeds 85°C, the sensor’s electronic module, the insulating diaphragm, and the filling fluid all begin to be affected. Silicone oil expands more rapidly above 110°C, causing zero-point drift; the sensitivity of the silicon piezoresistive strain gauge decreases above 125°C; and the dielectric constant of the capacitive chip drifts with temperature. In engineering contexts, “high-temperature DP” typically refers to a medium temperature ≥85°C, with a maximum of 400°C for remote diaphragm solutions and up to 600°C for special filling fluids.

Therefore, the core design principle of high-temperature differential pressure measurement solutions is simple: keep the electronic module away from the process end. There are three methods:

1. Extend the pressure tap or heat sink to allow the medium to cool naturally to below 85°C before entering the meter;
2. Add a capillary tube to the remote transmission diaphragm box to move the sensor from the process piping to a location easily accessible for maintenance;
3. Select high-temperature resistant process connectors (brazed stainless steel diaphragm box);

Cooling Strategies for Hot Process Connection

Select the solution according to the process temperature range: ≤200°C use an extended pressure tap; 200~400°C use a remote transmission diaphragm box; >400°C requires a water jacket or remote transmission diaphragm.

Extended Pressure Tap / Condensation Loop

The cheapest and most commonly used. Add a horizontal pressure tap of ≥500 mm between the process piping and the transmitter, making a downward U-bend. Steam condenses at the bend, forming a water column that isolates the transmitter from the process. Covers steam and hot water piping ≤300°C. The length and direction of the pressure taps on both sides must be symmetrical; otherwise, zero-point offset will occur.

Remote Diaphragm Seal + Capillary

The diaphragm seal directly connects to the process flange. The capillary transmits the pressure from the silicone oil to the transmitter. The upper limit for silicone oil filling is 400°C, and the upper limit for the filling fluid is 540°C. Standard capillary tubes are 1.5~10 m long; the longer the tube, the greater the zero-point drift. The capillary tubes on both sides are of equal length and symmetrically oriented, and are wrapped with rock wool insulation to reduce the influence of ambient temperature.

Water-Jacketed Adapter

A circulating cooling water jacket is added to the process connection to lower the flange temperature to below 80°C before it enters the transmitter. This covers high-temperature flue gas and molten media at 500~700°C and is standard equipment for aero-engine test benches and glass furnaces. An external cooling water system is required, with requirements for water quality and flow stability.

Heat Dissipation Fin

A section of stainless steel finned tube is added between the transmitter and the process, relying on natural convection for cooling. Its capacity is limited; when used alone, it only covers temperatures below 200°C. It can be used alone or as a supplement to the three solutions mentioned above, for example, by adding fins to the end of the remote transmission diaphragm box.

Industrial High-Temperature Differential Pressure Measurement Applications

Installation Notes for High-Temperature Service

Pressure Tap Arrangement

For gas or steam processes, the pressure tap should originate from the top of the pipeline, run upwards in a U-shape, and then descend to the transmitter. For liquid processes, it should originate horizontally from the centerline of the pipeline side to prevent air bubbles from entering. Both sides should have the same pipe diameter (Φ14×2 mm 316L stainless steel is standard), with a length difference controlled within 50 mm.

Valve Assembly Selection

For high-temperature services, a 5-valve assembly (two blocks + one equalizer + two vents) is recommended for convenient online zero-point calibration, isolation, and blowdown. The process pressure rating of the 5-valve assembly should be ≥ 1.5 times the transmitter’s rated value. A 3-valve assembly is suitable for normal temperature and pressure applications; however, in high-temperature scenarios, the lack of a vent hinders venting after diaphragm replacement.

Zero-Point Drift Compensation

For process static pressure > 2 MPa or process temperature > 150°C, static pressure zero-point calibration is mandatory. Record the zero-point output by shorting the high and low pressure sides. Retest monthly; recalibrate if drift >0.1% FS.

Grounding and Lightning Protection

The transmitter housing must be reliably grounded with a grounding resistance ≤4 Ω. Intrinsically safe circuits in hazardous areas should be equipped with Zener safety barriers according to IEC 60079-25. In areas prone to thunderstorms, add an SPD surge protector in parallel with the 4-20 mA signal circuit.

High Temperature Differential Pressure Transducers Selection Checklist

We recommend you check the following 7 items in order, as each item will affect the quotation we provide:

1. Maximum process medium temperature (°C): Determines whether remote transmission is required and the type of filling fluid;
2. Medium type: Gas, liquid, steam, slurry; specifies the filling fluid (silicone oil / high-temperature oil / NaK) and membrane material (316L / Hastelloy C / Tantalum / Monel);
3. Measurement range ΔP: Allow 1.5 times the actual value under operating conditions. Micro-differential pressure 1~5 kPa, large differential pressure 5~25 MPa;
4. Static pressure / Working pressure (MPa): Affects diaphragm rating and flange PN;
5. Accuracy class: 0.04% / 0.075% / 0.1% / 0.2% FS; Long-term stability ≤0.1%/year;
6. Output protocol: 4-20 mA HART / RS485 Modbus / Profibus PA / FF; Select according to DCS interface;
7. Explosion-proof and protection: Ex d/ia IIC T4-T6 / IP65-IP67; Select according to zone level and field environment;

Simplified decision based on temperature range:

• ≤85°C: Standard DP transmitter is sufficient
• 85~150°C: Extended pressure tube
• 150~400°C: Remote transmission diaphragm
• ＞400°C: Water jacket or remote transmission diaphragm

Frequently Asked Questions

Can a high-temperature DP transducer use a standard 5-valve manifold?

Yes, provided the manifold pressure rating is at least 1.5× the transmitter rated working pressure. Confirm the seal material at the same time: graphite withstands 540°C, PTFE caps at 200°C, Viton at 230°C. With remote diaphragm seals, the 5-valve manifold sits between the seal and the process, not between the capillary and the transmitter.

How long should the remote seal capillary be?

Shorter is better. Zero drift and ambient-temperature drift both scale with capillary length. Indoor environment: 1.5–3 m is typical. Outdoor with direct sunlight: keep within 5 m and add a reflective insulation jacket. Beyond 10 m is generally avoided unless both sides are perfectly matched in length, slope and insulation.

How should I read the accuracy spec of a high-temperature DP transmitter?

Field accuracy = base error + static-pressure effect + temperature effect. A base error of ±0.075% FS is the 20°C calibration value. Per IEC 61298 each 28°C ambient swing adds ±0.05% FS, and every 10 MPa of static pressure adds ±0.1% URL. A nominal “±0.075%” spec can become ±0.25% combined at 300°C / 10 MPa operating conditions. Always check combined error at your actual operating point.

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Zhang Wei

Zhang Wei, possesses 20 years of experience as an automation instrumentation engineer, specializing in the research, design, installation, commissioning, and maintenance of automation instruments.

Face to various instrument communication protocols (such as Modbus, Profibus, etc.), with solid hardware circuit design and software programming skills (proficient in C language and PLC programming). Has extensive project experience; projects he has led and participated in have all achieved outstanding results, improving product accuracy, reducing costs, and increasing production efficiency.

Possesses excellent communication and coordination skills and a strong team spirit, enabling him to quickly respond to customer needs and provide high-quality automation instrumentation solutions.