High Temperature Pressure Transmitter with Remote Diaphragm Seal

1. Why You Need It

Processes at 200-400°C — thermal oil, molten media, superheated steam — quickly destroy a transmitter mounted directly on the line. This high-temperature transmitter uses a remote diaphragm seal and capillary system that isolates the sensing element from the heat, while a DC704 high-temperature fill fluid transmits pressure reliably. A Hastelloy C-276 diaphragm handles corrosive media, and cooling extension options extend service to the most extreme duties.

2. Working Principle

Process pressure acts on a remote diaphragm seal mounted at the process connection. The seal's fill fluid — DC704, a silicone-based high-temperature fluid — transmits the pressure through a capillary to the transmitter's sensing element, which is located away from the heat. This isolation keeps the electronics at a safe ambient temperature while the seal and fill fluid handle process temperatures up to 400°C, with a response time of ≤10 ms.

3. Key Advantages

• Rated for process up to 400°C
• Remote diaphragm seal + capillary
• DC704 high-temperature fill fluid
• Hastelloy C-276 diaphragm
• Response time ≤10 ms
• 4-20 mA / 0-5 V / 0-10 V / RS485
• Multiple connection threads
• Range 0-35 kPa to 3.5 MPa
• Cooling extension options
• Industrial grade

Common Pain Points & Solutions

Application Cases

Technical Specifications

FAQ

Q: How does it withstand 400°C?

The transmitter uses a remote diaphragm seal and capillary system that physically separates the sensing element from the hot process. The seal, mounted at the process connection, transmits pressure through a capillary filled with DC704 high-temperature fluid to the electronics, which remain at ambient temperature. This isolation lets the seal handle process temperatures up to 400°C without overheating the sensor.

Q: What fill fluid is used?

The fill fluid is DC704, a silicone-based high-temperature fluid. It remains stable and does not vaporize or decompose at the high temperatures where standard fill fluids would fail. The fill fluid's thermal stability is critical, because any degradation would change the transmitted pressure and corrupt the measurement.

Q: What is the diaphragm material?

The diaphragm is Hastelloy C-276, a nickel-chromium-molybdenum alloy with excellent resistance to corrosion and high-temperature media. It withstands aggressive chemicals, hot oils and molten media that would attack standard stainless steel, ensuring long service life in demanding high-temperature applications.

Q: What is the measurement range?

The measurement range is 0-35 kPa to 3.5 MPa, covering low-pressure hot processes up to moderate high-pressure thermal duties. The span is configured for the application, and the transmitter is calibrated so the 4-20 mA output corresponds to the required pressure range.

Q: What is the response time?

The response time is ≤10 ms, providing fast feedback for thermal and process control loops. The capillary system is engineered to minimize the volume of fill fluid and its thermal effects, keeping the measurement responsive even at high temperatures.

Q: What connections are available?

Threaded process connections include G1/2, G1/4 and M20×1.5, with the remote diaphragm seal mounted at the process connection. The choice of thread depends on the vessel or pipe fitting, and the seal is selected to match the process pressure and temperature.

Q: Why use a remote seal instead of direct mounting?

Direct mounting exposes the transmitter's electronics and sensing element to the full process temperature, which degrades and eventually destroys them. A remote seal moves the sensor away from the heat, using a capillary and fill fluid to transmit pressure. This extends service life dramatically and is the standard solution for process temperatures above the sensor's safe limit.

Q: Can it handle corrosive media?

Yes. The Hastelloy C-276 diaphragm provides excellent corrosion resistance for aggressive chemicals, molten salts and hot corrosive media. For the most demanding media, the diaphragm material and fill fluid are selected together to match both the chemistry and the temperature, ensuring reliable long-term operation.

Q: What is the role of the cooling extension?

A cooling extension is an optional component that further reduces the temperature reaching the transmitter by adding thermal mass and surface area between the hot seal and the sensor. It is used in extreme high-temperature applications — such as superheated steam or molten media — to keep the electronics safely below their operating limit.

Q: Where is it used?

It is used in thermal oil heating systems, molten salt processes, superheated steam lines and hot oil food processing. Anywhere process temperatures exceed what a direct-mount transmitter can tolerate, the high-temperature remote-seal transmitter provides reliable pressure measurement without sacrificing sensor life.