Silicone oil is commonly used in pressure transmitters as a filling fluid between the diaphragm and the pressure-sensing element. Its properties make it ideal for transmitting pressure accurately while protecting the internal sensor components from environmental and process conditions.
Key Reasons for Using Silicone Oil
1. Efficient pressure transmission
Silicone oil is incompressible and has a stable viscosity across a wide range of temperatures. This ensures that the pressure applied to the diaphragm is transmitted uniformly to the sensor, enabling accurate readings.
2. High thermal stability
Silicone oil can withstand extreme temperatures, both high and low, without significant changes in its viscosity or performance. This makes it suitable for applications in harsh environments, such as industrial processes with fluctuating temperatures.
3. Chemical compatibility
Silicone oil is resistant to most chemicals, making it compatible with a wide range of process media, including corrosive liquids and gases. It ensures the longevity of the transmitter and prevents contamination of the process fluid.
4. Protection of the sensor
The oil acts as a barrier between the diaphragm and the internal sensor components, protecting the sensor from:
- Corrosion: Prevents direct contact with aggressive media.
- Mechanical damage: Absorbs pressure surges and vibrations.
- Contamination: Keeps particles or debris away from sensitive components.
5. Low compressibility
Due to its low compressibility, silicone oil ensures consistent pressure transmission, even under high static or dynamic loads, maintaining the accuracy of the measurements.
6. FDA approval for food-grade applications
Certain grades of silicone oil are FDA-approved, making it suitable for use in industries like food processing, pharmaceuticals, and life sciences where hygiene is critical.
Examples in Practice
- In the PT600 series by Pondus Instruments, silicone oil is used as the filling medium in the capillary system and sensor cavity to transfer pressure from the diaphragm to the piezoresistive sensor, ensuring precise measurements across a wide range of conditions.
- Silicone oil is also chosen for transmitters used in hygienic environments, such as the PT60 Type T, which meets the demanding requirements of clean-in-place (CIP) and sterilization-in-place (SIP) systems.
Alternatives to Silicone Oil
In some specialized applications, other filling fluids might be used:
- Fluorinated oils: For extreme chemical resistance.
- Glycerin or mineral oils: In certain non-corrosive applications.
- Vegetable oils: For eco-friendly or food-safe applications.
Conclusion
Silicone oil is widely used in pressure transmitters because of its excellent pressure transmission properties, thermal stability, and compatibility with a broad range of process conditions. It enhances the reliability and accuracy of the transmitter, making it a preferred choice in industrial, hygienic, and harsh environmental applications.
For more information or to explore pressure transmitters designed with silicone oil filling, contact Pondus Instruments today!
