What are the considerations regarding the filling fluid for pressure transmitters?
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Looking at the manual for the SMAR LD291 sample, it states that silicone oil or fluorine oil can be used as the filling fluid for the low-voltage side. What is the difference between these two?
There are differences in the operating temperatures: fluorinated oils have a wider temperature range. For example, silicone oils can be used at temperatures below 250 degrees, while fluorinated oils can operate at higher temperatures; of course, this temperature range is also dependent on the support provided by the manufacturer you choose. Also, if your medium is oxygen, it is recommended to use fluorine oil, as it is not flammable.
Generally, different filling fluids are chosen depending on the temperature of the medium
Since the expansion that occurs when the temperature of the filling fluid is high can lead to measurement errors, it is necessary to consider the temperature and pressure of the working medium when selecting a gauge. The same applies when choosing silicone oil; if the temperature is high, a high-temperature silicone oil should be used.
So, which type of filling fluid should be chosen for temperatures below -20?
It is determined by the medium and the temperature of the medium.
There is a type of low-temperature silicone oil that can be used, Syltherm XLT
Silicone oil is generally used: it has low corrosivity and is less affected by temperature changes.
Depends on temperature: –10∽250°C for standard silicone oils; –30∽180°C for silicone oils with lower performance; 10∽300°C for high-temperature silicone oils; –20∽120°C for fluorine-based oils that cannot be used in such conditions; –50∽100°C for low-temperature ethylene glycol-based fluids
The temperature ranges vary, and the filling fluids differ; the 1151HP Rosemount model seems to be filled with silicone oil and an inert fluid
You can go and look at some samples