Connecting a pressure transmitter to a hot process depends on two things: the temperature and the characteristics of the process fluid. Most pressure transmitters have a 212°F maximum temperature limit at the process connection.
Is the process fluid a clean, homogeneous liquid or does it have entrained solids or material?
If the process fluid is clean, you can connect the process to the transmitter with impulse lines (or ordinary tubing). This is least expensive solution and offers the most accurate pressure measurement.
For example, with a maximum temperature at the process connection of 212°F, will the process fluid be a liquid or will it solidify?
If the process fluid is still a liquid at 212°F, then impulse lines would be the best way to attach the transmitter to the process.
If the process temperature is above the 212°F process connection specification of the transmitter then due to the thermal impedance of half inch or smaller, un-insulated impulse tubing, you will lose 50°F per foot of impulse tubing. For example, for a 400°F process, you need 4-ft of impulse tubing to cool it to 200°F at the transmitter process connection.
If the process fluid solidifies below 212°F, then a remote seal would be the best way to attach the transmitter to that process.
What happens if the process fluid has entrained solids? How do you connect your pressure transmitter?
If the process fluid has entrained solids or material suspended in it, then a remote seal would be the best way to attach the transmitter to the process. The seal will provide the thermal impedance necessary to keep the process connection of the transmitter below the maximum of 212°F. Please be sure that the temperature limits of the remote seal fill fluid are not exceeded. Different temperatures require different fill fluids.
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