The issue of converting the negative pressure at the top of the vacuum tower to absolute pressure
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The issue of converting the negative pressure at the top of a vacuum distillation column to absolute pressure – for example, what is the absolute pressure corresponding to -70 KPa? Does it depend on the local atmospheric pressure of 95 KPa or on the standard atmospheric pressure?
Question: What does this atmospheric pressure refer to?
It is the local atmospheric pressure; the basic condition for design is the local atmospheric pressure.
The local atmospheric pressure ranges from 95 kPa to 70 kPa; when converted to gauge pressure, it is 20 kPa A
Is this related to the type of pressure transmitter?
Theoretically, it is related to the measurement principles of the instruments; for example, the measurement principles of pressure gauges and thermocouple vacuum gauges are different. But the measurement principle of normal pressure transmitters is the same; using the local atmospheric pressure is correct
Those that display negative pressure use the local atmospheric pressure as a reference, regardless of the type of pressure transmitter. For a gauge pressure gauge, it shows the reading directly.