Vacuum Vessel Level Measurement

Same as any other. High side of DP Transmitter for low level and low side to the head space.

Maybe this ilustration will help:

The dotted lines are alternate locations of the tubing. As long as the piping from the bottom of the vessel is < 10 x vessel diameter, there will not be a discernable difference between the shown tap and the alternate.

This setup will work for any vessel, under pressure or < 1 Atm. The caveat here is that you must know the temp and pressure of the system to determine the operating pressure of the DP transmitter and choose accordingly.

DP will work, but if remote seals are needed the operating temperature becomes a real factor. All DP transmitter manufacturers have a chart that shows the temperature and vacuum limits which the seal diaphragms can tolerate.

If the temperature is too high the fill fluid boils and the pressure can damage or pop the diaphragm.

Note the red arrow shows the border between vacuum and positive pressure, so much of the graph is in the vacuum range.

I would certainly check the limit to which an ordinary gauge pressure transmitter can handle whatever the vacuum pressure is, as well.

Radar can shoot through vacuum, but

- care has to be taken to seal process connection.

- the material must have adequate dielectric constant to return an echo.