I have an application I wanted to run past all.

I have a vessel under vacuum, 29" HG running at 380 degree F. trying to measure level. I chose a DP tranx with remote seals to remove the problems of a filled impulse line. the material is fatty acid, (animal fat). the density does change so I know the accuracy will be off.

the problem is that when they pull a vacuum the reading changes. we are getting a bigger difference in the level reading than expected. It seems as if the vacuum is effecting the reading. we have tried sonic, microwave and capacitance and they don't work. any suggestions?

 

You might consider the use of load cells instead. It would not account for density changes, but it will provide a better signal, in terms of mass instead of level.

 

At that temperature and vacuum level, there could be temperature or vacuum influence on the measurement.

The transmitter vendors publish an operating conditions limit chart for vacuum level vs temperature, usually for a specific fill fluid, like the one here:

http://postimg.org/image/4ep07udn5/

Is the transmitter operating within the prescribed limits?

Boiling fill fluid is a common issue.

 

Insure you are using a "Gauge Pressure" Transmitter, not an "Absolute Pressure" Transmitter. Absolute pressure will drift as barometric pressure changes.

Tim

 

I selected a fill fluid that can handle the higher temperature, 600 F. it is a gauge pressure, DP from Yokogawa. I have this on three separate operations that will do the same. as soon as they pull a vacuum, the reading shoots up to 103%.