I facing problem with calibrate range for application closed tank under vacuum.

zero level is 840 mm and span is 2840 mm from transmitter and vacuum not constant from 0 to 277 mbar

what can i do for find correct level? i used E+H level transmitter Cerabar S PMC71

not. this system connected to PLC and i think must be used equation for correct the level value according the pressure

 

You are trying to use the wrong model transmitter.

According the spec sheet, the Cerabar S PMC71 series is for "absolute pressure and gauge pressure" measurement.

http://tinyurl.com/qch8wqo

Your model transmitter is suitable for level measurement in tanks which are vented to atmosphere.

For level measurement in a closed, pressurized, unvented (to atmosphere) vessel, you need to use a differential pressure transmitter which has two pressure ports; one port senses the pressure at the bottom of the tank, the other senses the vacuum pressure and compensates for varying vacuum, atmospheric or positive pressure.

A calculation can't fix this; you need a sensing measurement of the vacuum and that's what differential pressure (DP) transmitters do.

 

Cerabar is not for tanks under vacuum. You have to use a differential pressure model, like Deltabar.

Daniel